Computer technician struggling with electronics: building an amplifier. - Page 1
Forum section: electronics / beginners

author: hitech95
author_rank: Regular Contributor
timestamp: May 23, 2015, 09:40:26 pm
content: Hello everyone.I am new. I just registered to solve a doubt ...Beginning with presentations, hoping not to bore you.My name is Nicolò (Nicholas) and I studied electronics at school. Now I realized that we were not taught much. I just realize that i'm not able to make a simple thing as an small power supply.Unfortunately, at school I have only studied theory and many things remain on paper...At this time I would like to build (to start) an audio amplifier .The idea for this amplifier was to use some boards and "merge them" to achieve an working amplifier.The features that I would like to achieve are:Tone control (High and Low)Volume controlSource Selectionamplifier for headphonesIR remote controlThe boards that I'm going to use are powered at 24V-30V. I thought to use 26V. They have an maximum absorption of 5A. (Before entering protection)Being a "dual mono" I opted to use two toroidal transformers (one per channel). With a quick calculation I found what I need 24V AC and 5A. So are two 120VA transformer.As boards have neither the rectifier nor the filter capacitors, I have to realize the board for the power. The cards are supplied with s single rail 26V-0V.Here, however, it makes it difficult. to achieve the functions described above, I need use a micro controller to manage everything. (I opted for a ATMega, so I can use the Arduino IDE)To realize the control tone, volume, etc. I was thinking of using aTDA7468; to achieve the headphones amplifier I thought of using aLM4880.To complicate matters, in the box I would put a DAC and a Raspberry. (The DAC is one of those made specifically for the Raspberry, the raspberry is one of the audio sources)I need to implement a system which allows to turn them on remotely (IR remote), and then the control electronics must always be powered. So there will also be a line of standby power.After filling you with all the necessary information you're probably wondering what the problem is.The problem is how make the power rails,calculate the capacitors, and design a security system (polyfuse, fuses, etc.) to power the whole.To the delight of many, I attach some scheme, hoping it can help you to understand. Many things are still in development and so many things could not be right.On attachments, you will find:The power supply section for power amplifiers. (those values I have been recommended in another forum), is one for each transformer.The board with electronics for the audio and its power.For 5V standby and to power the raspberry thought of using something like this:Whereas to power on and off the amplifier I thought of using a relay card.Who knows if they hold the 220V AC ....Thanks, hitech95.

author: hitech95
author_rank: Regular Contributor
timestamp: May 25, 2015, 05:15:41 pm
content: It's nice to see how a trivial problem as my is completely ignored just because there is a looong description.I only tried to give much detail as possible about what I'm doing.The problem is simple:how to realize the safety systems for the supply lines.Is good to use relays to control the two transformers? (220V)How do you recommend to turn on/off the power of raspberry? Relay or MOSFET or other? (I do not know how to use transistors and their derivatives)Bye, hitech95.EDIT: striped a sentence, it could be interpreted negatively.

author: Zero999
author_rank: Super Contributor
timestamp: May 25, 2015, 06:05:35 pm
content: Why use two transformers? One transformer should be able to power both channels.What are you using for the main power amplifier?It's probably best to design each component separately first.

author: Refrigerator
author_rank: Super Contributor
timestamp: May 25, 2015, 06:12:51 pm
content: If you're doing an analog audio amp there's many designs on the web how to do it, tone control can be easily done with an op-amp ( google "opamp tone control" ) TL082 datasheet has a simple tone control schematic.Class D amps are much more efficient but they also have some quirks ( output filtering, output noise, interference, EMI ).The headphone output can be fed directly from the op-amp tone control.If you're making your own power supply then don't forget to put big caps and make proper star-ground to further improve sound quality and overall stability.Also don't forget to do proper air flow in your amp enclosure so that hot air does not pass over any electrolytics to improve their life and keep the ESR low.Relays are good for switching the output of the amp on and off, for DC it is better to use transistors or FETs since relays have contact bounce and the raspberry might not like it.

author: hitech95
author_rank: Regular Contributor
timestamp: May 25, 2015, 06:16:38 pm
content: Quote from: Hero999 on May 25, 2015, 06:05:35 pmThe main aplifier is a board based on asta508by ST. (I buy italready made like this)(The voltage in the description is wrong according to the datasheet)<-- Wrong different ICI would use two transformers because I want to separate as much as possible the two channels.My "real problem" is that at school I worked only with digital electronics and a few on operational. (Inverting, non-inverting, differential)I've never made anything with "power". All I did is read some guide on the internet.One other thing is how to implement protection circuits for arduino and the raspberry.For example in HAT specification it is written that it takes in"ZVD" systemand I do not even know what it is.Bye, hitech95.EDIT: Fixed some mistakes.

author: hitech95
author_rank: Regular Contributor
timestamp: May 25, 2015, 06:20:33 pm
content: Quote from: Refrigerator on May 25, 2015, 06:12:51 pmOh an other reply.Sorry for the double post.Yes, as you'll see from the previous answer, I use a board that is already made.My problem is how to power the whole.For the management of the tones I've already written that I will use an IC because I need the remote control. (I have a lazy brother)Bye, hitech95EDIT: striped a sentence, it could be interpreted negatively.

author: Grapsus
author_rank: Regular Contributor
timestamp: May 25, 2015, 07:25:30 pm
content: Hi hitech95,Do I correctly understand your problem ?- You need 5V standby power to keep the RPi running- You need a bigger PSU for the audio circuit that could turned on and off by software in the RPiI think you're right about getting a small ready to use 230 VAC => 5 VDC module for the RPi. You can even take an entire USB charger if it fits in your enclosure.Regarding the big main PSU, you have several options, but since you're not familiar with power supply design I would advise you against building your own. That would be too dangerous without any gain in the final device. Just take an industrial power supply with the voltages you need and have the RPi to connect and disconnect it from mains with a suitable relay. Some PSUs even have a control signal so you'd only have to do the wiring.As a super cheap alternative, why don't you use an ATX PC PSU? It already has 5 V standby, 12 V outputs with plenty of power and the main power can be controlled with a logic /PS_ON signal.

author: Refrigerator
author_rank: Super Contributor
timestamp: May 25, 2015, 07:25:55 pm
content: Quote from: hitech95 on May 25, 2015, 06:20:33 pmBut plugging ready made modules into a whole, at least to me, sounds like no fun.

author: Ian.M
author_rank: Super Contributor
timestamp: May 25, 2015, 07:39:24 pm
content: Your PSU design is borked to start with. In the EU, the specification for the nominal 230V AC mains supply is +10%, -6%. If the transformer secondary is a nominal 24V RMS, the peak voltage on the reservoir capacitor can exceed 36V if the mains voltage is at its high limit and the load current is small. I doubt your 30V max modules will like that much.

author: Grapsus
author_rank: Regular Contributor
timestamp: May 25, 2015, 07:51:52 pm
content: I think our duty here is to discourage hitech95 from building his own PSU. It's way to dangerous with absolutely no gain. It's too early for someone starting with analog stuff to play around with the primary side of something. Without even talking about fuses, line filtering, inrush current limining, wire gages, PCB tracks width etc.

author: hitech95
author_rank: Regular Contributor
timestamp: May 25, 2015, 08:16:42 pm
content: Quote from: Ian.M on May 25, 2015, 07:39:24 pmCould you be more specific? I would like to learn. The values that you have seen me have been suggested without explaining.It is for this reason that I decided to write here.Quote from: Grapsus on May 25, 2015, 07:25:30 pmYea I need:5V to supply the arduino/atmega (standby and controls)5V for the PI12V to supply the tone IC (with a linear regulator down to 7V)26V to supply amplifiersQuote from: Grapsus on May 25, 2015, 07:51:52 pmI understand that is not easy to design something like that, but I want to learn.Unfortunately (in Italy) electronics is disappearing. There are more magazines, shops, specialized websites. Forums people (in italian) do not explain and throw me random numbers.Bye, hitech95.

author: hitech95
author_rank: Regular Contributor
timestamp: May 25, 2015, 08:22:05 pm
content: Quote from: Refrigerator on May 25, 2015, 07:25:55 pmUnfortunately draw a PCB and put all the SMD components is complicated.I've already tried, the result was not bad. But my pockets are empty. 5PCB € 140.What you seehereis the only thing I did "seriously" with electronics.

author: mariush
author_rank: Super Contributor
timestamp: May 25, 2015, 08:48:22 pm
content: The power supply schematic is a bit weird. I see there 2 x 10.000 uF + 1000uF which seems like a huge amount. When you plug that power supply into the mains with the capacitors discharged, the capacitors may pull so much power that you'll blow the fuse.So much capacitance isn't normally necessary, it's often cheaper/easier to just use a transformer with higher output voltage in the first place.As others mentioned, since the mains voltage can vary so much, the voltage on the secondary side can be a bit higher than the advertised value, by a few volts. Your 230v->24v has a 9.58 ratio, with 240v on the mains you suddenly have 25v AC.In addition, when a transformer is "idling" ( there's little power pulled from it), most transformers but especially < 50-75VA transformers will again output a much higher voltage, typically 5-10% more... so this will also add a few volts to the output. If you combine this with high mains voltage you wake up with 26-27v AC on the output of a transformer.The bridge rectifier converts the AC to DC, and the result is DC with peak voltages up to 1.414 x Vac, minus the losses in the bridge rectifier (2 x voltage drop on one diode)... knowing that we may have up to 26v AC at the output, this means you may have 1.414x26 = 37 volts, minus about 1.5-2v in the bridge rectifier, so about 35v.Therefore, you have to consider your peak voltages as anything between about 32v and 35v, depending on your mains voltage.Capacitors come here to smooth out the DC output and make sure the minimum voltage is always above a certain threshold. You can use a formula to approximate how much capacitance you need to keep the voltage above a minimum : C = current / [ 2 x AC mains frequency x (Vdc peak - Vdc min)] ...In your case, since your amplifier needs maximum 26 volts (and for the sake of an example let's say maximum 1.5A current), you can think of using a linear regulator to make sure the amplifier always gets only 26v. Linear regulators typically need a couple of voltages above the output voltage to work properly, so you need to make sure the linear regulator always has at least 28v to work, so now you can figure out how much capacitance to use ... C = 1.5 A / [2 x 50 Hz x (32v - 28v)] = 1.5 / 400 = 0.00375 Farads or 3750 uF ... any more capacitance will just raise the minimum voltage above 28v, so 4700uF will be safe and more than enough for this particular example.A cheap and simple linear regulator that would do this would be LM317http://www.ti.com/lit/ds/symlink/lm317.pdf... works with up to 40v DC so it won't mind 28-35v at input, will output 26v at 1.5A, all's good in the world.As for 5v and 12v for everything else, first of all make sure you don't need positive AND negative voltages for the opamps and tone ic or whatever else your circuit needs.You may want to use a smaller transformer with two secondary windings to get +12v and -12v, using the same techniques, lm317 and lm337 as linear regulators for +12v and -12v. For 5v, you could use a ready made usb charger or you could use an ebay bought dc-dc buck converter like the ones withxl4015or LM2576, lm2577, lm2596, just search these words on ebay and you'll find plenty of ready made boards for a few dollars.

author: hitech95
author_rank: Regular Contributor
timestamp: May 25, 2015, 09:07:06 pm
content: Thanks for the reply.I'm analyzing, and trying to understand your reasoning.Quote from: mariush on May 25, 2015, 08:48:22 pmOkQuote from: mariush on May 25, 2015, 08:48:22 pmCould you be more specific? I don't understand.Quote from: mariush on May 25, 2015, 08:48:22 pmOkQuote from: mariush on May 25, 2015, 08:48:22 pmI was advised to don't use a stabilized power supply. So as not to shackle the sound.Quote from: mariush on May 25, 2015, 08:48:22 pmI don't I need a dual power supply.I would find a switching power supply for 12V, then lower them to 7V with a linear regulator. (for the Tone/Input Select IC)Instead for 5V always thought of from the 12V but those for the raspberry I would filter so that the signal that comes out of the DAC is cleaner.Thanks , hitech95.

author: mariush
author_rank: Super Contributor
timestamp: May 25, 2015, 09:32:11 pm
content: Transformers are designed for a particular output power and voltage. Due to type, construction, magnetics and other factors, the output voltage is sort of guaranteed to be the one on the label only when devices connected to it pull some amount of power, let's say at least 10-20% of the transformer's rated power. When a device pulls less power from the transformer, the output voltage of the transformer may be higher than the one advertised on the label.The smaller the power rating of the transformer, the higher the "error margin" on the output voltage.For example, here's the datasheet for a series of transformers produced by Pro Power :http://www.farnell.com/datasheets/1508683.pdfYou have there a chart with two columns, one saying VA rating and one saying Reg%, that reg% column tells you how much can the voltage deviate from the advertised value.As you can see there, a very small transformer rated for only 6 VA, for example a 12v AC 6VA one, may output up to 12v + 24%, which is 12x1.24 = 14.88v AC,and that could screw up things if you don't take this into account.Transformers rated for higher power, like 50VA or 75VA, are typically at less than 10% as you can see in the datasheet, and that makes things easy.I was advised to don't use a stabilized power supply. So as not to shackle the sound.If the amplifier at any point uses maximum 26v at 1.4A or something like that, then using a linear regulator capable of up to 1.5A won't "shackle" the sound in any way. There are amplifiers that may pull more current for small periods of time, in which case I agree, a linear regulator may temporarily enter into a "protection" mode for a few milliseconds to prevent damage... but in this case you can use linear regulators capable of handling more current, like 3 or 5A.Alternatively, you can use transformers rated for less voltage, for example a 18v AC transformer.

author: hitech95
author_rank: Regular Contributor
timestamp: May 25, 2015, 09:49:30 pm
content: Quote from: mariush on May 25, 2015, 09:32:11 pmThe card is made to work from 12V up to 30V. (It should not exceed 30V DC). For this I chose a voltage of 26V.According to thedatasheetthe chip supports a maximum current of 9A, but typical of 6A. I wanted to limit the maximum current to 4A.I have seen some people use my same transformer to power a similar amplifier. I would like to understand why they did not do all of your considerations.Bye, hitech95

author: Zero999
author_rank: Super Contributor
timestamp: May 25, 2015, 10:28:02 pm
content: As said above, a 24VAC transformer is not suitable for powering an amplifier card with a maximum input voltage of 30VDC.AC voltages from transformers are specified in RMS voltages. A 24V transformer has a peak voltage of 24*root(2) =34V which is what you get on the filter capacitor, minus the rectifier losses and ripple. As explained above, under light loads, the voltage will be even higher, as transformers are specified under full load conditions, then the mains voltage could also be on the higher end of normal.

author: hitech95
author_rank: Regular Contributor
timestamp: May 25, 2015, 10:51:05 pm
content: Quote from: Hero999 on May 25, 2015, 10:28:02 pmI have understood, what I do not understand is why they do not have anything fried.Bye, hitech95.

author: rsjsouza
author_rank: Super Contributor
timestamp: May 26, 2015, 11:45:04 am
content: Quote from: hitech95 on May 25, 2015, 10:51:05 pmIf you are absolutely confident the transformer and the output power amplifier board are identical, it is possible that:- they are using a voltage regulator to trim the power supply output to the specified value (up to 30V);- they are relying on the device's specifications and not the board's specifications.Quote from: hitech95 on May 25, 2015, 10:51:05 pmThe power amplifier (PA) datasheet mentions it can support up to 36V in continuous mode (Table 6, VCCrow), therefore the main device may be working just fine despite the board's specifications. If you asked me, I wouldn't recommend doing this as the PA board may not provision the correct heat dissipation when operating at the 36V voltage level. This will reduce the lifespan of the device.Therefore, as others have said, if you want to use the PA board's specifications you must either use a voltage regulator or change the transformer.By the way, mariush's calculations about the capacitor are off. Probably he missed that each PA board can consume up to 5A, which would require at least 12500uF per power supply. (everything else is correct, though)Instead, if you go along with putting out 35V, also keep in mind the output current each PA will consume. The device datasheet mentions that, in Bridge-tied-load (BTL), it can output up to 160W when VCCis 35V.When talking about power, whatever comes out in the loudspeaker must be sourced by the power supply. Also, there are inneficiencies on the circuit (heat, etc) that the power supply must source as well. We don't know the efficiency of the PA board, but given the device is a class D, I would suspect it is high (above 70%, which means that up to 30% is consumed as heat, noise, etc.). In maximum output power and using the worst case scenario (70%), your power supply must source at least:Psupply= Pout/ (%efficiency/100) =160/0,7=228WIsupply= Psupply/ Vsupply=228/35=6,5AThis will require redesigning the power supply and using a different transformer which is not what you probably want...

author: hitech95
author_rank: Regular Contributor
timestamp: May 26, 2015, 11:58:00 am
content: Quote from: rsjsouza on May 26, 2015, 11:45:04 amI am writing here just to learn and to understand.What I do is what you suggest me to do. The only thing I "worry" is having to put a linear regulator. I found none of >5A for the voltage that I need.The boards that they use is based the same of mine but mine is mono:.This is fed with a 300VA 20V, that according to the calculations previously made are too many: [20 + (20 * 0.20)] * sqrt (2) = 33.94And 4 cap 10000 uF 50V.I start to think that they are crazy ...Bye, hitech95.

author: Ian.M
author_rank: Super Contributor
timestamp: May 26, 2015, 12:27:12 pm
content: Looking at the datasheet for the STA516B chip your supplier claims is on the modules,http://hifimediy.com/amplifiers/diy-amplifiers/T3-mono, S.T. recommend operation from a 50V rail. The module derates that to 48V. A good quality 240V primary 30V secondary transformer will give about 44V max on the reservoir cap. If you are using a 220V primary transformer you need a 28V one. That gives you an adequate margin for high mains conditions. If your preamp and other modules have a 30V max rating, use a linear regulator to feed them as their current consumption will be much lower. A low current negative rail can be provided from a capacitively coupled bridge rectifier. Make sure that all linear regulators have a high enough input voltage rating and are adequately heatsinked.

author: hitech95
author_rank: Regular Contributor
timestamp: May 26, 2015, 12:30:51 pm
content: Quote from: Ian.M on May 26, 2015, 12:27:12 pmYes but mine has a sta508 not a STA516B, I have the old version.Bye, hitech95.

author: Ian.M
author_rank: Super Contributor
timestamp: May 26, 2015, 12:38:21 pm
content: In that case, you need a lower voltage transformer or a commercial DC output regulated PSU module. If your design cant withstand 230V +10% (253V) AC input, it isn't fit for use in the EU.

author: hitech95
author_rank: Regular Contributor
timestamp: May 26, 2015, 12:40:22 pm
content: Quote from: Ian.M on May 26, 2015, 12:38:21 pmYea, I know. I need a lower Transformer or a Regulated supply. But HOW?I need 4.5A/5A at 26V with a linear regulator... I think that it is not so simple...

author: rsjsouza
author_rank: Super Contributor
timestamp: May 26, 2015, 05:46:34 pm
content: Quote from: hitech95 on May 26, 2015, 12:40:22 pmNo, it may not be trivial as you will have to assemble a circuit yourself.That said, the simplest way to have a linear regulator close to your specifications is to use aUA7824(24V, 1,5A) tied to an external high power PNP transistor - something similar to what is shown at "page 52" ofthis page(don't be fooled by the bad web design, as the guy is very experienced).If you intend to explore switching regulators but still keep the circuit simple, check theLM2679-ADJ.

author: hitech95
author_rank: Regular Contributor
timestamp: May 26, 2015, 05:53:58 pm
content: Quote from: rsjsouza on May 26, 2015, 05:46:34 pmInteresting even if you do not understand the operation. Unfortunately 24V are few.I would not use switching components for audio. Otherwise I would have used a ready-made power supplier.Bye, hitech95.

author: mariush
author_rank: Super Contributor
timestamp: May 26, 2015, 08:59:13 pm
content: There are linear regulators which can do high amperage, like LT1083 for example, which can do up to 7.5A .. unfortunately, this particular regulator can only handle up to 30v.There are linear regulators which can be connected in parallel to achieve higher currents... the one mentioned above (and LT1084 and LT1085, from the same family) can be configured like that.LT3086 for example can do up to 45v input, but can only do up to 2.1A ... however, it's possible to parallel 2 of those to get over 4A . They're expensive though, as most Linear ICs are (about 6-7$ a piece). There are cheaper linear regulators that can work together sharing the current.Older audio amplifiers use transistors to regulate the output voltage, somewhat similar to how bench power supplies do it. You could search for an old receiver/amplifier/something schematic on sites like electrotanya and get some inspiration from there. Or, have a look at the schematic attached (basically an opamp and some passives and a few transistors, after you remove the circuitry for relays and lcd display and so on which you wouldn't need)

author: hitech95
author_rank: Regular Contributor
timestamp: May 26, 2015, 09:18:03 pm
content: Quote from: mariush on May 26, 2015, 08:59:13 pmIt is probably the best choice. Although I do not know how to achieve it.If I understand it, I should find a transformer in which the output voltage is always greater than 26 + 2V. (Depending on the variations of the power grid)Probably at this point, should I use a switching power supply 28/30V and use a linear regulator to filter the power supply and bring it to 26V. In any case the problem would be is a regulator capable at least 30V and at least 5A.Quote from: mariush on May 26, 2015, 08:59:13 pmThis scares me. I am not able to use the transitor. (I've never learned)Bye, hitech95.

author: hitech95
author_rank: Regular Contributor
timestamp: May 26, 2015, 09:54:59 pm
content: I just found this:http://www.circuitdiagram.org/24v-5a-power-supply.htmlIt is an implementation similar to that suggested by rsjsouza, can someone explain the operation?From what I understand, the transistor is used to adjust the voltage and is controlled by the IC. But beyond that I do not understand each other.Bye, hitech95.

author: Ian.M
author_rank: Super Contributor
timestamp: May 26, 2015, 10:31:37 pm
content: There's really not much point in using a linear regulator to supply a class D output stage. As long as the switching frequency is well above the audio range and you have enough bulk capacitance to handle the maximum possible ripple current the output stage can pull, simply use a SMPSU. Run the preamp etc. at a lower voltage via a linear regulator to keep the switching hash out of that and make sure the preamp is well screened and you are most unlikely to be able to detect any difference compared to the same amplifier operating at the same rail voltages with an entirely linear PSU.

author: rsjsouza
author_rank: Super Contributor
timestamp: May 27, 2015, 11:46:26 am
content: Quote from: hitech95 on May 26, 2015, 09:54:59 pmWhen the power supply is turned on, the UA7824 will operate as it is intended (a voltage regulator) if the current is low - at this point the transistor is turned off and its voltage between the collector and emitter terminals (Vce) will be the same as the difference between the output of the rectifier and the output voltage of 24V.As the current flows from the in to the out pins of the UA7824, the resistor connected between the transistor's base and emitter pins will have a voltage across its terminals (ohm's law).As the current increases at about 0,65~0,7A, the voltage across the resistor's terminals will be 0,65~0,7V (1 ohm resistor), thus also increasing the voltage between the base and the emitter (Vbe) pins of the transistor. At that Vbevoltage, the transistor then starts to let current flow between the emitter and the collector terminals, which shares the current output with the UA7824. The way the transistor lets more current flow through these terminals is to reduce its collector emitter voltage or Vce.As the current increases, most of it is flowing through the transistor but the UA7824 still performs its intended function of regulating the voltage output. For example, if the transistor starts letting too much voltage go through its terminals (by reducing too much its Vce), the UA7824 will sense the voltage increase in the output and reduce its own current flow, which reduces the current flowing through the resistor, thus decreasing the Vbevoltage and consequently increasing the Vcevoltage.One important detail to consider is the fact this topology will dissipate a lot of heat (or power), thus reducing the available power to the PA itself. For example, if the output of the rectifier is around 30V at 5A, the transistor will have the voltage difference (30-24V) across its terminals and about 4~4,5A will flow through it, which means it will convert 27W (6V * 4,5A) to heat that will be dissipated through its case. This is more than 20% of 120W that the transformer can deliver and is the only reason why folks are suggesting to use a switching power supply.Quote from: Ian.M on May 26, 2015, 10:31:37 pmAlthough I agree 100% with this due to efficiency, I have seen in the past severe intermodulation noise between the SMPS and the class D output, especially when both switchers are out of sync. Keep in mind that intermodulation noise can happen even when the switchers are operating at very high frequencies, but close enough to reach the audible range. That can be fixed by syncing both switchers, but it may not be trivial.

author: Ian.M
author_rank: Super Contributor
timestamp: May 27, 2015, 01:50:55 pm
content: Quote from: rsjsouza on May 27, 2015, 11:46:26 amWhich is why I emphasised that there *MUST* be enough bulk capacitance to handle the ripple current with sufficiently small ripple voltage to minimise any intermodulation. Adding a large high current choke between the PSU and the reservoir capacitor bank will also be helpful.

author: hitech95
author_rank: Regular Contributor
timestamp: May 27, 2015, 02:47:13 pm
content: OK, you convinced me.You have explained a lot of things.So in summary, a linear regulator is out of the question for the cost and the energy dissipated. (Lost)At this point there are two choices: (At least the ones I know)A switching power supplySwitching regulator. In this case I can keep the two toroidal transformers and stabilize the voltage.(I think, but I'm not sure) that the best choice is the second one, because that way I can design the section of the capacitors in relation to my use.Does anyone have any recommend schematic or IC?@rsjsouzaThanks for the explanation, I had not considered the function of resistor (1Ohm).Hello, hitech95

author: rsjsouza
author_rank: Super Contributor
timestamp: May 27, 2015, 05:16:34 pm
content: Quote from: hitech95 on May 27, 2015, 02:47:13 pmAs I mentioned before, theLM2679may work for you. Also, they have aready-to-assemble PCB boardif you want to have some fun. You will have to check the device's datasheet to see the values of the components, though.You can also get an assembled development kit (I foundthis other onebased on theTPS54541) and modify it to suit the specs you need. To do these calculations, you can simply put the values in their online simulation/circuit design tools online (called webench).I did a quick test and gotthis design- schematics also attached. I used Vin= 30~36V, Vout= 26V, Iout= 5AI am pretty sure there are complete modules around on Alibaba, eBay, etc, but the info above is on the spirit of learning and assembling with practical tools.

author: hitech95
author_rank: Regular Contributor
timestamp: May 27, 2015, 09:21:12 pm
content: Quote from: rsjsouza on May 27, 2015, 05:16:34 pmWTF?EDIT:I gave it a quick read to the datasheet.Many things I have not clear. (Stupid deficiencies)Someone is kind enough to explain? (PWRGD is a output? Why there is a generator?, same for the Load...)Another question: how the hell do I can solder that thing? It is tiny!Doing a quick calculation, I noticed that I should do the tracks 3mm width, but now the entire IC is 3mm; how the hell do I do?Thanks, hitech95

author: hitech95
author_rank: Regular Contributor
timestamp: May 29, 2015, 12:43:57 pm
content: UP?

author: hitech95
author_rank: Regular Contributor
timestamp: May 30, 2015, 11:45:00 pm
content: Quote from: rsjsouza on May 27, 2015, 05:16:34 pmThird UP.I think it's better the LM2679. I'm not sure but it is easier to solder and should be even easier to dissipate.Unfortunately I lose the ability to know if the power has some problems. (PWRGD)I have read the datasheet but I did not understand how to calculate the values of some components. (Diode, condensers, etc.)Bye, hitech95.

author: hitech95
author_rank: Regular Contributor
timestamp: June 07, 2015, 09:44:07 pm
content: It seems the topic is dead. No one can answer my questions ...In short, I do not ask a scheme but would like to understand how to do.rsjsouza gave an example, with everything I need, but I did not understand what he did to find that solution. It seems difficult to achieve because of the IC package.I have no way to solder "dense" SMD components.Bye, hitech95

author: mariush
author_rank: Super Contributor
timestamp: June 08, 2015, 12:12:49 am
content: Quote from: hitech95 on June 07, 2015, 09:44:07 pmThen pick another IC with an easier to use package. Same with the SMD components, for probably 95% of the basic smd components out there (capacitors, diodes, inductors) there are through hole alternatives out there.Just go to an online store like digikey.com , farnell.com, mouser.com , tme.eu and go through their list of parts and find parts that match (or exceed) the specifications you need.That ti webbench software can give you circuit examples and for each part in the circuit, they usually offer alternate parts or suggest other parts if you change the slider (on the page) to trade between performance and used pcb area for example. You just have to be curious and interested enough to do some research and play around with that software.Look up at the parts they recommend, see what key specifications must be met, then look up the component code at the online stores I mentioned, or look up suggested alternatives if you don't find that exact part, or if you're really out of luck search for similar components that meet or exceed those specifications. It's really not hard, just annoying process, takes time.QuotePeople answer when there's something worthwhile to answer to.

author: Ian.M
author_rank: Super Contributor
timestamp: June 08, 2015, 12:35:31 am
content: Simply get some suitable switching regulator modules and get it up and running.Your mistake was getting both the amplifier modules and the incompatible transformers.If you want to design it yourself, don't order any parts before you have checked the whole design. If you are working around some part or module that was too good a deal to miss, don't get any other parts until you have worked out how the good deal parts requirements constrain the rest of the design.If you want to assemble this from loose components, why did you even buy amplifier modules rather than assembling them yourself?If you want the experience of assembling it yourself from individual components, start with a design published in a magazine for which a kit is available. The parts will have been chosen to work together and have appropriate voltage ratings.

author: hitech95
author_rank: Regular Contributor
timestamp: June 08, 2015, 06:40:27 pm
content: I decided to start from scratch.Then. I chose the new components, using some SMD resistors and SMD capacitors.I noticed a discrepancy in the datasheet of the LM4880 that I would use. I therefore ask you more experienced if it is so and how can I fix the possible problem.Reading the electrical characteristics it appears that it (LM4880) accept as input signal only a voltage ranging from -0.3V to Vdd + 0.3VIf I understand correctly it means that if I send a AC signal the chip can be damaged because it can't handle negative values.The reasoning that I just made is correct?I decided to use as a preamplifier,TDA7439DSapparently there may be a DC component up to 4V (VOUTDC, look onthe Datasheet). If I have not misunderstood I can use a capacitor for eliminate it.Remaining on TDA, I noticed there is a capacitor on the CREF Pin, but not understand which type should be.This question applies to all instead chip: The decoupling capacitor of that material feeds should put it? I've seen various solutions: ceramic, polyester, electrolytic, tantalum. You can explain how to choose the type of capacitor? I need to figure out what to put for the TDA and the LM.About the power final I got some 90W, 8 ohm speakers.Would that then the final can safely drive: 80W.Then V = sqrt (80 *= 25.3. So are the usual 26V.IMAX = (80W + 25%)/26 = 3.8 to so we can fit them in 4A.(The 25% is caused of inefficience, switch regulator, D class, other)Then again doing the sum I need at least 105VA.But this will be assessed later. For now I want to focus on the controller board.Thanks, hitech95

author: bson
author_rank: Unknown
timestamp: June 08, 2015, 07:35:03 pm
content: Make sure your rail caps are dimensioned for the worst case, which is the absolute max rail-to-rail voltage times some safety margin. This is needed because your ground will be coupled to safety earth, to the chassis, and if one of the rails shorts to the chassis this means half your caps will sit between the rails until the fuse or something else (like a rectifier) blows. You don't want this under any circumstance while you have the lid off and are poking around inside it to see what's going on (it may be a progressive failure you're trying to diagnose on a live supply that suddenly fails completely on you).

author: hitech95
author_rank: Regular Contributor
timestamp: June 08, 2015, 07:42:01 pm
content: Quote from: bson on June 08, 2015, 07:35:03 pmI must apologize but I do not know some words in English and therefore do not understand the explanation:rail capsrail-to-rail voltageIn theory there should be a safety fuse.I "know" that the voltage rating of a capacitor is approximately three times the voltage.Bye, hitech95

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 08, 2015, 08:02:35 pm
content: "rail" refers to the main positive and negative voltage supply wires. It is like the two steel rails that train cars run on. A rail on each side. When you look at a typical electronic schematic diagram you can see one wire ("rail") having the main positive power supply (typically at the top of the diagram). And then typically along the bottom of the diagram, the main negative supply "rail".When bson refers to "rail caps" he means the big filter capacitors on the main power supply "rails" (the positive power node, and the negative power node).The term "rail-to-rail" refers to the total voltage from the negative rail up to the positive rail. For example if you had -15V negative rail, and +15V positive rail, you would have 30V "rail-to-rail".Electrolytic capacitors are made in rather "standard" voltages like 10, 16, 25, 35, 50, 75, 100, 150V, etc. Of course you should always use a capacitor of higher voltage rating than the circuit is designed for. But I have never seen anybody use capacitors that are 3x over-rated. It is rare to see even 2x over-rated except at very low voltages. And many observe that using large electrolytics at a fraction of their rated voltage actually may be a disadvantage because they require something near the design voltage to develop the rated capacitance value.

author: hitech95
author_rank: Regular Contributor
timestamp: June 08, 2015, 08:11:30 pm
content: Quote from: Richard Crowley on June 08, 2015, 08:02:35 pmThanks for the explanation, now I understand.I do not remember who told me this thing of "multiply by 3".Now need to know which material for the cap.To power the headphone amplifier I found a LT1763-5. It seems to be easy to use and does what it needs. But also it had no need of many external components.Instead to provide 9V to the TDA I have found a L78L09.I'd say they are perfect for my needs.What do you say?Bye, hitech95.

author: oldway
author_rank: Super Contributor
timestamp: June 08, 2015, 08:27:04 pm
content: Why not to begin with an audio kit ?For example, a K4003 Velleman stereo amplifier kit.2 x 15Wrms in 4ohm or 2 x 10Wrms in 8ohm.Short circuit proof.You only need a 2x12V 80VA transformer.http://www.vellemanprojects.eu/downloads/0/illustrated/illustrated_assembly_manual_k4003_rev1.pdfFor tone control, you can use a K8084 Velleman volume and tone control preamplifier kit.http://www.vellemanprojects.eu/downloads/0/illustrated/illustrated_assembly_manual_k8084.pdf

author: hitech95
author_rank: Regular Contributor
timestamp: June 08, 2015, 08:29:28 pm
content: Quote from: oldway on June 08, 2015, 08:27:04 pmWhy should I? I want to learn how to make circuits, no soldering.Bye, hitech95.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 08, 2015, 08:43:16 pm
content: Quote from: hitech95 on June 08, 2015, 08:11:30 pmI do not understand the question? Most conventional larger power-supply filter capacitors are "aluminum electrolytic". I see no reason to use anything other than the most common kind of capacitor there.QuotePlease remind us which headphone amplifier you are using? And why you need a regulator for it?QuoteYes, 78L09 is probably a good regulator for the TDA7439 audio processor chip.QuoteWe typically say "bye" only at the END of a conversation, when we don't expect any further response.It seems strange for you to say "Bye" every time in the middle of this conversation.

author: hitech95
author_rank: Regular Contributor
timestamp: June 08, 2015, 08:54:18 pm
content: Quote from: Richard Crowley on June 08, 2015, 08:43:16 pmI do not understand what type of capacitor to use for each type of use.For example for the rail cap we use the electrolytic. For the decoupling capacitors are used instead of a lot of different types and I do not understand the "rule".Quote from: Richard Crowley on June 08, 2015, 08:43:16 pmI invite you to read this post:Quote from: hitech95 on June 08, 2015, 06:40:27 pmThe amplifier is a LM4880.Quote from: Richard Crowley on June 08, 2015, 08:43:16 pmAt least one thing I have chosen correctly.Quote from: Richard Crowley on June 08, 2015, 08:43:16 pmI apologize for the mistakes. It is probably best a "thanks".Thanks, hitech95.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 08, 2015, 09:51:50 pm
content: For larger value capacitors (generally over 1uF) we typically use aluminum electrolytic because of the space (and cost) efficiency.And for smaller value capacitors, there is a wider variety of types to choose from. Poly film are favorites of audiophiles.The LM4880 is specified for: "2.7V to 5.5V". WHY do you need ANY kind of voltage regulator there?That chip is made for portable applications so that it will continue to operate within spec while the battery discharges.Regulating the supply voltage for that chip appears to have no motivation here.

author: hitech95
author_rank: Regular Contributor
timestamp: June 08, 2015, 10:02:30 pm
content: Quote from: Richard Crowley on June 08, 2015, 09:51:50 pmI need the regulator because I haven't the 5V, I only 3.3V and 9V.Thanks, hitech95.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 08, 2015, 10:13:01 pm
content: Quote from: hitech95 on June 08, 2015, 10:02:30 pmBut the LM4880 will be very happy with 3.3V. It is well within the design parameters for supply voltage.

author: hitech95
author_rank: Regular Contributor
timestamp: June 08, 2015, 10:25:59 pm
content: Quote from: Richard Crowley on June 08, 2015, 10:13:01 pmOk.Can you explain me this?QuoteThanks, hitech95.

author: mariush
author_rank: Super Contributor
timestamp: June 08, 2015, 10:26:53 pm
content: Be careful about what 7809 regulator you use, aL78L09can provide onlyup to 100 mA, see datasheet:http://www.st.com/web/en/resource/technical/document/datasheet/CD00000446.pdf... and even then it will be a pain in the ass to keep its temperature down if it's in a TO-92 package. The standard 7809 in to-220 packages can do up to 1-1.5A (with a small heatsink attached to them)

author: hitech95
author_rank: Regular Contributor
timestamp: June 08, 2015, 10:39:09 pm
content: Quote from: mariush on June 08, 2015, 10:26:53 pmIt has to power only theTDA4839DS:IS Supply Currrent Min:4 Typ:7 Max:10 Unit: mAThanks, hitech95.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 08, 2015, 10:40:40 pm
content: Quote from: mariush on June 08, 2015, 10:26:53 pmWhich is 10x more than the TDA7439 load requires. (7~10 mA) So it is well able to handle such a small load.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 08, 2015, 10:44:19 pm
content: Quote from: hitech95 on June 08, 2015, 10:25:59 pmYes, that is true. But if you look at the suggested circuit, you will see that the amplifier is operated at VDD/2 which is well above 0V ground. Note that the AC audio signal coming in is DC-blocked with CI(the input capacitor) and the output is DC-blocked with CO(the output capacitor)

author: hitech95
author_rank: Regular Contributor
timestamp: June 08, 2015, 10:59:15 pm
content: Quote from: Richard Crowley on June 08, 2015, 10:44:19 pmSo how do I connect an audio source? If I am not mistaken the audio signal is AC.Thanks, hitech95.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 08, 2015, 11:22:42 pm
content: Quote from: hitech95 on June 08, 2015, 10:59:15 pmYou connect the audio source to the left side of Cias shown in the diagram where it says "Audio Input"If you have questions about reading the schematic diagrams, please ask and we can help you.

author: hitech95
author_rank: Regular Contributor
timestamp: June 08, 2015, 11:27:30 pm
content: Quote from: Richard Crowley on June 08, 2015, 11:22:42 pmUnfortunately I can not understand the solution.Good night / good morning depending on your time zone. For me it is time to go to sleep.

author: oldway
author_rank: Super Contributor
timestamp: June 09, 2015, 02:07:27 pm
content: Quote from: hitech95 on June 08, 2015, 08:29:28 pmI think it is not possible to learn to make circuits without knowledge of electricity and basic electronics.You are the wrong way...First look after electricity and electronics courses on Internet before trying to build an amplifier.

author: hitech95
author_rank: Regular Contributor
timestamp: June 09, 2015, 02:42:51 pm
content: Quote from: oldway on June 09, 2015, 02:07:27 pmI invite you to read the first post:Quote from: hitech95 on May 23, 2015, 09:40:26 pmI can understand a lot of things, but I can have gaps.To sum up, I make a list of everything I studied:Ohm's LawThévenin's theoremKirchhoff's circuit lawsElectrical networksLogic gates (AND OR NOT etc.)Latch (SR/D)Flip-flop (T/JK)Karnaugh mapCircuits: sinusoidalCircuits: response in time and in frequencyFilters of first and second orderBode plotOperational Amplifiers (Open loop and closed loop)Operational Amplifier: inverting and non-invertingDifferential amplifier with OP.buffer with OP.I/V converter and V/IAdders with OP(inverting that non-inverting)Filters (Integrator and differentiator with OP)ADC and DACSample and HoldAnalysis and design of a circuit for reading analog sensors. (Temp / pressure sensor)Information theory: entropy, words, useful information, etc.Thanks, hitech95.

author: Ian.M
author_rank: Super Contributor
timestamp: June 09, 2015, 03:16:00 pm
content: You wont gain much from kludging together off-the-shelf modules you don't fully understand. If you build from component level at least you have a full schematic, and if the instructions are any good, they will go into the circuit's operation in considerable detail.* Start with a published design.* Study it, do the design calcs and see if you get the same answers.* Build it from loose components, and test it, logging test data and checking how closely it matches simulation results.* Pick a section to improve, and isolate that section.* Design, build and test the replacement section.* Insert it in place of the isolated section, and retest complete system.Eventually you will have upgraded everything and will have an amplifier that's all your own work. At that point you can remove the old main board (and reconnect all the sections you isolated so its usable again), and connect the modules you designed back together, tidying up the layout as you go. You will now be ready to design a PCB for it and build a one board version.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 09, 2015, 03:34:25 pm
content: Quote from: hitech95 on June 09, 2015, 02:42:51 pmIf you understand all those things, then what is it about "Audio Input" that you don't understand?It seems rather obvious that is where you "connect an audio source".Have you drawn out the whole circuit showing how everything connects together?

author: hitech95
author_rank: Regular Contributor
timestamp: June 09, 2015, 03:40:43 pm
content: Quote from: Richard Crowley on June 09, 2015, 03:34:25 pmPerhaps I failed to make me understand.I meant: Many of the things you write I'm able to understand but some not. Although I studied electronics.I can not figure out how to connect an AC source (center 0V) to a chip that only accepts a positive signal (center VDD / 2).If I understand it the input capacitors only serve to eliminate the DC component of the signal.Thanks, hitech95.

author: Ian.M
author_rank: Super Contributor
timestamp: June 09, 2015, 03:46:22 pm
content: The coupling cap blocks DC. The far side of the coupling cap can then be biassed to whatever DC level is appropriate for the next stage.

author: hitech95
author_rank: Regular Contributor
timestamp: June 09, 2015, 04:01:41 pm
content: This part I did not understand:Quote from: Ian.M on June 09, 2015, 03:46:22 pm

author: Ian.M
author_rank: Super Contributor
timestamp: June 09, 2015, 04:13:04 pm
content: Line input side of cap: 0.894 Vpk-pk, 0V DC level (ground referenced).May have a resistor (e.g. 100K) to ground to discharge any static.Amplifier side of cap: 0.894 Vpk-pk, Vdd/2 DC level.DC level either set by the amplifier's negative feedback or by a potential divider across the supply rails (e.g. two 22K resistors).The DC voltage measured across the cap is the difference between the two DC levels.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 09, 2015, 04:16:51 pm
content: Perhaps you need to study more simple things like resistors and capacitors, how they work and how they are used.Google returned "About 14,700,000 results (0.32 seconds)" for: how does a capacitor workIn the circuit I cited, the left side of the capacitor can accept an audio signal which is zero-referenced (above and below ground),but the right side of the capacitor rests at VDD/2, which is the "operating point" of the op-amp inside the LM4880 integrated circuit.The capacitor BLOCKS the DC voltage difference, but it PASSES the AC signal (audio) through the capacitor.

author: hitech95
author_rank: Regular Contributor
timestamp: June 09, 2015, 04:24:06 pm
content: Quote from: Richard Crowley on June 09, 2015, 04:16:51 pmOk, now I understand.I had never seen a circuit of this type. I studied the only operational with dual voltage.I did not think that capacitors would work in this "reverse" way.Unfortunately I have studied only a few examples. Also no one has ever explained all the applications of a condenser.Question: it must be a polarized capacitor?Thanks, hitech95.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 09, 2015, 05:28:34 pm
content: Quote from: hitech95 on June 09, 2015, 04:24:06 pmIf you have enough space (and money) to put in a large non-polar capacitor that is OK.But for large-value capacitors, most people save space and money by using polar capacitors.Because they are smaller and less expensive for equivalent capacitance value.By "large value" a very rough dividing line I use is 1uF.

author: hitech95
author_rank: Regular Contributor
timestamp: June 09, 2015, 05:44:19 pm
content: Quote from: Richard Crowley on June 09, 2015, 05:28:34 pmI read some documents about capacitors. Unfortunately, nothing new ...Now I have to do is figure out the value of the capacitor to put.I also have to calculate the value of the resistors. (Gain)

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 09, 2015, 06:00:01 pm
content: The gain is calculated from the expected audio signal level from the source (your volume/tone control chip).The value of the capacitor is selected to provide adequate low-frequency performance.For example: if you assume a 20K load impedance (the value of Ri), you can use the standard formulas for calculating the reactance of the capacitor at a given frequency. I have a "RFC calculator" online at:http://www.rcrowley.com/rfc.htmIf you use a 0.5uF capacitor, it will have a reactance of 20K ohms at around 16 Hz.That means that if you use a 0.5uF capacitor for Ci, your circuit will have a 3dB rolloff at 16Hz. Which seems perfect for use with headphones.And for the output capacitor, Co, if you have 32 ohm load, you would need 312uF for a 3dB rolloff at 16Hz.

author: hitech95
author_rank: Regular Contributor
timestamp: June 09, 2015, 06:37:29 pm
content: Quote from: Richard Crowley on June 09, 2015, 06:00:01 pmToo fast. I did not understand how you did the math.Ugh, why not teach us these things in school ...EDIT:I did not understand the logic in associating the input resistance to the reactance of the capacitor.I did not understand what you mean by 3dB rolloff.

author: oldway
author_rank: Super Contributor
timestamp: June 09, 2015, 06:38:57 pm
content: I think you need a very basic and practical course like this one:http://www.learnerstv.com/Free-engineering-Video-lectures-ltv052-Page1.htm

author: hitech95
author_rank: Regular Contributor
timestamp: June 09, 2015, 06:43:01 pm
content: Quote from: oldway on June 09, 2015, 06:38:57 pmEhm... Ok...Problem: the stupid Flash Player...EDIT:It 'a shame, the pronunciation is very bad.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 09, 2015, 08:10:21 pm
content: At that particular point in the circuit (Ci) the "load impedance" consists of Ri.That is because the right end of Riis "virtual ground". Hopefully you learned that from studying op-amp circuits.Since we have a different DC reference in the source AC signal (the audio from your TDA7439) than the LM4880 wants, we must use a DC-blocking AC-coupling capacitor (Ci)The series capacitor Ciand the parallel resistance Riform a high-pass filter.So we must chose a value for Ciwhich is large enough to pass-through the lowest frequency of interest."Roll-off" refers to the decrease in the signal because of a filter function.Most of these terms are adequately defined and illustrated on Wikipedia:http://en.wikipedia.org/wiki/Roll-offIt is good practice to attempt to look up unfamiliar terms on Google or Wikipedia and study the explanations for yourself.Then if you don't understand the explanation, tell us what you don't understand and where you found it.We will be happy to help you understand the terms.But simply asking for an explanation without first trying to discover it yourself makes people think you are lazy and wanting us to do the work for you.Standard "audio frequency band" is 20Hz to 20KHz.So we would like to have the circuit pass everything from 20Hz to 20KHz without reducing the audio ("roll-off")The series capacitor Ciand the parallel resistance Rialso form a "voltage divider".But the "voltage division" depends on what frequency you are talking about.A very simple voltage divider with two equal resistors will divide the voltage in half.So, at a single frequency, if we select a capacitor whose reactance is equal to the load impedance,then we have a 50% voltage divider at that frequency. 50% is 3dB in terms of voltage.If I go to that RFC calculator page and plug in 20000 ohms, and 20Hz, it says that a 0.397885 uF capacitor is 20K ohms at 20Hz.So If I go back and select 20000 ohms, and use a "standard" capacitor value like 0.5uF, it says that at 15.91Hz, a 0.5uF capacitor = 20K ohms.That means that your frequency response will be down 3dB at 16Hz which sounds very good to me for a headphone amplifier.If you used a 1.0uF capacitor, you would have a 3dB-down frequency of 8Hz. And it is unlikely that your headphones will reproduce 8Hz.And you can use the same technique for selecting the output capacitor (Co) assuming you know the impedance of your headphones.

author: hitech95
author_rank: Regular Contributor
timestamp: June 09, 2015, 08:29:46 pm
content: Quote from: Richard Crowley on June 09, 2015, 08:10:21 pmYea, you're right!Quote from: Richard Crowley on June 09, 2015, 08:10:21 pmSo far, I'm there!Quote from: Richard Crowley on June 09, 2015, 08:10:21 pmMy fault, I was studying for an exam and I did not have time to check.I apologize if I gave the wrong impression. I'm here to learn, not to make you lose time.Quote from: Richard Crowley on June 09, 2015, 08:10:21 pmOh, now I understand the reasoning!Thanks, and sorry if I ask stupid questions.Unfortunately, I am realizing that what I learned is useless on the practical side.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 09, 2015, 08:48:24 pm
content: Quote from: hitech95 on June 09, 2015, 08:29:46 pmStudying for your exam is probably more important than this!QuoteIt is better to show that you are willing to learn for yourself and ask us questions you can't find for yourself.QuoteThe questions are not "stupid". There is a saying in English "The only stupid question is the one that you didn't ask."But it is sometimes difficult to understand what you know so we know what words to use.QuoteNo, that is probably not true. It simply does not apply to THIS particular problem.But it may be very useful information for OTHER problems.

author: hitech95
author_rank: Regular Contributor
timestamp: June 11, 2015, 02:06:52 pm
content: Quote from: Richard Crowley on June 09, 2015, 08:48:24 pmIn a moment of madness I had the idea that the gain varies depending on the input signal. This means that the output of the TDA must always have a signal at line level.This it also needed to calculate the gain of the headphones amplifier.My question is: I have to make a circuit that automatically adjust the gain? If so I have to make digital (The TDA has a GAIN register).Now, however, a problem arises: What solution?I decided to sample the signal after the MUX of the TDA, calculate and adjust the gain in the chip as a result of the calculations.Could it be enough? There are simpler solutions?This project is becoming more complicated than expected. But I'm learning so many new things.Thanks, hitech95.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 11, 2015, 03:49:10 pm
content: Yes I think you are still suffering from madness.If you want to make a practical audio amplifier circuit for speech/music listening, there is no reason for automatic gain.Adjusting the gain to maintain a constant output signal will effectively RUIN most speech or audio signals."Natural" sound that we hear normally has a wide variation in levels. If it was all the same level, it might drive us into madness.If you want to make an AGC (automatic gain control) there are many more factors that you have not even thought about yet.Like attack and release time, etc. Again suggest at least reading about it first:http://en.wikipedia.org/wiki/Automatic_gain_control.We often use automatic gain when we are recording and producing recordings.But it is rarely or never used at the end of the "signal chain" when replaying the recordings.

author: hitech95
author_rank: Regular Contributor
timestamp: June 11, 2015, 04:02:43 pm
content: Quote from: Richard Crowley on June 11, 2015, 03:49:10 pmThanks for the explanation.I have a question about this scheme:From what I understand CSis a bypass capacitor, and if I understand it takes to combat distortion and should be made of ceramic materials.Instead CBtakes to achieve ground VDD/ 2. I do not understand what kind it should be: electrolytic or ceramic.The two input capacitors I have chosen are 470nF polypropylene.Those output are 470uF electrolytic.I'm going crazy.Some components are available on farnell, some on RS and others DigiKey...I want to order some chips to test them on the breadboard and then make the PCB ...Thanks, hitech95.Bye, hitech95.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 11, 2015, 05:43:00 pm
content: Quote from: hitech95 on June 11, 2015, 04:02:43 pmCSis there to suppress any high-frequency oscillation that might happen. The materials are not critical. Its only purpose is to "short" (conduct) any high frequency AC directly to ground. Note that it should be located physically very close to the chip pin 8 and have a good, low-impedance path to ground (pin 4).QuoteThe type of capacitor is not critical. However, note that a 1uF non-polar capacitor will be quite large compared to a 1uF electrolytic, especially since it is operating at such a low voltage.

author: hitech95
author_rank: Regular Contributor
timestamp: June 11, 2015, 07:52:47 pm
content: Quote from: Richard Crowley on June 11, 2015, 05:43:00 pmThanks again.This is a draft of the PCB.I hope that is correct, (Or at least in part). I've never done anything with analog signals ...

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 11, 2015, 08:11:12 pm
content: Until you confirm that the schematic diagram is correct, laying out a PC board is premature.Did you share the schematic diagram? I don't remember seeing it.Your PC board image shows that it is not complete. There are many parts missing and/or not routed.That is what all those fine yellow lines show (they are "error messages")

author: hitech95
author_rank: Regular Contributor
timestamp: June 11, 2015, 08:28:36 pm
content: Quote from: Richard Crowley on June 11, 2015, 08:11:12 pmThe missing part is the digital section.A connector for the front panel, and connectors to relays. There is also a PCF8574T. (Needless) In the previous version the processor was on the front.The Schematic:LinkA connector for the front panel, and connectors to control Rale. There is also a PCF8574T. (Needless) In the previous version the processor was on the front.]LinkEDIT: borken URL