Guitar/Audio amp poor quality - Page 1
Forum section: electronics / beginners

author: SuperJeep
author_rank: Contributor
timestamp: August 18, 2011, 06:03:00 am
content: First of i'd like to say hi to everyone, just signed up (can't stop watching eevblog on youtube!) and can't wait to expand on my electronics background!Heres a problem I'm having with a guitar/audio amplifier I built using a TDA2030 chip.The schematic I followed is here:http://circuits.datasheetdir.com/271/TDA2030-circuits.jpg1.) can someone please explain what the arrow from the 1uF cap at pin 1 means, when it points to Vi?I just wired my input jack directly to the 1uf and then grounded it through a 22K resistor, is that correct?2.) It works, I can hear my guitar and mp3's through the speaker ( 30W 6ohm speaker) But It's very poor quality and I guess the term is "noisy" kind of static-ey even. EDIT( used 9-12 volt dc power adapter as a source)Is there any way I can filter this better? Or is it because the project is sitting on a solderless breadboard?I appreciate any help and look forward to lurching around on this forum!tl;dr? I'm basically looking to clean up static and bad sound quality on a TDA2030 audio amplifier circuit.

author: Unknown
author_rank: Unknown
timestamp: August 18, 2011, 06:12:09 am
content: As Dave might have said, "Thou Shalt Check Voltages"Most obvious thing to do is to check for ripple on your supply voltage.

author: Deepak
author_rank: Regular Contributor
timestamp: August 18, 2011, 06:54:55 am
content: It's a potentiometer - the top and bottom are the two outer terminals, and the arrow is the terminal for the wiper.http://www.kpsec.freeuk.com/symbol.htm#resistors

author: Kibi
author_rank: Unknown
timestamp: August 18, 2011, 07:55:52 am
content: Quote from: Deepak on August 18, 2011, 06:54:55 am^^ Ye, what he said ^^You need to connect one of the outer terminals of the 22K potentiometer to GND. The centre terminal, the one with the arrow on the circuit diagram, needs to connect to the 1uF capacitor. The input will be connected to the other outer terminal of the potentiometer and GND.

author: SuperJeep
author_rank: Contributor
timestamp: August 18, 2011, 10:11:07 am
content: Oh that makes sense now, thank you. Alright i re-wired the input and its still very choppy, as if im not getting the full signal from the input.I think its my power source. I simply plugged it straight into a direct 12volt wall adapter, But im reading things about the circuit needing a symmetric power supply but I don't understand what they are, nor do I have a center-tapped transformer.

author: Psi
author_rank: Super Contributor
timestamp: August 18, 2011, 11:11:32 am
content: The circuit you have doesn't need a symmetric power supply, it's designed to only need a single 12v supply.Try running it from some batteries, that will check if the problem is with your powersupply.If you don't have enough batteries for 12V you could try some wires to a car battery,but be careful when doing that. A car battery can supply a lot of energy and can destroy your circuit if you connect it up wrong. It can also give you serious burns if you short it out.

author: ciccio
author_rank: Frequent Contributor
timestamp: August 18, 2011, 11:22:54 am
content: The schematic is correct, it will work on a single voltage power supply, not on a dual voltage (+/-).The voltage gain is about 30 (150k / 4.7k) and is too low for good amplification of the signal from an electric guitar's pick-up. You need a preamplifier stage.Google for "electric guitar preamplifier" and you will find a lot of them, like the one I attach.This one needs dual power supplies for the op-amps, or you must add a "virtual ground" if you want to use a single voltage power supply.If you are interested, I can try to draw and post a complete schematic for the preamp, but I think that it is better to look for a kit, or at least for some project with the drawing of a PCB (you can copy the PCB on perf-board) because if you don't have some experience in grounding and correct components placement noise will always be a great problem.Please note: I don't want to discourage you (having the power amplifier working on perforated board is a good and respectable achievement for a beginner !!!).

author: SuperJeep
author_rank: Contributor
timestamp: August 18, 2011, 01:51:38 pm
content: I'm going to try a different power source and see if that cleans it up.EDIT: wow I ran the circuit with 4 AA batteries and it plays music really clear. I guess it really was my cheap power source. I'm taking a look at pre amps now.Alright so this thing works perfectly with my guitar too, amplifies the sound with a solid tone and barely any break up at volumes above what i need it for.Thank you everyone you've been very helpful!Just one more question, If 4AA batteries work perfectly and my wall wart adapter didn't, what could be the cause of that?

author: Unknown
author_rank: Unknown
timestamp: August 18, 2011, 02:31:27 pm
content: One little trick I used to pull is to connect a speaker and a cap across the power input and listen for the ripple. In the absence of test equipment it works pretty well. What is happening here is the cap blocking any DC and thus preventing the speaker from burning but letting pass any AC ripple to the speaker. Basically any humming or buzzing noise that you hear is the AC ripple of your power supply. To remedy this you need more filter caps on the power line (and) or a beefier transformer.A word of caution tough,do not forget the capacitorin series with the speaker, otherwise you will burn it.

author: SuperJeep
author_rank: Contributor
timestamp: August 18, 2011, 02:40:43 pm
content: ohh I see. I do hear alot of buzz when using my power adapter but almost none with the batteries. I guess I just need a better supply voltage which is relieving since my first amplifier actually works haha. I'm running a fat 1500uF cap in series with my speaker at all times, and an other across my power terminals.

author: Kibi
author_rank: Unknown
timestamp: August 19, 2011, 04:14:16 pm
content: Running a good amplifier like this off of a wall wart is not going to work very well.Granted, I have not seen the wall wart you are trying to use, but there is a very slim chance it is regulated at all and is unlikely able to maintain ripple free 12v supply above 150-200mA. An amplifier like that probably has a quiescent current in that range. The quiescent current is the minimum current required to run the amplifier and bias the output transistors with no signal input. When you actually feed a signal into the amplifier, the current increases.The power supply is an extremely important part of a power amplifier. Although an amplifier, well, amplifies the signal, it relies on the power supply to do this.Think of the amplifier as a fast acting switch which sits in-between your power supply and your loudspeaker. It just varies the amount of current flowing between the power supply and the loudspeaker. If the power supply is crappy, then you will get a crappy signal to your loudspeaker.If the TDA2030 is outputting 14W, it needs just over an amp at 12v to accomplish this, then you have to account for losses such as heat. For this setup I'd try and find or build a power supply that is capable of 12v, 2A minimum to get good results.

author: SuperJeep
author_rank: Contributor
timestamp: August 19, 2011, 05:19:52 pm
content: I bought this one from a dodgy electronics store for 5 bucks, its one of those variable ac/dc adapters so you can select voltages between 3 and 12volts. So your right about it being bad quality.I actually never knew how much of a difference a cleaner power source can have on a system, I'm quite the newbie haha. So If I wanted this thing to run off something other than AA bateries, what should I do? I apologize for asking so many questions in this thread, there's so much I have to learn! Would I just need to toss a voltage regulator IC into the circuit?

author: Unknown
author_rank: Unknown
timestamp: August 19, 2011, 05:44:25 pm
content: You can buy another one for 5$ and connect both of them in parallel.Or better still you can liberate a transformer from some junk and build your own power supply. A transformer from an old UPS will work like a charm. Those potted transformers from halogen spotlights work too. A big cap four diodes an you are good to go.

author: Bren
author_rank: Contributor
timestamp: August 19, 2011, 07:20:00 pm
content: A steady DC source is defiantly something to be desired in audio circuit design. This sets $500 audio preamplifier's apart from $2000 audio preamplifier's. Even the slightest ripple on the wall wart or power supply can be heard through the output, and is often amplified by the circuit itself.Two things to keep in mind when sourcing audio circuits:1. Never Ever use switching power supplies in audio circuit design or your going to face a lot of headaches in the future.Switching power supplies cause tones of ripple in the output and if not properly filtered (which many of theses online DIYcircuits are not), you will end up with a lot of noise in the circuit and on the output.2. Be aware of the current draw by the circuit and current supplied by the power supply.Starving a circuit for current or voltage will result in distortion, low amplitude, and an overall nasty sound.Bren

author: Unknown
author_rank: Unknown
timestamp: August 19, 2011, 08:28:29 pm
content: Quote from: Bren on August 19, 2011, 07:20:00 pmIf ripple is that critical, the designers should try designing an amp with a good power supply ripple rejection. Even a basic LM3875 IC power amplifier will have 100dB+ ripple rejection, and an opamp like a TL082 will have a similar figure. Of course switchers will be worse since PSRR tends to roll off with frequency.Quote from: Bren on August 19, 2011, 07:20:00 pmGuess the class D amplifiers only produce noise than, since it's basically a switching power supply as amplifier.

author: Zero999
author_rank: Super Contributor
timestamp: August 19, 2011, 08:51:53 pm
content: Try powering it off an 18V 3.5A lap top power supply.I'm surprised it worked from four NiMH batteries (4.8V in total), the TDA2003 isn't specified at voltages below 7.5V.The schematic is simply copied from the data sheet, which can be found below - I suggest you read it.http://www.datasheetcatalog.org/datasheet/stmicroelectronics/1458.pdf

author: SuperJeep
author_rank: Contributor
timestamp: August 20, 2011, 01:49:32 am
content: lots of informative replies thank you! Yeah it ran quite well off of 4 batteries, They were 1.5v alkaline though not NiMh although I should invest in some decent rechargeable batteries.I've made a quick video of the amp I made if anyone is curious. Go easy on me:P its my first project board so positioning of components probably isn't optimized.sorry about the quality

author: Zad
author_rank: Super Contributor
timestamp: August 20, 2011, 04:27:23 am
content: No need to apologise, that looks perfectly decent to me!

author: Unknown
author_rank: Unknown
timestamp: August 20, 2011, 05:41:49 am
content: Congratulations, it looks and sounds very good.

author: Zero999
author_rank: Super Contributor
timestamp: August 20, 2011, 10:40:43 am
content: Quote from: HAL-42b on August 19, 2011, 05:44:25 pmJust make sure they're the old fashioned low frequency iron cored type. Some newer high frequency halogen transformers are driven by an oscillator and output >20kHz which don't work open circuit, will cause traditional diodes to overheat and cause all sorts of trouble with noise.Quote from: Bren on August 19, 2011, 07:20:00 pmI don't think ripple is a problem here. If you read the datasheet for the TDA2003, you'll see it has a power supply rejection ratio of 50dB@100Hz which means that a ripple voltage on on the power supply will be divided by 1050/20= 316 so 1V of ripple on the supply will become 3.16mV at the output which is inaudible when put into a 6 Ohm speaker.Also anyone who even spends $500 on a preamplifier is an audiophool, let alone $2000 which should be enough for a decent hifi with good speakers and more. Modern op-amps which are good enough for audiophile use can be purchased very cheaply.QuoteThat's sound advice but only because the power supply rejection ratio of a typical audio amplifier decreases with increasing frequency.Yes maybe I shouldn't have suggested using a laptop power supply as it'll be an SMPS.QuoteI think that was the most likely problem, especially if the wall wart had a high impedance or was current limited by an electronic circuit so the voltage was suddenly dropping when the current through the speaker was at its peak.Quote from: SuperJeep on August 20, 2011, 01:49:32 amIf you measure the voltage across the AA cells, you'll probably find it drops way below 6V when the amplifier is playing music. You'll probably need to connect them to an oscilloscope to see this properly as the voltage will vary depending on the current through the speaker, it'll probably drop to 4V during the peaks.QuoteThanks for posting the video.How long do the batteries last for?Do you eventually want to run it from the mains are are you happy with batteries for now?For mains power you could use a 12V transformer, bridge rectifier an 4700uF capacitor.If you need to run it off a battery, a 12V 7Ah sealed lead acid battery with a 5A fuse is the way to go and you could build a charger for your next project.

author: SuperJeep
author_rank: Contributor
timestamp: August 20, 2011, 12:04:19 pm
content: haven't looked into how long the batteries last but I can't imagine it'll be for very long.This circuit will serve as a practice amp for my guitar (my current amp is too loud for late night use). Its also going to replace my laptop speakers when playing a movie without headphones so I'd probaby prefer running it off mains.I've retired a few computer power supplies for capacitors, bride recifier chips and there are a couple transformers on there aswell. Is there any way of checking the voltage of a transformer other than simply wiring it to mains and probing the open circuit voltage? I'll probaby run the amp with recharchables, make some more projects before playing with mains since I don't have any safety equipment and my only experience with high voltage is replacing a wall socket.Thanks for all the insight everyone, I am more than happy with the community on this forum!

author: Unknown
author_rank: Unknown
timestamp: August 20, 2011, 12:39:03 pm
content: Transformers from computer PSU's don't work, and they are dangerous too. Stick to big old iron-core transformers.

author: Zero999
author_rank: Super Contributor
timestamp: August 20, 2011, 12:54:02 pm
content: Yes, the transformer used inside a PC PSU is designed for high frequency (20KHz to 200kHz) operation, not 50Hz to 60Hz.You could just use the PC power supply as is but the output will be earthed you could run into problems with ground loops when connecting it to other mains powered equipment and it's an SMPS so it could be noisy.

author: ejeffrey
author_rank: Super Contributor
timestamp: August 20, 2011, 03:40:20 pm
content: Quote from: Hero999 on August 20, 2011, 10:40:43 amThis is not true. A typical speaker has a sensitivity of around 90 dBA @ 1 volt @ 1 meter. If you have one volt of ripple attenuated by 50 dB of PSRR (the data sheet I found said 36 dB), you will have 40 dBA output hum. In addition, PSRR is rejection relative to the input, so if the circuit has a gain of 30 dB, you will get 70Your point in general is true of course. Real power supplies should have far less than 1 V ripple, and even 50 dB PSRR is not particularly great. In real circuits it is not too hard to get ripple levels that contribute inaudibly to the output noise.The same is not necessarily true for all audio circuits. In particular, microphones that require a bias voltage or power for an onboard preamp may have very low PSRR. In that case, the preamp must take care to generate a very quiet microphone supply voltage that should usually be separate from the main supply. Also, a poorly done single-supply amplifier with a virtual earth can have very low PSRR. Switch mode power supplies can be used to good effect, but only with care. Most amplifiers have essentially zero PSRR at common switching frequencies, so you really must filter the supply to eliminate the noise, and beware of stray coupling paths.

author: Zero999
author_rank: Super Contributor
timestamp: August 20, 2011, 04:41:33 pm
content: Quote from: ejeffrey on August 20, 2011, 03:40:20 pmMeasurements such as 90dBA are normally made at 1kHz not 100Hz so that's not right at all.Even if the speaker's output power is the same at 100Hz as it is at 1kHz (it won't be) the dBA will be down by 20dB so 90dB now becomes 70dBA and what was 40dBA will be only 20dBA. In reality it'll be even less than that, this isn't a subwoofer, the little speaker's output probably be will be down by another 20dB@100Hz leaving 0dBA which is inaudible unless you hold the speaker next to your ear and will be completely drowned out by the music.Many audio amplifiers don't even have a regulated power supply, they often run directly off a rectified power supply. Fair enough, the TAD2003 is designed for an automotive power supply so doesn't have great power supply rejection.The LM3876 is better suited to mains powered amplifiers.http://www.national.com/ds/LM/LM3876.pdfQuoteThat's true, the greater the negative feedback, the greater the supply rejection.

author: Bren
author_rank: Contributor
timestamp: August 23, 2011, 01:51:27 am
content: QuoteThere's a major difference betweenpower amplifier, andpower supply.The class-D amplifier your speaking of is another beast entirely, it works on a completely different principle than the amplifier your trying to build and requires much more intricate circuit design. If you'd like to learn how class-D amplifiers function, there are plenty of documents online, just do a simple google search.If not, then in the simplest terms, Class-D amplifiers use a type of Pulse Width Modulation switching as aninput sourceto the power amplifier stage, the output of the power amplifier is then filtered to "reconstruct" the reference waveform before being sent to the load.This doesn't mean that they are sourced by non-rectified and unfiltered voltage. Class-D amplifiers require bus voltage filtering as much as any audio amplifier.Also, keep in mind that the gain in a class-d amplifiers stage is directly proportional to the bus voltage. Swings in bus voltage due to excessive power supply pumping causes distortion on a class-D output at lower frequencies. There are many different causes of noise in class-D amplifiers, power supply voltage fluctuations due to output impedance and reactive power flowing through the DC bus, is only one source of this noise.You are building a Hi-Fi amplifier? Regardless, Noise is Noise, although it can't be completely eliminated, reducing it, especially in a Hi-Fi audio amplifier is usually agood idea. In fact it's a good idea to reduce noise sources in any noise sensitive system, but I guess that goes without saying.My general advice for someone who is grabbing any old schematic online and trying to reproduce it, is to stay away from unregulated unfiltered switching power supplies unless you already know that the designer took the necessarily steps for the supply, or you really know what your doing.QuoteAs an audio/electronics engineer this makes me uneasy,QuoteThis is why.Even if the ripple itself is not heard through the output, it can contribute to output noise.QuoteTrue for the average home user. I design pre-amplifiers for recording studio use, part of my design mythology is to reduce or eliminate noise at any possible source, leaving the cleanest sound with slight coloration from the electronic components.Its a PITA to try an remix a track with noise, or poor audio coloration that shouldn't even be there all due to a badly designed, mediocre pre-amp.So as you can see, my application is different.

author: Unknown
author_rank: Unknown
timestamp: August 23, 2011, 06:23:28 pm
content: Quote from: Bren on August 23, 2011, 01:51:27 amThe difference is fairly minor in my opinion. A power supply is basically a power amplifier with an internal reference connected to the input. Of course the implementation and application is quite different.Quote from: Bren on August 23, 2011, 01:51:27 amWhich is similar to what an SMPS does. With proper filtering (actually easier since you can roll-off far below audio frequencies), you should get the same noise performance. Except that a class D amplifier doesn't have PSRR of the amplifier powered by the SMPS to reject some noise.Quote from: Bren on August 23, 2011, 01:51:27 amI'm not suggesting an unregulated power supply, just that it's usually not necessary to go overboard thanks to the PSRR of the amplifier.Quote from: Bren on August 23, 2011, 01:51:27 amSure, less noise is better. It only makes sense though if it's actually the dominant noise source.Quote from: Bren on August 23, 2011, 01:51:27 amFor power amplifiers, building a linearly regulated power supply requires huge heat sinks. And power amplifiers (apart from the class D and similar types) aren't the most power efficient to begin with due to biasing. So the other option would be a switcher I guess.QuoteGranted, studio use requires higher standards, especially since the signal tends to go through multiple pieces of equipment before it reaches it destination (although much of this is probably in digital form these days). However, even when designing for low noise, it makes sense to determine the dominant noise source and go from there, as opposed to blindly throwing money improving a power supply.

author: Bren
author_rank: Contributor
timestamp: August 23, 2011, 08:08:25 pm
content: QuoteWell, at least you understood what I was referring to.QuoteSimilar, but as you stated before,QuoteAnd when the implementation and application is different......?You usually take different precautions in the design process.It's like taking a jet engine and putting it on a horse and expecting the horse to run faster.QuoteTrue, amplifiers nowadays have great PSRR. In audio applications though (at least where I use them), its important to keep a few things in mine, one being circuit layout, and clean voltage supply. And why not? It seems like lazy engineering practice, as if to leave something half done and have an attitude of "well... it works good enough", especially when there's a possibility for poor circuit operation because of the half-assed design.Then again you have the usability factor. If your design works good enough, and it meets specs, its what customers want, then consider it done!QuoteDepends on how sensitive to the noise the system is, where its being applied or used, and the requirements of the system. I wouldn't want to use an amplifier that has a 1.7Vp-p output and 30% of that signal is effected by noise generated equally in various places in the system. Sure the noise doesnt have a dominant source, but its still going to sound like crap.QuoteOnce again, usability. I keep bringing up this usability factor, but the truth is, it's what separates good engineers from bad engineers. Good engineers keep this in mind when they design products, they think about the system in terms of its electrical performance, but they also have to consider the user.Sometimes sacrifices have to be made in electrical performance (efficiency and size being two examples) to accommodate the end user. Switchers definitely not the only option out there, some googling would open you up to a whole bunch of possibilities or even improvements to existing designs, try it, you'll be amazed.QuoteThis is called blind engineering, or brute force engineering. It's a very unwise practice, no self respecting engineer would do this. When I design, I start with dominant noise sources around the system and work down from there until noise levels are at acceptable values.I don't follow this half-assed "well it's good enough attitude" either, engineers that "do whatever it takes to get the job done" just aren't marketable in today's economy. Sometimes this requires a little extra time spent on a project, you'll see that it'll get you a long way in the industry.

author: Zero999
author_rank: Super Contributor
timestamp: August 24, 2011, 04:43:29 pm
content: Quote from: Bren on August 23, 2011, 08:08:25 pmWhat I don't understand is the let's over-engineer audio amplifiers to give near zero noise, THD, a huge bandwidth etc. attitude of audiophoolery.Nowhere else in engineering do I see people making things 10 times as expensive as they need to be for improvements which won't even be noticed unless state of the art test equipment is used. I mean why bother designing a power amplifier with a TDH of say 0.0001% when there will be more distortion in the best of the best speakers and room acoustics?Nowadays it's possible to produce a solid state amplifier which is much better than good enough for audio fairly cheaply. I don't understand why people bother spending much more, even for studio usage.

author: Bren
author_rank: Contributor
timestamp: August 24, 2011, 05:22:02 pm
content: Well to be honest, $500 for a studio grade pre-amp is already near the lower end of the spectrum as far as price goes. It's not all that uncommon to have a studio pre-amp around $2000. These are just standard industry prices. Expensive, maybe. But there is a lot more than just low noise, bandwidth and THD to consider when designing a pre-amp for studio use. Right down the the type of transformers used.For example, mediocre transformers can round off the waveforms, introduce phase shift, saturate at low levels, and color the sound with an uneven frequency response.The cost builds up in the components used and the construction. Labour costs are high, and the cost of parts are high. Then the question is for active components that do color the sound, what to use? Tubes, most often, or solid state designs? Passive components can also have a large impact on sonic quality, capacitors having the most effect. The difference between electrolytics, with their high dielectric absorption, poor temperature stability, wide tolerance and short life span, or film capacitors with dramatically less dielectric absorption than even the best electrolytic capacitors, which results in better low frequency realism, transient performance, and enhanced spatial accuracy.It really has nothing to do with "over engineering". It has to do with the following:The audio engineers of today have one thing in mind; that is, to take down the truest sound. Being able to do this allows them to do their job easier. Coupled with this are extra features of the pre-amp that the engineer might need. All of these things are taken into consideration when picking a studio grade pre-amplifier.The same could be said about electrical engineers. "who would spend 100X the cost on an oscilloscope from Agilent or Tektronix when someone can pick up a no name Chinese USB oscilloscope that's good enough to take measurements"... Well, the engineer will need the features and the more accurate measurements of a more expensive scope. This will allow them to do their job easier.It's really no different.

author: ejeffrey
author_rank: Super Contributor
timestamp: August 24, 2011, 05:30:18 pm
content: Quote from: alm on August 23, 2011, 06:23:28 pmActually they are quite different even in principle. Almost all power supplies have unipolar outputs and can only source current, while an amplifier must be able to sink as well. It is the difference between a 4-quadrant supply and a 1-quadrant supply. There do exist 2- and 4- quadrant power supplies for driving electromagnets and the like, and their internal topology is much like a power amplifier. However, your standard bench supply is not. Of course in the details almost all of their design characteristics are different, for instance power supplies rely heavily on filter to eliminate ripple and noise while amplifiers must do it all via negative feedback.Quote from: BrenOnly the cheapest and nastiest class-D amplifiers use open-loop PWM. Anything worth using has the gain set by feedback resistors like any other amplifier.Quote from: Hero999It is not even that. It is easy to design a power amplifier with near zero THD+noise. Any audio amplifier should have THD+noise far below audible levels not because it is necessary, but because it costs next to nothing and is simply a sign of lazy or incorrect engineering to make something that has sub-par performance in this respect. The same is true of bandwidth to a limited extent. Large full-power bandwidth is in a high power amplifier gets to be expensive. However, an audio amplifier should *not* have excessively high bandwidth -- any ultrasonic noise on the input should be filtered out rather than amplified and provided to the speakers. The high frequency roll-off should be set by component values not parasitics, and the amplifier should have plenty of open-loop small-signal bandwidth to make sure this happens. Again, it is not expensive or difficult to build an amplifier with enough open-loop bandwidth to satisfy this. The cost of an amplifier is almost completely dominated by the power rating. Once you account for the power supply, heat sink, and output transistors, making the rest of amplifier essentially perfect is practically free.The problem with most 'audiophile' stuff is that often it is not better at all, even inaudibly, than a less exotic amplifier. It is just random gold plating and expensive changes that actually provide no measurable benefit to output performance at all. Frequently they are even measurably worse due to 'interesting' design choices that both raise the price while lowering the quality.

author: Bren
author_rank: Contributor
timestamp: August 24, 2011, 05:36:19 pm
content: QuoteHaha, yeah I could have mentioned that.QuoteThis is definitely true in power amplifiers, I cant say the same applies for pre-amps.QuoteTrue for all devices.QuoteAlso true for all devices. Lets just compare Tektronix 2000 series scopes with their blazing fast waveform refresh rate, and their deep 2.5k memory (... sarcasm) and Agilent DSOX2000 scopes. Agilent has the obvious upper hand, but Tektronix scopes are still selling for twice the cost. I know what you're gonna say; the Tek2000 series scopes are a little dated (which means they should probably be dropping the cost on them a couple of grand). Anything by Tek now that is comparable to a Agilent DSOX is nearly twice the cost.I'll be interested to see if the amazing new Tektronix revolution is comparable, at the same costs.People just have to be careful with the things that they purchase. They have to do the research. It's like buying a luxury car and realizing it just doesn't perform like that ford tempo you had when you were a teen.

author: IanB
author_rank: Super Contributor
timestamp: August 24, 2011, 07:09:33 pm
content: Quote from: Hero999 on August 24, 2011, 04:43:29 pmI think it's worth noting that good engineers in all branches of industry will start by laying out a design using good design principles that is as near to ideal (or perfect) as possible. Thinking about the problem correctly in this way is pure professionalism and doing a job right. Once the ideal design is sketched out, the good engineer will go on to make considered simplifications for reasons of cost or practicality, in each case considering the impact on the design using appropriate cost/benefit criteria. The outcome should then be a practical and economic design fit that is fit for purpose, based on sound underlying principles.The bad "engineer" will merely bodge something together using woolly thinking and random cheap components and hope for the best.

author: Unknown
author_rank: Unknown
timestamp: August 24, 2011, 08:57:29 pm
content: Quote from: ejeffrey on August 24, 2011, 05:30:18 pmYou're correct, but from a noise point of view, a power supply shouldn't be worse than an amplifier, since it is easier to design as you point out. A good amplifier should make a fairly decent power supply (though stability will likely be worse). A power supply for amplifying audio... not so much. Although I'm sure someone built an amplifier from something like an LM317.

author: Zero999
author_rank: Super Contributor
timestamp: August 24, 2011, 11:21:53 pm
content: Quote from: Bren on August 24, 2011, 05:22:02 pmWhat do you mean by colour the sound? Is it just a fancy way of saying distort the sound?And why on earth would you put the analogue signal through a transformer? That's a very bad idea and should be avoided where ever possible. There are normally better ways of avoiding ground loops or just galvinically isolating a signal than a horrible transformer.QuoteWhat labour costs?What component costs?An excellent quality amplifier can be made from inexpensive op-amp ICs and assembled by machines.QuoteValves/tubes are just shit and a complete waste of money and solid state op-amps hardly colour the sound at all, assuming that means causing all sorts of distortion.Here are a couple of fine op-amps which are more than good enough for audio and are relatively inexpensive:AD797LM4562QuoteI understand that paragraph until you mentioned enhanced special accuracy?Yes electrolytic capacitors are not good for distortion and nether are ceramic which can be microphonic and cause oscillation if used in a preamplifier. Decent film capacitors are not that expensive though.Another thing I've never understood is why some audiophools swear by horrible carbon composition resistors when thin metal film resistors are much cheaper, less noisy and are also non-inductive.QuoteWhat extra features should a studio pre-amplifier have and why do they cost the earth?QuoteI disagree.There's always a need for a faster oscilloscope with more memory, channels higher precision, faster update rate etc. but why on earth would anyone want to spend ten times as much on an audio amplifier because it has a THD of 0.0001% rather than a cheaper one with a THD of 0.0005%? It's not like they can actually tell the different without using expensive test equipment.

author: DrGeoff
author_rank: Frequent Contributor
timestamp: August 24, 2011, 11:48:55 pm
content: Quote from: Hero999 on August 24, 2011, 11:21:53 pmAnalogue signals are often put through transformers in many professional situations. Look up 1176 compressor, one of the most widely used in the industry. It has an output transformer. It also has options for an input transformer, or op-amp input stage. Passive DI boxes use a transformer. Neve consoles are full of them on the mic input stages.Transformers are used for impedance matching and balancing. Particularly useful for high impedance, low output sources (such as guitar pickups) where a 1:5 transformer can be used to match it to a lower impedance balanced input stage. A good audio transformer is not cheap though, often $80-$120 for a mic input or line output transformer with good specs. It will not add much colour to the sound until it is driven hard, acting a bit like a limiter when the transfer curve becomes non-linear.

author: Bren
author_rank: Contributor
timestamp: August 25, 2011, 02:25:33 am
content: OK, OK, I agree with you in the fact that it's stupid for someone to pay $200 for cables, theseareas you say, "audiophools", through and through, no doubt. However, I'm not disagreeing with you that's there is no such thing as "audiophools". These people are just the type that don't know enough about the things they buy, and pay a premium for them. Is that to say that all things that are $500 or more are a waste of money? Of course it doesn't.QuoteComments like this just make me roll on the floor with laughter.I've seen this being argued by so many closed minded people time and time again. I definitely wont go into a debate about solid-state vs tubes, each are just as desirable as the the next, each have their place. I like to use both for different situations, sometimes a mixture of the two. If someone were to debate about that though, they should open a new thread, because guaranteed it'll be close to a billion pages long in less than a week.I still find it funny and somehow amazing how typical it is of people with limited knowledge in the audio industry to so quickly bash "audiophools" (sarcasm- by that I mean people who pay a premium and know exactly what their getting). I could go as far as to say that the majority of them also lack the understanding as to how electronic components change or color the sound of an audio signal, and whether or not that color(sound) is desirable.I do find all theses questions somewhat humorous (not insultingly so). I mean, I definitely don't have the motivation to answer all of them because it quite frankly has just become ridiculous. If you feel so inclined you can find many of the answers to the questions you've asked in online documents and journals, you can also ask audio/video recording artists, producers, and musicians. The answers you get should also clear up a lot of these misconceptions.QuoteOne of my all time favs, another one up there with it would be the LA-2A.

author: DrGeoff
author_rank: Frequent Contributor
timestamp: August 25, 2011, 02:46:42 am
content: Quote from: Hero999 on August 24, 2011, 11:21:53 pmFully balanced inputs and outputs.High quality XLR connectors.+24dBm input handling capabilty.Metering.For microphone pre-amplifiers:+48 phantom power.Up to 70dB gain with very low noise.Usually a transformer input stage for good balancing and impedance matching.

author: Zero999
author_rank: Super Contributor
timestamp: August 25, 2011, 01:18:39 pm
content: Quote from: DrGeoff on August 24, 2011, 11:48:55 pmSurely a better engineering solution would be to integrate a tiny pre-amplifier into the pick-up?Quote from: Bren on August 25, 2011, 02:25:33 amAll right I'll do some Googling.There's one question I have which I can't find an answer to: why are such ridiculously high bit rates mandated by some for digital sound?I mean why sample at 24-bits per sample at 192kHz? It's way, way over the top and completely pointless. Fair enough, maybe it's a good idea to do some digital signal processing with a much greater bandwidth and sample rate to avoid rounding errors but there's no point in using such an ADC. You may think I'm crazy but it's common sense when thermal noise is taken into account.For example, take a dynamic microphone with an impedance of 300R, at 300oK the equivalent thermal noise voltage is 997nVRMSover the audio bandwidth of 20KHz. Suppose the microphone is outputting a signal of 2mV, at 24-bits per sample the quantitisation level is 119.2*10-3V which is way into the noise margin so totally overkill.

author: ejeffrey
author_rank: Super Contributor
timestamp: August 25, 2011, 08:45:52 pm
content: Quote from: Hero999 on August 25, 2011, 01:18:39 pmPowered by what? This is common on microphones and the power is provided by the mixer via phantom power... which uses transformer coupling.Transformers provide second-to-none impedance balance and common mode rejection while avoiding high (differential) input impedance and the associated noise and ESD risk. Their main drawback is that they are expensiveQuoteMostly they are marketing bits. A high quality 24-bit audio ADC has somewhere in the neighborhood of 18 real bits and 6 marketing bits. However, once you have a sigma-delta ADC it costs you almost nothing to round up to 24 bits. They might even help a bit... Sigma-delta converters actually require a fair bit of dither to perform well, and by making the LSB deep below the noise floor you ensure that you always have enough dither to avoid quantization artifacts. The ADC could keep track of a 24 bit word for its internal FIR and only report the significant bits, but in reality they are going to need to be rounded to 16 or 24 for storage in a computer and 24 gives you a bit more leeway in your recording gain as well as some handy dynamic range for signal processing.The bit rate is a bit more puzzling. In the bad old days you would win by increasing the sample rate from 48 kHz to 96 or higher because you relaxed the requirements on the analog reconstruction filter. Even if your source was 16 bit / 48 kHz it might be advantageous to upsample to 96 kHz, apply a digital reconstruction filter to eliminate aliasing, and then use a lower order or lower Q analog filter. Now that sigma-delta DACs are universal, this is no longer necessary: they do this implicitly. They use digital noise shaping to shove all the noise up to the MHz region where it is trivial to filter.That said, it isn't expensive to do, and if you aren't starved for bandwidth or storage space, why not? Every audio CODEC I have seen allows you to select the bit rate, so you can run it at 48 kHz if you are pressed for bandwidth.

author: Zero999
author_rank: Super Contributor
timestamp: August 25, 2011, 09:24:18 pm
content: Quote from: ejeffrey on August 25, 2011, 08:45:52 pmBatteries, a small power jack from the PA or mixer.QuoteI suppose my point is if the signal is amplified as close to the source as possible then there should be no need for balancing or impedance matching because the signal is now large enough that hum shouldn't be a problem.QuoteThanks, that makes sense.

author: DrGeoff
author_rank: Frequent Contributor
timestamp: August 25, 2011, 09:39:54 pm
content: Quote from: Hero999 on August 25, 2011, 01:18:39 pmMaybe it is, and there are some that have active pickups. However the majority don't and, way back in the days when electric guitars and basses were invented, there wasn't any way to do it that would be able to be fitted into the instrument. As already pointed out, condenser microphones have a preamp in them, powered by a 48V phantom power supply.Quote from: Hero999 on August 25, 2011, 01:18:39 pmI think the same thing was said when 16 bits was chosen for CD's. There's now a push to re-release a lot of music at 24-bits (as downloads).24 bits in not way over the top when dealing with a lot of processing on the signal. The samples are usually converted to 32 bit floating point internally and these values used through the algorithms for the processing through the DAW. Generally when recording, however, you aren't using 24 bits, since you never record at 0dBFS. I'd usually peak at -12dBFS during recording, which is 2 bits less.Sample rate is a different story. I don't know anyone who is using 192kHz, most use 44.1, 48 or 96kHz. If I'm recording for a pop/rock/jazz CD release, I'll still use 44.1kHz at 24 bit rather than having to do a conversion later. For video, 48kHz is usually sufficient. It uses a lot less disc space too, which can easily grow quite large when dealing with an ever increasing number of tracks.

author: DrGeoff
author_rank: Frequent Contributor
timestamp: August 25, 2011, 09:51:33 pm
content: Quote from: Hero999 on August 25, 2011, 09:24:18 pmThere is always a need for balancing. There's a lot of noise around on stage with lighting rigs, amps etc. Balancing helps remove a lot of it easily. These days cable runs are shorter though, with wireless packs for guitarists and digital consoles running a fibre or cat5 cable between the stage and the FOH console and back to the amp racks.

author: Bren
author_rank: Contributor
timestamp: August 25, 2011, 10:15:49 pm
content: QuoteThis is especially true for live performances, but not just... Professional recording studios are an architectural specialty, and due to multiple noise isolated rooms or booths, the signal is almost never close to the source. You often have mic's plugged into patch panels and patch panels running cable through walls to the control room, and from the control room wall to the mixing desk. You could easily have a 30foot + length for the signal to travel before it meets the source.