Help finding components for headphone amplifier - Page 1
Forum section: electronics / projects

author: firstcolle
author_rank: Regular Contributor
timestamp: June 23, 2017, 11:26:18 am
content: Hi,I'm thinking about my next project and I would build an audiophile headphone amplifier.those are the fixed spec:- high audio quality- analog in/analog out- able to drive 8/16/32 Ohm headphone- digital volume control (encoder + picmicro maybe IR or BT remote)I'm looking for some IC amplifier that matches the high audio quality and maybe with i2c gain or a VCA. is there something in the market?or I have to think about a pre amplifier with i2c gain control and then a second stage for the amp?is there some project to take a look for start?many thanks!

author: Alex Nikitin
author_rank: Super Contributor
timestamp: June 23, 2017, 12:04:10 pm
content: Quote from: firstcolle on June 23, 2017, 11:26:18 amIMHO, these two requirements are mutually exclusive.CheersAlex

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 23, 2017, 02:50:49 pm
content: TI makes some high quality audio PGAs like the PGA2311/PGA4311.

author: Fungus
author_rank: Super Contributor
timestamp: June 23, 2017, 03:12:34 pm
content: What's the signal source?

author: tszaboo
author_rank: Super Contributor
timestamp: June 23, 2017, 03:15:43 pm
content: PGA2310/11 volume controlTPA6120A2 output amplifierOPA1612 or OPA1622 anyewhere else requiredThe issue is not the signal chain. The issue is reasonably powering it (like, not 230V input, and no noisy DC-DC converters), and having a high quality source (AKA: USB DAC)

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 23, 2017, 03:28:22 pm
content: If you can put in an internal DAC, you can use something like the PCM1792A which has a built in gain control.

author: Fungus
author_rank: Super Contributor
timestamp: June 23, 2017, 03:31:59 pm
content: Quote from: NANDBlog on June 23, 2017, 03:15:43 pmThat's why I asked what the source is.If it's USB then you can get a complete headphone DAC for under $10 on eBay.eg.http://www.ebay.com/itm/281827865856(randomly chosen seller)Chipset is this:http://www.ti.com/lit/ds/symlink/pcm2704.pdfIf you want 'audiophile' capacitors it's acouple of bucks extra.And if you don't trust the 2704's built-in amplifier you can haveexternal op-amp.

author: firstcolle
author_rank: Regular Contributor
timestamp: June 24, 2017, 11:25:35 am
content: hi all..the source will be only RCA analog input with line levels, so I prefer to not convert the signal into digital, process it and then reconvert into analog.potentially te audio source will be a turntable with a proper preamplifier.i'm going to look at the component you suggested.. thanks!!!

author: The Soulman
author_rank: Super Contributor
timestamp: June 24, 2017, 12:18:38 pm
content: For volume control you can look at voltage controlled amplifiers (VCA) such as from THATcorp.They are used in the most expensive Pro-audio equipment.Toshiba used to make nice digitally controlled volume control IC (TC94xx) but seem to be obsolete.Why do you need a digitally controlled volume control and not a motorized potentiometer?The actual power-amp shouldn't be difficult to make, at these low power requirements a single ended class-Atopology is very doable.Or copy a design from a high dollar commercial product.Or look at the c-moy op-amp based designs.

author: aries1470
author_rank: Regular Contributor
timestamp: June 24, 2017, 02:05:44 pm
content: Hi,besides the T.I. parts, Maxim (Dallas) has a great range, either push-button or i2c controlled.Here is alinkto their product portfolio. Just go to theLogarithmic

author: f5r5e5d
author_rank: Frequent Contributor
timestamp: June 24, 2017, 02:21:36 pm
content: http://www.njr.com/MUSES/series/MUSES72320.html

author: Alex Nikitin
author_rank: Super Contributor
timestamp: June 24, 2017, 03:14:58 pm
content: Quote from: firstcolle on June 24, 2017, 11:25:35 amEven a simple dual carbon track pot will be much better for the sound than any of these digital controls. If you need the remote capabilities and prefer not to sacrifice the sound quality you can use either a motorised pot or a relay controlled attenuator (6 relays will give you 0 to -64dB attenuation in 1dB steps).CheersAlex

author: Marco
author_rank: Super Contributor
timestamp: June 24, 2017, 05:20:29 pm
content: Quote from: f5r5e5d on June 24, 2017, 02:21:36 pmLM1972 is a bit less esoteric.

author: f5r5e5d
author_rank: Frequent Contributor
timestamp: June 24, 2017, 10:43:50 pm
content: Quote

author: BrianHG
author_rank: Super Contributor
timestamp: June 24, 2017, 11:24:42 pm
content: Quote from: Marco on June 24, 2017, 05:20:29 pmThe LM1972 has no gain, just -0db (full volume) and down to -78db with only 4.5v to 12v supply, which it only needs in this case since it wont amplify the audio level.MUSES does +31.5db to -111.5db.If power supply current is not a factor, and you want an excellent digital volume, class A headphone amp with a bit of kick, I would use the MUSES, powered at full 30v (+/-15v), have the output drive 2 x 30v ultra logic level (1.2-1.8v) mosfet gate directly operating in voltage follower mode, with a big 5 watt pull down resistor to -15v (only adjusted for a 1.5-2watt draw). With AC decoupling caps to drive the headphones/speakers. Controlled by the MCU of your choice.This makes a minimal 1 chip for gain and volume, digitally controlled, 2 opamps, or dual opamp & 2 mosfets (TO-220 packages with heatsink to radiate the 3-4 watts) for the most basic class A output, or, 2 NPN darlingtons for a tighter sound, again class A, for a nice minimal analog design. (No feedback on the output driving transistors.)Clean output with 0 crossover distortion, but, expensive & you need a hefty +/- 15v supply.There are nice cheaper solutions if you want to use a motorized mechanical volume control.

author: BrianHG
author_rank: Super Contributor
timestamp: June 24, 2017, 11:46:21 pm
content: You can always buy this guy:https://www.aliexpress.com/item/50-KA-Remote-Motor-Volume-Potentiometer-Control-Adjustable/2053612708.html?spm=2114.10010108.1000013.4.rPwWC0&traffic_analysisId=recommend_2088_2_82199_new&scm=1007.13339.82199.0&pvid=03f30272-400a-48fb-bd81-6f145cea8bf3&tpp=1And build a high quality headphone amp with a fixed 10db gain connected to it to drive your output.Or, a complete passive multi-channel pre-amp with this guy:https://www.aliexpress.com/item/Electronic-volume-control-board-With-mini-remote-control-Brand-new-remote-control-ALPS-motor-potentiometer-Pre/32645946961.html?spm=2114.10010108.1000014.6.rjlDjP&traffic_analysisId=recommend_3035_null_null_null&scm=1007.13338.84300.000000000000000&pvid=fd043381-de34-49db-bfb8-dcb4335592ce&tpp=1

author: Marco
author_rank: Super Contributor
timestamp: June 25, 2017, 12:33:06 am
content: Quote from: BrianHG on June 24, 2017, 11:24:42 pmAll that engineering spend on linearity, thrown away. Not that it matters.

author: BrianHG
author_rank: Super Contributor
timestamp: June 25, 2017, 01:42:00 am
content: Quote from: Marco on June 25, 2017, 12:33:06 amLinearity with Darlington BJTs wouldn't be too terrible, but, I like high current drives without feedback when driving cable and low power dynamic loads like headphones. But, that's just my ears...

author: f5r5e5d
author_rank: Frequent Contributor
timestamp: June 25, 2017, 09:00:42 pm
content: unless you need more V theres no point in descrete outputs for dynamic headphonesthe right op amps, particularly the CFA DSL drivers are faster in global feedback than many output Q followers you see in headphone project ampsthe TPA6120 is also happy pushing 100s of ma to within a volt or so of the railswrap one in a good 'audio' fet input op amp's global feedback loop and passives, pcb layout are bigger distortion sources

author: tszaboo
author_rank: Super Contributor
timestamp: June 25, 2017, 11:18:38 pm
content: Quote from: Fungus on June 23, 2017, 03:31:59 pmNone of these things qualify as audiophile. It is 192KHz 24 bit.And before we start a war: 24 bit is the next logical step for 16, might be an overkill. 192Khz makes reconstruction filter easier to make.TPA6120 can drive anything, except the planar headphones. Unless you want attery power, I dont see the reason to use anything else.Quote from: The Soulman on June 24, 2017, 12:18:38 pmCmoy is best, when one battery dies, and your amplifier is suddenly the headphone killer.http://nwavguy.blogspot.be/2011/07/cmoy-with-gain.htmlRead this guy's blog. He is the EE with audio passion. I wonder where did he disappear.

author: Fungus
author_rank: Super Contributor
timestamp: June 26, 2017, 08:19:58 am
content: Quote from: NANDBlog on June 25, 2017, 11:18:38 pmOh, we have a definition of that term now! Nothing less will do. Got it.

author: Fungus
author_rank: Super Contributor
timestamp: June 26, 2017, 09:02:35 am
content: Quote from: Alex Nikitin on June 23, 2017, 12:04:10 pmYou can get a motorized potentiometer, control the motor with the PIC.If this is a 'project' for listening to vinyl then I'd build something with valves as a bit more of a challenge.Where's the fun in using one of the hundreds of single-chip-solutions?

author: BrianHG
author_rank: Super Contributor
timestamp: June 26, 2017, 09:25:38 am
content: Quote from: Fungus on June 26, 2017, 09:02:35 amSee the links I placed in post #15...

author: Alex Nikitin
author_rank: Super Contributor
timestamp: June 26, 2017, 11:21:48 am
content: Quote from: BrianHG on June 26, 2017, 09:25:38 amThese links are most likely a waste of money if you aim at a half-decent sound quality. I did my first production remotely controlled volume with a motorised pot over 20 years ago, and the rule is - never have anything digital running in the same enclosure as the pot, and if it is that close to the pot as in the links you've posted you can forget about a quality sound. Only if the micro is in the sleep mode (no clock) most of the time except when it needs to receive the remote signal and operate the pot, you can place it close. Then you have a problem of a sleeping micro that has to react to an incoming remote signal... . I very much doubt these Chinese boards do anything of that kind.CheersAlex

author: Pitrsek
author_rank: Regular Contributor
timestamp: June 26, 2017, 04:54:55 pm
content: + for TPA6120

author: The Soulman
author_rank: Super Contributor
timestamp: June 26, 2017, 07:12:28 pm
content: Quote from: NANDBlog on June 25, 2017, 11:18:38 pmYes don't use a center tap on your battery's, make some half decent symmetrical regulated psu.

author: firstcolle
author_rank: Regular Contributor
timestamp: August 13, 2017, 05:29:58 pm
content: Hi everyone!first of all thanks for all the suggestions!! now I'm taking in consideration the PGA2311 + TPA6120 solution.I'm ok with the digital section (encoder + spi and OLED display) but I'm a little noob with the analog one. now the stupid questions.. can I connect straight the output from the PGA2311 to the TPA6120 input?? and for the PGA2311 input, do you suggest some buffer to match the impedance? the PGA2311 datasheet says that it works at the best with a 600Ohm impedance input... I know that all the commercial audio equipment may have a line output with low impedance.. so I'm ok with that?many many thanks!

author: firstcolle
author_rank: Regular Contributor
timestamp: August 20, 2017, 06:02:45 pm
content: Hi again!I've done a little prototype on breadboard and I found out that I can connect the PGA2311 direct to TPA6120, all works fine except the Mute by pulling low the Mute pin on the PGA2311, doing that cause an output of 2V from the TPA6120.. probably due to the internal PGA mute circuit. no problem if I load 0x00 in the volume register (software mute).now I'm looking to design a PSU that must have 5V for digital section, +5V -5V and +12v -12V for the analog section. My idea is to use a toroidal transformer with 2 secondary 0-15 0-15 VAC. The first one for the digital section and the second one for the analog (all the rails). I want to keep the 5V LDO on the first secondary always ON and use a soft switch to switch the digital section on and off and a relay for connecting the second secondary only when the digital section is On.I attach the first schematic, what do you think?I'm using LM2940 and LM2990 because I have them at home but I'm not sure if they could work fine in my application

author: Zero999
author_rank: Super Contributor
timestamp: August 20, 2017, 06:59:55 pm
content: Quote from: firstcolle on August 20, 2017, 06:02:45 pmIt looks fine but I find the combination of a linear power supply and class D amplifier bizarre. You have an efficient amplifier, then go and throw that away with a linear regulator, which burns off the extra volts as heat!I probably would have gone down the route of a traditional class AB amplifier and an unregulated power supply. It would achieve similar, if not better efficiency to the class D + linear regulator combination, without all the disadvantages and potential problems of a class D amplifier.EDIT: I was talking nonsense. He's not using a class D amplifier, see below.

author: firstcolle
author_rank: Regular Contributor
timestamp: August 22, 2017, 06:50:08 am
content: nice point of view.. what do you suggest for more efficiency but without creating noise and interferences?many thanks

author: tszaboo
author_rank: Super Contributor
timestamp: August 22, 2017, 08:26:09 am
content: Quote from: Hero999 on August 20, 2017, 06:59:55 pmQuotePower supply looks fine. Maybe add some TCS protection or Ferrite beads. Ferrite beads help a lot with the RF interference coming from eg mobile phones.

author: firstcolle
author_rank: Regular Contributor
timestamp: August 22, 2017, 09:00:20 am
content: Quote from: NANDBlog on August 22, 2017, 08:26:09 amI'm going to add some ferrite beads between analog and digital GND. may I have to add t also in other points?I'm also looking at the TPS65131 that offers positive and negative rails up to +-15V from single 5V supply.. but I'm not sure if it can introduce some interference and noise in an audio application (it's rated for audio in the datasheet)

author: tszaboo
author_rank: Super Contributor
timestamp: August 22, 2017, 09:10:08 am
content: Quote from: firstcolle on August 22, 2017, 09:00:20 amThe ferrite bead between GNDs... I'm not sure if that is a good idea. It is one of those things that can make things worse, and you might never know. I prefer keeping AGND and DGND tied together, and provide a continous GND plane. This is definetly better for EMC.TPS65131: While it lists audio applications, I dont know about it. Look at those nasty graphs at page 21 and 22. I see 50mV+ ripple on the rails. I have bad experience with "power saver" SMPSes with precision circuits. They go into power save mode, and suddenly they make audible noise and pollute everything around them with ripple.

author: firstcolle
author_rank: Regular Contributor
timestamp: August 22, 2017, 09:24:50 am
content: Quote from: NANDBlog on August 22, 2017, 09:10:08 amthanks for the advice on the TPD65131. I'm going with classical Linear PSU.I thought that Ferrite beads between the GND's was a good idea!!where I must put it for prevent RF interferences?

author: b_force
author_rank: Super Contributor
timestamp: August 22, 2017, 11:00:39 am
content: If it's just for headphones, the lme49600 is also a very good candidate.

author: tszaboo
author_rank: Super Contributor
timestamp: August 22, 2017, 12:29:18 pm
content: There is nothing wrong with the TPA6120A2 package. It has separate power pins, so it can be seperately powered. The package is not an issue for automated assembly, I run production with several thousand (different) high power opamp in the same package. For DIY, you just create a big holes under the thermal pad and food it with solder. It is good enough. I have a amp with it, and of course, it is as expected. Like not even there.The only downside of the amp is the output impedance. But I have a HD600 which is 300 Ohms, so not an issue.And power... With a watt in a headphone you can probably kill someone.

author: Hydron
author_rank: Super Contributor
timestamp: August 22, 2017, 01:36:12 pm
content: TPA6120 isn't too bad to solder with hot air - I've made an amp with one using on home etched double-sided PCB (extended the pad underneath to the sides of the part, ran a bunch of manual-bits-of-wire vias to the ground plan underneath).The main downsides to this chip are it's unnecessary speed (be careful with the feedback - no parallel capacitance and use the datasheet suggested feedback resistor!), and the 10 ohm output impedance requirement.For my amp I wrapped it within the feedback loop of an audio-specced fet input op-amp (some TI one, nothing particularly amazing, but it was in the parts box...) so DC characteristics were determined by the input op-amp, not the TPA part. As I was running the TPA chip in gain-of-2 mode I was also careful to set the external op-amp's gain above 2 (4 or 5 IIRC) to make sure it was running at at least unity gain for stability. Worked perfectly, I got good audio performance, very stiff current drive capability and low output impedance. There are however a couple of caveats to this method though:- Any op-amp/buffer inside a feedback loop should be faster than the outer part, as to not disturb it's stability (no issue in this case, the TPA6120 screams along)- Make sure everything it running at a stable gain- If the output is shorted then you've got a grunty op-amp dumping the full supply rail into it's output resistors, which will proceed to go up in a puff of magic smoke. To fix this I put an ohm or so in series with the headphones - makes the output impedance worse but at least a short will only apply 10x the normal output voltage over the 10R resistor rather than the full supply rail.Other notes:- I used a low noise switcher to make a negative 12V supply from the 12V input, and followed this with linear regulation to ~10V. Can't hear the difference compared to a linear supply (actually a little quieter, see below)- Be very careful to separate audio traces from other power traces. Star grounding is your friend. You can hear stuff that is invisible on a scope - my initial prototype with a linear power supply hummed because a tiny bit of the 50Hz input power was flowing through an audio ground due to a layout mistake.- I also incorporated a simple headphone protection circuit - the output is switched through a 5V coil relay with an 15V zener in series. If the total supply voltage drops below ~15V the headphones are open-circuited, hopefully avoiding any DC if one of the supplies fails.I'd probably do things a bit differently if i built on again, probably using some of the LME parts mentioned earlier in the thread, or at least work out a way to deal with the TPA6120 output impedance requirement more elegantly. Then again, I got everything designed and built in a weekend from parts on hand - the only things I bought were a plastic case and the potentiometer from the local Jaycar store.

author: firstcolle
author_rank: Regular Contributor
timestamp: August 22, 2017, 01:52:12 pm
content: again, many many thanks for all your suggestions... have many things to think on nowonly the last question for today:the PGA2311 datasheet report that the amp is capable to drive 660ohm loads but the TPA6120 has a 300Kohm resistance input. Is it better to put a buffer between these 2? I think not because of the TPA6120 absorb no current.. or I'm wrong?

author: xani
author_rank: Frequent Contributor
timestamp: August 22, 2017, 03:15:38 pm
content: Quote from: Alex Nikitin on June 23, 2017, 12:04:10 pmI smell audiophooleryBut you can always go oldschool way and have digitally controlled stepper motor to turn the pot

author: Zero999
author_rank: Super Contributor
timestamp: August 22, 2017, 05:38:28 pm
content: Quote from: NANDBlog on August 22, 2017, 08:26:09 amSorry, I was talking nonsense. I got confused with the part numbers and thought the volume control IC was a class D amplifier IC for some reason.Quote from: firstcolle on August 22, 2017, 06:50:08 amThe TPA6120 has a wide supply voltage range, +/-5V to +/-15V, so doesn't need a regulated power supply. If you use a transformer with a 9V-0-9V, you can power the TPA6120 directly off the unregulated DC off the rectifier.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 23, 2017, 03:11:15 am
content: Quote from: blueskull on August 22, 2017, 09:18:13 amExpect that to change now that USB-C is becoming a popular standard on smartphones. USB DACs are no longer a niche product, with the latest designs being a very scaled down digital amplifier. I was actually very surprised by the USB-C DAC that came with my Le Pro 3, easily beating the classic PCM2707 and almost managing to match a PCM1792A. (USB IDs seem to indicate a Saviaudio chip, of which it appears to be a custom part just for USB-C DACs.)