Heaphone Amplifier Requirements - Page 1
Forum section: electronics / projects

author: Obsidianxenon
author_rank: Contributor
timestamp: July 30, 2025, 01:49:17 am
content: If you've been active on here recently, you'll see I've made a few posts about my latest project, which is a headphone amplifier, and here is one of the (likely) few more to come:I only need to drive a pair of earphones now, but later on, I'm thinking of driving a pair of Sennheiser HD 424 headphones, and require an opamp that I can (hopefully) get from Jaycar to drive them. As far as I can gather, the impedance of the phones are 2000 ohms and require a power of >2V RMS at 2mw. If you can find any more info about power requirements for them it will be greatly appreciated as well. Any suggestions?Cheers.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 30, 2025, 02:31:27 am
content: Any half decent audio opamp will do. In fact, it's the low impedance headphones that need better opamps to sound good.

author: Messtechniker
author_rank: Frequent Contributor
timestamp: July 30, 2025, 05:18:44 am
content: For the HD424 a NE 5532 opamp will do nicely.Used such combination for decades. Until one sideof the HD 424 decided to die.

author: Obsidianxenon
author_rank: Contributor
timestamp: July 30, 2025, 06:17:21 am
content: Good to know. Just starting out with audio electronics so the more I learn from this project the better.

author: Obsidianxenon
author_rank: Contributor
timestamp: July 30, 2025, 06:30:39 am
content: Out of curiosity, is the LM4558 a suitable substitute? It's just that I can't get the NE5532 from where I'm getting all my other parts. Fine if not but can't blame me for trying.

author: aeg
author_rank: Regular Contributor
timestamp: July 30, 2025, 07:22:41 am
content: Can you get 2pcs of NE5534? Or how about NJM4556 or OPA134?

author: Obsidianxenon
author_rank: Contributor
timestamp: July 30, 2025, 07:24:22 am
content: Unfortunately nah. Looks like I'm going to have to look elsewhere for parts.

author: tszaboo
author_rank: Super Contributor
timestamp: July 30, 2025, 08:02:30 am
content: Look at the schematics of the O2 headphone amplifier. That is a well documented and measured amplifier that's easy to replicate.https://nwavguy.blogspot.com/2011/08/o2-summary.html

author: Zero999
author_rank: Super Contributor
timestamp: July 30, 2025, 08:10:26 am
content: How are you going to power it? Mains, USB, 12V from a car cigarette lighter socket, batteries: single use, rechargeable Li-ion etc. ?

author: magic
author_rank: Super Contributor
timestamp: July 30, 2025, 10:04:59 am
content: I'm not aware of LM4558 existing, but the various xx4558 types could be good enough - they are simple basic opamps with class AB output stages (not unbiased class B like LM358, which is not suitable) and they sometimes show up in audio applications. 2kΩ means 6mA at 12V output, which any general purpose opamp can do.One thing to watch out for in 4558 is that if the IN+ pin gets within ~1V of the negative rail, the output unconditionally jumps to the positive rail. Same thing as with TL072. This may occur if the negative rail fails and gets close to ground and the signal (also close to ground) is fed to IN+, and it results in a loud glitch and possibly damage of low impedance headphones (yours would probably survive). NE5532 doesn't have this issue.Trivia: many NE5532 sold on eBay/AliExpress/Amazon (or by shops that resell stuff from there) are actually some unknown Chinese 4558 inside

author: Messtechniker
author_rank: Frequent Contributor
timestamp: July 30, 2025, 12:55:38 pm
content: Quote from: Obsidianxenon on July 30, 2025, 06:30:39 amMan, its time to add a reliable supplier for your NE 5534s and 5532s. These have been the audio workhorses for many decades. And still are.Never buy them off Ebay, Amazon and alike. Too many fakes around there.Recommended reading: "Small Signal Audio Design" by Douglas Self (Audio Guru). Will put you really on track :-)Attachment taken from his book. I hope Mr. Self will not mind me doing so.Any PNP an NPN will do. Shoud have similar current gains. I.e. matched to some extent.Anyway welcome to the audio circuuits design club.

author: Vovk_Z
author_rank: Super Contributor
timestamp: July 30, 2025, 02:23:59 pm
content: Quote from: Messtechniker on July 30, 2025, 12:55:38 pmI want to add two my cents: TL072 is not good for audio, of cause, and must be replaced with any other good opamp (like LM833/NE5532 etc).In general, for loads larger then 50-100 R and few volts RMS I would use just opamps, without additional transistors. You need two opamps like LM6172 in parallel (one case) for such a load for one audio channel. You just have to use 10-33 R resistors to parallel them (before output connecting point).For >=600 R load you may use just one opamp (or two in parallel for reliability). There are a lot of them who can drive 600 R load very well, especially new ones.2k load can be happily driven by a lot of even cheap opamps, starting from LM833, NE5532 etc, with negligible THD (<0.001%).

author: tszaboo
author_rank: Super Contributor
timestamp: July 30, 2025, 02:33:37 pm
content: Quote from: Vovk_Z on July 30, 2025, 02:23:59 pmI think Mr Self included this schematic as a textbook example, not as a practical circuit to build in the 21st century.I mean the practical circuit is a single chip amp that takes I2S, has a built in capacitive voltage converter and outputs headphones directly.

author: themadhippy
author_rank: Super Contributor
timestamp: July 30, 2025, 02:38:21 pm
content: Quotebest not lift the lid on multiple bits of audio gear ,even some bloody expensive studio desks had the buggers by the bucket load.

author: Zero999
author_rank: Super Contributor
timestamp: July 30, 2025, 02:59:32 pm
content: Quote from: themadhippy on July 30, 2025, 02:38:21 pmYes, there's nothing wrong with TL072 for audio. It can be lower noise than the NE5532, in applications with a high source impedance, because it has a lower current noise, due to extremely low bias currents.Replacing op-amps in audio gear, without a thorough understanding of the circuit and why they're were chosen, is generally a bad idea. It can cause all sorts of problems such as latch-up and oscillation.

author: BrianHG
author_rank: Super Contributor
timestamp: July 30, 2025, 04:31:37 pm
content: I've used TL072/TLO74 with some expensive audio equipment. (real ones, not the fakes which give a crossover distortion bump as higher audio frequencies when the output is loaded.)Though, my gain settings were 0de, 4db, 6db and 10db.I would not use it as a phono preamp, but for 1x through 10x a line level signal, they are actually fairly excellent.

author: Messtechniker
author_rank: Frequent Contributor
timestamp: July 30, 2025, 05:28:55 pm
content: Always laughing at those audio fools randomly swapping OpAmps for "improved" sound.They forget that the audio signal has already passed though dozens of those horribleTL07X and NE5532/4s.The simple circuit above with be an adequate match for the Senn HD 424.Of course we can do better. But you will hardly notice it, if at all.

author: David Hess
author_rank: Super Contributor
timestamp: July 30, 2025, 06:43:02 pm
content: Quote from: Obsidianxenon on July 30, 2025, 01:49:17 amMost operational amplifiers will work fine for that. I would include a couple of transistors anyway allowing use with lower impedance headphones without better operational amplifiers.There are also configurations which allow multiple operational amplifiers to drive higher current loads.

author: Zero999
author_rank: Super Contributor
timestamp: July 30, 2025, 07:32:43 pm
content: Quote from: Obsidianxenon on July 30, 2025, 01:49:17 amI had a look though Jaycar. They have lots of op-amps/ICs which are suitable, but the best is the OPA4134.https://www.jaycar.com.au/opa2134pa-hi-performance-dual-audio-op-amp-dip8/p/ZL3972https://www.ti.com/lit/ds/symlink/opa4134.pdf

author: Obsidianxenon
author_rank: Contributor
timestamp: July 31, 2025, 12:32:45 am
content: Quote from: Messtechniker on July 30, 2025, 12:55:38 pmI'm able to get the 5534, will that do?

author: John B
author_rank: Frequent Contributor
timestamp: July 31, 2025, 02:14:13 am
content: They aren't equivalent parts, you may have stability issues with the ne5534, where the ne5532 will be stable.As an aside, Jaycar is probably the least desirable to get all your parts for a project. The markups are absurd for a component level project.For a project like this with many generic parts, it's worth checking out LCSC to price up a bulk buy of MELF resistors, SMD MLC capacitors, and op amps.Local suppliers like Element14, Mouser, and Digikey are worth pricing up too because they have shipping included if you buy more than ~$60AUD. These are a bit pricier when it comes to passive parts though. I usually stick to Texas Instruments and ST Micro etc for op amps, transistors etc, but I have also had good experiences with Asian brand substitutes too.

author: Zero999
author_rank: Super Contributor
timestamp: July 31, 2025, 07:54:16 am
content: Quote from: Obsidianxenon on July 31, 2025, 12:32:45 amThe NE5534 is single channel, whilst the NE5532 is two channel. It is faster than the NE5532, but is unstable at gains below 3, without an external capacitor. It has slightly lower noise and can be offset trimmed.I agree with the above that an NE5532 would be better, but two NE5534 will work.

author: Messtechniker
author_rank: Frequent Contributor
timestamp: July 31, 2025, 09:12:24 am
content: I'm able to get the 5534, will that do?The NE5534 is single channel, whilst the NE5532 is two channel. It is faster than the NE5532, but is unstable at gains below 3, without an external capacitor. It has slightly lower noise and can be offset trimmed.I agree with the above that an NE5532 would be better, but two NE5534 will work.Correct.

author: gamalot
author_rank: Super Contributor
timestamp: July 31, 2025, 10:14:18 am
content: Years ago I built a headphone amplifier using a TI TPA6120A2 and was very happy with it.

author: Obsidianxenon
author_rank: Contributor
timestamp: August 01, 2025, 01:23:08 am
content: Thanks everyone for the responses.I've decided to go with the LM833 due to a number of reasons including availability from Jaycar (I will find a better supplier after this project). Let me know if there are any major issues with this.I'll also have the arrangement with an NPN and PNP transistor on the output as per some of your advice. Obviously the full design is not finalised, but I shouldn't have any more problems relating to this topic.Cheers,Obsidianxenon

author: magic
author_rank: Super Contributor
timestamp: August 01, 2025, 08:44:19 am
content: You could try external transistors, but they will need to be biased into class A or AB (though class AB makes little sense here) and this will take a bunch of extra components.You may add 100Ω in series with the output, to isolate the amplifier from cable capacitance which could make it oscillate and cause unnecessary heating and/or distortion. The effect of such a resistor on 2kΩ headphones will be negligible.

author: Zero999
author_rank: Super Contributor
timestamp: August 01, 2025, 09:02:20 am
content: The LM833 is a good choice. It will be able to directly drive 2 kΩ headphones, with no additional transistors. The data sheet lists many of its specifications with a 2 kΩ load.A 100R series resistor is a good idea. Not only will it remove the effect of the cable resistance, but also the fact the headphones themselves might be capacitive at certain frequencies.

author: Obsidianxenon
author_rank: Contributor
timestamp: August 01, 2025, 09:39:34 am
content: I am using a pair of transistors so I can drive a whole range of headphones, not just the HD 424s. Thanks for the help, I'll keep the 100in mind.

author: John B
author_rank: Frequent Contributor
timestamp: August 01, 2025, 10:55:51 pm
content: There are a few downsides to using an external class AB output. Firstly you will need a scope and maybe some audio analysis software if you have a decent interface, in order to be sure the output transistors don't have any crossover distortion. Otherwise you will just have a worse quality product than simply taking the output of something like an NE5532.Secondly, you will need to add supporting circuitry like biasing transistors and trimpots in order to set just the right voltage difference across the output transistors. This is so you can eliminate the crossover distortion while not burning power with excessive quiescent current. There's nothing wrong with a class AB booster stage when done right, but it's mainly in situations where you need to drive low impedances, which require more current than the op amps are capable of driving without distortion.Since you are aiming your amp towards higher impedance headphones, don't overestimate your power needs. People get hung up thinking they need 1W RMS of power directly piped into their eardrums. In reality you will want a restricted power output power stage. But don't be fooled, a few paralleled NE5532 will have plenty of power to damage your eardrums.The addition of an output resistance is a good idea because you shouldn't assume you will always be using such high impedance headphones. You'll get quite the shock if you get careless and forget youre plugging in 32 ohm headphones with the volume up......I would simply use a couple of NE5532s (or whatever your choice) summing their outputs in parallel, each with their own summing resistance such that the effective output impedance is around ~100-120ohm. Aiming for higher is fine since you are using very high impedance headphones. That would be the best solution if you are aiming for quality and simplicity. If you are wanting to create and experiment with a discrete class AB output for the sake of learning, go ahead, but it's not really necessary from a design perspective.

author: Obsidianxenon
author_rank: Contributor
timestamp: August 03, 2025, 09:56:56 pm
content: What needs to be fixed with my current design?

author: John B
author_rank: Frequent Contributor
timestamp: August 03, 2025, 11:26:30 pm
content: Quote from: Obsidianxenon on August 03, 2025, 09:56:56 pmHonestly a fair bit! Firstly, the outputs from your op amps aren't class AB biased, they're class B. Around the crossover between the NPN and PNP transistor starting to conduct, the op amp has to quickly shoot up/down in voltage and will create very audible crossover distortion.One type of biasing for class AB looks more like the circuit you're trying to create a virtual ground with. Diode biasing (using D1 and D2) for class AB is "OK" for light loads such as headphones, but you have to fiddle with your resistances (R21, R22, as well as the current influenced by R19 and R20).Personally I would skip on the virtual ground idea. Life is much simpler if you can supply V+, V- and a solid ground plane to the op amps.Try having a look at this circuit sim link and see if you can get some ideas from the biasing transistor that sets the voltage drop across the output transistors:linkBut you could avoid it all by driving headphones direct from op amps!

author: John B
author_rank: Frequent Contributor
timestamp: August 03, 2025, 11:41:17 pm
content: There are many ways to parallel op amps, depending on bandwidth requirements and whether you need to factor voltage drop into the feedback loop. In this case you have the easiest requirements: audio frequencies are low frequency, and you want them to have an output impedance.linkYou can simply try adding as many buffers and summing them together, such that their individual output impedances sum to around ~120ohm. This will all depend on the range of headphones you wish to drive, ie lower impedance > more current > more op amps. Your 2k headphones are unusually high. I typically use 250ohm headphones, general consumer ones could be 32 or lower.

author: Obsidianxenon
author_rank: Contributor
timestamp: August 03, 2025, 11:49:36 pm
content: Quote from: John B on August 03, 2025, 11:26:30 pmSo unfortunately a V+ and V- rail isn't directly possible, hence the virtual ground.Also I have been told that for lower impedance headphones, simply driving from op amps isn't enough, but correct me if I'm wrong. I would like to be able to use a range of headphones with this project.Thanks for the links, I will have a look at them later on and change the circuit.

author: John B
author_rank: Frequent Contributor
timestamp: August 04, 2025, 12:23:30 am
content: Quote from: Obsidianxenon on August 03, 2025, 11:49:36 pmYou can always test how much you really need. If you have an existing headphone amp / any headphone output, try to measure the voltages at the output while changing the volume up until it's uncomfortably loud. Use the lowest impedance headphones you have.If you can feed in a sine wave signal, take the RMS voltage * 1.414 to give a peak voltage, divide by headphone impedance. This will give you a rough peak current figure. Add a little for additional headroom. That will be the total current the paralleled op amps have to supply without distortion.

author: BrianHG
author_rank: Super Contributor
timestamp: August 04, 2025, 01:09:52 am
content: I've done dip8 dual opamps, in 1:1, IE output tied straight to adjacent negative feedback input, 5 stacked ontop of each other with space for cooling, with a series 1 ohm resistor at all the outputs tied together to make a single output.With a +/-15v supply, I was able to drive stereo 8 ohm speakers to around 2 watts x2 before distortion.In front of my towered opamp stack, I had another dual opamp to set gain and handle the volume control.I later tried 1 amp output opamps from Motorolla in dip 8, got around 20 watts stereo output.Today, this guy is still available:https://www.st.com/content/ccc/resource/technical/document/datasheet/e0/f7/2a/94/3a/a1/4d/1c/CD00156396.pdf/files/CD00156396.pdf/jcr:content/translations/en.CD00156396.pdfMany others exist too in the 350ma to 500ma output range.Use a high quality J-fet/Mosfet input opamp for your voltage gain prior to drive the high power opamp in a 1:1 gain ratio.

author: BrianHG
author_rank: Super Contributor
timestamp: August 04, 2025, 02:54:25 am
content: A dual opamp to destroy your ears...https://www.digikey.com/en/products/detail/texas-instruments/ALM2403QPWPRQ1/13627106Rail-Rail, 24v at low current drive and will drive 500ma for 32ohm or 16ohm headphones.Short-circuit protected.

author: 2N3055
author_rank: Super Contributor
timestamp: August 04, 2025, 07:54:43 am
content: To OP.Just get NJM4556A in DIP case and give it clean +- 12V power. Use it in normal noninverting opamp config. There are schematics everywhere.

author: Obsidianxenon
author_rank: Contributor
timestamp: August 05, 2025, 07:36:50 am
content: I can only apologise for my lack of knowledge in audio electronics at the moment. Gotta start somewhere.Anyways what do you reckon about the circuit now?EDIT: Just realised the lower power rail is connected wrongly to the amplify output. Just ignore that.

author: Zero999
author_rank: Super Contributor
timestamp: August 05, 2025, 08:08:25 am
content: Quote from: Obsidianxenon on August 05, 2025, 07:36:50 amThat's not much better I'm afraid. The Schottly diodes have far too lower voltage drop to bias the output stage into class AB.The output transistors require about 0.7V between the base and emitter to turn on and there are two of them, effectively in series. Schottky diodes drop about 0.3V, so you have a total of 0.6V, when you need 1.4V, plus a little more.I suggest you stick to your high impedance headphones, driven directly from the op-amp for now.

author: Obsidianxenon
author_rank: Contributor
timestamp: August 05, 2025, 08:11:23 am
content: Oh ok I must be reading the datasheet wrong. How did you figure out the voltage drop?

author: Zero999
author_rank: Super Contributor
timestamp: August 05, 2025, 08:20:05 am
content: Quote from: Obsidianxenon on August 05, 2025, 08:11:23 amSee figure 3. In fact I was wrong, the voltage drop will be much less than 0.3V, as you only have tiny bias current.https://www.vishay.com/docs/88525/1n5817.pdf

author: Obsidianxenon
author_rank: Contributor
timestamp: August 05, 2025, 08:22:50 am
content: Right, right. In that case do you think a regular silicon diode would suffice, or should I risk it with resistive biasing and probably a trimpot?

author: Zero999
author_rank: Super Contributor
timestamp: August 05, 2025, 09:30:32 am
content: One problem with these circuits is the biasing resistors limit the drive to the output transistors. The op-amp redirects the current from the biasing resistors into either power supply rail, thereby turning of the respective transistor, rather than actually driving it on.This circuit solves that problem by using AC coupling capacitors to bypass the biasing network, allowing the op-amp to drive the transistors.https://sound-au.com/project113.htmI simulated a variation of the above schematic in the following thread.https://www.eevblog.com/forum/beginners/ab-class-amplifier-schematic-analysis-optimization/msg2436483/#msg2436483It requires a dual power supply, but can be redesigned to work off a single 9V or 12V supply, although it won't be able to deliver as much power.

author: tszaboo
author_rank: Super Contributor
timestamp: August 05, 2025, 10:37:01 am
content: Quote from: Obsidianxenon on August 05, 2025, 07:36:50 amYou should start with simple circuits. For example no output transistors, as others suggested. It's an extra layer of added complexity. Also I wouldn't even attempt doing anything like that, output transistors, before I spent a day or two simulating the circuit. It looks simple, but the devil is in the details. You can find out for example the PSRR at a certain frequency of your opamp just by reading the datasheet. How much is it, if you add output transistors? How does the turn-on transient look like? Will it pop out your eardrums if you have a phone call next to it?

author: Obsidianxenon
author_rank: Contributor
timestamp: August 05, 2025, 11:28:55 pm
content: Quote from: Zero999 on August 05, 2025, 09:30:32 amI'm going to go off for a while and do some extensive simulating as per some others' request. Thanks for the circuit and just to confirm: my rail splitter circuit would be ok for this?

author: Messtechniker
author_rank: Frequent Contributor
timestamp: August 06, 2025, 08:06:44 am
content: Quote from: Obsidianxenon on August 05, 2025, 11:28:55 pmExcellent idea. Helps you to really understand which component is doing what.Do simulations (MicroCap - pretty steep learning curve, by the way) all the time especially in connection with difficult repairs on complex (multiple loopback) circuits.Sometimes even lucky to simulate the specific failure.

author: Zero999
author_rank: Super Contributor
timestamp: August 06, 2025, 08:39:28 am
content: Quote from: Obsidianxenon on August 05, 2025, 11:28:55 pmPresumably you mean the rail splitter in the post linked below?https://www.eevblog.com/forum/projects/heaphone-amplifier-requirements/msg6001023/#msg6001023Yes, that will work. Why did you choose such large values for C7 & C8? It will work but 10µF will fine, if anything use higher values say 220µF for C9 & C10, since they pass the most current. I would look into designing the rail splitter so the transistors just handle the tiny DC bias currents, with the capacitors passing the power. I'll post a schematic later.Regarding simulation. I had problems finding an LM833 model which works with LTSpice. The one I found from ON Semiconductor worked, but I have no idea about the accuracy. The TI one didn't work with LTSpice but should work with TINA-TI.

author: Obsidianxenon
author_rank: Contributor
timestamp: August 06, 2025, 08:43:12 am
content: Yes that is the one I was referring to. The rail splitter is not my design, I'm using the discrete one from this website:https://tangentsoft.com/elec/vgrounds.htmlYou're right though, I simply copied over the circuit to make a point.

author: David Hess
author_rank: Super Contributor
timestamp: August 06, 2025, 08:52:47 am
content: I would use the boosted operational amplifier design shown below, with changes, but operation is tricky.The output operates closer to the supply rails, and current limiting is present, but distortion is may be worse and it requires a single operational amplifier package per output because it relies on the supply pins to drive the discrete output stage.

author: Zero999
author_rank: Super Contributor
timestamp: August 06, 2025, 10:33:16 am
content: Quote from: David Hess on August 06, 2025, 08:52:47 amA dual op-amp can be used with both sections connected in parallel.https://e2e.ti.com/blogs_/archives/b/thesignal/posts/paralleling-op-amps-is-it-possibleThat circuit requires a basic understanding of how the op-amp's output stage works.Here's a schematic showing the internals of an op-amp in a similar circuit.https://www.eevblog.com/forum/beginners/non-standard-op-amp-configuration/msg780325/#msg780325

author: David Hess
author_rank: Super Contributor
timestamp: August 06, 2025, 03:05:59 pm
content: Quote from: Zero999 on August 06, 2025, 10:33:16 amIt sure can, and parallel operation is a good way to get more output drive and power dissipation, or one section can be disabled, but either way, two packages will be required for two channels if this circuit is used.

author: Messtechniker
author_rank: Frequent Contributor
timestamp: August 06, 2025, 03:07:21 pm
content: Quote from: David Hess on August 06, 2025, 08:52:47 amAt distortiion levels of around 3% for most loudspeakers and probably headphones also, you will have nothing to worry about at amplifier distortion levels lower by a factor of 10 or more. Its hard to find any loudspeaker distortion measurement results, because they are so "bad".

author: Zero999
author_rank: Super Contributor
timestamp: August 06, 2025, 07:50:35 pm
content: Quote from: David Hess on August 06, 2025, 08:52:47 amJust bypass the biasing diodes with capacitors. It will result in the same low voltage drop as the pass transistors and the channels in a dual op-amp can be used individually.Here's a simulation showing the difference between bypass and no bypass capacitors. In both cases, the op-amps are ideal, rail-to-rail, with the outputs restricted to the power supply voltages. The top plot is without the bypass capacitors, well they're 1pF but that's too low to make any difference. The bottom plot with 47µF bypass capacitors.When there are no bypass capacitors it clips at just over 8V and with them the output reaches the full 10V, with little distortion.

author: Obsidianxenon
author_rank: Contributor
timestamp: August 06, 2025, 09:21:13 pm
content: Thanks for the visualisation. Is that LTSPICE or something else?

author: Zero999
author_rank: Super Contributor
timestamp: August 06, 2025, 09:29:51 pm
content: Quote from: Obsidianxenon on August 06, 2025, 09:21:13 pmYes. It's LTSpice, which is my favourite simulator. Although many find it hard to learn the UI, I've found it to be one of the fastest for schematic entry, after learning it of course. What's more challenging is there's no obvious way to do many things, so a search engine and this forum are your friends.There are alternatives such as TINA-TI and MicroCap which are also free and might even be better suited to this application if you want to simulate the LM833, but finding accurate models is often a challenge, regardless of what program you use.

author: BrianHG
author_rank: Super Contributor
timestamp: August 06, 2025, 11:02:19 pm
content: You could just use a single TPA6120A2 premium headphone opamp.+/- 15 volt, driving up to 700ma per channel.https://www.mouser.com/ProductDetail/Texas-Instruments/TPA6120A2DWPR?qs=ojKcPFmCWSXiGd7G5JhN2A%3D%3DOr, just buy this guy and modify it to your liking:You wont get easier or cheaper than this!!!

author: John B
author_rank: Frequent Contributor
timestamp: August 06, 2025, 11:42:58 pm
content: I think a lot of the suggestions in here are missing a critical piece of design criteria: what is the actual goal of the project? I'm getting the impression that the OP wants to experiment with various subcircuits, ie virtual ground, discrete class AB output. In which case, just build it up and learn about why things aren't working the way you'd expect or hope.If the goal is high quality signal amplification, a simpler approach driving directly from op amps with a split supply would be the way to go. But I understand it takes away some of the fun.

author: bson
author_rank: Unknown
timestamp: August 07, 2025, 09:41:55 pm
content: Any modern opamp, like LME49720 will work nicely. Skip the NE5532, its gain distortion goes up dramatically as load drops bellow 200 ohm or so - it's only specified with a 600 ohm. Using it to build filters and other uses it didn't handle well due to this is part of what gave opamps such a terrible reputation in the 70s and early 80s. Modern opamps like the aforementioned LME49720 can drive just about anything you throw at it and will sound better at it than any functionally equivalent analog circuit you can build.

author: Obsidianxenon
author_rank: Contributor
timestamp: August 09, 2025, 01:19:18 am
content: Now I'm confused. I ran the circuit through LTSpice and there doesn't seem to be crossover distortion regardless of what diode I use, silicon or schottky.Green is the input signal, blue is the output signal.Am I doing something wrong?

author: John B
author_rank: Frequent Contributor
timestamp: August 09, 2025, 01:57:24 am
content: Quote from: Obsidianxenon on August 09, 2025, 01:19:18 amWhat is the simulation model of the opamp? It may be a theoretically perfect opamp rather than a simulated real world opamp.Have a look at the output of the opamp to see how it has to slew very quickly around the zero crossing point, where one of the output transistors will turn off and the other turn on.In a class AB output, neither transistor should fully turn off, therefore no crossover distortion.

author: Calvin
author_rank: Regular Contributor
timestamp: August 09, 2025, 07:47:09 am
content: Hi,I´d suggest You´d rather stick with the designs of #42 or #52.You would want to have some input signal conditioning, like bandwidth limiting ahead of the OPA (#42: C1/R1. I´d also add a HF-lowpass, R2 plus a small cap from R2 to gnd, say ~1nF film cap)As OPAs TexasInstruments JFET-input OPAs like OPA604, OPA134 etc. have proven to function well.You need to run the biasing diodes and the bases of output transistors on sufficient current ... 100k are way too much ... see the 6k8 in #42Generally try to keep the resistor values low as this is generally advantageous regarding noise ... Your feedback resistors are such a caseDon´t use a trimpot in the feedback loop ... if the wiper opens gain increases, which might kill Your attached can.If You want to use a trimpot use it from the inv-pin to gnd ... connected that way gain decreases in case of an open wiper ... or use a volume-pot in front of the amplifier in first place.If You use a volume-pot make sure the signal remans dc-free .... otherwise add dc-blocking caps to and from.To prevent possible oscillation You often find a small cap in parallel to the feedback resistor ... typically something between 22pF to 100pF suffices (film or COG/NPO).A output resistor also helps stabilizing against capacitive loads ... typically 15R to 50R suffice .... make sure the resistor can handle the heat power.Just one cap of ~10µF across the biasing diodes is fully sufficient.Use transistors of sufficient wattage ... TO126 or TO220 types like the proverbial BD139/140 might be fine even without additional cooling fins, when run in class a up to ~20mA.Rethink Your power supply! Your schematic describes what could be called a heat generator not a filter or regulator.You may use passive filtering or a transitorized capacitance multiplier, or a combination of both.Put some effort in a decent layout. Stable working and considerable differences in THD+noise figures as well as hum may be associated with the layout and cabling.regardsCalvin

author: Zero999
author_rank: Super Contributor
timestamp: August 09, 2025, 11:10:56 am
content: Quote from: Obsidianxenon on August 09, 2025, 01:19:18 amThe crossover distortion is there, even if it isn't obvious, under your test conditions. It becomes more noticeable at low output levels and higher frequencies.Negative feedback also helps to reduce it. If the output of the op-amp is plotted it's even greater.Here's a simulation showing the difference between Schottky and silicon diodes. The red traces are when the diodes are 1N4148 and the green traces when the diodes are the 1N5817