What headphone amp?

[Fancy Lime]

Hey everyone,

I want to build me a headphone amp for jamming to an aux source like a drum machine and also for testing other things I build. So it needs to be "reasonably HiFi", meaning no blatantly audible distortions or colorations but it is not supposed to be the ultimate ultra-linear studio reference headphone amp. I just want to be able to judge what I feed into it fairly realistically. I want it to be able to drive a range of common studio headphones, so about 25-250Ω, at useful volumes (meaning not an iPhone output, not 1000mW either). I am thinking about either something with a LM386 as the output stage, or something with a discrete AB output stage similar to the mxr headphone amp.

Has anyone tried any of those and can tell me right away that either of these designs will be bad for my purpose before I sink a lot of time into this?

I want to use a 9V power supply but am thinking about charge-pumping it to 18ish V. Worth the extra trouble for my purpose?

Does anyone have additional suggestions? A cmoy-style thing probably wont generate enough output for high-ohm headphones, right? Discrete class A MOSFET outputs bring with them the necessity of heat sinks, which I'd like to avoid if necessary.

I read some criticism about the mxr headphone amp related to some missing protection but I can't remember where or what it was exactly.

Thanks for any input,
Andy

[MaxPower]

This is a project I've been meaning to get around to as well. Hopefully you'll get some good  recommendations.

If not, one option is audio amplifier chips. I used one to build a battery powered guitar amp. Just search for audio amplifiers at mouser or some other electronic parts supplier. The data sheets usually give pretty good detail as to how to use them and they often include a schematic of a practical circuit.

[PRR]

Build a 9V '386 amp. Use NJM chips. Try it.

It sure will be ample in 32 Ohms. I've had hi-Z phones which needed more supply voltage (I used to use 30V for extreme level) but those phones are mostly gone.

[Fancy Lime]

Alright, thanks Paul! I was leaning that way due to lower parts count and complexity so good to hear that that should work.

Whats the reasoning behind wanting to use NJM/JRC instead of NSC/TI chips? I've read that they are "better" before, just could not find objective reasons why or how. Thing is, I could not find a source for 386 JRCs in Europe after some research. At least non of my usual suspects carry them. Does anyone know a source?

I have a bunch of LM386-1s lying around and could get my hands on LM386-3s and -4s. Any preference there? The data sheet suggests they should be equaly suited for 9V, low wattage applications, but then again data sheets are never all there is to a device.

Instead of higher supply voltage I was toying with the idea of a bridged output. Not the first thing I'll try, seems like single '386s should work well enough with my main cans (80Ω Beyerdynamic DT700-M). But for 250 or even 600Ω cans, worth a try or unnecessary?

Cheers,
Andy

[PRR]

You  can't do stereo bridge with standard 3-contact headphone plug.

[Hugomess]

haven't cracked it open but i have an old blood noise headphone amp that i really like.

[anotherjim]

386? Try Bitsbox. They have 3 options, including NJM.

My studio headphones, I think the lowest impedance I have is 80ohm.
From 9v supply, I wonder if they could do much.

The standard domestic 30ohm-ish cans would be plenty loud. My old Sennheiser HD201 (24ohm) were cheap, are comfortable, sound decent & still going strong. Surprisingly, they still make them, which says something.

I wouldn't shy away from the 386 option with the convenience of 9v supply, just get headphones to suit. Will be so much simpler.
Avoid clipping the 386 - let it have minimum standard gain. Some of the mini-amp designs boost the thing to death.
386 seems perfectly happy driving both cans in parallel from 9v if you're happy with mono.

[Fancy Lime]

@ Paul
Yes, that's clear. I was thinking to either make it mono in this case or mod my cans. Was planning to change the non-detachable cable with a detachable at some point anyway. And once I'm at it I might as well change it to 4 leads with a 4-pole mini xlr. But the bridge option is kind of the next step and only really interesting if I am not happy with the simpler version. Probably unnecessary for my cans, was just exploring the possibility. Especially for 600Ω studio headphones (rare but I know several people who have old and loved ones) the bridged mono version might be nice, no? Maybe some clever switching between "normal" stereo and bridged mono could be cooked up. I have to think about that and make a schematic but "it feels possible". And since we are apparently now out the far end of the age of reason and only the "feeling of truth" matters any more... Oh wait, electronics still work according to science, thank goodness.

@ Jim
Thanks for the Bitsbox hint. They have the "NJM386BD - Equiv to LM386N-4". That leaves the question: Is it better or actually the same, for my intents and purposes, as the LM386N-4, which I can get easily and locally without having to mail order a mere handful of parts?

[marcelomd]

Hi,

I shared a schematic some time ago: Here.

I has instrument and aux in. Stereo output. It's pretty flat and works well.

EDIT: I used a NJM4556 as mixer and output driver. It's a 4558 with 70mA output and very low distortion. See here.

[anotherjim]

Far as I know, the LM386-N4 has recently gone out of production. The NJM part is the same grade and still is produced.

[PRR]

Historically the '386 was designed for pocket radios but mostly used in dial-up modems. The sound quality was tolerable at first but I see many reports of crappy sound which may mean production was biased for low standby power rather than tolerable low-level distortion.

NJM has always been about the sound.

IAC, use a socket here.

Many car-sound chips are 2-channel and will work 9V to 15V. These may be a better bet.

[Fancy Lime]

@ Paul
Aha, different production priorities but same theoretical specs, that explains it. Thanks! I'd be open to try a "modern" dedicated 2-channel audio chip. People keep referring to them in headphone amp discussions. Unfortunately I have not seen one mentioned that was actually available anywhere. If you can point me to a reasonably common one, I'd appreciate that a lot. I kept coming back to the '386 because it is as ubiquitous as the common cold (but sounds better).

@ Jim
Hm. Still the Texas variant seems more common in European online shops. TI seems to completely dominate the "general" European electronics market for ICs, from what I can tell. JRC chips seem to be relatively limited to specialized audio shops and even those carry mostly the NJM4558 because: tube screamer! But thanks again for the Bitsbox tip, I'll just order there and be happy.

@ Marcelo
Yeah, I originally considered the 4556 as an alternative too. But I gave up on it after being unable to find the NJM4556 anywhere. Not only do people keep confusing it with the 4558, so does Google. Keeps telling me "did you mean: 4558". Damn it Google, I know what I mean! So I got a bit frustrated with that. Do you know an NJM4556 source in Europe?

Andy

[boppy100]

tda2822m (L) works fine with 32R phones. Don't know about higher impedance phones.  Just use the datasheet circuit

[marcelomd]

Hi,

I don't know any local store over there, but these chips are common in consumer audio equipment, so any store that supplies parts for repair shops must have them.

I bought them from a local merchant in ebay. They were reasonably priced, meaning they are not considered exotic.

You can try using the full part name: NJM4556AD for DIP8, or the old/alternate part number: JRC4556.

Found them in eBay.de and on Mouser.de.