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Discreet DC-coupled portable amp schematic?

post #1 of 9
Thread Starter 
Hi,

I was wondering if any of you kind folks know of a good discreet, DC-coupled portable headphone amp schematic? No opamps, no signal path caps, just super basic, with volume control and that's it.

I've been playing around with DIY audio in music for a few years (I designed and build two bass guitars, and I've built a bass preamp from schematics online) but I'm new to the headphone stuff. As a matter of fact, I'm building my first DIY amp right now (AMB mini^3 to push my J-moneyed D2000's). I'm good with a soldering iron, I can make my own PCBs, I can reflow with a toaster, I can read a schematic, but I can't design an audio circuit, at least not yet. Getting my learn on, though.
post #2 of 9
How small?

How good?

A super basic discrete amp will sound worse than an opamp based amp. Simple isn't better. It's just a DIY wish.

All amps can be made portable. There's a world of possibilities.
post #3 of 9
transportable jisbos
post #4 of 9
post #5 of 9
why not just build a diamond buffer and carefully trim DC offset?
post #6 of 9
^you mean an open loop diamond buffer?

They don't like driving low impedance loads and IMO if you were to trim a diamond buffer the only way to do it is to introduce an offset error to the CCS to nullify the differences between NPN and PNP complementary parts.

You can introduce the offset to the input but that's what we all want to avoid heh.
post #7 of 9
Thread Starter 
I'm obviously betraying my limited knowledge in audio circuit design. I've built preamps for bass guitars, and JFETs seem to sound pretty good in bass guitar amps. I'm seeing the difference is, though, that the 'voicing' you get with JFETs and caps in the signal path are desirable in that application, but in audio reproduction, we want as little of that as possible. No worries, I'll stick to chip amps for now. Just thought it would be fun.
post #8 of 9
There's nothing wrong with JFETs in the signal chain. If cascoded or CFP they can make a very good input stage.

If you want, you can build a discrete amp that's on par with high quality opamps, just don't expect it to be as simple as two or three transistors and some resistors. One of the simlest yet good would be something like in the link above, preferably improved with cascoded input stage and a diamond buffer output stage.
post #9 of 9
Quote:
Originally Posted by barnaclebeau View Post
I'm obviously betraying my limited knowledge in audio circuit design. I've built preamps for bass guitars, and JFETs seem to sound pretty good in bass guitar amps. I'm seeing the difference is, though, that the 'voicing' you get with JFETs and caps in the signal path are desirable in that application, but in audio reproduction, we want as little of that as possible. No worries, I'll stick to chip amps for now. Just thought it would be fun.
JFETs are used as the input stage in a wide range of very good DIY headphone amps. B22, Dynalo, Dynahi, Blue Hawaii, CKKIII, Exstata, etc etc etc. Of course, these are all desktop amps which follow the JFET input with big output buffers. And they are all DC coupled with no caps in the signal path.

It is logistically difficult to do this in a portable amp. Too much PCB real estate and too much current draw. OPAMPs do really make a lot of sense here.
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