Marsh headphone amp from Linear Audio

[jackinnj]

Originally Posted by RNMarsh

That's a nice variation on what has become what might be called the better topologies in use today .... current-mode, too.

TPA6120A2 from TI is current mode as well. It's in a "DWP" package which means that its approx 500x500 mils! Of course, being CFB it requires a pair of opamp buffers.

[RNMarsh]

Originally Posted by coluke

Output drift is less than about |5| mV over 2 hours or so @ about 100 mA Iq (fairly stable, and this was somewhat the real challenge with such a low Zout design goal), en plein air and with a far-from-optimum layout: not a precision DC amplifier at all , but seems fine for audio - actually a DC servo coluld be not necessary at all, although I've already tested one, just to be on the safe side.



Agree - that's why I'm so curious about your amplifier.

L.

I thought that would be a problem -- dc drift/offset --and a challenge. Let me add this, now ---> some circuits which depend on servo to compensate for poor offset/drift will unbalance the amp's distortion null and the distortion will go up... So, yes, you need to start with as stable as possible design without servo... servo should only be used for very fine tuning. Some servo have got a bad rap for making sound bad.... maybe this is why. But, you can do without the servo if careful. ..... watch it over longer time and look over a wide range of expected temp range (not MIL range).

I am now in the middle of nowhere using satellite ($$$) but I couldnt help myself. Thx for the interesting feedback --RNM

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[Telstar]

I've read the article at last. A bit short, and leave me wonder what to do to raise the current. Very smart the input stage instead, that tickles me enough to want to try the amp, but probably with different output devices.

PS: thd20 has been measured? The only reference to closed loop performance is <.001% thd which doesn't tell much.

[jackinnj]

maybe i should make up some kits of matched input and output devices.

[Telstar]

Originally Posted by jackinnj

maybe i should make up some kits of matched input and output devices.

yes please

[rjm]

I've just finished reading this entire thread, all 245 posts.

It was exceedingly onerous.

Discussing a circuit without having the schematic is like, oh, screw it, make up your own analogy. I'll probably grab a copy of Linear Audio. As Jan said, these kinds of publications are thin on the ground now, and will probably disappear completely in the not too distant future. That's not really the point. The point is there is a ~250 post thread about a headphone amplifier with only the buffer version presented. It's needlessly frustrating to wade through.

Could we get a "public domain" version of the full amplifier schematic posted here, please? It doesn't have to be annotated, it can have the part values redacted, you can even "black box" bits if you need to ...

[rjm]

Coluke, your circuit interests me. It's a variation on a theme I catch a glimpse of from time to time, but I've never tracked it down to any comprehensive source. Can you give me a little bit of background on it?

[Telstar]

Originally Posted by rjm

I've just finished reading this entire thread, all 245 posts.

It was exceedingly onerous.

tsk tsk, amateur
Try reading the blowtorch thread

Could we get a "public domain" version of the full amplifier schematic posted here, please? It doesn't have to be annotated, it can have the part values redacted, you can even "black box" bits if you need to ...[/QUOTE]

I have my paper copy, but I agree with this request; it wouldn't do any harn to LA imo.

[SY]

Ask Jan's permission. Or as the tube guys would say, "Frag Jan Zuerst."

[coluke]

Originally Posted by rjm

It's a variation on a theme I catch a glimpse of from time to time, but I've never tracked it down to any comprehensive source. Can you give me a little bit of background on it?

Hi rjm - if a comprehensive source of information about CF architectures exists at all, I haven't found it yet . My starting point were the Sergio Franco's chapter on CF Amplifiers in Analog Circuit Design - Art, Science and Personalities by Jim Williams, and an old (1994) article by Smith, Koen and Witulski: Evolution of High-Speed Operational Amplfier Architectures - imho both are worth a thorough read. You can find the very same topology (or a quite similar one) in a number of DSs/ANs by National (OA-31), Linear (LT1228, LT1395) and ADI (AD844) - it seems a well established and good performing architecture, and it works very well indeed even with discretes.

L.