AKSA's Lender Preamp with 40Vpp Output

[Ultima Thule]

Beutiful result!
Can someone explain why we choose P devices in the IPS?
I asked same question 3 days ago under the link below where a similar schematics was presented by Zen Mod (~4 posts above mine), but no answer yet.
About possible Babelfish J interest

[Nico Ras]

So the output is 7mW, what will you do with that?

[AKSA]

Output is low impedance (<5R), but limited to 12mA CCS. This can nicely drive a small output stage, single ended or PP. The buffer, Q4, could be made a FET or even increase current to 30mA. That would boogie!

UT, if you use pnp for the LTP, it mandates npn VAS, and my experience is that npn VAS has lower parasitics and greater GBW than pnp in the same role.

HD

[Samuel Jayaraj]

Also generally PNP in LTP gives lower current noise, doesn't it? Reason why a lot of phono preamps were designed that way. Not sure if it matters here with signal levels involved. Ofcourse, as Hugh said, it also allows for NPN VAS which is just what you want for its desired characteristics.

[PMA]

I do not think it would be audible, but why is there that ninth of some 0.002%?? The 9th is usually 110 - 130 dB below the fundamental. Just curious where it is created.

[juma]

Originally Posted by PMA

...why is there that ninth ...

Yes, and the 5th is way too high - maybe some measuring setup artifact ?

Using PNP LTP in single rail PSU circuit is good for the PSRR too.

Anyway I'd lose Q4 and unstrangle Q3, let the LTP breathe, change CCS and at least bootstrap the tail of of the LTP. Gain should be higher so that weaker sources and/or quieter recordings can bring enough voltage swing at the output. Drive capability should stay about the same.

Roughly, something like this (R1/R2 divider might need some adjusting to ensure symmetrical clipping and freq.compensation should be checked in vivo. Practical details like PSU bypassing and similar are logical addition) :

[xrk971]

I'm wondering where the 5th and 9th are from too as not in sim. I should change audio interface and PC to see if it clears up.

Juma, thank you for the suggested schematic. I don't believe it is the same topology anymore though. Have you simulated it yet? Looks interesting. It could be a headphone amp with a larger C2 and higher bias, as could Aksa' circuit.

...if you use pnp for the LTP, it mandates npn VAS, and my experience is that npn VAS has lower parasitics and greater GBW than pnp in the same role.

This now seems perfectly clear and a great reason. I have wondered myself.

[juma]

Originally Posted by xrk971

... Have you simulated it yet? ...

Sorry but no, I only built it. Yes, I know that these days simulation is more valuable than the real build but I'm an old-fashioned guy...
Actually, that sch. is part of the power amp I made some time ago (imagine one pair of Lateral MOSFETs added at the output, with one LED between the Gates to bias them).

[Bigun]

I looked at a similar topology many years ago but never built it (yet) TGM4 amplifier

However, what is shown in post#1 is not quite the Lender circuit. The original circuit, 'invented' by Rudolph Lender when he was at Motorola uses a different arrangement with two transistors. I do remember asking Hugh about it too...

Originally Posted by AKSA

Gareth,

Tried the Lender, simulated it also. No OLG advantage over a single ended drive to a stock common emitter VAS, and no discernible advantage sonically. However, it does combine some elements of CM, tending to force current balance in the LTP by adjusting VAS current. But this may not be very useful if the VAS current is fixed anyways, as it normally is.

Cheers,

Hugh

[xrk971]

Originally Posted by Bigun

I looked at a similar topology many years ago but never built it (yet)...

However, what is shown in post#1 is not quite the Lender circuit. The original circuit, 'invented' by Rudolph Lender when he was at Motorola uses a different arrangement with two transistors. I do remember asking Hugh about it too...

Agreed, hence which is why I said "inspired by" Lender. Nice amp design the TGM4, what does TGM stand for?