Real World TMC/ETMC applications

[ostripper]

Split off from the thread "Bob Cordells power amplifier book" , this thread will deal with the history , theory , applications ,and simulations associated with the latest , greatest... "devastatingly effective" little trick to grace the AB amplifier.

I have just about completed 4 new TMC capable amplifiers. I only have a 20mhz CRO and 2 DMM's, but hope to "show and tell" in a convincing manner to gain the trust of the community.

I also have been running a juryrigged "blameless" based TMC creation plus , SNG001 (member) , has built the finished unit as well. This means it will not blow up , in fact both myself and SNG are enjoying some nice audio.

We already know (maybe not everyone ??) The Baxandall Papers: Transitional Miller compensation the history/ basic theory ... let's move on to the application(s).

OS

[ostripper]

Real "no brainer" , add the 2 caps and 1 resistor, have 1/10 the total THD , much less at HF. An added bonus of really cutting out the odd harmonics , regardless of topology. I think this is the result of negating the output stage Xover distortion (H3/5/7/9).

A TMC applied AB amp has the output spectra of some of the larger Class A output stages I have worked on / simulated / repaired ... (genesis stealth). Output FFT also matches the Vout FFT of the class A standard EF2 driver stage ... so you are essentially listening to a faithful representation of your VAS.

Quite any easy decision to add 1 more cap / resistor to achieve a tenfold improvement. PIX 1 = no tmc # 2= TMC 100pF/270pF - 470 R network.

OS

[Krisfr]

I can hardly wait till you incorporate TMC into the KO Goldmund Killer and give some feedback as to the listening experiences. When board layouts be available?

[ostripper]

Originally Posted by Krisfr

I can hardly wait till you incorporate TMC into the KO Goldmund Killer and give some feedback as to the listening experiences. When board layouts be available?

I am stuffin' them now. Check out that VAS ! quite HD. I do have a feeling BOTH of them with TMC will blow just about any amp out there "out of the water". REALLY!!

OS

[Rafael L]

Hi OS,
Its distortion is low, but has residual of high harmonic. What is the RE of TRs output and Bias?
I am suspecting that is in Under Bias!

[Bonsai]

Nice work OStripper. Looking forward top seeing the performance on the final amp.

[VHF man]

Originally Posted by ostripper

... so you are essentially listening to a faithful representation of your VAS.
OS

Hi OS

I think that's a good point.

I'm building a blameless amp at the moment using the Motorola thermaltrac devices. The VAS is the usual EF with beta enhancer using high beta devices - so the potential to reduce OS distortion with TMC is high.
I'm looking to minimise the usual dominating odd order distortion spectra - even at low levels so I like the fact that TMC allows the flexibility to add a little more degeneration at the LTP - since the LTP transconductance is no longer the lone force in reducing OS distortion at 20kHz. The fact that a single ended gain stage can now be a determiner of the end THD spectra in a blameless topology can only be a good thing from a SQ POV.

To fully realise the benefits possible with TMC is a goal for all of us - and that means optimising the VAS and VAS topology. The poor VAS has often taken a back seat when it comes to creative design thinking. Indeed I can think of a local (Aus) designer that doesn't actually use a VAS.

However, with TMC the VAS can now be used to distribute NFB in a way that was not possible before. With TMC it's no longer the least important stage in a blameless generic 3 stage design.

[WuYit]

ostripper,

The simulator does not TOTALLY lie !!!

Simulation guru says "Even a blind hen sometimes finds a grain of corn".

An added bonus of really cutting out the odd harmonics , regardless of topology.

TMC is much smarter than I thought, but how in the world...

I think this is the result of negating the output stage Xover distortion (H3/5/7/9).

Most likely, it`s incredibly smart.

[mt490]

If you applied it to a symmetric topology like a leach you'd still get odd order distortion effects wouldn't you?

The profile that we're seeing is really only because it's a singleton type feedback in the case of the Linn and blameless type amplifiers and as a result exhibits single-ended residuals.

[wahab]

Originally Posted by mt490

If you applied it to a symmetric topology like a leach you'd still get odd order distortion effects wouldn't you?

The profile that we're seeing is really only because it's a singleton type feedback in the case of the Linn and blameless type amplifiers and as a result exhibits single-ended residuals.

not at all, as a symetrical differential show the same outcome
provided it s designed adequatly.
The problem for such an implementation in a leach amp
arise from the VAS limited gain, hence it will not be as efficient
as in a blameless..
One has to increase the gain of this stage, and that s what
i did since , for some reasons, i prefer symetrical designs...