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Old 12th December 2010, 11:16 PM   #1
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Default Real World TMC/ETMC applications

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
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Last edited by ostripper; 12th December 2010 at 11:20 PM.
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Old 12th December 2010, 11:38 PM   #2
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Default The simulator does not TOTALLY lie !!!

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
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Last edited by ostripper; 12th December 2010 at 11:46 PM.
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Old 12th December 2010, 11:48 PM   #3
Krisfr is offline Krisfr  United States
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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?
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Old 12th December 2010, 11:54 PM   #4
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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!!

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Old 13th December 2010, 07:27 AM   #5
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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!
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Old 13th December 2010, 08:31 AM   #6
Bonsai is offline Bonsai  Taiwan
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Nice work OStripper. Looking forward top seeing the performance on the final amp.
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Old 13th December 2010, 09:25 AM   #7
VHF man is offline VHF man  Australia
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Originally Posted by ostripper View Post
... 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.
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Old 13th December 2010, 10:40 AM   #8
WuYit is offline WuYit  Sweden
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ostripper,
Quote:
The simulator does not TOTALLY lie !!!
Simulation guru says "Even a blind hen sometimes finds a grain of corn".
Quote:
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...
Quote:
I think this is the result of negating the output stage Xover distortion (H3/5/7/9).
Most likely, it`s incredibly smart.
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Old 13th December 2010, 11:12 AM   #9
mt490 is offline mt490  Australia
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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.
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Old 13th December 2010, 11:33 AM   #10
wahab is offline wahab  Algeria
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Quote:
Originally Posted by mt490 View Post
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...

Last edited by wahab; 13th December 2010 at 11:35 AM.
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