TIM Distortion, High Speed Transistors & the AU-X1

[<eargiant]

Tony is working on a Sansui AU-X1 (unfortunately his example is in pretty rough condition internally). I thought some members here might enjoy the technical aspects of this video:

This is what my originals looked like on one of the heatsinks when they were re-set during restoration.



This is my spare set of LAPT transistors just in case the "parasites" attack.

 

[GrimSurfer]

Very informative. What a beautifully build amp. Great idea keeping a set of spares.

 

[<eargiant]

Final part in the video series of an AU-X1 restoration. Objective and subjective impressions (from a self proclaimed objectivist skeptic) ...

 

[Speedskater]

TIM distortion is NOT a real thing, it's a decades old misunderstanding!
Someone needs to read Bob Cordell, Doug Self & Bruno Putzeys.

 

[Out-Of-Phase]

Cognitive Bias in the brain. It's real.

 

[M Code]

TIM distortion is NOT a real thing, it's a decades old misunderstanding!
Someone needs to read Bob Cordell, Doug Self & Bruno Putzeys.

So respected electronic engineers like Nelson Pass, Matti Ottla, John Curl, Bart Locanthi were mis-informed...

Just my $0.02...

 

[Speedskater]

So respected electronic engineers like Nelson Pass, Matti Ottla, John Curl, Bart Locanthi were mis-informed...
Just my $0.02...

Yep, they were.
And John Curl still is.

 

[Out-Of-Phase]

<eargiant, is your Sansui AU-X1 amp an early model or a later model?

 

[Speedskater]

TIM was four decades ago! Later they realized that it was just a type of IM distortion or Slewing-Induced Distortion (SID). That is too much negative feedback for the bandwidth of the amplifier.
Bruno Putzeys has a nice paper on the subject:

Negative feedback in audio amplifiers:
Why there is no such thing as too much

https://www.edn.com/design/consumer/4418798/Negative-feedback-in-audio-amplifiers--Why-there-is-no-such-thing-as-too-much
https://www.edn.com/design/consumer/4420162/Negative-feedback-in-audio-amplifiers--Why-there-is-no-such-thing-as-too-much--Part-2-

 

[M Code]

TIM was four decades ago! Later they realized that it was just a type of IM distortion or Slewing-Induced Distortion (SID). That is too much negative feedback for the bandwidth of the amplifier.
Bruno Putzeys has a nice paper on the subject:

Negative feedback in audio amplifiers:
Why there is no such thing as too much

https://www.edn.com/design/consumer/4418798/Negative-feedback-in-audio-amplifiers--Why-there-is-no-such-thing-as-too-much
https://www.edn.com/design/consumer/4420162/Negative-feedback-in-audio-amplifiers--Why-there-is-no-such-thing-as-too-much--Part-2-

I reviewed the (3) mentioned engineers but found that most of their development was done for powered loudspeakers not amplifiers. Bruno Putzey has done a certain amount of amplifier development work but this was done for his Class D circuits for Hypex, note that Hypex is well regarded for its sonic qualities. Do U have anymore references for the above (3) mentioned engineers that can support their position. Also please include any award winning reviews for their amplifiers if available...
Thanks..

Just my $0.02...

 

[Speedskater]

Do U have anymore references for the above (3) mentioned engineers that can support their position.

Both Doug Self and Bob Cordell have recent books.
As for Bruno Putzey, see the above links.

 

[M Code]

Both Doug Self and Bob Cordell have recent books.
As for Bruno Putzey, see the above links.

Thank U..
Noted their respective books on Amazon...
I was hoping to find any products, test reports, AES abstracts, reviews or product endorsements they might have done. Putting theory into writings within a book is 1 thing but in the end do they in fact end up implemented into actual products..

Just my $0.02...

 

[PENG]

Thank U..
Noted their respective books on Amazon...
I was hoping to find any products, test reports, AES abstracts, reviews or product endorsements they might have done. Putting theory into writings within a book is 1 thing but in the end do they in fact end up implemented into actual products..

Just my $0.02...

There don't seem to be too many recent technical articles/papers on TIM. Aside from Bruno Putzey's, there is an 1981 (vs Otala's 1977) IEEE publication if you are interested. I was a member of both the IEE and IEEE years ago and am trying to subscribe in order to read the full text, below is the link to download and the abstract (if you are not subscribed..).

https://ieeexplore.ieee.org/abstract/document/1163553/metrics

"Abstract:
Otala's suggested rules for eliminating transient intermodulation distortion (TIMD) in a low-pass feedback amplifier have been widely and wrongly interpreted as being necessary. In fact, the necessary and sufficient condition, for avoiding gross TIMD with a broad-band input signal, is that the forward-path stages before the dominant pole should not clip on a signal input which is twice the amplitude of full rated input to the complete amplifier including feedback. When the input signal is band limited, this dipping criterion can be relaxed by a factor approximately equal to the ratio of the (signal 3 dB bandwidth) to the (amplifier closed-loop 3 dB bandwidth). In both cases the condition is essentially independent of the low-frequency loop gain. There is no TIMD penalty whatsoever in using a large amount of feedback, provided the forward-path gain is concentrated in stages that do not precede the dominant pole. All the usual benefits of feedback accrue with increasing loop gain."

There is also the typically more down to earth style Rod Elliot's:

http://sound.whsites.net/articles/distortion+fb.htm#a41

 

[mtrycrafts]

Yep, they were.
And John Curl still is.

And, he swallowed the audio wooo pill on top of that.

 

[Out-Of-Phase]

Very informative. What a beautifully build amp. Great idea keeping a set of spares.

LOL

 

[Swerd]

Thank U..
Noted their respective books on Amazon...
I was hoping to find any products, test reports, AES abstracts, reviews or product endorsements they might have done. Putting theory into writings within a book is 1 thing but in the end do they in fact end up implemented into actual products.

Bob Cordell published a 2-part article in Audio magazine in February & March 1980, at the height of the controversy surrounding Transient Intermodulation Distortion and its relationship with negative feedback. The article discussed the origins of TIM and the transient nature of music that can bring it on. It pointed out that amplifiers with inadequate slew rate margin are the ones prone to TIM. Moreover, the article demonstrated that large amounts of negative feedback, when properly applied, do not in any way contribute to TIM.

http://www.cordellaudio.com/papers/another_view_of_tim.pdf

http://www.cordellaudio.com/papers/another_view_of_tim_II.pdf

 

[M Code]

Bob Cordell published a 2-part article in Audio magazine in February & March 1980, at the height of the controversy surrounding Transient Intermodulation Distortion and its relationship with negative feedback. The article discussed the origins of TIM and the transient nature of music that can bring it on. It pointed out that amplifiers with inadequate slew rate margin are the ones prone to TIM. Moreover, the article demonstrated that large amounts of negative feedback, when properly applied, do not in any way contribute to TIM.

http://www.cordellaudio.com/papers/another_view_of_tim.pdf

http://www.cordellaudio.com/papers/another_view_of_tim_II.pdf

Informative articles, thank U..
I was aware about the slew rate factor...

Just my $0.02...

 

[<eargiant]

https://web.archive.org/web/20131110011700/http://www.q-audio.com/johncurl.pdf


https://www.passlabs.com/press/audio-distortion-and-feedback