TWE-1 Clipping section

[Vivek]

Please help me to understand this clipping section of the Ethos TWE-1






https://www.youtube.com/watch?v=3dERsaZ2eFQ


https://www.pedalpcb.com/docs/Derailer.pdf
https://www.pedalpcb.com/product/derailer/

[Vivek]

Is it trying to mimic tube sag
Where the circuit remembers what happened in the short time period before the current instant

By caps charging up and changing the clipping point

[r080]

It kind of looks like "regular" clipping with the zeners, with a bridge rectifier to mix in some octaving for second harmonics.

[iainpunk]

It kind of looks like "regular" clipping with the zeners, with a bridge rectifier to mix in some octaving for second harmonics.

doubt the four diodes are generating ''even order harmonics'' or any slight octaving at all, since its symmetrical.
it reminds me more of a comressor, and the signal that gets put in modulates the voltage on the caps, basically lowering the volume at the first attack, without much distortion at all. the distortion comes form the zeners here.

cheers

[r080]

Interesting. I had never heard of that before. Diode Bridge Compressor?

[teemuk]

This is similar one to old "Thomas Organ" limiter and even more similar to Quilter/Pignose/Rivera/Ampeg/Line 6 distortion circuit. It simulates clipping of a class-AB amp.

Hint: The diodes are initially forward biased so they clip the signal by "disconnecting" the signal path when they reach reverse bias state. This is opposite to more common shunt clipping configuration where initially reverse biased diodes clip the signal by "connecting" the (shunt) signal path in forward biased state. Nevertheless, you can visualise what the circuit does in conditions where input signal is smaller or higher than the applied forward bias voltage.

[PRR]

This is similar one to old ......

Goes right back to circa 1950 analog computers. May be in Korn and Korn, I dunno, my copy got too mildewy to have around.

(No, not that Korn!) (No, not ksh either!)

Granino A. Korn and Theresa M. Korn. ELECTRONIC ANALOG AND HYBRID COMPUTERS  description

[Vivek]

It kind of looks like "regular" clipping with the zeners, with a bridge rectifier to mix in some octaving for second harmonics.

doubt the four diodes are generating ''even order harmonics'' or any slight octaving at all, since its symmetrical.
it reminds me more of a comressor, and the signal that gets put in modulates the voltage on the caps, basically lowering the volume at the first attack, without much distortion at all. the distortion comes form the zeners here.

cheers

Iain, I was looking forward to your comment. You are the inhouse expert on such odd diode configurations !!

I tried to do thought experiment and then also used SPICE. I feel you are right. There is compression on attack due to caps charging up.

This is similar one to old "Thomas Organ" limiter and even more similar to Quilter/Pignose/Rivera/Ampeg/Line 6 distortion circuit. It simulates clipping of a class-AB amp.

I did remember RG Keen's analysis of the Thomas Organ Limiter, it's on my to do list to make the limit point modulateable somehow.


Could you post links to schematics of other amps that use somewhat similar device to bring in compression or movement into the output waveform. Thank you.


PS : These days I have been re-re-reading your analysis of the SansAmp GT2 from your ebook. Thank you very much for that article.

[Vivek]

Thanks to the gurus on this forum for their guidance !!


SPICE file for ETHOS TWE-1




I applied input pulses of 2vp @ 1Khz (one second on, one second off) to study the attack and this is what the output did :



Zoomed in, to try and calculate time constants. I see some distortion







Yes, SPICE surely shows distortion with 2Vp inputs (Because the Zeners are 1.8V)



Here is the DC buildup on Cap C14:



Here is the output versus time for input signals of different peak voltage.
It is very strange that higher input signals results in lower output level, like some kind of sag maybe ?




Next, I will attempt to study the release.

[teemuk]

https://patents.google.com/patent/US20130136278A1/en