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-   -   VAS to LTP Feedback Capacitor Question (A bit like in the A40) (http://www.diyaudio.com/forums/pass-labs/67931-vas-ltp-feedback-capacitor-question-bit-like-a40.html)

primalsea 15th November 2005 09:07 PM

VAS to LTP Feedback Capacitor Question (A bit like in the A40)
 
While trying out various feedback schemes on my simulator I noticed that if I connect cdom across the base of the VAS and the feedback input of the LTP there is a improvment in the HF phase response. The freq. response remains unchanged.

It's just like what Nelson Pass does on the A40 except that he connects the capacitor to the collector of the VAS, not the base.

My simulator showed a better result for the prior than the N.P method.

Also I guess that doing this wont load the LTP so much at high frequencies as the feedback input of the LTP is at the same potential as the LTP output.

However with no equipment to test this in practice and the fact that my simulator has lead me astray before I have no idea if this is a good idea.

Also I doubt that I am the 1st person to do this.

I might just do it and see how the amp sounds. Just wanted to know if anyone has done this, even if it sounds like a good idea.

The amp simulated is very similar to ESP project 3 except that bias is set by a pot rather than diodes. schematic can be got from Rod Elliot's site.

Nelson Pass 15th November 2005 09:31 PM

I have not seen this done, but you should be able to try it
on a real circuit easily enough.

:cool:


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