Do you get a switch-on "thump" from reducing the i/p stage gain (405-2)?

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14-Oct-2019 02:29 PM

DavidA-C

DavidA-C

Posts: 2

I wondered how many other people have tried a number of modifications illustrated by Bernd Ludwig, for example reducing the gain of the front-end op-amp (OPA604) from 15 down to 4.6?

When you note the data sheet for the OPA604, you can see the THD+Noise against Frequency and reducing the gain down from 15 should give a much better distortion performance.  But, and approximately, I = (Vin-Vout)/(Rin+Rf).  So, reducing  R6 from 330k to 100k will bring in just over three times more i/p current - an improved sound (I claim), but a noticeable switch-on thump, a thump that was addressed in the 606 (?).

Thoughts, anyone?

David A-C

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