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Bias output stage via AVC

Posted: Tue Jan 02, 2024 10:15 am
by avcLover
Hi All,

I'm thinking of using fixed bias and kill two birds with one stone, volume and bias. Been experimenting with SIT transistors, a simple 2SK79/2SK60 SET.

2SK79 has 2K rp, loaded with 18K, the AVC at the output helps to lower the impedance. 2uf coupling capacitor for the equivalent 25K reactance of the AVC with a 6V battery at the bottom. I think some microampere of current may be present. Will that be an issue for the AVC nickel core?

Here's a mock-up
avc.PNG (49.5 KiB) Viewed 1856 times

Re: Bias output stage via AVC

Posted: Tue Jan 02, 2024 1:00 pm
by dave slagle

Your circuit will work fine as drawn and the DC offset is not a problem since as you mentioned, the current will be in the µA range. However introducing a switch to change levels to a situation with DC offset and an inductor (AVC) will open up the possibility of some audible transient "pops" every time you change level. Think of a spark plug coil pack. A small 12V DC pulse can create a several thousand volt spike to fire the plug. This same situation can happen on a much smaller scale when you add a DC voltage potential to the autoformer switching.