Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dscottguitars on March 16, 2013, 02:24:52 pm

Title: Mid Boost
Post by: dscottguitars on March 16, 2013, 02:24:52 pm

Hi,

I have a mid boost circuit on channels 1 and 2.  The circuit is from a Fender Concert (80's Rivera reissue era).  I changed the value of the caps for better midrange-they don't match because that's what I had.  It works great on channel 2, but on channel 1 there is way too much boost.

How can I tame that?  Is it the 10 meg resistor that gives it the boost?

Thanks,

Daniel

Title: Re: Mid Boost
Post by: alerich on March 16, 2013, 02:49:06 pm

The 10M resistor serves two purposes, neither having to do with the effect from what I can see. It keeps the switch from popping when you open and close the switch. When the switch is open the 10M resistance also effectively removes the .0022 cap from the circuit. Closing the switch removes the 10M resistor (shorting it) and just puts the cap across the normal 250pf tone cap of the tone stack. If you want to reduce the effect try a smaller value cap in place of the .0022. That should bypass less of the signal around the tone stack directly to the treble pot.

Title: Re: Mid Boost
Post by: dscottguitars on March 16, 2013, 05:40:20 pm

That worked!!  Thanks....