Biasing the BE-OD

[mybud]

Hi folks: Just built this over the weekend and can’t seem to bias it correctly. Measured voltages between ground and pins 2 and 3 of IC2 read just under 4V and adjusting the trimmer makes very little change. It’s also over-loud and the gain control functions correctly only between 7 and 10 o’clock or so. Any advice (voltages to aim for and correct place to measure changes) will be greatly appreciated as always.

Thanks, mybud

[Billy]

Your VB should be the same as the voltage on IC3B pin 7

You’d get half power 4.5v ish at the junction of the voltage divider R21 and 22 then drop a little after R23

I’m not a 100% If R23 would act as a voltage divider with R22 if it did I’d estimate around 3.6v if your power supply puts out exactly 9v

So whatever you get at pin 7 IC3B is your VB less a little voltage drop through components

Post some nice clear pictures so we can have a look you can check your gain pot as outlined here

Boogie 57 GAIN pot

[mybud]

Thanks Billy, appreciated. Will post some pix asap.

[Author]

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