Modding the Green Pre Output Fader

I'm wondering if there is a fairly easy way to change the output fader into an output trim, say 6-10 dB. With my limited knowledge, I am seeing the 10K Log Pot (R13) acting as a voltage divider. If that is correct, wouldn't adding an additional resistor from the bottom leg of the pot to ground work, or would that effect the overall gain of U2B adversely...?

Thanks
Andrew

(Note, the last pair of op-amps in the following schematic are 5532s, not LM883/TL071s as they are notated)

Hi
Ground on up schematic is connected to input pin. I redrawed it.

Nice project :thumb:
Duka

Yes, a 10K resistor between pot R13 and ground will give you down to -6dB trim only. Make it a 4K7, and you have approximately up to -10dB trim. Shouldn't affect the circuit in any case.

Jakob E.

Wow, sweet, not only is it easy, but I understand it too!

Duka, thanks for the catch, you also seem to have a slightly more recent version of the schematic there, cleaner with better labeling, I'm happily adding it to my stash.

thanks Jakob

I can't say that i do.....

but, I'd like to know what this accomplishes?

Well, an output fader allows you to adjust the gain from no attenuation, to total attenuation. A trim allows you to lower the overall gain by a much smaller amount, such as 6dB or 10dB. With a full fader, making a small adjustment is difficult, as a little bit of a move makes a big change. I would prefer setting my overall gain with the rotary switch, and if need be, taking a dB or two off with the trim.

10K resistor between pot R13 and ground will give you down to -6dB trim

-9.5dB. See R45.

See R45.

Click to expand...

Dang..!

After work/etc... sidestepping my Green project, I have returned, and I was planning on implementing this mod. I really was hoping for a 6 dB trim, and with PRR's addition, I wasn't sure what the new resistor's value should be.

Well, I downloaded a SPICE simulator to try and figure it out myself, and I can't seem to duplicate PRR's prediction. The added resistor from the Pot to ground affects the total attenuation as I expected, but changing the R45 value doesn't seem to matter at all!? Even removing it entirely doesn't seem to affect the circuit!

Any help on how to better understand this? Any voltage divider calulators out there like this one. (The ones I have found differ in their circuit somewhat)

Thanks
Andrew