VU Meter Buffer Amp Gain

[echo zulu]

What's a simple way - using a minimum of components - to adjust the gain of this VU meter circuit by approx. +/-1db?:



Component values:
--------------------
R125, R128 = 470K
R129 = 10 ohms
C103, C105 = 22uf
IC26 = TL071

Would adding a 100 ohm pot in series with the feedback loop from pin #2 to pin #6 work?


...Thanks.

 

[abbey road d enfer]

What's a simple way - using a minimum of components - to adjust the gain of this VU meter circuit by approx. +/-1db?:

Simply, no "simple way. For attenuation, you could probably increase R129, how much I don't know, since it depends on th meter's characteristics. For gain, you need to reconfigure the amp for gain, i.e. insert a resistor between the opamp's output and its inverting input and add a resistor to "ground" from inverting input.
For gain AND attenuation, you need to do the "gain " mod and add a trimmer in place of R125.

 

[echo zulu]

Thanks. If it will work, increasing R129 would probably be enough, as I only need to match one VU to another (left & right channels).

I would prefer not to cut traces on the mixer's existing PCB, but would inserting this pot work?:

 

[JohnRoberts]

no... It is a unity gain follower.

To add +/- gain trim would involve padding input -1dB, then adding a variable feedback R, and r to ground to deliver 0dB to +2dB for overall +/-1dB.

100 ohm is not a practical value for any of those components.

JR

 

[echo zulu]

R129 was replaced with a 100 ohm 1% resistor, resulting in a little less than 1dB attenuation - just what was needed, and without introducing any apparent problems.

I appreciate the assistance .