unity-gain single-pot fx-loop level control

[Marco Pancaldi]

Hello,
this link is to the old ADA MP-1 send-return section: http://adadepot.com/mods/ada_mp1b/ADAMP1jck.jpg
I'm intrested to built an FX send-return box to best match levels between amp/preamp and digital FX.

I'm not sure to understand completely this circuit: from the ADA manual I know it's unity gain but the real basig gain should be 1.5 (send) and 2 (return) - variable under pots control, of course.
Another issue: the resistors R10-R9, R14-R7 have not the same values...so I need some help to define the numbers to cutomize at best the circuit.

Thanks!
m.p.

[Dave H]

I'm not sure to understand completely this circuit: from the ADA manual I know it's unity gain but the real basig gain should be 1.5 (send) and 2 (return) - variable under pots control, of course.
Another issue: the resistors R10-R9, R14-R7 have not the same values...so I need some help to define the numbers to cutomize at best the circuit.

The dual gang pot P2 adjusts the signal level of the effects loop but the loop is unity gain send to receive because as the gain of the send amp is increased the gain of the receive amp is reduced.

U9 pins 5,6,7 is the send amp. U9 pins 1,2,3 is the receive amp. With P2 fully CCW the gain of the send amp is 1/10.2 and the gain of the receive amp is 10.2. With P2 fully CW the gain of the send amp is 5.3 and the gain of the receive amp is 1/5.3

[Marco Pancaldi]

Thanks Dave. If not too complex, can you explain how the gain is calculated? I guess values of resistors R10-R9, R14-R7 can be tweaked for optimization...

The dual gang pot P2 adjusts the signal level of the effects loop but the loop is unity gain send to receive because as the gain of the send amp is increased the gain of the receive amp is reduced.

U9 pins 5,6,7 is the send amp. U9 pins 1,2,3 is the receive amp. With P2 fully CCW the gain of the send amp is 1/10.2 and the gain of the receive amp is 10.2. With P2 fully CW the gain of the send amp is 5.3 and the gain of the receive amp is 1/5.3