How to adjust NAD C370 ISC circuit?

[Conrad Hoffman]

The manual seems to want -50 to -100 mV between the two test points, but they don't specify which way to measure and the test points are backwards from what the manual shows. The setting is very sensitive to line voltage and can be set either side of zero.

Does anybody know which way the comparators are supposed to flip and/or how to test the circuit for correct operation?

I looked at other NAD amps and they seem to have various versions of the circuit and various different ways of adjusting them.

Thanks,
Conrad

 

[vzaichenko]

Hi Conrad,

These values are always specified referenced to Ground, if not specified otherwise.
TP9 is the Ground, TP10 is the point where you are expected to set -50...-100 mV ("Common" lead of DMM - TP9, "Signal" lead of DMM - TP10).

Cheers,
Valery

 

[Conrad Hoffman]

Thanks Valery, that makes sense. The location diagram has the test points labeled backwards, so I was trying to second-guess NAD. I set it up as you described (per the schematic, not the location outline) and it seems to work well. FWIW, the ISC voltage is bias dependent, line voltage dependent and warm-up dependent. The best method is to use 3 meters and watch everything at the same time. The values will be wildly wrong on power-up, but will settle closer in a minute and stabilize in 5-10 minutes. Then one can fine tune the bias to 5.5 mV and the ISC to -75 mV.

 

[blutengel]

Hi trying to adjust setting on my nad 370 which way round does meter go to adjust bias, because isc won't adjust properly, it fluctuates between -275 mv to -30 mv