NAD 3020A Muting circuit??

[bmmach]

Hi all,

I've recently acquired a NAD 3020a amplifier; it had a continuous hum immediately after power-on which persisted in the background regardless of the volume level.

My first step was to replace the 4x2200uF caps for the main amp as well as 2x470uF caps for the pre-amplifier; this cleared the constant hum but I still heard some distortion after switching on the amplifier which soon cleared.

My solution was to re-cap the entire amplifier with audio quality caps and the improvement in sound has been significant especially on the treble - high frequency. The bass has also improved and no distortion is occuring while the caps in the circuit take long to charge.

My only issue is with the Muting circuit. On turning on the audio muting switch, the effect seems to be turn it into Mono mode; I initially thought there was a problem so I opened it up to look up the circuit; All the components seem to be operating alright;

On looking carefully at the circuit board, it's actually labelled as the Mono Switch; I just need someone with a NAD 3020 to confirm that this is the case with their amplfier too. basically this amplifier uses the mon switch to mute with some very minimal effect.

thanks

[bmmach]

Solved this problem easily - seems like the fascia on my nad 3020a belongs to nad 3020 original; NAD changed the muting switch to one for mono/stereo operation on the NAD 3020a and NAD 3020b which share alot on common.

They also included a MC/MM circuit in them that was not present in the NAD 3020. Made it more versatile on the phono operation.

[ingenieus]

Would be interesting to know how the amp ended up with a fascia from one model and a circuit board from another. A previous owner probably managed to fry the entire board, which then got replaced...