Scott A437 Strange noise in both speaker

[Radas]

My Scott A437 amplifier makes a strange noise on both speakers when turning on.

After that, it works correctly. Could you also help me with the Bias adjustment?

Where should I place the probes and which resistor should I adjust to get 5mV?

Thank you very much for your help

 

[Dan13105]

Welcome to Audikarma. That sound when turning on could be caused by inrush current charging the capacitors, and this unit not having a speaker relay (that i could find). Some noise when turning on a unit without speaker protection relays is normal. Try turning the volume knob all the way down before turning it on, and seeing if that helps. You can also turn off the speakers with the switch before powering up to eliminate any turn on thump. The pots you need to adjust for bias and DC offset, and appropriate probe locations are listed here. I use clip on leads and make all connections with it powered off, you don't want to short your outputs



In case you need it, you can download the entire service manual here.

https://www.scribd.com/document/702883908/Service-Manual-Scott-a-417-437-457

 

[Radas]

Thanks a lot!