arcam alpha 8 problem

[dandan1]

hello everyone i have a bit of a problem with my amp, its humming quite loudly and as the volume is turned up the humming level increases but even at low volume the humming is loud enough to be heard. ive asked my dad and he had no idea on what the problem could be but he said to take the wires out and only leave the speakers plugged in and then see if it still hummed unfortunately it did i then tried with his sony amp and it was completely silent at full volume but mine cant turn up halfway before the humming is too loud. it also has a few other problems as it crackles when changing the volume at low levels and theleft speaker output is blown. any help on how to stop is apreciated or is it time for a new amp.
thanks dan

[Mooly]

So with all leads disconnected (apart from speakers) and the volume turned down it still hums ?

First I would measure the DC offset on the speaker terminals to make sure there is NO DC voltage present. Meter should show ZERO volts DC.

That's the first step... after that we need to see a circuit and do more detailed tests.

[dandan1]

yes with just the speakers connected it will still hum but it gets louder as its turned up, so with music playing you can still hear the humming but you notice it much more at lower levels and also after about 20 mins of playing music the humming increases again and it just sounds like the sub is constantly playing. if that makes sense

[dandan1]

sorry i forgot to ask how would you check, would you just use a multimeter and plug
it into both speaker terminals?

[dandan1]

Sorry I forgot to ask would you use a multimeter and just plug that into the speaker terminals or something different.
Thanks
dan

[Mooly]

OK...

Just re reading your first post. You say one channel is also blown ?

So this needs systematic faultfinding. The humming "might" be related to the blown channel if that channel is drawing excess current. There are a lot of unknowns with this and so the best advice I can give is for you to see if you can come up with a circuit diagram, or full service manual and then all things are possible.

Also without knowing your experience and the test equipment you have a available makes this more difficult. Have you opened the amp up and done any basic tests... maybe checking output transistors for obvious shorts on the blown channel etc or looking for obvious signs of distress in any components such as leaky or bulging electroylitic cap.