Slightly OT - Intermittent noise on HiFi amp

DartmoorHedgehog

Sorry for the off-topic post, but I know there are people on here who may be able to point me in the right direction.

I use an oldish (1980s I would guess) HiFi amp (solid state) as a power amp on my home studio/PC setup.  Recently it's started randomly making a noise that sounds almost like waves breaking.  It's definitely the amp because it still does it even if I turn the mixer off or even unplug the input cables.

Every now and then there is a pop, then the whooshing/wave breaking noise for some time, then quiet again.  I thought it was some sort of interference, but then noticed that hitting the amp can make it stop or start doing it.  I can't see anything obviously loose, no bulgy capacitors, no suicidal spiders.  Gave all the switches and pots a wiggle.

It's not worth spending too much time (and certainly not money) on, but if any of you resident amp gurus recognise the symptoms and can suggest where I should look for a dodgy joint or whatever I'd be most grateful

Rocker

I often hear similar wave like sounds from my PC system.  Only when nothing is happening or nothing being played through the system.  It is no different if I use the headphone out on the PC or my preferred USB out. No idea what is causing it.

DartmoorHedgehog

It's weird - I thought it was interference, either radio or through the mains, but it still happens with everything but the amp turned off, and hitting it seems to have an effect - which makes me think it must be something in the amp itself, like a loose joint or dodgy switch/relay connection somewhere.

ecc83

Almost certainly a bad joint. Take the chassis out and go over the print with a glass. Does the VC have an effect?

Can you gve make and model number? I might be able to find a scemo.

Dave.

DartmoorHedgehog

Thanks Dave.  That's what I suspected but can't see anything from the top of the board.  I'll have to take it out sometime when I can be bothered and have a look at the underneath.

I think it's a Rotel, probably RA-840 BX3 or BX4.  Will have a look later...

DartmoorHedgehog

It's a BX3

Danny1969

Bad joint be my guess too .... look for things that get hot .. ceramic resistors, driver transistors etc. Heat leads to bad joints so start with the components that get hot

DartmoorHedgehog

Sorted
Couldn't see anything obvious on the "hot" things, so I went round the board poking with a stick until I found out what affected the noise.  Turned out to be a normal little transistor - hardly had any solder on one of the legs, so I don't think it was properly done when new.  Resoldered that and all is well again.