Electronics > Repair
Guitar amplifier makes a loud pop noise (power spike?) when turning on
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d3vCr0w:
Hi people, I got a guitar amplifier (Marshall Valvestate 8100) a couple of weeks ago and it works but makes a loud pop noise when I turn it on, is it normal?
Here is a video https://youtu.be/FT8pAYjkWKY

Thanks by the way.
Kekke466:
Hello, some popping is to be expected in most guitar amplifiers. Yours does seem a bit extreme. In some situations it can be solved with a series resistor and capacitor on the standby switch. (I don't think yours has a standby switch). In some amplifiers they solve it with relays to prevent popping.

In your amp, every time you switch it on you get an arc, if the internal contacts  of the switch are burned in (because of arcing), the resistance of the switch contacts keeps going up. Try measuring the resistance of the switch, if it is quite high. One thing you could do is replace the on-off switch. You won't get rid of the pop but the buzzing sound coming together with the pop might stop.
d3vCr0w:
Alright, I'll take a look to the on-off switch once I get home, thanks for the tip. And, could the power spike be present because of the main power capacitors not working properly? As far as I understand after the power transformer and the diode rectifier there are two big capacitors which 'filter' and 'smooth' the energy going to the amp.
HB9EVI:
You'd have a considerable hum, if the smoothing caps didn't do their job, so no
as far as I can see from the schematic, there is no speaker bypass relay, so the pop when powering up is inevitable. If it is more intense than it should be, hmm maybe, maybe not...
Audiorepair:
That turn on pop is pretty bad IMHO, but the design has nothing to prevent it.

You might want to take a look at the +/- 15 volt supply caps too.
These rails (unusually) supply the bias voltage for the power amp.

In fact, why not just replace the two main PSU caps and the two 15 volt rail caps anyway, we know they fail or get sick.
Not a big or difficult or expensive job really, and pretty good insurance if you intend to keep the amp.

Use good quality 105 degree rated caps, they only cost a tiny bit more.
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