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Turn on Thump and turn of "pop" K100C-8 [message #25965] Sun, 26 February 2017 16:27 Go to next message
Saransk is currently offline  Saransk
Messages: 20
Registered: February 2017
Location: Northern Virginia
Junior Member
Picked up a "working" K100C-8 for basically shipping - and got a nice deal.
I've worked on amps for almost 40 years - first Kustom Tuck-N-Roll
Needs all 4 speakers and some cabinet work
Electronics seem to be in good shape - but show the usual aging. (New jacks for sure)
The usual grime and such, but no evidence of any "hacked" repair work.
After some capacitor replacing, and changing the AC cord and switch out for a 3-prong I fired it up

There is a loud "thump" when it turns on - not sure if that is normal, I know it can be typical for direct coupled amps.
And sort of of "pop" when I turned it off.
Voltages seem in good shape
Normal side works fine, Effect side - not so fine. (volume goes up then down - have to look at the feedback loop - issues with the tone stack)
The usual noise and such

Right now I'd like to find out if a turn-on "thump" is common, if not, any suggestions.
There is about 21mV dc on the output and it does swing back and forth when I shut down.
Is the thump just part of the "charm" (I once used a Fender FM100 that thumped enough to scare you) - or can it be lessened

Thanks
Re: Turn on Thump and turn of "pop" K100C-8 [message #25966 is a reply to message #25965] Sun, 26 February 2017 17:17 Go to previous message
chicagobill
Messages: 2005
Registered: April 2003
Senior Member
Welcome to the place. Turn on thump is pretty normal in a healthy Kustom amp.

As you know, as the power amp comes up to voltage, the two sides of the push pull circuit are not always perfectly even, so the amp will thump. A lot of modern designs will add circuitry to lessen or hide the thump, but these Kustoms are old school.

Again, welcome to the place.
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