Valvestate 8200: pop/thump on powerup

[Van Esch]

Hello everyone,

My 8200 produces an enormous thump on powerup. The scary loud type. I´ve renewed every cap on the powerboard( http://www.drtube.com/schematics/mar...8280-63-02.pdf ) : no difference. I tested with the whole amp hooked up and with only the powerboard to the speakers: same result. Leaving out one of the speakers(left or right) I get a pop on either side.
I have resoldered the board and looked for anything unusual but nothing..

I´ve gone through a lot of posts on the subject and read about fixing arcing in the on switch, muting circuits and resistors placed over incoming power. I want to save my speakers! After the pop noise the amp works fine by the way!

Greetings, Bram.

[Enzo]

It is a solid state amp. The loudness of anything it sends to the speaker is limited by the power supply voltages. Those are the same voltage limits that cause clipping when the amp tries to exceed them. Clipping is the upper limit on output excursion. SO basically, the power on/off thump is no louder than the loudest sound the amap makes during operation. SO if the speaker can stand the full power of the amp during play, it will be OK with the thump.

[DrGonz78]

Like Enzo said... Ditto...

But I actually was reading posts tonight on this issue since I have a Fender SS amp on my bench that makes that annoying popping noise. Another thing that Enzo had said on SS Guitar Amps site is to isolate the problem from preamp to power amp. So in the words of Enzo... he said to plug something in the power amp in jack to isolate and disconnect the preamp. Then turn on or off to see if it pops. If it pops then you know it is on the power amp side of things. The other thing that was on that post was that then you can turn amp switch on w/ amp not plugged and then plug in the amp to see if you get a pop or unplug to see if you get a pop. If the switch is arcing the plug method will help determine this symptom. Which I just did about an hour ago and it is my switch that is arcing.

Tomorrow I will try using capacitors or even resistors hooked up to the poles of the switch to see if that will help reduce the pop sound.

Edit: oh but first I will clean all the contacts on on the board and the power switch to make sure that it is not just simply oxidization on the contacts.

[Jazz P Bass]

If you would like to prove out if it is a power switch issue or not, unplug the amp, turn the power switch on & then plug the amp in to the outlet.
If the thump is gone, it may be a switch circuit problem.

[Van Esch]

I´ve tried the outlet trick, no difference, even with only one switch on the lead.

Even if my own cabinet can handle it, I still want to get rid of it. I use cabinets at the rehearsal studio and they´re not happy when I hit the switch... The thump is definitely not something it´s always had.

[Van Esch]

The preamp has been disconnected and makes no difference, likewise on the powerplug trick... The resistor seems like a good solution! If in the end the cause can´t be found I´ll definitely try that!