Hoffman Princeton reverb crackles at high volume

[Paulycoo]

Hello again all!
Thanks to sluckey et al I have a beautiful Princeton reverb build. It sounds gorgeous including reverb and tremolo.
Apart from when I crank it up over 7.
I get this crackling sound when I play chords.
I removed the chassis and put electrical tape all around the edge that may be touching the copper shielding sheet stuck onto the cabinet top.
Replaced chassis.
Still the same.
Anyone help where to look first?
Thanks for helping
Paul McNamara

[SILVERGUN]

Have you /can you try a different speaker?

[Paulycoo]

Yeah good idea will do first thing tomorrow...its a brand new jupiter 10"
Thanks Paul McNamara

[pompeiisneaks]

Some pictures of the guts may help.  If you did the stock hoffman PR, links to the schematic and layout makes it quicker for people to review.  Crackling could be arcing somewhere and at high volumes the highest current is being pushed through, makes me suspicious of a few things:

1. dry solder joint not being perfect for transmission somewhere
2. tube socket connections not tight enough causing arcing

etc.

You could also just try turning it to that volume level, and open the chassis up and tap around with a chopstick and see if you  hear the noise getting worse or disappearing.  That may focus your efforts on the 'where' of the issue.

Are the tubes all new?  If not maybe one of them is having issues?

~Phil

[PRR]

> chassis and put electrical tape all around the edge that may be touching the copper shielding sheet

These should touch. And electrical tape won't last long.

I'd be thinking bad joint, not arcing; though arcing is possible.

[bnwitt]

What PRR said.  I'd check solder joints.

[Ed_Chambley]

Had a phase inverter unbalanced once enough to cause crossover which sounded awful at higher volumes. Also I had artificial center taps drift twice and got worse at more volume.


I would check PRR comments first tho. Makes sense vibration at louder volume.

[Paulycoo]

Thanks to everyone, much appreciated.
I opened it up. Turned everything up.
Tapped with chopstick and found a 0.047uf cap attached to the bass pot crackles upon being tapped.
New one on order.
Brilliant advice all thanks.
I read on the net about shielding on cab not touching properly all around the chassis lip causing crackles when vibrating...
Should I remove the electrical tape stopping them touching?
I presume that the shielding stops rf? Does it have to make a complete circuit like a faraday cage?

Thanks all!
Best regards Paul McNamara

[davidwpack]

I would try reflowing your solder first before replacing it. Crackles are indicative of bad solder joints.

[Paulycoo]

Ahhh...never thought of that.
Nice one thanks.

[bnwitt]

Amp start up and testing should always include chop sticking all components and tube pins in order to check for bad solder joints.

[Willabe]

I read on the net about shielding on cab not touching properly all around the chassis lip causing crackles when vibrating...
Should I remove the electrical tape stopping them touching?
I presume that the shielding stops rf? Does it have to make a complete circuit like a faraday cage?

Yes, I would take the tape back off.

[Paulycoo]

Thanks guys!!!!
I realised the joint.
Perfect.
Will take the tape off as advised.
I've learnt so much from troubleshooting
Chapeau to all you who helped!!!
Amp sounds incredible.
Cheers Paul McNamara