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Good evening...This is a weird one???Maybe???? I have both of these Hughes and Kettner amps here and both are doing the same thing...When they are first powered up, the gain control in the drive channel is very scratchy and noisey...sounds like a bad control....I replaced it with a new one from the manufacturer's distributor only to discover that the same problem is still there. Now for another twist...After the amp warms up for about 20 minutes or so, the noise dissapears and the control is very quiet as you rotate it through it's range.....If you power the amp down and let it cool off for about 20 minutes or so and then power it back up, the noise and scratchy sounds are back...until the amp heats up....So now I have ordered more pots from a different pot manufacturer and when I get them, I will temporarly install one to see if the same problem exists with another pot. I checked the noisy pots with an analogue multimeter to check for erratic operation but the pots seem to have a very smooth rotation according to the swing of the needle in the meter....Any thoughts anybody......
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Not having the schematic, I am guessing.
It sounds like a capacitor may be 'leaking' Vdc into the pot circuit. -
OK. Thanks Jazz P.....I'll give all the caps in the general area a squirt of component cooler after it warms up to see if the noise returns...I have to get a Yamaha PSR 2000 off the bench first....
Thanks,
BernieComment
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In some amps the DC on the pot can come from the preamp tube itself. As your problem is going away once it is warmed up, this may be the case. Some amps are finicky with preamp tubes in this regard.Originally posted by Enzo
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OK. Thanks g-gone....I am working on it now actually.....There are two boards in this amp...all tubes are on one board and all the front panel controls, switching, op-amps, etc are on the other board...looks like the two ECC83's drive the EL84's....at least one of them do....I'll check it out and let you know how I made out.
Thanks,
BernieComment
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There we go. Back again. I tried what you suggested g-gone.....no such luck....I tried letting the amp warm up as well till the scratchiness dissapeared and then use cold spray on the surrounding components but no luck there either. It still sounds exactly like a noisey pot but after it warms up the scratchines slowly goes away....then all you get is the usual electronic noise that is present when you max everything up...very strange indeed...I received a couple of pots today...they don't mount the same but I can install them temporarly just to see if the noise remains...that is the only thing I can think of right now to either eliminate or confirm a bad pot....once I do that then I can go from there. I shall be back......Wish me luck....
Cheers,
BernieComment
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Did you actually try and measure with your voltmeter to see if there really is any dc leakage on the pot terminals?Originally posted by bsco View PostComment
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