low gain distortion from svt 3 pro

ScottyAx800 · #1 05-28-2011, 11:30 AM

Bought an SVT 3 pro recently. Up until yesterday, the thing sounded great. I use the low gain setting (around 9-10 o'clock) to get a nice and clean yet tubey sound through a 410HLF.

Yesterday I plugged in, and now a little bit of crappy-sounding distortion is hanging on the notes I play. The amp still responds normally to everything else I do - dynamics and articulation, etc. The distortion intensifies a bit when I play double/triple stops. I have tried to eliminate different problems in the signal path by plugging in different instruments, speaker/instrument cables, and cabinets to the amp. I also plugged my SWR California Blonde into the same power outlet, and got no distortion out of that amp. The only other possible thing I can think of is taking it back to somewhere where I know I am getting a good sound and plug it in there.

This amp is practically brand new, has been gigged once and used at a handful of rehearsals. It has never been dropped or otherwise abused in any way. What then, could possibly cause this amp to lose sound quality? Is it possible that the circuit in my house is not giving enough power to the tubes? My SS SWR amp sounds fine through the same circuit. Could there be dust in the input/output jacks or in the amp that could be causing the fuzz? Any suggestions, advice or shared experiences would be greatly appreciated.

pedulla1 · #2 05-28-2011, 12:36 PM

The amp probably needs biasing. Take it to a tech or contact Jerrold Tiers on TB. He worked for Ampeg.

BassmanPaul · #3 05-28-2011, 02:53 PM

Quote:

Originally Posted by pedulla1

The amp probably needs biasing. Take it to a tech or contact Jerrold Tiers on TB. He worked for Ampeg.

This is my take on the problem too.

ScottyAx800 · #4 05-28-2011, 07:22 PM

Biasing for preamp tubes? Up until now I only knew of power amp tubes needing biasing.

dmrogers · #5 05-28-2011, 07:30 PM

I agree, it (the MOSFETS) needs biasing. I had an SVT3Pro and it did the same thing after several years of ownership. I re-biased it myself, however, I am familiar with electronics, I worked in electronics in the past.

If you don't know what you are doing, you could damage the amp, or worse, hurt yourself.

Take it to a tech.