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Can't escape crap distortion

5/27/2000 9:41 PM
Chris Harden	Can't escape crap distortion Many of you may have allready read posts relating to my amp experiments, and I'm grateful for the help I have recieved so far. Here's my latest question for you to ponder. My preamp currently has 3 gain stages feeding into a single 6V6. A basic description follows. Stage 1: 1/2 12AX7 no bypass capacitor, 10nF coupling to stage 2. 260V B+ Stage 2: 1/2 12AT7 1uF cathode bypass, 22nF coupling to passive Bandaxall tone control. 280V B+ Stage 3: 1/2 12AT7 no bypass, 280V B+ Unfortunately it isn't sounding too good. The distortion is very rough, especially on lower notes, probably what you describe as farting due to blocking distortion. I've tried reducing the size of the coupling capacitors and increasing the grid stoppers but it doesn't help. Would the fact that my power supply may be slightly under-rated, make a large difference to the tone. There is plently of smoothing in the main filter bank, and there is power supply decoupling between, the power valve and stage 1 and stages 2,3. Any ideas please. If you require more info to work with then I can supply it. Thanks Chris

5/27/2000 9:41 PM

Chris Harden

Can't escape crap distortion

Many of you may have allready read posts relating to my amp experiments, and I'm grateful for the help I have recieved so far.

Here's my latest question for you to ponder. My preamp currently has 3 gain stages feeding into a single 6V6. A basic description follows.

Stage 1: 1/2 12AX7 no bypass capacitor, 10nF coupling to stage 2. 260V B+

Stage 2: 1/2 12AT7 1uF cathode bypass, 22nF coupling to passive Bandaxall tone control. 280V B+

Stage 3: 1/2 12AT7 no bypass, 280V B+

Unfortunately it isn't sounding too good. The distortion is very rough, especially on lower notes, probably what you describe as farting due to blocking distortion. I've tried reducing the size of the coupling capacitors and increasing the grid stoppers but it doesn't help.

Would the fact that my power supply may be slightly under-rated, make a large difference to the tone. There is plently of smoothing in the main filter bank, and there is power supply decoupling between, the power valve and stage 1 and stages 2,3.

Any ideas please. If you require more info to work with then I can supply it.

Thanks

Chris

Replies:

BWilliamson Have you tried moving the tone stac... -- 5/27/2000 11:16 PM
Steve Ahola Chris: &... -- 5/28/2000 11:16 AM
Nate S. What's the B+ for the 6V6? I made a... -- 5/28/2000 1:16 PM
Carl Z First thing that comes to mind is t... -- 5/28/2000 1:53 PM
Stephen Conner Hi Chris,Like Carl ... -- 5/28/2000 11:11 PM