Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TIMBO on April 02, 2013, 01:45:10 pm
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Hi guys, In my last build (JP Hiwatt now Plexi 6V6) I had a large amount of Fizz even with on guitar plugged in but only with volume controls at max. I checked my TOS as I did not remember it having much with no guitar plugged in and volumes at max (It was very quiet as I thought)
With guitar plugged in the Fizz was way too loud and kicking in at about half volume, this was a real KILLJOY :BangHead: :cussing:
After rehashing JP and building a circuit that was more mainstream (Plexi 6V6) thinking that it was just the build in general and one of those things even though I tried to lay it out like the Hiwatt :sad2:
Mark Huss has great schems and provides lots of info for layouts etc. and this I followed as best as possible and the Fizz remained regardless.
Thanks to those that added some input but anything I tried failed.
The plexi sounds great but the fizz was starting to get to me and I was ready to commit it to the cupboard of "well it almost worked" (getting a little crowded in there)
I thought I would try some of T's smoothing caps on the power resistors of V1b hoping that it would clean up a little of the bite that the amp was producing but this had little effect (Trying a range up to 500p ) not sure the range that could be applied or whether this was a safe thing to do but I was DESPARATE so I pushed on and hitting the 820p the fizz was REDUCED to half :m15
WOW, so I worked backwards and added some values up to 500p to V3b and again hitting 820p reduced more so I applied the same to V3a and now I have only a very small amount at max volume :icon_biggrin:
Other things were also removed,one was I had a high pitch squeal when volume turned to about 8. I now can get max volume and NO squeal.
I also have had a problem with a BUZZ that would go away when touching the strings, adding these caps seem to have help with this some.
I use 3w metal oxide resistors for dropping and plate resistors as these are all I can get at the rating and these have been said to used in this part of the amp.
I have yet to try this in my other amps to see what happens. Thanks :icon_biggrin:
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Good info! Out of curiosity, what flavor of resistors were you using in signal path (carbon comp, carbon film, metal film)?
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I also have had a problem with a BUZZ that would go away when touching the strings, adding these caps seem to have help with this some.
When I have had that happen, it's been a grounding problem.
With respect, Tubenit
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Hi guys, I use .7w metal film throughout the amps but can't get 2 or 3w from my supplier.
T, I know the buzz is a grounding issue thats been a real pain, this is why I tried a different layout (M Huss Hiwatt) to see if I could jag a build that may fix the problem. I followed his grounding to a T but I am still getting BUZZ. Thanks
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The most challenging buzz that I had on an amp build turned out to be a bad potentiometer. It was really sort of an odd thing and I had ALOT of trouble diagnosing it, but replacing the pot resolved it. Another time, I had a ground from a pot to the buss ground that showed to be good on my meter but was apparently still not making good enough contact.
None of that may help you, but I thought I'd toss it out? You do such incredible cool builds, I'd love for this one to be as noise free as possible for you.
With respect, Tubenit
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Hey T, I look it this way,the more I build these things the closer I get to " THE ULTIMIT AMP " what ever that is :icon_biggrin:
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Timbo,
I wished we lived in the same city. I enjoy the innovation behind your build approachs and would love to be there to help trouble shoot this one with you and then jam out on our homebrew designs!
:thumbsup:
Have fun with your build and stick with it til you get it where you want it. Once you get a solution, please let us know what you worked out.
With respect, Tubenit