Reducing the FIZZ and BUZZ

[TIMBO]

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   

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 

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   

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 

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

[thelonious]

Good info! Out of curiosity, what flavor of resistors were you using in signal path (carbon comp, carbon film, metal film)?

[tubenit]

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

[TIMBO]

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

[tubenit]

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

[TIMBO]

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 

[tubenit]

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!

 

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