Fuzz/Phase shifting effect (muskito flying by) in the mids

[Ricky Lee]

PPIMV will enhance the buzz as well and the buzz is more noticeable to me on top the high strings as apposed to a fuzz sound on top the low/wound strings.

[Billy Batz]

PPIMV will enhance the buzz as well and the buzz is more noticeable to me on top the high strings as apposed to a fuzz sound on top the low/wound strings.

I have heard someone say that about PPIVMVs before. If thats the case Id think it has to be a PI thing. If your at real low volumes and getting it then its got to be in the PI. I used a SS preamo injected into the PI input (disconnected from the preamp) and I get it. Taking the preamp out to a DI or a clean amp doesnt do it.

I notice it a lot doing double stops and intervals up high.

[Billy Batz]

My goodness your clip is the SAME EXACT buzz over the note I have to the hair, 99.99% same damn thing.....ok I'll go read your post now...

Lol sorry. This topic has covered a lot of ground in old threads so I was trying to squeeze all the info I can remember about trying to fix this thing in there.

Also because its been a while since this topic has surfaced and it seems as good a time as any to check it out again. Maybe someone has some insight. Fill us in on the prgoress with the scope.

[5150loveeddie]

PPIMV will enhance the buzz as well and the buzz is more noticeable to me on top the high strings as apposed to a fuzz sound on top the low/wound strings.

I have heard someone say that about PPIVMVs before. If thats the case Id think it has to be a PI thing. If your at real low volumes and getting it then its got to be in the PI. I used a SS preamo injected into the PI input (disconnected from the preamp) and I get it. Taking the preamp out to a DI or a clean amp doesnt do it.

I notice it a lot doing double stops and intervals up high.

I don't have PPMV in that amp, all stock basicly, plates are little high, 110k for a hair more gain, the rest is stock specs..

[5150loveeddie]

My goodness your clip is the SAME EXACT buzz over the note I have to the hair, 99.99% same damn thing.....ok I'll go read your post now...

Lol sorry. This topic has covered a lot of ground in old threads so I was trying to squeeze all the info I can remember about trying to fix this thing in there.

Also because its been a while since this topic has surfaced and it seems as good a time as any to check it out again. Maybe someone has some insight. Fill us in on the prgoress with the scope.

I didn't read that earlier thread so thx bro, it is appreciated.... here we go again now. Have the perfect amp here for scope learning...

It must be a design problem!!

[Billy Batz]

PPIMV will enhance the buzz as well and the buzz is more noticeable to me on top the high strings as apposed to a fuzz sound on top the low/wound strings.

I have heard someone say that about PPIVMVs before. If thats the case Id think it has to be a PI thing. If your at real low volumes and getting it then its got to be in the PI. I used a SS preamo injected into the PI input (disconnected from the preamp) and I get it. Taking the preamp out to a DI or a clean amp doesnt do it.

I notice it a lot doing double stops and intervals up high.

I don't have PPMV in that amp, all stock basicly, plates are little high, 110k for a hair more gain, the rest is stock specs..

I just meant if your using one it makes it worse when you set it low. So some people say anyway. And if thats the case, taking into account my experiments isolating it to the PI input or later, it really must be happeneing in the PI somewhere since your running hte ouput clean with a PPIVMV set low. I dont know. I disconnected NFB. Thats not it. I replaced the output couplers tho at this point I know its not leaky caps. Not in so many amps.

Ive thought a lot before about getting this
https://amptechtools.powweb.com/scope.htm
It would help.

[5150loveeddie]

I have heard someone say that about PPIVMVs before. If thats the case Id think it has to be a PI thing. If your at real low volumes and getting it then its got to be in the PI. I used a SS preamo injected into the PI input (disconnected from the preamp) and I get it. Taking the preamp out to a DI or a clean amp doesnt do it.

I notice it a lot doing double stops and intervals up high.

I don't have PPMV in that amp, all stock basicly, plates are little high, 110k for a hair more gain, the rest is stock specs..

I just meant if your using one it makes it worse when you set it low. So some people say anyway. And if thats the case, taking into account my experiments isolating it to the PI input or later, it really must be happeneing in the PI somewhere since your running hte ouput clean with a PPIVMV set low. I dont know. I disconnected NFB. Thats not it. I replaced the output couplers tho at this point I know its not leaky caps. Not in so many amps.

Ive thought a lot before about getting this
https://amptechtools.powweb.com/scope.htm
It would help.

That is the scope I'm getting.

It is a design snag, I don't see a component problem here as it is a common issue.

I'll try to shield sections in the mean time, I know Philips make a military version of the mustards, they are lime in color, those caps are shielded, but they are very difficult to get, I don't have any yet.. Is there a way to shield caps/resistors easily, like a wrapping material that would isolated them?

With most of your troubleshooting done so far it will help out.

[Ricky Lee]

That's the tool that would probably find the source for the buzz issue.

[Froumy]

Even if it is a design issue, the fact that some people have it worse, would lead you to believe that there is a solution. It might be a good idea to have the guys that have it post all of their specs, component by component, in the PI section, to compare with the guys that don't have it. It could be your problem next build.

Even though it appears to be in the output section, could it be something like a particularly inductive board/material or chassis, etc...? Hitting the PI too hard? IIRC the PI section is fairly unbalanced to begin with. Could yours be a little more unbalanced? etc...

For me, getting good with the scope is taking a little time. Hopefully these guys can help. Dan, were you able to scope yours?

Either way, the fact that a few guys have it, may make it easier to solve, if everyone pitches in...

[MarkCameron]

Check the grounding around the PI. If its an old Marshall with those black lock washers....change them... they dont have the best contact. Another thing.... try running a wire from the speaker jack ground to the presence pot ground lug. Dont twist the b+ to the output transformer with the wires going to the output tube plates. Iv had some amps that just had bad transformers do this too

[5150loveeddie]

Mr Cameron, do you mean the primaries of the OT not to twist them (pins3)? Or the CT of the OT not to be twisted with the primaries?

I found this also that may help, but I didn't do it personnaly yet..

1.Shorten the leads going to the grids of the output tubes as short as possible.
2. Use shielded wire on the input jacks.
3. Take the coupling cap off the first gain stage of each channel and mount it directly on the pot.
4. Take the two merger resistors off the board and mount them on the wiper of the pots ( make sure and use the compensating cap across the correct one of them).

[MarkCameron]

Mr Cameron, do you mean the primaries of the OT not to twist them (pins3)? Or the CT of the OT not to be twisted with the primaries?

I found this also that may help, but I didn't do it personnaly yet..

1.Shorten the leads going to the grids of the output tubes as short as possible.
2. Use shielded wire on the input jacks.
3. Take the coupling cap off the first gain stage of each channel and mount it directly on the pot.
4. Take the two merger resistors off the board and mount them on the wiper of the pots ( make sure and use the compensating cap across the correct one of them).

"the CT of the OT not to be twisted with the primaries"

also I twist the leads going to the output grids

[Billy Batz]

Check the grounding around the PI. If its an old Marshall with those black lock washers....change them... they dont have the best contact. Another thing.... try running a wire from the speaker jack ground to the presence pot ground lug. Dont twist the b+ to the output transformer with the wires going to the output tube plates. Iv had some amps that just had bad transformers do this too

I had the grid wires twisted originally. Ive since replced that twist with shielded cable.

One of the things I tried early on with this issue was rearranging the grounds. I now have the speaker jack/OT common grounded to the PI with the presence pot ground. Originally they were all grounded separately. I was suggested to work on the bias ground so I moved them all around and had no change. Then after I thought I narrowed it down to the PI I redid it liek I said. The 'optimum' grounding.

And my CT and OT primaries are separate so thats not it. Also Ive had several OTs in this amp. Like I said I tried everything. Its driving me mad.

Im really grateful for any thoughts on this. If I could find a fix for this Id be happy as a fly in s#*t. This noise is my albatross. Like I said its in all my marshall builds that Ive had or done since I noticed it (and they arent all dressed/grounded/wired the same) as well as 2 Fender builds. Voltage doesnt seem to be related.

The one thing that kills it is when I run EL84s in those amps (with yellow jackets). Its there with any other tubes (KT66, EL34, 6550) and its there with 2 tubes pulled. Actually I shoudl try pulling 3 tubes and see if its there but Im almost sure I did that before and if it wasnt there Id have jumped on that- as in why would that cure it- emailing people with that info etc..

[Josse]

I had the same phenomenon with my at the time new SLP after rebuilding it with a handbuild ptp board and an new OT. I assumed that I made mistakes with components/soldering/lead dress, whatever. After intense experimentation for weeks and months with all kinds of correcting/rebuilding/modding I was about to give up, and the moskito sound still drove me nuts...

Anyway, somehow I finally thought it could be a problem with the chassis grounding quality. So I removed the complete guts and cleaned the inside and top surface of the chassis with sandpaper - et voil

[Billy Batz]

Thanks for the info Josse. Its interesting defiitely but you assume that was what fixed it because thats what you were intending but any number of things couldve happend when you ripped it apart and rebuilt it. I know someone else who redid the wiring in his amp and claimed it went away afterwards. To bad he couldnt do it one section at a time.

I have about 7 amps Ive done ni the last 4 eyars or so that I know all do this. The chassis are all different. That Metro coated steel, the brushed aluminum, plain aluminum and plain steel. Plus more then one person whose emailed me to compare notes on this business have admited privately their builds all do this. Im not saying its impossible but before Id go ripping an amp apart and rebuilding it because the surface could be a bit dirty, Id need something more compelling. Someone else can feel free tho If they have similar success then Ill start getting my amps all ready for a major gutting.