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

[Ricky Lee]

I did a little experimenting today and I noticed by removing the .68uf v2a bypass cap or exchanging it with a 330uf the buzzing greatly subsided. Makes sense because as I've said earlier the buzz to me is more noticeable on the high strings (notes). Also, None of the builds I've ever done that were aluminum chassis do the buzz thing but the steel chassis buzz. Supposedly the steal chassis is less conductive than the aluminum so maybe that's something to think about. I don't want to even imagine another nightmare with a conductive board.

[5150loveeddie]

I did a little experimenting today and I noticed by removing the .68uf v2a bypass cap or exchanging it with a 330uf the buzzing greatly subsided. Makes sense because as I've said earlier the buzz to me is more noticeable on the high strings (notes). Also, None of the builds I've ever done that were aluminum chassis do the buzz thing but the steel chassis buzz. Supposedly the steal chassis is less conductive than the aluminum so maybe that's something to think about. I don't want to even imagine another nightmare with a conductive board.

Was that with el34 in alum?

Anyone knows Denis Cornell in the UK, a friend told me that guy made an article on the problem and explains it... Have to find the article, I just e-mail him with the question.....

[Ricky Lee]

Either 66 or 34 in aluminum chassis with no buzz. Let me know if you find Dennis's article I'd love to read it.

[5150loveeddie]

Either 66 or 34 in aluminum chassis with no buzz. Let me know if you find Dennis's article I'd love to read it.

Dennis's respond to the clip I send him (Dan's)

quote:
JF
Your problem is layout ?
It is just as important as the circuit it self. What is happening is that the signal has a oscillation on it when the amp is driven hard.
This is common and caused by:-
Incorrect component layout.
Lack of screening of sanative leads.
Incorrect earth returns.
Good luck
Denis
en quote

Lack of screening of sanative leads, what does that means in French I mean in English

[Ricky Lee]

Sanative: Having the power to cure; healing or restorative: a sanative environment of mountains and fresh air.

I love those $10.00 words especially those that no body knows what they mean except the dictionary! In layman's terms I get that he's saying bad lead dress and improper grounding is the cause. If that's the case there's a lot of improperly built amps running around out there since many of them do the buzz thing.

[5150loveeddie]

Sanative: Having the power to cure; healing or restorative: a sanative environment of mountains and fresh air.

I love those $10.00 words especially those that no body knows what they mean except the dictionary! In layman's terms I get that he's saying bad lead dress and improper grounding is the cause. If that's the case there's a lot of improperly built amps running around out there since many of them do the buzz thing.

Oh well.......

[Billy Batz]

I did a little experimenting today and I noticed by removing the .68uf v2a bypass cap or exchanging it with a 330uf the buzzing greatly subsided. Makes sense because as I've said earlier the buzz to me is more noticeable on the high strings (notes). Also, None of the builds I've ever done that were aluminum chassis do the buzz thing but the steel chassis buzz. Supposedly the steal chassis is less conductive than the aluminum so maybe that's something to think about. I don't want to even imagine another nightmare with a conductive board.

Its possible theres more then one cause but as Ive said I disconnected the preamp altogether and run a SS preamp'd signal into the PI and the noise was all there. Similarly I ran the preamp out to a DI and there was no trace of it- as in it was something post preamp. Changing the values definitely effects the noise but taht doesnt make it the cause.

The same is Dennis' response. We all follow marshall which isnt the best design as far as lead dress and grounding but Im not satisfied with tha t. I really believe its seomthing less abstract. A specific improper ground or wire not just the responce most people give-theres oscillation or bad grounding. Thats true of every vintage design and thats probably explains why vintage amps probably do it in great numbers too but Ive had a million noises to fix in amps and they are never so specifically the same from one amp tot he next. The only variance is how audible it is, similar to ghosting. No matter how I play around with the lead dress or the grounds its EXACTLY the same. Wheras every other oscillation you deal with is like a beast unto itself and when you move wires around they change a lot.

[5150loveeddie]

Does anybody here gets the "SNAG/noise/buzz" in an aluminium made chassis amp??

[Billy Batz]

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.

I know you were hoping for the simple answer but chassis material is not it.

[5150loveeddie]

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.

I know you were hoping for the simple answer but chassis material is not it.

Ah ok I forgot that one, will have to make a list of things you've done so I remember

[Froumy]

My questions may be off base, but I can't help wondering....

Interesting that the EL84/yellow jackets don't do it. Possible clue, any way. EL84's draw about half the current of EL34's, no? Any chance that that the PT just isn't playing nice under full load? Anyone try pulling 2 tubes in 100 watt, for giggles?(does it happen in both 50W and 100W?)

Do the yellow jackets drop the voltage in the PI section to just below induction levels?

El84's will be sending a lower signal to the OT.... Something there? Would lowering that signal help? I know with a presence squeal and fully attenuated(dummy load), I can hear my OT screeching when I crank the presence. Does the OT make any noise with a dummy load?

It does raise the tubes from the chassis, and away from the OT, but I doubt that's it...

Don't capacitors have a certain amount of parasitic inductance? Is it possible that vintage caps have a higher PI and are more susceptible to it under full load? Wonder if those shielded caps will work for you? Or caps with really low inductance? Just read something about a Faraday shield, used to help eliminate stray capacitance, for when caps are run in parallell, to eliminate noise(usually higher freq's).

http://www.analog.com/library/analogDia ... ry/21.html

Something to read, anyway. Sorry for all the questions... Just fishing. Can't hurt to ask if sparks something else, though. Good luck!

[5150loveeddie]

My questions may be off base, but I can't help wondering....

Interesting that the EL84/yellow jackets don't do it. Possible clue, any way. EL84's draw about half the current of EL34's, no? Any chance that that the PT just isn't playing nice under full load? Anyone try pulling 2 tubes in 100 watt, for giggles?(does it happen in both 50W and 100W?)

Do the yellow jackets drop the voltage in the PI section to just below induction levels?

El84's will be sending a lower signal to the OT.... Something there? Would lowering that signal help? I know with a presence squeal and fully attenuated(dummy load), I can hear my OT screeching when I crank the presence. Does the OT make any noise with a dummy load?

It does raise the tubes from the chassis, and away from the OT, but I doubt that's it...

Don't capacitors have a certain amount of parasitic inductance? Is it possible that vintage caps have a higher PI and are more susceptible to it under full load? Wonder if those shielded caps will work for you? Or caps with really low inductance? Just read something about a Faraday shield, used to help eliminate stray capacitance, for when caps are run in parallell, to eliminate noise(usually higher freq's).

http://www.analog.com/library/analogDia ... ry/21.html

Something to read, anyway. Sorry for all the questions... Just fishing. Can't hurt to ask if sparks something else, though. Good luck!

Interesting page here...

Have a qts also for those who knows. I found some type of metalic tape, the ones use in air duct assembly, I guess it is aluminum, thin as a sheet of paper and very sticky on one side, was wondering if this could act as a type of shield..?

[Froumy]

I was afraid this post might die. That simply can't happen.

5150(Stephane?), don't read too far into that post. The solution could be there, but who knows? Important to be aware of the variables, though. I troubleshoot engineered and designed telephony circuits for a living. Completely different animal, but there is a constant. When all the obvious solutions fail, it comes time to ask the ridiculus questions. Sometimes they shed light. sometimes not. Standard designs do not always work, but there is ALWAYS a solution, if you care to find it. This one sounds like a total bitch, but if enough tube guru's(I am not), pitch in, you ought to get somewhere.

Have you proved that your problem is in the output section, like Dan has? DO NOT make assumptions. Do you have your scope yet? Has Dan scoped his output section of all of his builds? With, and without yellowjackets? Corresponding voltages as well. Guys that have it(or not) should post the scope view and voltages if they can. I'll do what I can.

Re-read the thread. Billy Batz says it does it with 2 tubes pulled. Prove it again, if this a 100W. Unless the PT is woefully underdesigned, this should help to elimintate the PT.

Sidenote: Seems like some players with keen ears are very tuned into this. Nice chops from Billybatz, and 5150loveeddie. Been wanting to bump this link to the top for a while, but somebody locked it. I don't typically like shred, but with the rhythmn of this one, OUCH. I would have been offended if someone hadn't ripped over it. Big time thumbs up, from a guy who doesn't care about shred.
http://forum.metroamp.com/viewtopic.php ... mback+clip

If you dig deep enough, there is always a solution.

[Billy Batz]

I wasnt going to let it die I was just waiting for 5150 to get his scope data together. That was basically where it stopped for me. I came to the decision its something at least somewhat inherent and until I got a scope Id learn to live with it. At the time I was going to get one as soon as I could but I never did. I was sidetracked by work and other things but Im glad to come back to it. I wouldnt be surprised if there was multiple contributors to this noise but something about the nature of it, how consistently similar it sounds sets it apart from other noises Ive had to deal with and with the playing around Ive done it just really hits me as possibly one specific thing and probably post-preamp. For instance I have a MV (pre PI) on the one fedner and when thats set low it doesnt do it.

Ive got a list of things Ive thought about trying since this thread has been up. The next time its on the bench Ill try them out. I never have every amp in its cab, ever, but right now I do lol. Usually theres always one open ont he bench.

[Froumy]

Any progress?

5150, if you didn't get a signal generator, here's a free program that might help:

http://www.david-taylor.pwp.blueyonder. ... l#SweepGen

I really hope it shows something concrete... Good luck.