Traynor YGM-3 Sensitive/Noisy Tremelo

[nateflanigan]

Hello, I'm working on debugging a Traynor YGM-3 Tremelo circuit.


http://el34world.com/charts/Schematics/files/traynor/traynor_guitarmate_ygm3.pdf


Here are the symptoms...


- When engaged the tremelo has a sort of high end chirpy oscillation.  The more the rate knob is increased the more the problem increases.


- At times there is some ticking even with the depth knob all the way down.  The rate of the ticking changes with the rate knob.  I can get the sound to go away by moving around some wires, then at different volume or EQ settings it will come back, and the game of cat and mouse goes on.


-So far none of the lead moving about has altered the chirping oscillation.


Here's what I've done...


-Recapped most of the amp.  I haven't done the bias supply filter caps yet.


Recapping tamed the chirpy sound a bit, turning my guitars tone or volume knobs down affects it but nothing makes it go away completely. 


I need to order some parts for the bias caps, I'm thinking I'll hit the power supply dropping resistors as well.  Anything else I should be looking at before I place my parts order?


Thanks!

[super&plexi]

think I remember something about cutting even just one inch of wire in that circuit can tame problems...just can't remember which one...ha!  Think if you look it up on youtube you'll find a bunch of stuff related to that amp, hope that helps until the more savvy get to you.

[jjasilli]

Also checkout skywire cure:  http://el34world.com/Forum/index.php?topic=16157.5;wap2

[nateflanigan]

Whoa, Time Electronics is pretty next level.  Super&Plexi, if that bit about the wire comes back to you please do share.

[sluckey]

There's a pretty good chance that new bias caps will fix this.

[nateflanigan]

That sure would be nice. 

[nateflanigan]

So, I'm still not there yet.  I've replaced the bias filter caps.  Moving around the leads with a pair of pliers I found one that was really sensitive, I replaced that with shield wire.  Tapping on components I found that the coupling cap going into the PI was noisy, replaced that.  All this has helped but the trem still has this ultra high end chirpy oscillation to it.  Is there a way to test for board capacitance, is it enough to show up on a standard DMM?  I plan on replacing the three 0.01 caps in the trem circuit, at this point I feel like I'm randomly trying things. 


Any advice?  Any voltages or measurements I can check?


Otherwise, I've got the amp sounding really good.

[nateflanigan]

Here's something interesting I just noticed.  With the amp on, no guitar plugged in, volume all the way down, if I bring up the intensity the oscillation creeps in.  If I bring up the reverb level the oscillation fades, with the reverb all the way up, it's gone completely.  The tremolo circuit and the reverb recovery circuit share V6 (which is a brand new tube).  No idea what to make of that.

[nateflanigan]

Solved!  Man, that was a tough one.  I noticed that the schematic I was using wasn't 100% correct, so I scrolled down and saw that there are some alternate versions.  Two versions have a 47pf cap across the plates of the PI one version doesn't.  You guessed it, the amp I'm working on doesn't have the 47pf cap.  I strapped a decade box across the PI and dialed in a value that quelled the oscillation, turns out 330pf did the trick.  This feels a bit like a bandaid more than a real fix, but the amp is sounding great now.

[Colas LeGrippa]

These old amps need love. You got to replace all the cathode caps before doin' anything else. Replace the filtering caps as well. New caps equal less oscillation.
  A small cap accross the plates is a trick engineers found to get rid of oscillation or possible oscillation. I have built tens of amplifiers and never needed to add small caps accross this and that to cure  a problem.
In an amp you need:

-good filtering
-grid stoppers
-good grounding
-shielded cables for audio
-and good lead dress.

If you do that all right, you don't need any trick of the ninja to get rid of the parasitic oscillation 'cause you have none. Many amplifiers were badly designed and instead of being sent to the garbage, they were fixed with tricks that cure the symptons but not the illness. With age, problems start to come back 'cause the small caps here and there lost their power and overall oscillation is rising. All the other caps too become weak and you start to hear cracks , scratches, pops.

[nateflanigan]

These old amps need love. You got to replace all the cathode caps before doin' anything else. Replace the filtering caps as well.

Yup, that was move #1.  I like to replace all the high current resistors as well, I've yet to encounter a situation where it made a HUGE difference but it always seems to make the amp stand up a little straighter.

[Colas LeGrippa]

yep !