Tubescreamer Pot noise problems

[jophus]

Dear all,

Just getting together a Tubescreamer from the tonepad pcb. We can't easily get the exact parts here in the UK, so a few substitutions;

one of the 510k 's is a 470k
0.027uf is a o.022
0.22uf's are normal, not tant
51pf is a 47pf
1uf np s are both standard (enormous!) orange jobs

The problem- low effect output, and when I try to turn up any of the pots, I get a screaching sound- not the 'screaming' I was hoping for!

Voltage readings;

9v = 9.33

ic1 = 

1 = 4.65
2= 4.8
3 = 4.56
4= 0
5=4.66
6=4.66
7=4.65
8=9.33                       which sounds ok?

q1=

c= 9.33
b=2.95
e=2.61

q2=

c=9.33
b=2.95
e=2.61

From using a probe  Ican detect that the screaching is coming from the pots, esp the level one, and also the second 1uf capacitor

Please does anyone have any ideas?

Are my substituted componants causing problems? If you hadn't guessed, I'm a bit new to this game, and it's all a bit trial nd error- any thoughts much appreciated!!

Cheers

Joe

[jophus]

o the only other substitution is the tone pot- a 22k not a 20k

Aain, help from someone with more knowledge than me would be greatly appreciated- I've tried pretty much everythnig I can think of...

Cheers

Joe

[jophus]

IS THERE ANYBODY OUT THERE???

I've been listening to the same horrible static noise for hours now while I try and debug
Did  I post something wrong? I've given as much detail as I can.
Surely someone out there has some suggestions? What is the point of having a forum if no one is going to offer any assistance??

I'm seriously considering putting the whole bloody lot in the bin and stick the soldering iron on ebay.....

[petemoore]

From using a probe  Ican detect that the screaching is coming from the pots, esp the level one, and also the second 1uf capacitor

Please does anyone have any ideas?
  I've never had a screaching pot, being a resistive divider I can't see how it could produce screeching by itself.

Are my substituted componants causing problems? If you hadn't guessed, I'm a bit new to this game, and it's all a bit trial nd error- any thoughts much appreciated!!
  Substitution values all look fine, probably can't tell any difference between any of them and the stock' values [basically they 'are' stock values, because they're within 10%...' 
  Yupp...gets frustrating, has to be a wiring error of some kind...
  Polarity of the caps..
  The opamp voltages look good, the buffer transistors voltage I'm less familiar with..[I'd just see if output sounds like input on them, that and they both have about the same voltages would be proof good enough for me.
  What does 'the pot screeches' sound like, and under what conditions does it happen?
  Pot turned up a certain amount or..While pot is being turned ?
 

[jophus]

http://picasaweb.google.com/JDA.Han%^&*/UntitledAlbum/photo#5162807816670625714

This is a pic of the scematic, and the points at which I've tested with my rudimentary probe, and the results- tick= signal, cross = screecing distortion. I've rewired the pots, but it hasn't seemed to help- the problems seem to start around the diode area.

feedback/distortion/sceech kicks in at about 1/3 a turn on all the pots!

many thanks!

Joe

[Zben3129]

Strange...

Try removing the pot and 51k resistor. Then solder something around 350-500k resistor from pin 2 to pin 1 (where the resistance of pot+resistor was before), and also check to see that your 51pf cap is actually a 51 and not something else. Could you tell me what kind of diodes you are using?

Something I found strange...You said screeching occurs with all pots around 1/3...if you have the gain pot half up but volume and tone lower than the 1/3 screech zone, is there still screech?

Zach

[jophus]

 The diodes are 1n914's , 3 of them

The 51pf has been replaced with a 47pf

I'll try sticking in a 500k when I can, see if that improves things

turning the pots just affects the oscillation- I now have noise at any setting- putting my thumb on te end of the guitar cable makes a low tone, turning tone all the way up gives a screech like an old kettle boiling!