Clyde McCoy clone issues

[harrisxr650]

If the wah is true bypass, then does your guitar volume pot crackle when it's in bypass? That would indicate a possible DC leakage in whatever you plug in to.

Yes its true by pass and no guitar volume does not crackle when wah its by passed.

BR

[Rob Strand]

Yes its true by pass and no guitar volume does not crackle when wah its by passed.

So it's likely the DC is coming from the unit itself.

One option is leakage through the two caps.    However, there's also the possibility of bad connections on the grounds somewhere which cause ground at one point to be at a slightly different voltage to another point on the ground.

What you can do is measure between a few points on the grounds.  Chassis to few points on the PCB then measure between those points on the PCB.

Also my dmm has an option for mv so i check it again and on lug 3 it starts from 20mv and goes down to 0mv and 0.1mv to lugs 2 & 3 .

0.1mv could be at the error margin i guess

If you want some confidence the DC is real, reverse the meter leads and the positive voltage should be the same value but negative.   If the magnitude of the measurement is different with the meter probes reversed it's a sign the DMM  is showing spurious readings or the DMM itself has a DC offset internally - that could even show show up as a reading with the DMM probes shorted together.

If you find the DC voltage is real and not caused by bad ground connections you could simply replace the caps going to the pot one at a time.  A DC voltage between pot terminals 1 and 3 which doesn't depends on the pedal position means it's likely the leaky cap is the one on pot terminal 3.  If the DC voltage between pots terminals 1 and 3 depends on the pot position then it's likely the leaky cap is the one on pot terminal 1 terminal 2.    False DC measurements could show up as measurements that are dependent on the pot position.
Typo corrected.

[harrisxr650]

Yes its true by pass and no guitar volume does not crackle when wah its by passed.

One option is leakage through the two caps.    However, there's also the possibility of bad connections on the grounds somewhere which cause ground at one point to be at a slightly different voltage to another point on the ground.

What you can do is measure between a few points on the grounds.  Chassis to few points on the PCB then measure between those points on the PCB.

I'm not sure I understand how to do that. Sorry😊

[harrisxr650]

Yes its true by pass and no guitar volume does not crackle when wah its by passed.

One option is leakage through the two caps.    However, there's also the possibility of bad connections on the grounds somewhere which cause ground at one point to be at a slightly different voltage to another point on the ground.

What you can do is measure between a few points on the grounds.  Chassis to few points on the PCB then measure between those points on the PCB.

I'm not sure I understand how to do that. Sorry😊

Ok ignore previous post. i should learn to read more carefully 

[Rob Strand]

Ok ignore previous post. i should learn to read more carefully 

No worries.

With these weird problems it helps to check as much as possible.    That might mean checking stuff which we would normally never bother to check.

[harrisxr650]

Ok ignore previous post. i should learn to read more carefully 

No worries.

With these weird problems it helps to check as much as possible.    That might mean checking stuff which we would normally never bother to check.

Ok.
 Replaced the 220nf caps with some pio military grade i had lying around.
The dc scratchiness reduced dramatically,

its still there but its reduced a lot.

I couldnt get a stable reading from my dmm so i decided to swap both caps.
any ideas how to completely eliminate it? better caps?

Note that i havent test in a real amp yet. only with bias fx

Also now there is a clipping ( clearly its clipping) issue now on the toe position.
first thing in the morning i will play a bit with the vocal and gain resistors to see if it can be tamed somehow,
may change the sweep cap for a larger one ( 12nf or 15nf) but i will leave the cap last.

BR


BR
 

[Rob Strand]

Replaced the 220nf caps with some pio military grade i had lying around.
The dc scratchiness reduced dramatically,

its still there but its reduced a lot.

I couldnt get a stable reading from my dmm so i decided to swap both caps.
any ideas how to completely eliminate it? better caps?

It's good it helped but it's very odd for film caps to be so leaky.  Especially after replacing them with new parts from a different batch.  Leakage can also come from PCB.    The problem can be reduced by cleaning the PCB but it can also come back.   It can also make the problem temporarily worse if the cleaner affects leakage or permanently worse if the cleaner leaves a residue!  Another way is to avoid the PCB altogether:   Lift the cap leads going to pin 3 of the pot and pin 2 of the pot then solder wires from the lifted cap leads to the pot directly.   

There's a whole stack of tricks to reduce the leakage.   It's not normal to have to worry about such issues on an audio circuit!

Maybe the cause is somewhere else,  perhaps something to do with the way your grounds are wired throughout the pedal.   How is the ground on the output socket wired?

Also now there is a clipping ( clearly its clipping) issue now on the toe position.

So that's another thing which doesn't make sense.  There's no reason why clipping should appear after changing those caps.   The caps shouldn't affect the behaviour of the signal enough to make any noticeable change in levels or cause clipping to occur.

When I see stuff which doesn't makes sense it always ends up that there *is* a problem.  Something which is assumed to true/correct but turns out not to be.
FWIW, it seems you aren't the only one.   (Assuming the case is cap leakage in the first place in both your case and this case.  I don' really agree with the use of electrolytics as a solution.)

https://www.%66%72%65%65%73%74%6f%6d%70%62%6f%78%65%73.org/museum/gaussmarkov.net/circuits/noomerang/

[Rob Strand]

If you want to try some obscure things, here's a way to remove the cap the leakage,



If you don't have any 1uF's you can use the  220nF' you had in there previously - there might be a very small amount of low frequency roll-off with the 220nF's but the important part of the test is if it solves the crackle.  Mount the parts R1, R2, C1, C2 at the pot.

[EDIT:  In retrospect,  it might be better to set R1 = 2M2 and take the output off pin 3 of the pot.   If R1 is 100k it will load down Q1 a bit, which then reduces Q1's gain by a small amount,  and that will affect the sweep range at lower frequencies.]

[harrisxr650]

Maybe the cause is somewhere else,  perhaps something to do with the way your grounds are wired throughout the pedal.   How is the ground on the output socket wired?

I used a stereo input jack and run ''-'' from power jack there to switch off battery when a cable is not inserted ( i can remove it and simplify it if you think it might cause any problems).
Also all circuits grounds go to input jack sleeve (from pot lug 1 also), and since the output and input jack are connected through the enclosure ( checked with dmm) i didnt bother to run another wire from output jack.


[/quote]
So that's another thing which doesn't make sense.  There's no reason why clipping should appear after changing those caps.   The caps shouldn't affect the behaviour of the signal enough to make any noticeable change in levels or cause clipping to occur.

When I see stuff which doesn't makes sense it always ends up that there *is* a problem.  Something which is assumed to true/correct but turns out not to be.
[/quote]

I dont now much of electronics but i dont think the cause of the clipping are the caps across pots lugs. its more like you said at first place, ''very hot input signal'', when i reduce guitar volume from guitar to 7-8 it doesnt appear.

BR

[duck_arse]

Ok ignore previous post. i should learn to read more carefully 

No worries.

With these weird problems it helps to check as much as possible.    That might mean checking stuff which we would normally never bother to check.

Ok.
 Replaced the 220nf caps with some pio military grade i had lying around.
The dc scratchiness reduced dramatically,

its still there but its reduced a lot.

I couldnt get a stable reading from my dmm so i decided to swap both caps.
any ideas how to completely eliminate it? better caps?

Note that i havent test in a real amp yet. only with bias fx

Also now there is a clipping ( clearly its clipping) issue now on the toe position.
first thing in the morning i will play a bit with the vocal and gain resistors to see if it can be tamed somehow,
may change the sweep cap for a larger one ( 12nf or 15nf) but i will leave the cap last.

BR


BR

how come when I quot your post, that huge empty space disappears? any idea what caused it in your post?

[harrisxr650]

Ok ignore previous post. i should learn to read more carefully 

No worries.

With these weird problems it helps to check as much as possible.    That might mean checking stuff which we would normally never bother to check.

Ok.
 Replaced the 220nf caps with some pio military grade i had lying around.
The dc scratchiness reduced dramatically,

its still there but its reduced a lot.

I couldnt get a stable reading from my dmm so i decided to swap both caps.
any ideas how to completely eliminate it? better caps?

Note that i havent test in a real amp yet. only with bias fx

Also now there is a clipping ( clearly its clipping) issue now on the toe position.
first thing in the morning i will play a bit with the vocal and gain resistors to see if it can be tamed somehow,
may change the sweep cap for a larger one ( 12nf or 15nf) but i will leave the cap last.

BR


BR

how come when I quot your post, that huge empty space disappears? any idea what caused it in your post?

Dont have a clue

[Rob Strand]

I used a stereo input jack and run ''-'' from power jack there to switch off battery when a cable is not inserted ( i can remove it and simplify it if you think it might cause any problems).
Also all circuits grounds go to input jack sleeve (from pot lug 1 also), and since the output and input jack are connected through the enclosure ( checked with dmm) i didnt bother to run another wire from output jack.

That way of connecting should be OK.   You could try moving pot lug pin 1 to a ground point on the PCB.  Perhaps move pin 1 of the pot to the ground side of the 10k resistor on the emitter of Q2.   I really think that change is worth trying.

I dont now much of electronics but i dont think the cause of the clipping are the caps across pots lugs. its more like you said at first place, ''very hot input signal'', when i reduce guitar volume from guitar to 7-8 it doesnt appear.

The way you phrased the comment about clipping made me think it clipped more after the cap change than before.   If you are happy the caps haven't changed the clipping that's OK.

[harrisxr650]

I used a stereo input jack and run ''-'' from power jack there to switch off battery when a cable is not inserted ( i can remove it and simplify it if you think it might cause any problems).
Also all circuits grounds go to input jack sleeve (from pot lug 1 also), and since the output and input jack are connected through the enclosure ( checked with dmm) i didnt bother to run another wire from output jack.

That way of connecting should be OK.   You could try moving pot lug pin 1 to a ground point on the PCB.  Perhaps move pin 1 of the pot to the ground side of the 10k resistor on the emitter of Q2.   I really think that change is worth trying.

You mean like this? ( orange lines)

[Rob Strand]

You mean like this? ( orange lines)

Yes.

In terms of simple connections it's the same as what you already have, just a ground point,  *BUT*  it's physically different and it might change something electrically.

[harrisxr650]

Ok. Will give it a shot later and see how it goes

Br

[anotherjim]

Did you clean the PCB? IPA is the kindest.
There can be etchant residue and some flux types can't be left on the board. Ordinary rosin cored solder gives zero problems but some have been caught out with unsuitable stuff from e-bay etc.

[harrisxr650]

You mean like this? ( orange lines)

Yes.

In terms of simple connections it's the same as what you already have, just a ground point,  *BUT*  it's physically different and it might change something electrically.

Yeap! that did the trick!
Moving pot lug pin 1 to the ground side of the 10k resistor on the emitter of Q2 and no more dc scratchiness and (weird though)  no bad clipping in the toe position.
Got a full working McCoy clone now

Guys you are the best! Thanks for all the tips and for being patient with a noob diyer.

[Rob Strand]

Yeap! that did the trick!
Moving pot lug pin 1 to the ground side of the 10k resistor on the emitter of Q2 and no more dc scratchiness and (weird though)  no bad clipping in the toe position.
Got a full working McCoy clone now

Guys you are the best! Thanks for all the tips and for being patient with a noob diyer.

Cool stuff.   Thanks for sticking with it.

It's a *very* subtle problem and I'm sure there's  builds out there which have this issue in various degrees.

If you want an explanation why it works:   
- The guitar signal is fairly small and noise and scratchy sounds are much smaller again.   
- Next is DC across a pot creates a small signal when you move the pot and that promotes scatchness.
- So here's the hard part.   In your build there is a ground wire between the PCB and the input jack.   This wire has
resistance.  The resistance very small and can usually be ignored.    The pedal itself pulls small amount
of current.   That cause a tiny tiny voltage drop across the wire:  V = I * R = pedal current * small wire resistance.
- When you connect the pot ground to the input jack direct that small DC drop appears across the pot.
  So when you move the pot it creates the scratchy noise.
  For no scratchy signal the pot ground needs to be the same as the circuit ground and a good ground connection
  point is the ground on the emitter resistor of Q2.

So a lot of details creating a problem which in an ideal world should not exist at all.

(As a side effect it probably reduces RF interference and risk of oscillation.  Which could explain the clipping fix.
  In that case the DC explanation is incorrect)

[harrisxr650]

Yeap! that did the trick!
Moving pot lug pin 1 to the ground side of the 10k resistor on the emitter of Q2 and no more dc scratchiness and (weird though)  no bad clipping in the toe position.
Got a full working McCoy clone now

Guys you are the best! Thanks for all the tips and for being patient with a noob diyer.

Cool stuff.   Thanks for sticking with it.

It's a *very* subtle problem and I'm sure there's  builds out there which have this issue in various degrees.

If you want an explanation why it works:   
- The guitar signal is fairly small and noise and scratchy sounds are much smaller again.   
- Next is DC across a pot creates a small signal when you move the pot and that promotes scatchness.
- So here's the hard part.   In your build there is a ground wire between the PCB and the input jack.   This wire has
resistance.  The resistance very small and can usually be ignored.    The pedal itself pulls small amount
of current.   That cause a tiny tiny voltage drop across the wire:  V = I * R = pedal current * small wire resistance.
- When you connect the pot ground to the input jack direct that small DC drop appears across the pot.
  So when you move the pot it creates the scratchy noise.
  For no scratchy signal the pot ground needs to be the same as the circuit ground and a good ground connection
  point is the ground on the emitter resistor of Q2.

So a lot of details creating a problem which in an ideal world should not exist at all.

(As a side effect it probably reduces RF interference and risk of oscillation.  Which could explain the clipping fix.
  In that case the DC explanation is incorrect)

Thanks a  lot for the explanation,
My electronics knowledge is limited to the very basics.
So any additional information is good for me to collect more knowledge,
Plus i'm getting more experienced for future builds

Thanks again

[harrisxr650]

Aaaaand back as well the cracking is back..

But i think i found the problem.

More over,
last time i thought it was solved but it wasnt. Indeed the cracking was gone as i tested it but when i went to rehearsal with my band 2 days ago, and upon using the wah, it started cracking again.

It didnt go bad as soon as i started rocking it but after 15 secs more or less.

So i opened it up yesterday and thought that the only part that i haven't triple check is the pot ( a brand new 100k deluxe ProPot).

Removed it and solder in its place a simple 100k alpha pot. BANG! no more crackling!

A played for more than an hour  with no issues, before i started inspecting more thoroughly the pro pot.

The casing was tightly fitted, lugs where ok, but control shaft had a gap and it could move a bit off center.
I've also noticed that the phenolic wafer was loose...

so i opened up the casing and the carbon track was covered with some kind of grease, but it was too much, along with dust. i guess the wiper couldnt establish a firm connection with the track due to the loose wafer and the off centre shaft and along with the dust and grease inside it created all the crackling noise. 

the reason i couldnt find the problem before its because when you applied a small pressure to the  wafer then the wiper could make proper contact so no crackling produced. Thats why i didnt noticed it when  put it in my old crybaby...
Because in order to test it i was holding the pot and turn it by hand....the funny thing. i got a second Propot and it had the exact same problem out of the box....

I can probably get a refund for the second and get something else. right now i'm with an old pot..its working but the taper its a bit..meh..

any suggestions for a good pot?
i was looking for  Joe Gagan 100k smooth pot but its discontinued and none in EU seems to have a single piece. i can find only 250k, 500k and the 50k bommerang for the Gagan series.

Pretty much all of the other brands are available.

BR

Harris