Hi everyone,
Its been a long time since i last posted something here and also a while from building my last pedal :P .
I've just finished my clyde clone with a custom pcb layout bought from a supplier in Europe with a Whipple inductor and ICAR pot. The only change i've made to the original components values is the 1k5 resistor to 1k8
i've used mostly modern components (except for the huge PIO caps i had from an unfinished project :D).
The issue i've run into is that, when the pedal is rocked to the toe position and when hitting with no excessive force the strings, the sound it gets distorted from the middle of the pot travel and on,
It doesnt happen when i play softly,,but very very softly..
i've tried the pot and the inductor to my old crybaby and they work fine.
Q1 & Q2 are both BC 108b and i didnt measure the hfe on them before solder them to the board.
what i should start looking to get it debugged?
By reading in the forum my first thought is to check trannies hfe and replace them accordingly if needed?
Or maybe a faulty transistor?
I've attached a pic of the guts also.
BR
Harris
(https://i.postimg.cc/R3G1s3TW/241410236-368932444931547-5797651127553371211-n.jpg) (https://postimg.cc/R3G1s3TW)
If you have a multimeter, measure the voltages on the transistors. That's the best place to start.
If the biasing is off it will clip earlier.
As to the cause, one possibility is you could have E and C flipped on the transistors. However, I'd expect the wah behaviour to be off if that's the case. Wrong part values or shorts is another reason.
You can knock-back the gain by increasing the 68k base resistor perhaps better the 470 ohm emitter resistor. Unfortunately this will mess with the wah characteristics.
Quote from: Rob Strand on September 04, 2021, 07:15:45 PM
If you have a multimeter, measure the voltages on the transistors. That's the best place to start.
If the biasing is off it will clip earlier.
As to the cause, one possibility is you could have E and C flipped on the transistors. However, I'd expect the wah behaviour to be off if that's the case. Wrong part values or shorts is another reason.
You can knock-back the gain by increasing the 68k base resistor perhaps better the 470 ohm emitter resistor. Unfortunately this will mess with the wah characteristics.
Hey Rob, thanks for the feedback
forgive me for my ignorance,,,do i measure voltages with pedal on or off?
br
Quoteforgive me for my ignorance,,,do i measure voltages with pedal on or off?
You need to be powered but in this case it doesn't make much difference if it's in effect or bypass mode.
Good idea to plug in a guitar (to enable power) and turn volumes to zero.
Turn amp down to stop "bangs" coming through if you slip. No amp also fine.
You need to be powered but in this case it doesn't make much difference if it's in effect or bypass mode.
Good idea to plug in a guitar (to enable power) and turn volumes to zero.
Turn amp down to stop "bangs" coming through if you slip. No amp also fine.
[/quote]
From what i read, in other posts about wah trannies, voltage in Q1 is totally off?
Q1
E 0.11v
B 0.69v
C 4.33v
Q2
E 3.24v
B 3.68v
C 9.15v
QuoteFrom what i read, in other posts about wah trannies, voltage in Q1 is totally off?
Q1
E 0.11v
B 0.69v
C 4.33v
Q2
E 3.24v
B 3.68v
C 9.15v
They all look spot-on text-book wah voltages!
If you want to read a bit go to this page,
http://www.geofex.com/Article_Folders/wahpedl/wahped.htm
Scroll down about 12% down the page to "The Vox Mystery" then a few paragraphs in RG shows some bias calculations.
This page has the voltages on the schematic,
https://www.electrosmash.com/vox-v847-analysis
It seems your input signal might be a little hot. Would you consider your signal hotter than normal?
If you want to drop the wah gain/level you will to makes some mods. It's a little unconventional to have to do that.
As a sanity check, check the values of your 68k and your 1k8 (modded from 1k5 as per first post).
Quote from: Rob Strand on September 05, 2021, 05:43:19 AM
If you want to read a bit go to this page,
http://www.geofex.com/Article_Folders/wahpedl/wahped.htm
Scroll down about 12% down the page to "The Vox Mystery" then a few paragraphs in RG shows some bias calculations.
This page has the voltages on the schematic,
https://www.electrosmash.com/vox-v847-analysis
It seems your input signal might be a little hot. Would you consider your signal hotter than normal?
If you want to drop the wah gain/level you will to makes some mods. It's a little unconventional to have to do that.
i dont consider signal to be that hot, although there is no distortion when i hit the strings softly, but i can hear a slight ''whiss'' whenrocking a the pedal but not hitting the strings. the pups on my guitar are burstbuckers 1&2 and on the other guitar are dimarzio 36th anniversary (both). i can try lowering pups although i'm not sure it will have an impact. Also i might be able to record a clip later on to make you understand better.
Quote from: Rob Strand on September 05, 2021, 06:08:11 AM
As a sanity check, check the values of your 68k and your 1k8 (modded from 1k5 as per first post).
i did and the values are correct. Since i'm a bit above unity gain can raise a bit the input res value? lets say 75k? or it would be better to rise the 470ohm to 510 ohm?
Also by mistake i wrought that i used bc 108b transistors. I used bc 109b for both Q1 & Q2
BR
Quotei dont consider signal to be that hot, although there is no distortion when i hit the strings softly, but i can hear a slight ''whiss'' whenrocking a the pedal but not hitting the strings.
The "whiss" doesn't sound good. You can try a 47pF from Q2's base to ground. This come up on a recent thread by anotherjim. It seems very unlikely the same obscure problem occurred on two units about the same time(!) but you can see if it removes the "whiss".
Quotei did and the values are correct. Since i'm a bit above unity gain can raise a bit the input res value? lets say 75k? or it would be better to rise the 470ohm to 510 ohm?
You would probably be best just increasing the 68k as that will reduce the gain with the least impact on the wah characteristic.
You will probably need to at least go to 82k or even 100k.
The 470R messes with the sweep and it's effect on signal gain depends on the transistor gains.
QuoteAlso by mistake i wrought that i used bc 108b transistors. I used bc 109b for both Q1 & Q2
Any 'b' transistors will pretty much do the same thing.
Quote from: Rob Strand on September 05, 2021, 06:43:05 PM
Quotei dont consider signal to be that hot, although there is no distortion when i hit the strings softly, but i can hear a slight ''whiss'' whenrocking a the pedal but not hitting the strings.
The "whiss" doesn't sound good. You can try a 47pF from Q2's base to ground. This come up on a recent thread by anotherjim. It seems very unlikely the same obscure problem occurred on two units about the same time(!) but you can see if it removes the "whiss".
Quotei did and the values are correct. Since i'm a bit above unity gain can raise a bit the input res value? lets say 75k? or it would be better to rise the 470ohm to 510 ohm?
You would probably be best just increasing the 68k as that will reduce the gain with the least impact on the wah characteristic.
You will probably need to at least go to 82k or even 100k.
The 470R messes with the sweep and it's effect on signal gain depends on the transistor gains.
QuoteAlso by mistake i wrought that i used bc 108b transistors. I used bc 109b for both Q1 & Q2
Any 'b' transistors will pretty much do the same thing.
Ok then i guess the best thing to do replace the 68k res with a 100k pot and adjust the input gain first, and check everything else after that.
what might be the cause of the''whiisss'' effect?
Thanks
Quotewhat might be the cause of the''whiisss'' effect?
In the context of my last answer it would mean the circuit is oscillating at high frequencies.
It could be normal as well, I would have to hear it.
Another possibility is there something wrong with your build and for some reason (don't know what at this point) the gain is high. The high gain would then make the pedal seem noisy. The high gain would also explain why you are getting overloads.
The way you would normally test that is to put in a sine wave and adjust the level so it doesn't clip. Set the pedal down, then measure the level on the output of the wah, adjust the sine-wave frequency to find the maximum level. Repeat the test with the pedal up. You can then compare gain at the peaks with what you expect from a wah (around 18dB or so, depending on your transistor gains and inductor resistance).
i'm attaching the schematic from fuzz central on which the pcb is based and the layout of the pcb,
Pcb is fabricated form a pro which makes and sells a lot of them so i doubt the issue is on the pcb, however i did check the traces with a dmm and it seems fine. i will try to record a clip later on and post it here in case it helps more
(https://i.postimg.cc/68N1frTt/layout.jpg) (https://postimg.cc/68N1frTt)
(https://i.postimg.cc/Mnb3PnjR/schematic.jpg) (https://postimg.cc/Mnb3PnjR)
One very subtle point is there was two versions of the 1967 McCoy Wah with the Halo inductor. The earliest one had halo inductor with a small centre hole in the ferrite core. Typically the resistor across the inductor was 100k (the red 100k on your schematic). The next had a halo inductor with a large centre hole in the ferrite core. Typically the resistor across the inductor was 33k. [There a few examples of small centre hole inductors with 33k's as well.]
The two inductors had difference specs. Especially the DC resistance. The Whipple inductor is a Halo clone. It clones the halo with the large centre hole in the ferrite core. That means to mimic the correct vintage inductor the 100k resistor should be 33k.
The 100k will in fact boost the peaks. I don't know if its your problem but it is a difference.
Having said that, there's plenty of people out there who take any old wah and tinker with the parallel inductor resistor. I'm not aware of them complaining of overloads.
Please don't think I've dissected hundreds of vintage wahs. All I can say is I have collected some info on the early Halo inductors and my findings match what others have said. (I have only found one possible contradiction and that may have been an error on the authors part.)
Another observation is you DC voltages are very much as expected. That means a considerable fraction of your build *must* be correct. It wouldn't take much of a fault to put those voltages off. So things that would affect the (AC) gain but not the DC voltages would be a short across the 68k. You could measure the resistance in-circuit (un powered). There's not much else.
Quote from: Rob Strand on September 06, 2021, 06:27:51 AM
Another observation is you DC voltages are very much as expected. That means a considerable fraction of your build *must* be correct. It wouldn't take much of a fault to put those voltages off. So things that would affect the (AC) gain but not the DC voltages would be a short across the 68k. You could measure the resistance in-circuit (un powered). There's not much else.
Ok.. here is a weird thing,
i just plugged in to record a short clip with the issue, i had removed the bottom cover from yesterday in order to check the input and the 1k5 to 1k8 resistors. but i didnt test it once i;ve put them back.
Now the pedal is sound as it should be. no clipping or whiss on clean channel or with my overdrives etc...
could it be the input resistor, since its socketed, it didnt make 100% contact on the socket and thus it left all the signal flow through the circuit?
i'm gonna test it more the next 2-3 days and see if the issue appears again.
Thanks for the help Rob,
I hope that this was the problem.
BR
Harris
QuoteOk.. here is a weird thing,
i just plugged in to record a short clip with the issue, i had removed the bottom cover from yesterday in order to check the input and the 1k5 to 1k8 resistors. but i didnt test it once i;ve put them back.
Now the pedal is sound as it should be. no clipping or whiss on clean channel or with my overdrives etc...
could it be the input resistor, since its socketed, it didnt make 100% contact on the socket and thus it left all the signal flow through the circuit?
i'm gonna test it more the next 2-3 days and see if the issue appears again.
Thanks for the help Rob,
I hope that this was the problem.
Well, all I can say is bad connections can do some weird stuff and they do come and go without any pattern - probably the most annoying types of faults in the electronics are intermittent ones!
However, it's unlikely a bad connection would *increase* the gain.
With a new build, nothing can be ruled out.
The Q2 b-e voltage at 0.44 looks marginal, but it could be the meter loading on the 470k causing a lower base voltage reading.
Try tapping around with a coqtail stick or back of a pencil to catch a bad connection. These can be inside components. Be gentle with the inductor - you don't want its coil winding fractured.
QuoteThe Q2 b-e voltage at 0.44 looks marginal, but it could be the meter loading on the 470k causing a lower base voltage reading.
It's definitely meter loading (10M ohm input impedance meter). Q1 gain of around 320, comes out at Vbe1=610mV to 620mV.
All looks good for BC109B.
Quote from: anotherjim on September 06, 2021, 09:00:57 AM
With a new build, nothing can be ruled out.
The Q2 b-e voltage at 0.44 looks marginal, but it could be the meter loading on the 470k causing a lower base voltage reading.
Try tapping around with a coqtail stick or back of a pencil to catch a bad connection. These can be inside components. Be gentle with the inductor - you don't want its coil winding fractured.
That was the first thing i did, triple checked and found no bad connection.
didnt had time to play around a bit today will do tomorrow and will check again for bad connection in case i've missed something.
Im going to check the 100k resistor parallel to the inductor as Rob suggested, maybe put a pot and see if lowering the resistance eliminates the issue.
Thanks both for the help :)
QuoteIm going to check the 100k resistor parallel to the inductor as Rob suggested, maybe put a pot and see if lowering the resistance eliminates the issue.
Going from 100k to 33k will knock peak levels down by about 3dB.
It only affects the peaks but maybe that's enough to stop overload.
Hi Harris :)
Changing the 100k Q resistor to a lower value as suggested earlier would make things a bit smoother. Your transistors seem just fine and the build looks good. The burstbuckers are really powerful pickups and could easily drive the way into overdrive as it is not biased to be very clean in general.
Another thing to try is going for 18v power supply which will give more headroom and "presence"
Rock on!
Dan
Here is a short clip with the issue. It might sound like a bad pot but it isnt
Listen to wah noise.mp3 by Harris Hatzianestis on #SoundCloud
https://soundcloud.app.goo.gl/3RwQo
QuoteHere is a short clip with the issue. It might sound like a bad pot but it isnt
Listen to wah noise.mp3 by Harris Hatzianestis on #SoundCloud
https://soundcloud.app.goo.gl/3RwQo
To me honest I'm not sure what noise to listen to. At 10 seconds there seems to be a lot of mechanical noise but I don't know if that is *only* the pedal rocking back and forth. I can't make out any electrical type noise.
The thing that stood out to me is the wah effect itself seems a bit weak. Perhaps the sign of a problem.
For example see this clip about 1 min in with a clean signal,
https://www.youtube.com/watch?v=LpHxOB-VSDM
ok. got some time to fool around today so i though it would be wise to check again, before i start to replace components, for mistakes and all the things mentioned in this topic.
So i checked for: bad or cracked solder joints, short circuits, errors in the values of the components, transistor voltages, voltage leak on pot.
Everything looks perfect.
Though i've noticed something i haven't before,
The tension clutch (dont know if its the correct terminology of the part) was pushing way too much the rack gear against the pinion, too much!
I removed the tension clutch , opened a bit more the hole with a drill and re adjust.
Now i havent tested on a real amp, will do a bit later. instead i test on my pc with bias fx, could heard the issue there as well before.
The scratching-clipping issue (really i dont know how to describe it, it sounds like both...) is gone.
the pedal sounds as it should be, at least on pc.
Also i another strange thing, i user a wooden pencil to poke components inside, every time i poked the inductor i could hear it from the speakers, is this normal?
I will hold a small basket untill i test it on a real amp and provide any additional info here whether tyhe problem is solved or not.
BR
(https://i.postimg.cc/dkDKswQj/242052522-151714910468393-8504973108945822784-n.jpg) (https://postimg.cc/dkDKswQj)
The inductor coil can be microphonic. Ideally, it would be wax impregnated just like guitar pickups should be.
It might explain why mechanism noise got into the audio.
Quote from: anotherjim on September 14, 2021, 08:22:06 AM
The inductor coil can be microphonic. Ideally, it would be wax impregnated just like guitar pickups should be.
It might explain why mechanism noise got into the audio.
ok.. i just checked with a toothpick and the coil around the ferrite is moving. should i consider this a flaw?
Beside pot waxing the coil would it be a big deal if i use a couple super glue drops to stabilize it?
BR
I'd do something about that. Superglue is a bit fierce, I would run some clear varnish in or even button polish (old school shellac based stuff).
Quote from: anotherjim on September 14, 2021, 10:40:30 AM
I'd do something about that. Superglue is a bit fierce, I would run some clear varnish in or even button polish (old school shellac based stuff).
excellent. i will give it a shot later on the day and see how it goes
Thanks
QuoteI will hold a small basket untill i test it on a real amp .....
pardon my ignorance and possible cultural insensitivity, but why are you holding a basket? is there something in the basket?
Quote from: duck_arse on September 14, 2021, 11:12:31 AM
QuoteI will hold a small basket untill i test it on a real amp .....
pardon my ignorance and possible cultural insensitivity, but why are you holding a basket? is there something in the basket?
:icon_lol: :icon_lol:
It's a a Greek proverb that sais: "When you hear of many cherries, hold a small basket."
It's about not having big expectations for something until you are 100% sure that (in this case) will work 🤣🤣
QuoteThe scratching-clipping issue (really i dont know how to describe it, it sounds like both...) is gone.
the pedal sounds as it should be, at least on pc.
I don't understand what the cause was mbut it's good news you solved it.
QuoteAlso i another strange thing, i user a wooden pencil to poke components inside, every time i poked the inductor i could hear it from the speakers, is this normal?
I'm with anotherjim on the wax. You might not be able to remove the problem entirely. Look at some of those stack of dimes inductors they are are dipped. That's pretty severe as well.
Quote from: Rob Strand on September 14, 2021, 05:58:44 PM
QuoteThe scratching-clipping issue (really i dont know how to describe it, it sounds like both...) is gone.
the pedal sounds as it should be, at least on pc.
I don't understand what the cause was mbut it's good news you solved it.
QuoteAlso i another strange thing, i user a wooden pencil to poke components inside, every time i poked the inductor i could hear it from the speakers, is this normal?
I'm with anotherjim on the wax. You might not be able to remove the problem entirely. Look at some of those stack of dimes inductors they are are dipped. That's pretty severe as well.
i didnt solve it. I though i did because i was rocking the pedal with my hand, but once i stepped the scratching was there.
I did what anotherjim said but it reduced the problem very very slightly. I think im gonna get a new inductor and see how it goes from there.
One (more) question. if i got it right..since the inductor is not waxed properly and the coil is moving, the inductor pick ups the mechanical noise created from the shaft and the pedal spring when rocking the pedal. Could it be the case?
Thanks
Quotei didnt solve it. I though i did because i was rocking the pedal with my hand, but once i stepped the scratching was there.
Oh man, what a pain.
QuoteI did what anotherjim said but it reduced the problem very very slightly. I think im gonna get a new inductor and see how it goes from there.
One (more) question. if i got it right..since the inductor is not waxed properly and the coil is moving, the inductor pick ups the mechanical noise created from the shaft and the pedal spring when rocking the pedal. Could it be the case?
I suspect that's the part of the problem but you could do a test: Remove the inductor but connect it back the PCB via two thin flexible wires about 300mm long. Twist the wires a locate the inductor outside of the box preferably without the wires mechanically touching the enclosure. Lay the inductor on something soft like a T-shirt/towel/soft-foam. See if the problem improves. You might a bit more mains buzz but don't worry about that.
Techically an unmagnetized ferrite core shouldn't have microphonics.
However,
- the circuit as a small amount of DC current through the coil
- the gain of the amplifier from perspective of the inductor is high
- there's a lot of turns on the inductor
(- it's even possible the coil manufacturer magnetizes to core a bit. That's speculation you would would need to check with a compass located close to the core.)
All those add-up to a possibility of microphonics. In use you can get other microphonics effects because the signal creates a field in the core.
Ok,, recorded a new clip. and i think is a bit clearer now.
https://soundcloud.com/harris-hatzianestis/wah-track-12
From 00.00 - 00.05, is the effect by passed
from 00.05 - 00.14, effect is on and you can clearly hear the scratching noise
from 00.14 - end, effect is on, with guitar plugged in, guitar volume on 100% and i just rock it without playing.
Quote from: harrisxr650 on September 14, 2021, 01:12:22 PM
Quote from: duck_arse on September 14, 2021, 11:12:31 AM
QuoteI will hold a small basket untill i test it on a real amp .....
pardon my ignorance and possible cultural insensitivity, but why are you holding a basket? is there something in the basket?
:icon_lol: :icon_lol:
It's a a Greek proverb that sais: "When you hear of many cherries, hold a small basket."
It's about not having big expectations for something until you are 100% sure that (in this case) will work 🤣🤣
somewhat akin to
don't count your chickens before they've hatched. those cherries could go on top of a cake ..... :cherries: :cherries: :cherries:
Would I be way off base to suggest that it sounds a bit like DC noise on the pot? I have had volume pedals with a perfectly good pot going into poorly filtered amps which made exactly that sound, where the scratchiness only appears while there's an audible signal. This sounds more like that to me than microphonics, where you'd expect to still hear the noise at the end when there's no guitar being played...
Quote from: pacealot on September 15, 2021, 11:56:25 AM
Would I be way off base to suggest that it sounds a bit like DC noise on the pot? I have had volume pedals with a perfectly good pot going into poorly filtered amps which made exactly that sound, where the scratchiness only appears while there's an audible signal. This sounds more like that to me than microphonics, where you'd expect to still hear the noise at the end when there's no guitar being played...
Yes it sound like DC leak to the pot.
But I measure 0 to it, nor to the 220nf caps
Unless it's a small leakage and my dmm cannot measure it?
Assuming it is DC on the pot. Adding a small cap, lets say 220pf, from the pcb output to ground will probably fix this right?
Sounds like a bad pot or DC to me.
QuoteUnless it's a small leakage and my dmm cannot measure it?
It's possible the DMM can't see it especially if you have a 1M ohm input impedance DMM. If the board has an issue you would expect to see something.
Sometimes weird problems have weird causes. Perhaps the DC isn't coming from the wha but from the circuit you are plugging into.
As a test, not a solution, you can place a 100nF cap between the PCB Output terminal and the switch. Just place the added cap between the output terminal on the PCB and the wire. The cap removes any DC from the output socket feeding back into the circuit to the pot.
QuoteAssuming it is DC on the pot. Adding a small cap, lets say 220pf, from the pcb output to ground will probably fix this right?
A cap to ground won't directly affect DC. If you want to try a cap you need a small cap (47pF) from the base of Q2 to ground (as per anotherjims recent thread). This high frequency stops oscillation issues which can appear as crackles and hiss - all sorts of bad stuff. It's a long shot but you can try it.
One thing i forgot,
Yesterday as i was poking the components with the pencil, besides the inductor, i got noise through the amp while poking Q1, Is this normal?
Then, while searching the net, i came across this thread
https://www.diystompboxes.com/smfforum/index.php?topic=121812.0
By the way with what anotherjim proposed to do with the inductor in order to stabilize the coil i dont get any poking sound now.
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 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.
Quote from: anotherjim on September 16, 2021, 02:15:34 PM
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
QuoteYes 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.
QuoteAlso 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.
Quote from: Rob Strand on September 16, 2021, 04:57:09 PM
QuoteYes 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😊
Quote from: harrisxr650 on September 16, 2021, 05:37:07 PM
Quote from: Rob Strand on September 16, 2021, 04:57:09 PM
QuoteYes 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 :D
QuoteOk ignore previous post. i should learn to read more carefully :D
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.
Quote from: Rob Strand on September 17, 2021, 06:42:29 AM
QuoteOk ignore previous post. i should learn to read more carefully :D
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
QuoteReplaced 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?
QuoteAlso 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/
If you want to try some obscure things, here's a way to remove the cap the leakage,
(https://i.postimg.cc/94gMWpvN/Leakage-less-Wah-pot-connection.png) (https://postimg.cc/94gMWpvN)
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.]
Quote from: Rob Strand on September 17, 2021, 07:06:36 PM
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
Quote from: harrisxr650 on September 17, 2021, 06:12:34 PM
Quote from: Rob Strand on September 17, 2021, 06:42:29 AM
QuoteOk ignore previous post. i should learn to read more carefully :D
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?
Quote from: duck_arse on September 18, 2021, 10:18:56 AM
Quote from: harrisxr650 on September 17, 2021, 06:12:34 PM
Quote from: Rob Strand on September 17, 2021, 06:42:29 AM
QuoteOk ignore previous post. i should learn to read more carefully :D
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 :D
QuoteI 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.
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.
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.
Quote from: Rob Strand on September 18, 2021, 06:50:18 PM
QuoteI 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)
(https://i.postimg.cc/LhbVDGbK/mccoyschematic2.jpg) (https://postimg.cc/LhbVDGbK)
(https://i.postimg.cc/JGH52Kfy/wah2.jpg) (https://postimg.cc/JGH52Kfy)
QuoteYou 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.
Ok. Will give it a shot later and see how it goes
Br
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.
Quote from: Rob Strand on September 19, 2021, 07:31:44 AM
QuoteYou 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 :D
Guys you are the best! Thanks for all the tips and for being patient with a noob diyer. :D
QuoteYeap! 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 :D
Guys you are the best! Thanks for all the tips and for being patient with a noob diyer. :D
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)
Quote from: Rob Strand on September 19, 2021, 05:58:42 PM
QuoteYeap! 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 :D
Guys you are the best! Thanks for all the tips and for being patient with a noob diyer. :D
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
Aaaaand back :D 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
All pots have grease in them. It's a worry for trying to squirt any solvent-based contact cleaner in there - it thins that grease which should just lube the shaft then it can run all over the carbon track. I do suspect the grease used has changed in recent years. Maybe the old stuff was made of something now frowned upon in these enlightened times?
Quote from: anotherjim on September 27, 2021, 02:05:06 PM
All pots have grease in them. It's a worry for trying to squirt any solvent-based contact cleaner in there - it thins that grease which should just lube the shaft then it can run all over the carbon track. I do suspect the grease used has changed in recent years. Maybe the old stuff was made of something now frowned upon in these enlightened times?
Problem is that the insides of the pot was a mess. Too much grease plus the loose shaft and water.
The was no signs that the pot was used or opened so I assume bad QC?
I believe all the above contributed to the issue. 2nd pot had the loose shaft and water as well. I didn't open it in order to get a refund.
I've already ordered a Joe Gagan pot to put in.
Br
QuoteI've already ordered a Joe Gagan pot to put in.
See how it goes. Intermittent behaviours are really tough. You only really know you solved it if you see the fault. Changing stuff out you have to play the wait and see game over a long period.
The surprising thing is moving that pot wire had a large effect. Didn't it stop the clipping issue as well as the crackling? So either that helped but didn't solve the issue, or, you are seeing random behaviour and touching anything in the general area is changing the behaviour (for good or bad).
A common fault with pots is the rivets on the terminals don't have solid connections between terminals and track. With something like a wah pedal, where there are mechanical vibrations, the pedal movements could any promote bad contacts to crackle.
Hopefully the new pot works out.
If it doesn't you should try anotherjims cap on the base of Q2 to ground (say 22pF to 47pF). Mount the cap close to Q2. I'd also leave the pot ground wire connected to the ground side of the Q2's emitter resistor.
Some years ago I built a wah with the Whipple inductor, and the CTS-made pot that they often bundle with it on Ebay. The pot is not sealed, and the one I had got scratchy not long after installation. I ended up replacing it with a Hot Potz 1 that I got from Small Bear, that solved it. But later I started noticing problems with other new CTS pots, in my guitar and my amp, getting scratchy after maybe a month of use. Trial and error found that cleaning all the factory grease out with a general electronics cleaner, then relubricating with Deoxit, then the pots are good to go. But I haven't tried that on the CTS wah pot, it's still around here in a bag of parts somewhere.
Side note, the current Dunlop rectangular plastic Hot Potz II(?) is actually a very nice wah pot. It doesn't look so cool, but it has a good taper and should last much longer than carbon track pots.
I also think the grease in some pots can get runny in high temperatures like during a heatwave.
I like the HotPotz. Worth the money. I've found general pots that look the same physically but no 100k in the range.
Open side pots can have dust caps fitted, but I've only seen them for 16mm like Alpha.
Quote from: Rob Strand on September 27, 2021, 07:04:23 PM
QuoteI've already ordered a Joe Gagan pot to put in.
See how it goes. Intermittent behaviours are really tough. You only really know you solved it if you see the fault. Changing stuff out you have to play the wait and see game over a long period.
The surprising thing is moving that pot wire had a large effect. Didn't it stop the clipping issue as well as the crackling? So either that helped but didn't solve the issue, or, you are seeing random behaviour and touching anything in the general area is changing the behaviour (for good or bad).
A common fault with pots is the rivets on the terminals don't have solid connections between terminals and track. With something like a wah pedal, where there are mechanical vibrations, the pedal movements could any promote bad contacts to crackle.
Hopefully the new pot works out.
If it doesn't you should try anotherjims cap on the base of Q2 to ground (say 22pF to 47pF). Mount the cap close to Q2. I'd also leave the pot ground wire connected to the ground side of the Q2's emitter resistor.
My guess is that by moving the wire from lug one i applied some pressure to the wafer and the made the wiper temporarily to make better contact with the carbon track. but the problem wasnt only the wafer.
I did the following to be sure the pot is bad. used a wooden clothespin to apply some pressure to the wafer. that eliminated the most of the problem, but the pot shaft is loose as well.
Turning the pot with hand didnt bring up the crackling, but when i started, at the same time, to turn and move the shaft a bit off center it started again. New pot had the same loose shaft so i didnt bother to solder it.
Thats why i decided to order a new, better quality, pot.
Every other component is triple checked to be within specs, voltages looks ok, i maintain a wariness about the inductor but after what anotherjim suggested to do it seems to be ok
The trick with moving the wire eliminate completely the clipping issue,
As soon as i get the new pot i will install it play a couple of days ( or a couple of minutes...depends :D ) and see how it goes.
Thaks again for the info
BR
Harris