Clyde McCoy clone issues  [SOLVED]

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harrisxr650
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Post by harrisxr650 »

Hi everyone,

I have already asked the same question in the neighboring forum,
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 109b and i didnt measure the hfe on them before solder them to the board.

what i should start looking to get it debugged?
transistor voltages looks fine

Q1
E 0.11v
B 0.69v
C 4.33v

Q2
E 3.24v
B 3.68v
C 9.15v

I member from the other forum said that the input signal might be too hot

The pups on my guitars 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 any impact

I've attached a pic of the guts also.
BR
Harris
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Manfred
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Post by Manfred »

Please attach the schematic and the PCB layout with the used component values for a better error analysis.
Is the PCB etched by yourself or purchased.

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harrisxr650
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Post by harrisxr650 »

Manfred wrote: 05 Sep 2021, 22:11 Please attach the schematic and the PCB layout with the used component values for a better error analysis.
Is the PCB etched by yourself or purchased.
totally forgot them..sorry
there you go
the schematic is from fuzzcentral

The pcb is fabricated from arteffect, checking tracks with dmm looks fine
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layout.JPG
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Manfred
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Post by Manfred »

I ran a simulation with BC109B transistors.
The voltage values at the terminals of Q1 were very close to what you read.
For Q2 the values were as I expected different from your measurement, because the 9.15V at the collector was suspicious.
I ran further simultions with collector resistors 0, 10 and 100 ohms and got the voltage values what you read.
I guess you installed a wrong resistor with 10 or 100 ohms instead the 1 Kilohm resistor on the Collector of Q2 or there is a short circuit between the collector of Q2 to 9VDC.
Last gave gave exactly the values you measured.

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harrisxr650
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Post by harrisxr650 »

Manfred wrote: 06 Sep 2021, 19:43 I ran a simulation with BC109B transistors.
The voltage values at the terminals of Q1 were very close to what you read.
For Q2 the values were as I expected different from your measurement, because the 9.15V at the collector was suspicious.
I ran further simultions with collector resistors 0, 10 and 100 ohms and got the voltage values what you read.
I guess you installed a wrong resistor with 10 or 100 ohms instead the 1 Kilohm resistor on the Collector of Q2 or there is a short circuit between the collector of Q2 to 9VDC.
Last gave gave exactly the values you measured.
Thanks for the detailed feedback,
I just got back from work and i doubt my mind is clear enough to check right now :P
will do first thing in the morning though and post my findings.
Thanks again

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Post by harrisxr650 »

Ok.. checked the 1k resistor and its value is correct.

No short circuit between Q2 collector and 9vdc also.

I was reading a Wah analysis found on https://www.electrosmash.com/vox-v847-analysis
It has a schematic with voltages and my transistors findings looks very close text-book wah voltages.
Could it be a faulty transistor?
I've read something like that... cant recall on which website though.

BR

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Post by Manfred »

I ran the simualtion with 9 volts battery voltage, but the real battery has a voltage of about 9.4 volts.
I repeated the simualtion with this 9.4 volts,
the voltage values are now close to your measured values.
Sorry, my fault, the circuit works correctly.

Q1
Measurement / Simulation
E 0.11v / 0.10V
B 0.69v / 0.7V
C 4.33v / 4.43V

Q2
Measurement / Simulation
E 3.24v / 3.22V
B 3.68v / 3.83V
C 9.15v / 9.08V

The highest gain is always at the center frequency given by the pedal position.
I ran a simulation where I fed in a sinusoidal voltage at the current center frequency.
I found that the output signal starts to deform at an input voltage of about 240 Millivolts peak-to-peak.
I then increased the emitter resistor of Q1 from 470 Ohms to 1 Kiloohm, thereby the deformation starts from about 450 Millivolts peak-to-peak.
The gain of the pedal goes down to 60%,
You can try it out if this gain is enough.
If not, you can still swap the resistor with 68 Kilohms for one with 33 kilohms then the gain goes down to 90%,
but in this case the deformation of the output signal starts already at 310 Millivolts peak-to-peak

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Post by harrisxr650 »

Manfred wrote: 09 Sep 2021, 00:21
The highest gain is always at the center frequency given by the pedal position.
I ran a simulation where I fed in a sinusoidal voltage at the current center frequency.
I found that the output signal starts to deform at an input voltage of about 240 Millivolts peak-to-peak.
I then increased the emitter resistor of Q1 from 470 Ohms to 1 Kiloohm, thereby the deformation starts from about 450 Millivolts peak-to-peak.
The gain of the pedal goes down to 60%,
You can try it out if this gain is enough.
If not, you can still swap the resistor with 68 Kilohms for one with 33 kilohms then the gain goes down to 90%,
but in this case the deformation of the output signal starts already at 310 Millivolts peak-to-peak
Thanks for the answer,
No need to apologies though, your information is valuable and helps me have a better understanding of the circuit :)

One last thing though since i'm a hobbyist and i dont now much about electronics except the very basics .

Since the Q1 emitter resistor messes with the sweep, and its effect on signal chain, will it have any impact on the tonal characteristics of the pedal?
Could it be better to increase the input (68k) res with a higher value? Will this reduce the gain with the least impact on the tone?
when you say ''swap the 68k res with a 33k you mean the on that is parallel with the inductor right?

BR
Harris

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Post by Manfred »

Since the Q1 emitter resistor messes with the sweep, and its effect on signal chain, will it have any impact on the tonal characteristics of the pedal?
Could it be better to increase the input (68k) res with a higher value? Will this reduce the gain with the least impact on the tone?
when you say ''swap the 68k res with a 33k you mean the on that is parallel with the inductor right?
I meant the 68 kOhm resistor between the coupling capacitor and the base of Q1.
This resistor determines the input impedance and is partly responsible for the overall gain of the pedal.
Changing the 470 Ohm emitter resistor to 1 kOhm does not change the tonal character.
By replacing the 68 kOhm resistor with 33 kOhm, the input resistance of the pedal goes down to half the value,
the value of the coupling resistor at the input would then have to be increased to 22 nF.
Make a trial with the emitter resistor of 1 kOhm and keep the 68 kOhm.
See if the distortion of the output signal disappears and if the gain loss is much.

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Post by harrisxr650 »

Manfred wrote: 09 Sep 2021, 12:23 Make a trial with the emitter resistor of 1 kOhm and keep the 68 kOhm.
See if the distortion of the output signal disappears and if the gain loss is much.
Ok. Will dona test with the q1-emitter rea and post the results.

Thanks 🙏

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Post by harrisxr650 »

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 it 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?
should i consider the inductor is not well waxed and its micropohonic? could be the cause of the clipping-scratching?

I will hold a small basket untill i test it on a real amp and provide any additional info here whether the problem is solved or not.

BR
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Post by harrisxr650 »

Ok. for anyone else having the same problem.

Moving pot lug pin 1 to the ground side of the 10k resistor on the emitter of Q2 eliminated the problem without changing any component value.

Got a full working McCoy clone.

Thanks for the tips ;)
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Post by Manfred »

Thanks for the information, good to hear the wah is working now.
Crazy error. :scratch:
I suspect there was feedback via a voltage drop between potentimeter lug and ground caused by a ground current.

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Post by harrisxr650 »

Manfred wrote: 19 Sep 2021, 20:39 Thanks for the information, good to hear the wah is working now.
Crazy error. :scratch:
I suspect there was feedback via a voltage drop between potentimeter lug and ground caused by a ground current.
Indeed .
That made me go crazy for a week
I debugged it with the help of Rob Strand. He pointed me to do this since the circuit and voltages where on spot and there wasn't any error regarding components values or short circuit etc.

More over his explanation was the following

''- 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.

As a side effect it probably reduces RF interference and risk of oscillation''

So all credits to him
BR

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