Fortin Zuul  [traced]

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plush
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Post by plush »

Manfred wrote:IMO to cause confusion or maybe to make a unpolarized capacitor in the case of two electrolytes capacitors or tantals
Here the equivalent circuit:
MuzzleDetail.jpg
Or maybe even to achieve some visuals, who knows, some people prefer pretty pcbs that are somewhat symmetrical )

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Post by modman »

So sorry this thread got locked by accident while moving it. My bad.
Please, support freestompboxes.org on Patreon for just 1 pcb per year! Or donate directly through PayPal

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plush
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Post by plush »

guiddruid wrote:Build docs uploaded now; https://www.pedalpcb.com/docs/PedalPCB-Muzzle.pdf
Also OA3 needs + and - to be swapped.

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Post by bugg »

plush wrote:
guiddruid wrote:Build docs uploaded now; https://www.pedalpcb.com/docs/PedalPCB-Muzzle.pdf
Also OA3 needs + and - to be swapped.
Just to clarify... the pin numbers were correct, the graphical symbol just needed to be updated. It's corrected now.

The C7 / R7 / C8 junction really confuses the hell out of me... They aren't polarized caps so polarity isn't the issue.
Sometimes in mass production it's more economical to use two of the same part rather than two different parts. However, it's odd that the resistor is in the middle of the network... :hmmm:

Would there be any benefit to reducing the amount of AC voltage drop across each of the individual capacitors?

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Post by guiddruid »

C7/R7/C8 - 99% this is just a cut & paste mistake when adding an emitter-follower input buffer to the Marshall circuit J0K3RX linked to. The resistor between the two capacitors is functionally equivalent to what Manfred drew - order doesn't make any difference. Other than polarised caps (not the case here, and a bit of a hacky circuit anyway), the only other reason I can think of to do this (again, not in this context) would be to protect against short-circuit failures. So, I'd suggest 99% chance it's a cut & paste mistake by Fortin. 1% chance he incorrectly thought this did something useful.

I suspect the differences in some of the capacitor values between the Marshall & PedalPCB schematics may be down to measurement accuracy (bugg, does this seem likely?), though the differences look too small to make any audible difference. Adding an isolation transformer to the key input would be a nice improvement, along with a buffered key pass-through.

The Marshall circuit likely started from the app note here, but is in no way a simple copy; http://www.thatcorp.com/datashts/dn100.pdf

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Post by bmxguitarsbmx »

BTW, the Marshall jcm800kk schematic is not 100% of the amp I had in my shop. Which, usually is to be expected.

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Post by plush »

guiddruid wrote: though the differences look too small to make any audible difference.
Afaik, VCA's have pretty low input impedance, lowering the cap value will affect the signal.
Can't tell if their RMS detector is the same, though. Will have to test with 4301-s. Sad thing they are discontinued.
Adding an isolation transformer to the key input would be a nice improvement, along with a buffered key pass-through.
Welp, the key pass-through is already buffered. And there are no affordable signal transformers with wide dynamic range. Your idea is good though.

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Post by psychodave »

I have the Zuul pedal and mine has issues. While using the key input in the loop, when I turn the pedal off it causes a really bad buzz. The way I was able to correct the issue was to remove the ground on the key input cable. Clearly there is an issue with it. Any thoughts on how to fix it?

Also, the pedal adds quite a bit of drive when turning it on... it’s far from transparent. I’m not sure if this is due to the issue above or not. Just figured I’d mention it.

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Post by guiddruid »

Try turning the gate control to minimum & playing softly with the pedal on - I suspect you'll hear the buzz then too, which is caused by a ground loop.
Because the key input is not isolated, you're connecting the ground at very different points in your signal chain together, which can cause the problem you've found. I used an isolated buffer to drive the key input to fix this.

I have not noticed a big difference in the sound between on vs off, though it is just noticeable. May depend what you've got connected.

Plush - if you just isolated the key input, you could probably get away without an amazing hifi transformer, although you may not be able to buffer a key output very easily - http://www.hexeguitar.com/diy/gear/buffsplit

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plush
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Post by plush »

guiddruid wrote: Plush - if you just isolated the key input, you could probably get away without an amazing hifi transformer, although you may not be able to buffer a key output very easily - http://www.hexeguitar.com/diy/gear/buffsplit
Sorry, I don't get what you ary trying to tell me.

If you simply throw in some low quality transformer, it will have quite noticeable corner frequencies, leading to poor performance, compared to non-isolated key input.

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Post by caspercody »

I built the Zuul pedal from Pedal PCB, and you DO NOT connect the key to ground...

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Post by plush »

caspercody wrote:I built the Zuul pedal from Pedal PCB, and you DO NOT connect the key to ground...
This :thumbsup

There's really no need for key's ground connection, if the rest of the circuit is already referenced.

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Post by guiddruid »

Not connecting the ground makes sense. The key input on the Zuul does have a ground connection though.

Something like this might be a better approach to producing a buffered key pass-through; https://www.ti.com/lit/an/sloa143/sloa143.pdf
Then again, perhaps just making the key input really high impedance & not connecting the grounds would be enough?

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Post by caspercody »

Here is the reply from PedalPCB when I built mine:

The three pads near the bottom are for setting the threshold range. You can either use a mini slide switch or a triple pin header with a jumper.
https://www.taydaelectronics.com/electr ... 24vdc.html

The two pads near pin 1 of the THAT are for the Key jack.
You'll need a switching 1/4" jack for that. The pad on the left goes to the Tip lug, the pad on the right goes to the Switched Tip lug. (not to be confused with the Sleeve or Ring)
https://www.taydaelectronics.com/6-35mm ... -jack.html

All other wiring is common to the other projects.

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Post by psychodave »

Here is a video I made of the hum. The hum was in the ungated signal as well. Once I removed the ground on the key input, the hum was gone.

https://youtu.be/RBKB_NxgLQI

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Post by equinox »

Dave

Try it with a different amp (other than the Cameron) for shits and giggles and see if it follows the amp or not.

Eq

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Post by dlazzarini »

I built the same pedal from pedal pcb. I received an updated board that did have a ground pad for the key input. I did use it but now I’m wondering. The pedal is awesome and works fantastic but one minor little thing I noticed is that when I’m not playing and the gate is shut, if I lightly rake over the treble strings I can very faintly hear it bleed through to the amp. No unwanted hiss or hum, just the strings faintly. When I play the gate kicks open and works as it’s supposed. Could this slight bleed be ground related?

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Post by guiddruid »

The "gate" is not on/off. As the level of the key signal reduces, the input->output gain reduces more quickly. For example, key halves in amplitude results in gain dropping by 4. (not actual numbers, just for example).

If you turn the control knob up you should hear the "bleed through" get quieter & eventually disappear.

I don't think the ground will make any difference - it'll either cause a nasty hum (when the pedal is bypassed) or it won't.

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Post by Silverhair »

where do you get the THAT4301 IC?, I'm located in Mexico, but I buy mostly from the US

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Post by caspercody »

I bought mine from PedelPCB

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