Guv'nor tonestack problem

[Lars F]

Hi Forum!

Have a Guv'nor build where the tonestack isn't working. The mid potentiometer is cutting mid frequencies when turned clockwise. The bass and treble pot's act as expected.
Checked all the component values an reflowed the joints, but still nothing. Would have changed the pot, but ran out. Any ideas?
Schematic --> https://www.dropbox.com/s/z9c1dtu7fv6o6dk/aion-equinox-guvnor-documentation.pdf?dl=1

Thanks!

Regards,

Lars

[Plexi]

Hi Lars!
Do you mean, that a fully clockwise, its scooped?
Pot checked? Limiter 100R resistor?
http://www.freeinfosociety.com/electronics/schematics/audio/pictures/marshallguvnor.gif

[Lars F]

Hi Plexi!

I think that's what I mean. When the pot is turned fully clockwise and you expect a boost, instead you get a cut in the mid. A scooped sound. Resistor is ok, haven't taken the pot out to check. It is a small 9mm pot and a double sided PCB, so am afraid to damage it. Have ordered spares and will try to change the pot once the spare pot's arrive.

Regards,

Lars

[anotherjim]

Is it a PCB error I wonder? From the schematic the pot wiper should go to ground fully clockwise because pot lug 3 is ground. Is that so?
It sounds like it works, but backwards.

[Lars F]

The PCB should be good - others have build it without problems.
Yes, the wiper goes to ground when the pot is fully clockwise. The pot do seem to be working.
I'm not really sure it works backwards as it seem to cut most in the last 25% of the pot rotation and not add much when turned counter clockwise. Have no original to compare with though..

Thanks!

Regards,

Lars

[Lars F]

Checked again and it does boost mid all the way counter clockwise. What am I not seeing? Surely it couldn't be a rev log pot marked as a lin pot?

Regards,

Lars

[Lars F]

Had a reply from Kevin @ Aion Electronics and he says it might be a PCB layout error and advised to just reverse the outer pins on the pot. Hopefully that will solve the issue.

Regards,

Lars

[deadastronaut]

i sometimes use log pots backwards....(rather than buying reverse log..)

they do work quite nicely.

but confuse the user..

[Lars F]

Rewired the pot and all is fine. So beware if you have a current revision Equinox/Guv'nor PCB from Aion Electronics.
According to Kevin the issue will be fixed in the next revision.

Regards,

Lars

[Lars F]

Here it is all boxed up..

Regards,

Lars

[anotherjim]

So was the schematic wrong also, that presumably led to the pcb error?

[Lars F]

So was the schematic wrong also, that presumably led to the pcb error?

I think that was it. Don't have a schematic from Marshall, so can only refer to the one included in the build documentation, but that seems to correspond to the PCB.

It was nice to get a fast and honest reply from Kevin @ Aion. It's an easy fix, so no big deal..

It's a pretty cool sound - reminds me of my old JCM800 half stack. Been playing single note riffs all night!

Regards,

Lars

[Haradax]

Yes, the schematic is wrong. I had the same issue with mids pot. I've reported this to Aion and Kevin admitted the mistake.
Interestingly, two years have passed and no one reports it, and then two guys in the same week.

I solved the problem by soldering only middle leg of the pot to the PCB.
Other two legs carefully bend, and connect them by two short wires to each others place (leg-1 to pad-3, and leg-3 to pad-1)

I've also noticed that this project as many other on line schematics have 10k log pot for treble control, but original have 10k linear pot. I saw it in one original unit, as in many online pictures. Never saw a log. pot in that place.

I must say that this is my favorite dirt pedal ever.  As Lars F says iz sounds like JCM800.
I've tried many "marshall in a box" pedal, but none of them isn't close to DriveMaster / Guv'n'or.

[Lars F]

The documentation from Aion has the treble pot as linear? Both schematic and BOM.

Have tried a few opamps and the LM833 is my favorite so far.

Regards,

Lars