fuzz pedal mod

[Greg_L]

Disclaimer...I do not f@#% with guitar pedals. Ever. Don't use them, don't work on them, don't like them. My friends do though, unfortunately, so I get asked about them. I still consider myself a novice though so I'm not sure what to say sometimes.

For example...my buddy came across some mod for one of his pedals and he's asking me what it does. Example below...



Looks to me like it's lifting one leg of the clipping diodes via switch. Is this correct?

[Helmholtz]

Does the mod work as intended?

Picture is not very clear. Is this an on-off-on switch?

Seems he wants to switch between 3 Si diodes and 2 LEDs for different clipping.

[Greg_L]

Does the mod work as intended?

Picture is not very clear. Is this an on-off-on switch?

Seems he wants to switch between 3 Si diodes and 2 LEDs for different clipping.

Right. As far as I know it is an on-off-on switch and the intent is to switch between the diodes and LEDs. I don't have much info besides the pics and that little snippet of a schematic. The mod removes three of the diodes facing the same way and puts them on one leg of a switch. So you can have standard operation, three diodes removed, or LEDs instead of those three diodes..

Does the mod work as intended? I'm not sure but I presume it does otherwise my buddy wouldn't be asking me why it works. My only answer is that you're removing half of the clipping string with the switch for a different "flavor" of clipping. I don't know if that's correct though.

[Helmholtz]

So you can have standard operation, three diodes removed, or LEDs instead of those three diodes..

Yes, that's how I see it.
So symmetrical clipping and only odd harmonics with original wiring and different degrees of asymmetrical clipping with even harmonics in the other 2 positions.

[Greg_L]

Yes, that's how I see it.
So symmetrical clipping and only odd harmonics with original wiring and different degrees of asymmetrical clipping with even harmonics in the other 2 positions.

That's the way I see it too. Thanks.

[Helmholtz]

I would feed a say 10mV sine signal and scope the output of the opamp.

[Greg_L]

I would feed a say 10mV sine signal and scope the output of the opamp.

Good idea. If I ever get the pedal into my own hands I certainly will.

[Mick Bailey]

Switching the back-to-back diodes in clipping circuits is quite common and gives a broader range of characteristics. The higher the total forward voltage of the diode string, the higher the clean headroom before clipping occurs. If the forward voltage of the string is asymmetric, then clipping occurs on one half of the waveform earlier than the other. The asymmetry can be had from an imbalance in the number of diodes of the same type, or by using diodes with a different forward voltage drop - Ge+Si or Si+LED are common. Depending what amp I'm running, I like the sound of asymmetric distortion, though it depends on the level of drive and guitar's volume setting. I go for a slight asymmetry - just one diode difference with Si. There's a sweet-spot in the settings of the pedal though. Too much asymmetry and it sounds strange on the lower strings - more like a speaker fault.

[Greg_L]

Switching the back-to-back diodes in clipping circuits is quite common and gives a broader range of characteristics. The higher the total forward voltage of the diode string, the higher the clean headroom before clipping occurs. If the forward voltage of the string is asymmetric, then clipping occurs on one half of the waveform earlier than the other. The asymmetry can be had from an imbalance in the number of diodes of the same type, or by using diodes with a different forward voltage drop - Ge+Si or Si+LED are common. Depending what amp I'm running, I like the sound of asymmetric distortion, though it depends on the level of drive and guitar's volume setting. I go for a slight asymmetry - just one diode difference with Si. There's a sweet-spot in the settings of the pedal though. Too much asymmetry and it sounds strange on the lower strings - more like a speaker fault.

That explains it nicely, thank you.

[Krystal]

Your friend wants the JHS pumpkin patch mod done to his Electro Harmonix Op amp Big Muff. It should be pretty easily achieved.
I think this should help : https://www.freestompboxes.org/viewt...umpkin#p295626
Scroll down a bit for a schematic.

[Greg_L]

Your friend wants the JHS pumpkin patch mod done to his Electro Harmonix Op amp Big Muff. It should be pretty easily achieved.
I think this should help : https://www.freestompboxes.org/viewt...umpkin#p295626
Scroll down a bit for a schematic.

Interesting, thanks!

[Helmholtz]

The other thread shows the same picture.

[Greg_L]

The other thread shows the same picture.

Yeah I bet he got the pics from the same place and sent them to me. I already knew they weren't his pics.