"Farting" when using LED's in Distortion ...

[MartyMart]

.... anyone else have this problem ( no not THAT kind of fart ! )
Just playing with a "DS-1" type of circuit and when run at minimum gain
and playing a little "backed off" there isnt really "clean" tone just a kind
of splatty "fart" to the distortion !
Turn up a bit, or dial the gain up and all is fine.
My DS-1 with LED's ( feedback loop ) also does the same thing too .... grrrr 

Is this just the product of using LED's as clipping diodes then ?
Other than that I like the "tone" from using them .... and the volume increase too !

Marty.

[GreenEye]

have you tried it with humbuckers versus single coils, or just plain different guitars?  point being, sometimes one of my axes likes a certain clipping diode better than another.

[NoFi]

I noticed the same kind of thing on turbo rats, nice when pushed, crackly when backed of.. I guess leds just FART when used for overdrives type of sounds...
Very sad because i like their tone too.

[vanhansen]

No farting problems with mine when backed off.  The LEDs I used are the little round red ones that came in the Radio Shack assortment pack.  They light up as you play, which is what the seeing eye mod is really.  They sound great.  I played it through a Mission Amps 18 watter last weekend and it sounded wonderful.  The farting could be dependent on the forward voltage of the LED.

[Toney]

Yes, it certainly sounds like the voltage threshold for your leds is not being reached with the guitar's volume backed off.
A little boost in front?

[Connoisseur of Distortion]

my guess... place a resistor (1 Meg to start) in parallel with the LEDs. gradually reduce until it behaves properly...

i think this will help, but you might wait on input from a guru...

[MartyMart]

Thanks for the replies .... forward voltage is what I expected, but here's the thing :

DS-1 :
This is using a pair of 3mm "ordinary" LED's ( taken from Boss status indicators ) and are used
just like the "seeing eye" mod ..... still "farty" at low gain !

The circuit that I'm playing with on the breadboard is similar, but a bit lower gain, it's a kind
of "full range" boost ( no colouration ) with a drive option and a twisted BMP tone stack.
I'm using a dual 100k pot and adding in a clean path like the sparkle drive.
This has "standard" 3mm yellow LED's which I think are slightly larger forward voltage
compared to red ... ?? ( could be wrong )
I'll try the parallel resistor idea and perhaps make it less "symetrical" maybe 1 red LED and 2 X 1N4148
or something ...
Those "just on the edge of breakup" tones are the hardest to get just right !
Getting "just on the edge of Fart" tones isn't the idea

Marty.

[WGTP]

IMHO the transistion between clean and distortion is where the SS stuff fails the most vs. tubes.  Might try reducing the bass thru the clipping circuit.  With the LED's having a higher clipping threshold than the SI's that might effect the interaction with the OP AMP.  I think this is the area that diodes and op amps need the most improvement in.  Might try a MOSFET instead.