pedals - DOD YJM - questions....

[1N914]

the DOD YJM pedal... i saw a schem on this site, and think it has clipping diodes, and was thinking if this pedal design would work with a SS amp,  so that it isnt being used as a voltage booster, more like just your ave. pedal.... basically i need a pedal in my setup to be a good soloing tone, and i built the joe heart drive (which rocks) but it seems more like a riffing pedal.

also any schematics on a slapback echo effect would be greatly appreciated!! maddogbarkley@hotmail.com

thanks alot!!

Mike

[1N914]

heres a link to the schematic...

http://www.diystompboxes.com/pedals/schems/yjm308.GIF

[petemoore]

That's a DIST+!
 Er very close to...
 I would socket the input cap....  .001uf is going to chop some 'thickness' off....Of course the OA gets socketted....as well as the diodes...
 This circuit is somewat flexible tonewise depending on these component choices.
 I have a box I finished a couple weeks ago that I've been using...a DIST+ [two ge diodes] and I 'think' it's a .047uf incap on there...JRC4558, I like this OA 'better' opinion than 741's, seems to run cleaner and lower noise...if you Want more dirt/noise, build it for a single OA chip, then try 741's or 5534's or whatever single OA's, FWIU the 741's [low-gradiness?]  is integral to the sound of the original DIST+'s.
 Looks like ying we decided he likes the 4558's?

[keko]

That's a DIST+!  Er very close to...

I once did two dist+ boards. One worked, one didn't

so Last night I decided to bring back to live the second one, and I fitted to be DOD's od 250, wich is what yngwi used...isn't it?

anyway, it sound waaaaay better than the dist+. Less gain, but more 'balanced' tone, smooth crunch (is this possible  :wink:  ?)

[Johan]

the dist+ also has a 10k volumepot, not 100k...it makes a significant difference...

Johan

[Mark Hammer]

1) The posted schematic which is linked to by 1N914 (did you ever used to play for that Toronto punk band The Diodes?) is incorrect.  The junction between the 100R resistor and the 22k resistor on the power should go to the V+ pin on the chip.  That is, there is a 100R resistor in series between the battery and *anywhere else* the battery connects to in the circuit.

2) The YGM 308 uses a pair of silicon diodes for clipping rather than the Ge diodes used by the Dist+.   These will clip a little differently when you look on a scope, but most importantly, they will be clipping less often and less of the signal because they have a higher threshold of clipping, and will also set a higher ceiling on maximum output level.  The same amount of "gain" is applied in the Dist+ and YGM 308, but it sounds like less because the different diodes are more tolerant of the same amount of gain applied to the input signal.  Because the output level is potentially higher, you can also use the pedal to overdrive the amp a little more which also contributes to the tone differently.  But of course that would depend on how you set the controls.  I'm confident there are many control-setting combinations that yield tone identical to the Dist+.

3) I'm not sure what the specific effect is, given the difference in op-amps, but the Vref bias current is radically different for the DOD and MXR pedals.  The pair of resistors that form the voltage divider to provide the V+/2 floating ground or reference voltage partly determine the amount of current in that bias voltage.  In the Dist+, the divider resistors are 1meg (!!) while in the YGM they are 22k.  Pretty big difference. If that ain't enough, the resistor along which this bias voltage has to travel to reach the non-inverting pin is also 1meg on the Dist+ but only 470k in the YGM 308.  It is easy to imagine the 741 and 4558 have different bias current needs, since they are different chips, but that is one helluva difference in what they are *allowed* to see.  Do not underestimate the importance of power-supply differences between these beasts in creating their respective sounds.  It's not all in the chips and diodes.

I am hoping one of the more technically apt types will be able to elaborate on the putative role of these bias current differences, and either set me straight or make it clearer.

[Phorhas]

The 22k Vref network look more like that of the DOD 250 (kinda like the D+'s soulmate, huh...)

but it had a 1M res. to the OA as well.