G.G.G. GRO Null Carrier Mod?

[soupbone]

I was looking at some of Dano's(beavisaudio) pedal builds,and saw his Dan A. Green Ringer build.I saw a knob on the top,and he said it was for the,"Null Carrier Mod".I have a g.g.g. GRO that I built a couple of years ago.I went to g.g.g.'s page,and there was a schematic from J.C. Mallet,I'm just confused on how this mod is implemented?I think it said it uses a 22k linear pot?If anybody has built one,or knows about it,I need some help!Grazie!-s.b.

[Mark Hammer]

There is no carrier null on the GR because there is no oscillator to serve as carrier.  But that's really just a matter of what it's called.  The mod itself works well.

Producing a strong octave needs the two outputs of Q2 to be as equal as possible.  JC's mod is intended to optimize that matching by inserting a series resistance with one of the outputs.  Probably best to use a trimpot, rather than fixed resistor.   Selecting diodes with the same forward voltage will help a lot.

[soupbone]

There is no carrier null on the GR because there is no oscillator to serve as carrier.  But that's really just a matter of what it's called.  The mod itself works well.

Producing a strong octave needs the two outputs of Q2 to be as equal as possible.  JC's mod is intended to optimize that matching by inserting a series resistance with one of the outputs.  Probably best to use a trimpot, rather than fixed resistor.   Selecting diodes with the same forward voltage will help a lot.

If you were going to tweak it on the fly Mark,wouldn't you need the 22k pot?I have no idea where to get a 22k linear pot.Kind of an odd value.Thanks Mark!

[Mark Hammer]

Well, it's just a variable resistance.  You can use whatever you want, as long as it has a suitable range of possible resistances, and has enough dialability for the circumstance.  I wouldn't want to use a 1M trimpot, given the likelihood that the needed level-matching resistance is going to be <10k.  But a 10k or 20k or 22k or 25k trimpot will probably do the task nicely.  And, as suggested, picking your diodes for relatively matched forward voltage will remove some of the matching burden from the trimpot.  JC's mod is essentially to pick up the slack arising from uneven values of the 10k emitter and collector resistances on Q2, uneven diode Vf, and unequal 68k resistors.  You could probably match all of those things, but it is much easier to just use whatever is in your parts drawer, and tweak a trimpot until you nail it.

[soupbone]

Well, it's just a variable resistance.  You can use whatever you want, as long as it has a suitable range of possible resistances, and has enough dialability for the circumstance.  I wouldn't want to use a 1M trimpot, given the likelihood that the needed level-matching resistance is going to be <10k.  But a 10k or 20k or 22k or 25k trimpot will probably do the task nicely.  And, as suggested, picking your diodes for relatively matched forward voltage will remove some of the matching burden from the trimpot.  JC's mod is essentially to pick up the slack arising from uneven values of the 10k emitter and collector resistances on Q2, uneven diode Vf, and unequal 68k resistors.  You could probably match all of those things, but it is much easier to just use whatever is in your parts drawer, and tweak a trimpot until you nail it.

Ok,I get it now.My only other question is there a component that desoldering,and then putting the trimpot in it's place?Thanks Mark!

[Mark Hammer]

I think there may be a few words missing from your post, but my sense is that you're wondering if there is a place on the board where you could install a trimpot, without having to design a completely new layout.

nah, can't see it.  Which is why you may want to consider the route of using matched 10k, 68k resistors and matched diodes.  If perfing or veroing, then a trimpot is easier, and more precise.  If you're trying to get it all onto the stock PCB, matching key components may be the easier, or more straightforward alternative.

Just know that whatever way you achieve optimization, this is unlikely to end up as any sort of where-have-you-been-all-my-life effect.  It's fun and yields its fair share of silly moments, to be sure, but not especially inspiring.  So long as your expectations are modest, you'll do alright.

[soupbone]

I think there may be a few words missing from your post, but my sense is that you're wondering if there is a place on the board where you could install a trimpot, without having to design a completely new layout.

nah, can't see it.  Which is why you may want to consider the route of using matched 10k, 68k resistors and matched diodes.  If perfing or veroing, then a trimpot is easier, and more precise.  If you're trying to get it all onto the stock PCB, matching key components may be the easier, or more straightforward alternative.

Just know that whatever way you achieve optimization, this is unlikely to end up as any sort of where-have-you-been-all-my-life effect.  It's fun and yields its fair share of silly moments, to be sure, but not especially inspiring.  So long as your expectations are modest, you'll do alright.

Excellent analysis as always!Thanks Mark! 

[Buzz]

Just know that whatever way you achieve optimization, this is unlikely to end up as any sort of where-have-you-been-all-my-life effect.  It's fun and yields its fair share of silly moments, to be sure, but not especially inspiring.  So long as your expectations are modest, you'll do alright.

I spent a while on the green ringer as an early project. I matched the diodes ( as best I could ) the resistors and even the capacitors. I also used a 20k pot as per the null mod.

It all worked. Mark's quote pretty much sums up the result.

Never really found a use for it, but I learned alot on the way.