DOD 440 430k vs 470K

[lapsteelman]

I found a GGG DOD 440 board I had bought years ago and had forgotten about....I'm all done except I don't have a 430k Resistor for R12.  I've read that some units had 470k..

I can easily put 330k and 100k in series and get the proper resistance, but the board wouldn't look as neat...(OCD..I know)  or I can just drop in 470k.

For the folks who have played around with this circuit... Is it going to be big difference in the sound?

http://www.generalguitargadgets.com/pdf/ggg_ef440_sc.pdf

[Kipper4]

Sure you can, it's your build you can use what you want.
I'd think it will slightly increase the gain of the dry signal going to the output, so it won't be as pronounced quack effect.
You can always scale up R11 maybe try a 250k. To compensate for the 470k.
Alternately you can use parallel resistors to make up the 430k value. (2x860k)
It might be a little neater than series R on the board.
How often will you see it? It might just play on your mind every time you quack it.
The mind games begin.

[Mark Hammer]

The 430k feedback resistor sets the gain and Q of the filter.  I can't find it at the moment, but I've posted a mod for the DOD440 several times, that involves making that 430k path variable.  The mod was suggested by former DOD engineer David DiFrancesco, so I figure it has some substance.  I installed a 3-way toggle on mine  to add a bit more resistance, and a bit more than that, in addition to stock.  More than 100-120k additional resistance and it starts to oscillate.

So 470k should give you a nice emphatic filter sound.  NO need to futz around to mimic 430k.

[Kipper4]

So there's a nfb loop with a gain of ~2 and a positive feedback loop of ~2 at rest.
And the nfb loops sets the Q and gain right?
Although the positive feed back loop might be higher at rest, I guess it depends on if the vactrol LEDs are bright or dark at rest.
Hmmmm

[Mark Hammer]

They're dark-ish.  The tuning pot feeds the LEDs with a DC offset/bias voltage to set minimum brightness.

I learned this the hard way, by using a white LED for a homebrew optoisolator.  The forward voltage of the LED was high enough that I needed to goose it a bit with the tuning/Range pot, or else it would behave weirdly, coming on suddenly and extremely.  Swapping the white LED for a red one improved matters greatly.

[Kipper4]

Thanks Marks.
Those rectifiers can be tricky beasts.
Currently working on a Auto Wah with a +9v adaptation of the mutron iii envelope detector.
It's not playing ball too well, I suspect it's the slow 500ms turn off time of the vactrol I'm using. Nsl32.
I'm away right now on vacation. So theory is all I have to work with. No breadboard.
I'll be looking to resolve some issues when I'm on home soil.
I appreciate your input and knowledge.

[Blitz Krieg]

Currently working on a Auto Wah with a +9v adaptation of the mutron iii envelope detector.

have you looked at the Mini Q-tron?

[Blitz Krieg]

I can't find it at the moment, but I've posted a mod for the DOD440 several times,

http://www.diystompboxes.com/smfforum/index.php?topic=17057.msg98297#msg98297

http://www.diystompboxes.com/smfforum/index.php?topic=112323.msg1036299#msg1036299

http://www.diystompboxes.com/smfforum/index.php?topic=108747.msg992207#msg992207

[Kipper4]

Thanks Blitz. I can't remember ever trying it out though.
Filed to favourites for now.