OD trimmer on the back wall

angelodp · Post by **angelodp** » Sun Aug 16, 2009 4:55 pm

On the Glaswerks SODSII they use a pot w/ knob on the rear for the OD Trim. I assume that this is done by ear as I do not see any notches or markings for specific resistance levels. Dogears, you have one of these amps , I believe. Do you set this on the fly.

ange

dogears · Post by **dogears** » Sun Aug 16, 2009 8:42 pm

Nope.... I opened the amp and adjusted for my benchmark settings. I measured then marked the back with a silver paint sharpie. I set to my mark and then tweak to taste if need be.

angelodp wrote:On the Glaswerks SODSII they use a pot w/ knob on the rear for the OD Trim. I assume that this is done by ear as I do not see any notches or markings for specific resistance levels. Dogears, you have one of these amps , I believe. Do you set this on the fly.

ange

butwhatif · Post by **butwhatif** » Sun Aug 16, 2009 9:10 pm

Fww, to me the trimmer setting changes the sound in a big way. If you are counting on a certain sound to be there when u plug in, it can be difficult to get it back unless u r paying attention to the exact value of the trim w a meter. I prefer going in and adjusting for a sweet spot, and then leaving it alone.

angelodp · Post by **angelodp** » Sun Aug 16, 2009 9:57 pm

I should have known that you ( dogears ) would be more precise about things. Silver sharpie it is. I know I am fanatic about seeing gut shots, but any chance you could show us how that was implemented. Did you use a typical CTS 50k pot or something else.
I concur that the sweet spot is something worth noting as a specific value. But since so many of us switch around on guitars I imagine that the sweet spot alters with say a Strat to an HB guitar.

butwhatif · Post by **butwhatif** » Sun Aug 16, 2009 10:21 pm

My 2 cents---i just think that the trim setting alters the character of the od a lot. Cool, hot, fizzy, muddy, thin, classic, singin, balanced, all avail by twisting the trimmer- It took me awhile to find the spot i like in my main amp. If it works for someone, cool, but i like guitars to sound different.

Structo · Post by **Structo** » Mon Aug 17, 2009 12:27 am

Can someone explain why the trimmer needs padding?

I don't understand the difference between having a 100K trimmer on the board to having a 100K pot on the back or front panel as long as you shield the sensitive leads. (grid?)

Also, if you used a higher value pot (<100K) wouldn't that make it much touchier to adjust?

heisthl · Post by **heisthl** » Mon Aug 17, 2009 12:36 am

Structo wrote:Can someone explain why the trimmer needs padding?

I don't understand the difference between having a 100K trimmer on the board to having a 100K pot on the back or front panel as long as you shield the sensitive leads. (grid?)

Also, if you used a higher value pot (<100K) wouldn't that make it much touchier to adjust?

The idea is to have the panel mounted pot always be in the usable range of adjustment. No need to have it below 18k or above 68k where either you would have no sound or way too much gain.

Structo · Post by **Structo** » Mon Aug 17, 2009 12:45 am

Ah, so it keeps it more in the happy spot.

Thanks, Henry.

angelodp · Post by **angelodp** » Mon Aug 17, 2009 3:35 am

I assume that linear taper is correct here. Also, the pot can be various sizes as long as its the 50k. If I understand correctly, there is only signal on this pot, no high voltage.

ange

Structo · Post by **Structo** » Mon Aug 17, 2009 5:29 am

I don't think trimmers are tapered so it is probably linear.

No hot juice there, it's feeding the grid.

angelodp · Post by **angelodp** » Mon Aug 17, 2009 5:39 am

Thanks Tom

bluesfendermanblues · Post by **bluesfendermanblues** » Mon Aug 17, 2009 6:16 am

heisthl wrote:
Structo wrote:Can someone explain why the trimmer needs padding?

I don't understand the difference between having a 100K trimmer on the board to having a 100K pot on the back or front panel as long as you shield the sensitive leads. (grid?)

Also, if you used a higher value pot (<100K) wouldn't that make it much touchier to adjust?
The idea is to have the panel mounted pot always be in the usable range of adjustment. No need to have it below 18k or above 68k where either you would have no sound or way too much gain.

FWIW my amp (100k, classic stack) sounds great with the trimmer at 12k. (Setup is Strat, vol at 2 o'clock - all other controls at 12 o'clock and master to taste.)

angelodp · Post by **angelodp** » Tue Aug 18, 2009 3:08 pm

Scott, why use ( you suggest ) the audio taper pot and not linear on the trimmer.

ange

dogears · Post by **dogears** » Tue Aug 18, 2009 4:17 pm

My concern is putting 25K at noon. The linear pots will be more touchy and there is more margin of setting error. I wanted fine resolution at my preferred setting. In a fixed internal trimmer, it does nto matter since it is fixed and not easily changed. With an external, the pot can be easily twisted and I wanted noonish to be where I set it. A millimeter one way or another will not matter as much with the audio pot.

angelodp wrote:Scott, why use ( you suggest ) the audio taper pot and not linear on the trimmer.

ange

dogears · Post by **dogears** » Tue Aug 18, 2009 5:43 pm

Doh.... Thanks to Gary for pinting out the obvious!

Use a 50K linear fed by a 270K resistor! I feel dumb... LOL

Tube Amp Archive

OD trimmer on the back wall

Glaswerks

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