OD trimmer on the back wall

[angelodp]

I know I saw some pics on this, but I cannot find them again. I am interested in having more direct access to the OD trim pot. Any issues with setting this up on the back wall near the loop in/out.

ange

[briane]

I've done it with no problem. Though in those cases it was under 2 inches away from where I would have put the trimmer.

I now put a pot on the top of the chassy myself (about 1/2 inch away from where trimmer would have gone). No dummies turning the knob to see what it does late at night. I can just imagine a tech call there 'the od does not work anymore and I dont know why'. Anyways if its just for yourself no worries there.

If you know where it is you can reach in and tweak it.

[angelodp]

Thanks, I know what you mean. I don't suspect I will have that issue as I play in mostly. Just wondering if the routing of wires is a cause for concern. I have a couple of 100K bias pots for a Fender i could use or go with a smaller unit like Moss has suggested on the Blue Monkey. Might you have a pic or two of your install handy.

best ange

[heisthl]

I've done it with no problem. Though in those cases it was under 2 inches away from where I would have put the trimmer.

I now put a pot on the top of the chassy myself (about 1/2 inch away from where trimmer would have gone). No dummies turning the knob to see what it does late at night. I can just imagine a tech call there 'the od does not work anymore and I dont know why'. Anyways if its just for yourself no worries there.

If you know where it is you can reach in and tweak it.

Assuming non-HRM, use a 50k pot on the front panel with a 24k feeder and a 24k ground lift. There is no problem with distance (although you should shield the wiper to V2A Rg lead) and the offset resistors insure the OD works at all settings.

[ChrisM]

I remember Moss (Brownote, I think that's his name) posted a pic showing how he posted his OD trimmer on the chassis back panel.

His trimmer was more like an actually trim pot rather than a normal pot though. It was just a tiny thread sticking out the back that could be adjusted with a small flat head screw driver. Wouldn't mind knowing where to get a pot like that.

[gilgalad101]

I've done it with no problem. Though in those cases it was under 2 inches away from where I would have put the trimmer.

I now put a pot on the top of the chassy myself (about 1/2 inch away from where trimmer would have gone). No dummies turning the knob to see what it does late at night. I can just imagine a tech call there 'the od does not work anymore and I dont know why'. Anyways if its just for yourself no worries there.

If you know where it is you can reach in and tweak it.

Assuming non-HRM, use a 50k pot on the front panel with a 24k feeder and a 24k ground lift. There is no problem with distance (although you should shield the wiper to V2A Rg lead) and the offset resistors insure the OD works at all settings.

What values would you suggest for an HRM or, to be more specific, a Bluesmaster?

[heisthl]

I haven't kept up with the current state of the Bluesmaster, the last one I built was using a 100k trimpot so the values of 24k/50k/24k should work fine. HRM woudl require different values but basically you figure out the usable trimpot range and then size a panel control pot and support resistors (to keep it in the range) accordingly.

[angelodp]

h, are you placing the trimmer on the front panel in your amps??

a

[heisthl]

Only by customer request

[angelodp]

Might this work out then, or is it preferable to put the resistors on the board?

ange

[IMG:498:1039]http://i260.photobucket.com/albums/ii9/ ... -mod-1.jpg[/img]

[bluesfendermanblues]

You might as well ad a treble bleed pot - a 500ka pot with a 1nf cap - I have done this on my OTS 50w, which had to empty holes on the back. One for the OD pot, one for the treble bleed pot paralleled on the OD master pot.

[dogears]

IMO, 24k-50k pot-24k is not the right padding.

I would do 18k-50k audio taper - 33k. The 18k would be the ground tail.

This puts 25k at the noon position.

24K tail is fine, but the pot may live in the off position, and you have no ability to set below 24k. fwiw, real Dumbles have been seen with lesser settings. You run the input gain hot and trimmer low.

[dogears]

Not a bad idea. I'd use a 1 Meg Audio pot though. Even full on, there is still a bleed effect, even with a 1M! Plus, the noon setting is about 150K. This is the max bleed I would ever want. I think a 47K tail may not be a bad idea as well.

You might as well ad a treble bleed pot - a 500ka pot with a 1nf cap - I have done this on my OTS 50w, which had to empty holes on the back. One for the OD pot, one for the treble bleed pot paralleled on the OD master pot.

[angelodp]

Ok nice options to consider. what about the position of the 24k's or does it mater at all? Any chance you could post a shot of how you implemented the
treble bleed pot?? Dogears, do any real dumbles have an OD trimmer that is accessible at either the front or rear wall??

ange

[ToneMerc]

His trimmer was more like an actually trim pot rather than a normal pot though. It was just a tiny thread sticking out the back that could be adjusted with a small flat head screw driver. Wouldn't mind knowing where to get a pot like that.

Chris, I have a build in progress using that style of trimpot (RV6N type long shaft)

NTE SU1041S28

http://www.brownnote.net/forum/viewtopic.php?t=1458