Value of drive Pot

[telekingdom]

So, I've been tweaking the first (non HRM) OD section of my Redplate Cosmic Dust towards the fat, single note honk of Dumble #183.

I first tried a 250K 'drive' pot instead of the Redplates stock 100K (250K is stock for the volume pot) and it did get me closer to where I want to go...but maybe too much.

After some searching I see I have a NOS Clarostat 200K pot...can't think of a good reason not to try it.

After putting the 250K pot in, I also added the 180K pad resistor in front of the volume pot and oddly now have a B and E string that actually breaks up some with hardly any sustain, which is not cool. It doesn't seem like the pot value would cause this, what am I missing? Any thoughts?

I did lower the snubber caps value to 94pf from the stock 270pf...

[davescustom]

Simplifying things with Little blabla.. Higher the value of drive pot more overdrive you have.. Lowering pot value = less overdrive. Tonal differencies.. You have to try and see what you like.

Any sound sample of of This "breakup"?

The snubber change... Maybe too much..

[Charlie Wilson]

Hello, I asked the question awhile back about 250k for a drive pot. What I found was that the higher you go with the value, the more gain you get but it also shifts were the amp wants to distort the most to lower frequencies. I guess this means the higher frequencies are attenuated by the higher value resistance and don't hit the overdrive circuit as hard. I HATE the sound of distorted midrange and bass with a clean treble sound sitting on top of it. In my Low Plate Classic what I really wanted was a more compressed(singing) sounding treble and a tighter bass, so I went back to the 100k value.
CW

[ToneMerc]

So, I've been tweaking the first (non HRM) OD section of my Redplate Cosmic Dust towards the fat, single note honk of Dumble #183.

I first tried a 250K 'drive' pot instead of the Redplates stock 100K (250K is stock for the volume pot) and it did get me closer to where I want to go...but maybe too much.

After some searching I see I have a NOS Clarostat 200K pot...can't think of a good reason not to try it.

After putting the 250K pot in, I also added the 180K pad resistor in front of the volume pot and oddly now have a B and E string that actually breaks up some with hardly any sustain, which is not cool. It doesn't seem like the pot value would cause this, what am I missing? Any thoughts?

I did lower the snubber caps value to 94pf from the stock 270pf...

A couple of times I have used 250k pots that are 15-20% lower in value and and for my tastes depending upon he circuit I like doing that. Nevertheless, I would not changed the resistor or lowered the snubbers while at the same time altering the drive pot value.

TM

[Charlie Wilson]

Hello, or maybe a 100k pot that measures high. It seems like even a few K one way or the other makes a sonic difference in the overdrive circuit with the potentiometer and series resistor values.
CW

[ToneMerc]

Hello, or maybe a 100k pot that measures high. It seems like even a few K one way or the other makes a sonic difference in the overdrive circuit with the potentiometer and series resistor values.
CW

CW, that's exactly why I feel every out of tolerance value can be useful.

TM

[telekingdom]

I’ll give the 200K a go and see what it sounds like. I do understand the higher value = more gain, just thought it weird it changed the top end so much; though that might be the snubbers, which would make more sense.

I don’t have a clip, guess I could make one. But I would use the analogy of trying to stuff 10lbs of sh!t in a 5 lb bag. It sounds as though the B and E strings are choking on too much harmonic content.
The amp has glorious harmonic feedback, even at ultra low volumes.

Thank you all for the feedback.

[Charlie Wilson]

Hello, maybe try clipping some parallel resistors across the drive pot and series resistors to get a feel for how much a few k one way or the other will change the sound. I think you will be surprised.
CW

[telekingdom]

Thanks CW, that of course makes great sense.

I’ve settled on a drive pot that measures 212K and that sounds great. Very fat and dynamic with a bottom end that is still very workable with tons of gain on tap (I can still easily dial in smooth and buzzless OD).

I’m going to tinker with the series resistor…go in the direction of the 150K amps and see how that sounds. Maybe put in a pot to try many values.

I need to change the snubbers to the correct cermaic disc types. I had some NOS phillips film Polys that were conveniently on hand, but probably the wrong choice tone wise. Maybe the cause of the weird high end artifacts?

[Charlie Wilson]

Hello, are your snubbers still 94pf? I would like to add that Henry is a very friendly helpful guy and since he built your amp maybe shoot him an email.
CW

[telekingdom]

Yes, still 94pf.
Henry is a great guy, but I think I wore him out with questions regarding a switching schem and I best leave him alone. ; )

[Charlie Wilson]

Yeah, I get it. I have probably wore out a few people with all of my questions. You may want to try the stock values for the snubbers, I assume 270pf. That may clean up the high end a bit. I am curious though, why did you lower them?
CW

[telekingdom]

Hi CW

I lowered the snubbers and changed the rest of the values for a straight clone of #183 in Drive 1.

I am curious though, why did you lower them?
CW

[Charlie Wilson]

Hello, those snubbers are there to control oscillations and smooth the high end. I know #183 has rather low value snubbers and some people don't have them at all but you may want to try the original 270pf again and see if that gets rid of the high end artifacts. You may also want to try some different tubes in the OD slot.
CW

[Structo]

Yes, #183 has 25pf snubbers on V2.

Too low pf and it's pretty fizzy sounding on my amp.

I think I may have around 200pf on mine.

Those two resistors on V2 from plate to OD pots can be used to fine tune the top end as well.

180K and 150K on #183

The higher the values, the more top end will be attenuated.