Slope resistor switch

[angelodp]

Just wondering if any have implemented a select switch for the slope resistor. Say 150/100

[Bob-I]

Not on a Dumble type, but a friend of mine swears by a slope resistor pot. He puts in the minimum resistance he wants in a fixed resistor and adds a pot in series. I saw a Marshall he did with a 33K and 100K pot. Very effective. Minimum slope was 33K, max 133k.

[angelodp]

Ok so how does the high DC get handled. Can you suggest a method for the Dlite.

[Structo]

Have you tried a different slope resistor in your amp Ange?

The next time I have my amp open I'm going to try a 120K and if I don't like that, then a 100K.

It's supposed to make the bass and mid pot more audibly adjustable.

Right now I don't feel that my bass and mid pot do much.
Sure if I turn them both all the way down I can hear it.
I know they are somewhat interactive, it just doesn't seem like a good management of bass or mids in my amp.

[dave g]

Ok so how does the high DC get handled. Can you suggest a method for the Dlite.

There is no DC across the slope resistor.

[JD0x0]

i suggested a slope resistor pot a while ago. on my new amp it isnt possible since i have the HRM on the front panel also. I have a switch that puts a 76K resistor in series with the 33k so it's selectable between 33K and about 100K

[Firestorm]

Not on a Dumble type, but a friend of mine swears by a slope resistor pot. He puts in the minimum resistance he wants in a fixed resistor and adds a pot in series. I saw a Marshall he did with a 33K and 100K pot. Very effective. Minimum slope was 33K, max 133k.

Almost exactly what Mike Holland did on the Little Jimi amp. It was described as a way to adjust the response of the tone stack for different guitars and pickups. As Dave G says, there's no DC through the resistor, but there is a pretty high voltage potential. Maybe not so great to bring that out to the control panel in case a lead comes loose. Holland blocked the plate voltage with something like a .1 so there's a little effect on frequency response.

[Bob-I]

Ok so how does the high DC get handled. Can you suggest a method for the Dlite.

Oh yea, I forgot about that. There IS about 200V DC on that resistor. You'll need to put a coupling cap before the resistor to block that DC. I'd use a .1uF from the plate of V1a to the tone stack.

[kd]

Unless I'm screwed up on my thinking today(possible), there has to be DC voltage at the slope resistor. It would be seeing whatever voltage the plate is seeing. Am I wrong?

Ken

[ayan]

Unless I'm screwed up on my thinking today(possible), there has to be DC voltage at the slope resistor. It would be seeing whatever voltage the plate is seeing. Am I wrong?

Ken

You're right, Ken. Exception would be if there were a coupling cap after the preamp tube and before the tone stack, which I believe Andy still does in the Fuchs amps.

Gil

[Structo]

Would a DC blocking cap there affect the tone?

I've noticed before sometimes my volume pot gets a little scratchy.
Not bad enough really to address but there nonetheless.

[talbany]

Would a DC blocking cap there affect the tone?

I've noticed before sometimes my volume pot gets a little scratchy.
Not bad enough really to address but there nonetheless.

Yeah.. It effects breakup.. Never cared for it myself..

Tony

[dave g]

Unless I'm screwed up on my thinking today(possible), there has to be DC voltage at the slope resistor. It would be seeing whatever voltage the plate is seeing. Am I wrong?

Ken

You're right, Ken. Exception would be if there were a coupling cap after the preamp tube and before the tone stack, which I believe Andy still does in the Fuchs amps.

Gil

Come on guys

No, there is no DC voltage across the slope resistor.

While one end is connected to a DC potential at the plate, the other end is only connected to the bass and mid caps - so how can any DC current possibly flow through the resistor?

There's just as much DC current flowing through the slope resistor as there is flowing through a volume pot connected to ground (read: NONE WHATSOEVER) , because after all "ground" is still "DC" (just at 0 volts).

The only potential hazard would be one of the potentiometer lugs shorting to the case, and hence the chassis. Personally, I'd be more afraid of dielectric punchthrough in a coupling cap, or the grid of V1A shorting to the plate...

[talbany]

Actually it would need to be wired like a variable resistor.. If you ground the bottom like a Volume control you will be shunting voltage to ground. For a Dumble style stack I would add a 100k linear pot in series with a 50k fixed resistor so that you could adjust it from 50k to 150k..Keep in mind it might scratch..also if it's carbon trace it will effect tone.


Tony

[angelodp]

This is great info. Is there any particular pot manufacturer you would recommend, or is it all the same. I suppose it could be a trimmer set-up, but an off-board setup on the rear panel might be cool.