Plexi normal channel pot questions

[stickyfinger]

How much effect would the value of the normal channel vol pot make to the bright channel circuit? Lets just say that the bright channel is 1M and a 250k is used for the normal channel. I don't use the normal channel ever keeping its vol on 0. Using lower measured valued pots in that spot might be ideal.

With the mixer resistors and 560pf bright cap has me wondering what a 250k pot might do to the bright channels circuit.

 

[william vogel]

How much effect would the value of the normal channel vol pot make to the bright channel circuit? Lets just say that the bright channel is 1M and a 250k is used for the normal channel. I don't use the normal channel ever keeping its vol on 0. Using lower measured valued pots in that spot might be ideal.

With the mixer resistors and 560pf bright cap has me wondering what a 250k pot might do to the bright channels circuit.

Leaving the normal volume pot on 0 is shunting the signal to ground through the 470k mix resistor only. Switching to a 250k will have no effect. Turning up the normal channel pot to about 7 will put the wiper equally in the middle of its total resistance and will shunt less of your bright volume to ground with the original 1Meg pot. Changing the pot will change nothing. You’ll gain more signal to V2 by turning the original volume pot to 7.

 

[Sigs]

I need a 5K log pot for presence but can't find one, so if I fit a 10k log and if this is turned up half way, is this the same as 5k up full?

 

[playloud]

I need a 5K log pot for presence but can't find one, so if I fit a 10k log and if this is turned up half way, is this the same as 5k up full?

Not quite. It's worth reviewing the schematic here:



If you use a 10k pot turned halfway, that's equivalent to adding an extra 5k resistor between the regular presence circuit up full (0.1uf bypassing 5k resistor) and the PI.

A better bet might be to put a 10k resistor in parallel with the 10k pot (e.g. across the outer lugs). This would give you the usual behaviour with the pot turned up full, and at 0. It will change a bit in between.

If I were you, I would get a modern 5k pot (the Tocos look good), build the thing, and then replace with period-correct if/when you're able to find one.

 

[TAZIN]

I need a 5K log pot for presence but can't find one, so if I fit a 10k log and if this is turned up half way, is this the same as 5k up full?

The Presence pot should 5K Linear taper not a Log.

 

[playloud]

The Presence pot should 5K Linear taper not a Log.

This too!

 

[neikeel]

The correct 5k lin is near impossible to find. I have bought every one I have seen over past few years.
I think that a lot got chucked erroneously by people thinking D.C. scratch was failing pot.
Matamp must have had a supply issue in early 70s as it was pretty standard to use 10k with 10k resistor in parallel (marked up on schematics as such).
Afraid I only have one in a current project build.

 

[Sigs]

So if you used linear pots when it asks for log pots, what does it do to the amp ?

 

[PelliX]

So if you used linear pots when it asks for log pots, what does it do to the amp ?

Nothing, just the taper changes. The amp doesn't care, it's more a user experience thing.

 

[ThreeChordWonder]

I got one at amplifiedparts.com:

https://www.amplifiedparts.com/products/potentiometer-alpha-linear-38-bushing

 

[Sigs]

I got one at amplifiedparts.com:

https://www.amplifiedparts.com/products/potentiometer-alpha-linear-38-bushing

That's not the type we're looking for, the image shows what we're look for, if you find any let us know.

 

[ThreeChordWonder]

Well, if you want antiques made from unobtainium and wood from Noah's ark...

One thing you might be able to do is to swap the guts from the new pot into the old pot's casing. If the old pot is cream crackered, what have you got to lose?

 

[Sigs]

Well, if you want antiques made from unobtainium and wood from Noah's ark...

One thing you might be able to do is to swap the guts from the new pot into the old pot's casing. If the old pot is cream crackered, what have you got to lose?

This is what I said " I need a 5K log pot for presence but can't find one, so if I fit a 10k log and if this is turned up half way, is this the same as 5k up full? "

I doubt anyone with a vintage Marshall would fit the pot you recommended, but thanks for the recommendation.

 

[ThreeChordWonder]

I take your point (I once knew a guy who had a concourse Vincent Black Shadow bought new by his grandfather with a broken kickstart return spring), but...

It depends if one wants a vintage Marshall that works and can be used or one that doesn't and can't.

You could always fit the new replacement pot until an antique one comes along.