Rotary Pot Question....

[zozoe]

Hiya.. Here's my application; there's a resistor right before my Amp's volume pot, and I want to remove it and be able to insert a pot at that point & be able to easily swap values to alter overdrive. Am I on the right track with this 2 Pole 8 way pot, and all I need is to run two wires from this pot? & where would those 2 wires go? There's 18 lugs,, 16 for the 8 resistors, & 2 extra...?
Many thanks, Kenny

[roberto]

This should help you understand. Also, a book of electronics is suggested if you want to learn some safety rules when modifying high voltage tube amps.

[PaulD]

The item shown in your picture is a rotary switch, not a pot, and it cannot be used on it's own to replace a single fixed value resistor (it could possibly be used to switch between several different fixed value resistors if that is what you want to do). More information would be needed to be able to give advice on this such as what the amplifier is and ideally a schematic but based on what you describe, which sounds like there is a series resistor before the volume pot, I think it is unlikely that changing the value of that series resistance would have any significant effect on overdrive levels.

I'm not sure what the relevance of the diagram in post #2 is as that seems to show a switch connected to some diodes and LED's which are grounded at one end and does not seem to be relevant to this situation.

[roberto]

Ciao PauldD,

what the user wants to do, is to substitute the classic Marshall 470k//470p combo (or any other combo used by other producers, or just a resistor) before the gain pot, with other values.
This ABSOLUTELY changes the gain of the amp!

As for my image, the purpose was to show that he needs something external to connect the resistors connected to the different pins.
The fact that are diodes is absolutely not relevant, as he is not even aware of what it does, nor what it is its name.
That's why I suggested to read an electronic book with safety instructions for high voltage electronics.

[Kagliostro]

What about to use a pot connected as rehostat ?



Franco

p.s.: Ciao Robi

[roberto]

Ciao Franco,

I guess he wants to change the cap too, otherwise instead of having EG 470k fixed resistor and 500k pot, it would be better to have just 1M pot.
But who knows, maybe he just want to do what you said!

[zozoe]

Hi all~~ It's a Masco MA25 P.A. amp that my tech modded one of the amp's two inputs for a gainier sound. Here's a shot of the resistors (with what are perhaps tiny diodes connected?) going to the volume for that modded channel, and he said if I lowered the value, I would get more gain. With the total 3.8k ohms it's at now, it's nice, and I want to mess with dropping in different higher values for less breakup, hence my desire to use a rotary that would offer me options. Of course, before I proceed, I will lift one of those resistors to give me 7.6k, to try and see if I'm heading in the right direction. Thanks for all the direction & precautions.

20200128_180821.jpg

[PaulD]

I can't see for sure from the photo where the other ends of the diodes are connected but I'm guessing they go to ground? In which case this is a diode clipper circuit and the value of the resistor(s) will control how much of the signal goes through the diodes and gets clipped (strictly speaking it is not affecting the gain of the amp, it is clipping / distorting the signal in a similar way that an effects pedal would).

The simplest way to make this adjustable, as suggested in post #5, would be to use a pot wired as a variable resistor rather than switching fixed value resistors (something like a 10K pot would probably be appropriate).

[roberto]

If it is like that, a lowert resistor will mean more distortion, but less volume and a more squashed sound.

[PaulD]

Just to clarify here is how you would need to wire the pot (this assumes you want the pot to increase the clipping/distortion effect as it is turned clockwise)

[zozoe]

see below...

[zozoe]

So, in using a 10k pot, that'll be my starting point in resistance when full counter-clockwise, and as I turn up the pot, the resistance goes What if I want to start at let's say 7k? I don't want it to go below 2k,,, I don't know what no load would do to the circuit...? How would I make that happen, if even possible?
Thanks

[sluckey]

Put a 2K resistor in series with a 5K pot. That gives 7K max, 2K min.

[zozoe]

SLUCKEY,,,,or anyone,,the 2k resistor will attach to which 2 lugs? Can you kindly draw me a diagram & include the resistor connection as well as the connections that go to the amp? That would really help, & I'll gladly abandon my rotary idea...
Here's what the pot will look like:

20200130_013257.jpg

[roberto]

Connect one pin of the resistor to pins 1&2 of the pot, then the other pin of the resistor has to be connected to the rest of the circuit.