Rotary Pot Question....

[ksl]

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 
 

[gardo]

Without knowing what kind of amp or seeing any details,  I would say it’s a good way to ruin the amp

[WRGKMC]

What amp model and why are you wanting to do this.  Do you understand the consequences of changing any components values in a circuit.

Do you have a schematic,  have you checked to see if this mod before or are you simply assuming this is how its done. 

Adding resistance in series with a pot is unlikely to give you the results you want.  You already have that available to you by the way.  The volume pot on a guitar does add resistance across the input to decrease signal strength.  You can easily swap the center and end leg on a guitars volume pot ir add an additional pot in series and see if you like the results. 

I wouldn't advise messing with the amps actual circuits for any reason at all.  Chances are any resistor near the pot has more then one function.  Typically they supply voltage/current that biases the amplifying device.  If so, its highly likely you'll wind up shutting the device down or just the opposite, blowing it out feeding too much current.

The problem with tinkering circuit values is the components are probably running at their optimum value already and probably don't have more then a 5% variance available before you start making a circuit sound bad.  Changing a component by 10% can shut a circuit down and 20% will likely start smoke your circuits.  This is being optimistic too. Older mass produced circuits typically had large component tolerances so even a bad batch of parts would still run OK. Newer amps, finely tuned can have components with military specs exceeding no more then 1 percent and small variances can fry entire circuits which is very easy to do especially when someone is obviously clueless in what they are trying to do.   

Beginners will typically assume everything is simple DC voltage and resistance and that simply isn't the case.  Amp circuits are far more complex then anything inside a guitar.   Most components have more then one function and can supply both AC and DC voltage/current at the same time, something you aren't even aware of until you've formally studied electronics and have moved from studying basic DC and are well into understanding how AC and DC circuits work together and against each other.  A resistor in the first stage can supply bias and pass a signal at the same time. 

If your problem is too much gain, then adding resistance before the first gain stage is the same as turning down your guitars volume pot.  Adding additional resistance can be done in the guitar itself and you'll know what those results will be when you try it. 

Chances are that's not the solution and that's not where you'd go to fix it.  If a circuit has too much clipping/saturation its because the first gain stage is pushing the next gain stage to much or the second gain stage is pushing the third stage too much, or the preamp is overdriving the power amp.  If so you'd either need to reduce the gain in these intermediary stages or reduce how well those stages amplify.  Many amps incorporate clipping diodes like many distortion boxed do too.  You could change the value of those diodes so that take a stronger signal before they begin clipping.

I could come up with dozens of other possible scenario's depending on the type of amp involved.  Tube, Transistor or hybrid all have multiple gain stages.  The question really comes down to why the stock amp sounds bad.  Often times a guitarist had hot rodded over wound  pickups that will distort even the cleanest amp. Simply switching to a vintage wind can do wonders in freeing up clean headspace.  If the amp still distorts too much then get something cleaner.  There aren't many cheap fixes for the SS amps.  Tube amps can have some things like installing cleaner, lower gain tubes and biasing them to have more clean headroom.  The last thing you want to do is jack with stuff where you don't understand the consequences of those actions.  It will wind up killing what you got then you got to start over from scratch.  There aren't many qualified techs willing to work for peanuts either.  The going rate is at least $100 an hour whether they can fix it or not so keep that in mind when you blow something up. 

Post the model of amp.  I'll check the circuit for you and give you the best options as an electronic tech. 

 

 

 

 

[daddymack]

also, that is not a potentiometer, it is a rotary switch.

Seriously, as others have said, this is not a good idea and will not get you what you want...just changing the resistor value may actually make the amp non-functional....do you have a schematic for the amp?

Is this that old Gibby you've been tinkering with?

[Grant Harding]

If you can find the right rotary potentiometer switch with the right diode setting, but take it to a pro to have the work done. 

[Phil O'Keefe]

Yeah, you definitely don't want to use a rotary switch (which is what you showed a picture of) - even if the mod you're proposing is possible and won't hurt the amp (which we have no way of knowing without knowing what the amp is and looking at a schematic) that's the wrong component to use. 

A potentiometer is a variable resistance component. Like a fixed resistor, but one that can cover a range of resistance values, depending on how it is adjusted. It MIGHT be possible to replace a fixed resistor with a pot, but it would have to be in the correct range, and there could be problems if the pot is set at or near the extremes of its range; in some positions, the pot might provide too much, or not enough resistance for the amp to safely handle. 

I would STRONGLY recommend that you take the amplifier to a qualified electronic technician for any mods of this sort that you might be considering. Remember that amplifiers, especially tube amps, can have LETHAL voltages inside them - and the capacitors in the amp can store that charge for a significant amount of time, even once the amp is unplugged from the wall outlet, so if you don't know exactly what you're doing and exactly how to do it SAFELY, it's always best to stay away from the inside of your amp. 

 

[Phil O'Keefe]

15 minutes ago, Grant Harding said:

If you can find the right rotary potentiometer switch with the right diode setting, but take it to a pro to have the work done. 

In order to use a rotary switch, it would have to be wired in such a way that each switch position used a different fixed resistor, each with a different resistance value. That way, you'd be able to switch between them. 

Replacing a fixed resistor with a diode? Not a good idea... 

 

 

[ksl]

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.