Strat switch

[Luthierwnc]

Here is a re-do of a post I put on a recent thread that didn't get any traction there. With all the talk of making a more Strat friendly amp, I doodled up this switch idea for the tone stack.

The idea is that you have your choice between the skyliner and the '80's voice (more or less). I plan to use a 3P2T mini on the panel between the mid and bass pots. Those pots would be dual ganged Alpha 24mm guys. IIRC, it is pretty easy to pry the back pot off and replace it with a matching unit. Since these are available in both log and linear values, it should just be a matter of mixing and matching. I omitted the 10m resistors, mid, deep and R/J for clarity but you get the idea.

If you see any problems or an easier way to do this, comments are welcome.

Cheers, Skip

[greiswig]

I was hoping you'd put this out on its own. Thanks.

I've been thinking about something along these lines as well, but it's a little hard to read what your diagram is doing. Maybe put some labels (which pot is which, where the in/outs lead to, etc.) in the diagram so those of us who are having a hard time visualizing how this fits in the circuit could read it more easily.

The mid pot acts solely as a variable resistor (wiper and input tied), so you could just switch a parallel resistor in with a 250k pot and get 100k. But having the higher value on the pot only means changing the setting on the mid knob a bit (I think), so you might find that one value pot is an adequate right for both cap values.

[Luthierwnc]

I wanted to keep the two voices as stock as possible. One side is a skyliner with a .01 mid cap and 250ka pot and a .1 bass cap with a 500ka pot across a .001 cap and 10k tail resistor. The other side is an '80's style with a .047 mid cap into a 100kl pot and a .1 bass cap into a 250ka pot, no parallel cap and a 1k tail resistor.

It switches at three points; the ground to choose the mid cap and pot, the ground to choose the maximum resistance on the bass cap and the bass wiper tied to the PAB. By putting the switch between the bass and mid pots there is very little extra wiring. The D'Lite has an even simpler PAB that could be used.

The same Mouser page that has the 24mm Alpha pots usually used here has dual-ganged pots in either log or linear values. These are pretty easy to take apart and reattach. You can pop the back pot off one and replace it with the back from another value. In the bass case, I'll have a 500ka up front and a 250ka in back. For the mid, I'll have a 250ka up front and a 100kl behind. The only extra real estate on the board is the extra mid cap.

On stage, I'll still need to dial the tone controls to suit but this switch is intended for guitar changes so I don't have to do it on the fly.

Let's see if anyone else chimes in.

sh

[skyboltone]

I'd like to be able to comment Skip, but I think maybe it's just a matter of doing it and then sharing how it comes out. I think we've all gone down the skyliner track out of consensus and the try one thing at a time bit. Gil's recent comments on the 80's values definitely has me thinking. I'm still playing with basic architecture on mine. I kinda jumped in without taking the time to consider that there are reasons for putting things in certain places. When my current project is complete I intend to jump back on my D build and basically start over.

Looks like a good plan. Keep us posted.

Dan

[heisthl]

The same Mouser page that has the 24mm Alpha pots usually used here has dual-ganged pots in either log or linear values. These are pretty easy to take apart and reattach. You can pop the back pot off one and replace it with the back from another value.

I must be an idiot - I have never been able to figure out how to separate the shaft from the rear carbon wafer so I could mix and match dual pots. All the dual Alpha's I've tried are a pressed assembly that doesn't come apart. Have you actually done this? The "back" as you call it is just a metal shield. Please help me understand how to do this - thanks.

[Luthierwnc]

I have done this before but couldn't remember if it was an Alpha. So...I pried the fingers off a single pot. Then I took a couple screwdrivers and pried the plastic wiper assembly off the shaft. It puts up a bit of a fight but it comes off undamaged if you apply the pressure evenly. In the pic you see the shaft, plastic wiper assembly and the phenolic wafer with the carbon. IIRC, the dual units look the same. All you need to do is replace the carbon unit with a different value, squeeze the wiper back on and attach the case. I'll need to get a few dualies with my next Mouser order to be sure I'm not hosing ya.

Cheers, Skip

PS How about the idea on the schematic?

[toneman]

just odered CTS 250KA/500KA ---CTS 100KL/250KA concentric pots from HAS Sound. 13.95 for the first one and 24.95 for the second wich is custom made. He also sells black concentic knobs

[Luthierwnc]

Concentric pots would be even better for "set it and forget it."

My problem is that I can't read the damn knobs anymore. The more important the gig, the worse the light. I can reset the tone controls fast enough (not much and not often) if I can see them. It occured to me that I could even use a 4P2T switch with an LED so I know which one is on. There are some concentric guitar pots and knobs in the "graveyard drawer" but not in audio/linear combinations. Hack butchering one of those might be more complex. These Alpha jobs take five minutes.

There is also a part of me that likes getting both pots for six bucks

sh

[Luthierwnc]

I ordered 500ka, 250ka and 100kl Alpha dual-ganged pots to see if I could eat my own cooking. In the attached picture it shows the back plate removed but that isn't necessary. You do have to pry the fingers on one side of the back case off gently. It will slide off easily. Then gently pry the plastic wiper assembly off. Be careful to remember the alignment and take a look at the how the wiper contacts come down before you do.

The wiper assembly and phenolic carbon disc are identical to the single pots and the wipers are the same in all values. You may need to pry the wiper contacts back out if they were compressed during removal. Just swap discs and press the wiper back on. On one, I needed to use a socket and lightly peen it into place. Slide the back case back on and force the fingers back into the housing.

Now I have a 500ka/250ka for the bass pot and a 250ka/100kl mid pot. I probably won't get to this project for a month or two but I did want to see if the theory would work. YMMV.

Skip

[heisthl]

Q? WHen you remove the wiper (plastic assembly) can you move the shaft in and out at that point or is it still being held somehow by the front gang pot? I'm asking because to my eyes it looks like the factory places the wiper on the metal shaft nib and then squashes the nib so the wiper stays on with tension and possibly retricts how much the shaft can move in and out. If either or both is true I would question the reliability of pressing the wiper assembly back on over the smashed nib, first because the wiper assembly might not stay in place because of wiper tension and second If it also holds the shaft, pulling or pushing the knob might dislodge the wiper assembly. I suppose epoxy could be used.

[Luthierwnc]

When you take the wiper off there is some play but these double pots have an extra sleeve on the shaft. I don't know how the first pot in the assembly is attached. The plastic on the wiper is pretty stout but I did over-bend one of them pulling it off and it was a little loose going back on. The solution was to peen the plastic in a little with a hot blade screwdriver. Once it is back together, you can't tell it was ever apart.

If the opening in the wiper needed adhesive, I think I'd use something softer than epoxy. Plastic cement, liquid nails, caulk ... something that could stick to the plastic and never completely harden. Since the rectangular metal is the shaft itself, you could also chuck in in a vise and peen the pot metal with a screwdriver or punch. FWIW, you get a couple extra wipers doing all this plus I had the pot I took apart in the first post for parts.

The one tricky part is pulling the wiper the first time. It is hard to pry it out evenly without pinching the delicate springs. Levering it from one side only tends to widen the plastic. I clamped the shaft in a vise and used two paint can openers on either side like a bearing puller.

[heisthl]

I going to try one but it sounds like it's ok to do in your own amp but a little risky in a customer build. Of course in your own build you could just tack some resistance across the pot to get the lower value if you didn't care about screwing with the taper.

[skyboltone]

Plastic cement, liquid nails, caulk ... something that could stick to the plastic and never completely harden.

3M 5200 marine caulk. Available in 4 oz toothpaste tubes. Extraordinary void filling adhesive, soluable only in xylene....Goof Off. I've heard of yards attempting to pull the keel off sailboats; pulling all the fasteners and the 2 ton keel holding on by 5200 only. I use it for perminant stuff on the boat.

Dan

[Luthierwnc]

For a customer build I'd definately try it out first. If you don't have any problems widening the wiper opening in removal, you're putting it back the same way the factory did. The fingers on the case need some special attention. I sharpened a jewelers screwdriver like a chisel (I have lots of them for guitar inlay) to use as a pry bar. If you only peel back the two on one side, the other two will help realign the assembly when you put it back on. Notches in the phenolic line up pretty nicely but you may need to lightly tap the fingers with a punch to secure it.

As far as hanging a resistor on the pot, you'd lose the taper these things seem so touchy about. Doing both pots took 15 minutes and five of that was doing one twice and taking some pictures. Even if the experiment is a total bust, you're only out six bucks.

Overall, I say it worked as well as I had hoped. I still need to see if it sounds good and/or makes a difference in the versatility of the amp. My favorite guitar is a USA Custom Strat with a 3.5 lb ash body. I shot a traditional Fiesta Red nitro finish. Beefy neck, Kinmans. Plays like butter. I haven't been able to make it sound good enough through my other D builds to crack the top two and I only ever take two guitars with me -- usually just one. OTOH, I have a Frankentele that is moving up with a bullet sh

[greiswig]

As far as hanging a resistor on the pot, you'd lose the taper these things seem so touchy about. Doing both pots took 15 minutes and five of that was doing one twice and taking some pictures. Even if the experiment is a total bust, you're only out six bucks.

I'm not sure whether you're referring to my earlier suggestion that you could switch a resistor in, in parallel between the tied wiper/lug1 and lug2, but if so I can't understand how a parallel resistor would affect the taper at all. It would change the Y axis values, but the shape of the taper should still be the same, shouldn't it?