Dual concentric pots?

[rspst14]

Hey guys, has anyone tried these pots before? I was going to get a new set of pots, and I thought it might be nice to have two volume and two tone controls. In this picture, am I correct in assuming the top knob controls the top pot, and the bottom one controls the bottom pot?

http://www.stewmac.com/shop/Electro...ol_pots_and_knobs/5/Control_Pots.html#details

Ryan

 

[Artie]

Re: Dual concentric pots?

Just the opposite, the top knob controls the bottom pot. Remember, the control shaft has to pass through the other.

Imagine having one pot. Now drill a hole through it, place an axle through it, and attach another pot and knob.

Think of it as "inside" and "outside", rather than top and bottom.

 

[Artie]

Re: Dual concentric pots?

Oh yeah, and be aware of the oddball behavior you get when you put two volume controls on a single guitar. It may not work the way you want.

Personally, I prefer just one of each.

 

[rspst14]

Re: Dual concentric pots?

Hey Artie, what type of oddball behavior are you referring to?

Ryan

 

[Artie]

Re: Dual concentric pots?

Perhaps I shouldn't have refered to it as "oddball", because they're are a million LP's out there with this type of control system. (As Robert_S pointed out to me.)

Here's the deal, you can wire your two vol's ineither of two different ways:

1. The hot wire of the p'ups goes to the "end" of the pot, and the output is taken from the wiper. This is what I would call the "normal" way, which gives you the problem of each volume controling both p'ups. With the 3-way in the middle, turning down either volume control will kill both p'ups.

2. The hot wire of the p'up goes to the wiper, and the output comes from the end. This is normal LP wiring. The problem here is that as you turn down the volume, you change the tonal characteristics of the p'up. If you start with 500k pots, at half volume, you effectively have 250k's. That may not be what you want to happen, although LP users have lived with it for years.

Thats basically it. A compromise one way or the other.

 

[rspst14]

Re: Dual concentric pots?

http://guitarelectronics.zoovy.com/product/WDUHH3T2201

so that would be an example of the first wiring method? This is what I had planned on doing, and I rarely use the middle position of the switch. Just to clarify, if I had it wired like this and in the middle switch position, the volume would be at 5 if I had one volume at 10 and one at 5...correct? Thanks for your help.

Ryan

 

[HolyDirt]

Re: Dual concentric pots?

http://guitarelectronics.zoovy.com/product/WDUHH3T2201

so that would be an example of the first wiring method? This is what I had planned on doing, and I rarely use the middle position of the switch. Just to clarify, if I had it wired like this and in the middle switch position, the volume would be at 5 if I had one volume at 10 and one at 5...correct? Thanks for your help.

Ryan

what artie was talkign about is a shorting of the ground, so, when in the middle possition on the pickup switch, when one volume pot was at zero, and the other, say 10, there woul dbe no sound coming form the guitar, but when the pot on zero goes to 1, the sound comes back

 

[Artie]

Re: Dual concentric pots?

Yes and no . . . its not quite that simple electrically. Lets start with the easy part, and this all assumes having the 3-way in the middle. If either volume is on zero, you'll have no sound. Now lets say you have the 3-way switched to the neck, and both volumes on 10, and you're using 500k pots. As soon as you flip the switch to the middle, both p'ups "see" a 250k pot. So, you'll have the combined effect of switching in two pickups, while effectively changing the pots to 250's.

Now, as you roll the volume down, on one pot, to 5, you're adding the parallel resistance of a 500k and a 250k pot. In other words, its not quite a linear change, or effect.

But . . . be sure to take all this with a grain of salt. There's been many people using two-volume guitars, happily for years. I just don't care for it personally.

Edit: Hi HolyDirt. I was composing my reply while you were. The "yes and no" wasn't to you. You are exactly correct.

 

[rspst14]

Re: Dual concentric pots?

Thanks for all the help guys...I think I may just stick with one volume and one tone on this guitar.

Ryan

 

[Kent S.]

Re: Dual concentric pots?

Yes and no . . . its not quite that simple electrically. Lets start with the easy part, and this all assumes having the 3-way in the middle. If either volume is on zero, you'll have no sound. Now lets say you have the 3-way switched to the neck, and both volumes on 10, and you're using 500k pots. As soon as you flip the switch to the middle, both p'ups "see" a 250k pot. So, you'll have the combined effect of switching in two pickups, while effectively changing the pots to 250's.

Now, as you roll the volume down, on one pot, to 5, you're adding the parallel resistance of a 500k and a 250k pot. In other words, its not quite a linear change, or effect.

But . . . be sure to take all this with a grain of salt. There's been many people using two-volume guitars, happily for years. I just don't care for it personally.

The above had more to it, but I deleted part of it in the quoting process by mistake ....Anyway ....
The only way you can get around it is to actively buffer the individual pups' output directly ... and that means active preamps (one per pup), and it also produces other results, like the parallel pup connection doesn't interact with each other as they do passively ... so it changes their tone.
Like Artie said, it's all a giant set of pros and cons ... as the saying goes ... *There ain't no free lunch in audio.* ... I forget where I read that, but its true.

 

[Artie]

Re: Dual concentric pots?

There is another way to do this thats reasonably good, albeit, with a few caveats:

1. This is theoretical - I haven't tried it yet, but there's no reason for it not to work.
2. It requires a good quality audio-grade isolation transformer that can cost as much as a good pickup.
3. There will be a slight loss of high-end, that may be compensated for by using 1-meg pots, or using pickups with a higher, brighter tone than originaly planned.

Benefits:

1. True isolated dual-volume control.
2. Complete electrical isolation from the amp. Eliminates any shock hazard from guitar.

Here's the small version:

SHIFT - Click here, for full size version:

Dual Volume controls, using isolation transformer

Note: Alco style 3-way is wired backwards from the conventional way. Both contacts are "open" in the middle, rather than "closed".

 

[Kent S.]

Re: Dual concentric pots?

Interesting, if I'm looking at it correctly (actually just extremely sleepy), I wonder what suitable primary/secondary impedances, and primary/secondary turn ratio would be for it. I'm still wondering if the load stays constant though, I'll have to think about it later. I'm assuming the transformer is sheilded. Hey do you have a part number handy for that Alco brand switch? Thanks. :sleepy: :sleeping:

 

[Artie]

Re: Dual concentric pots?

Those switches are sold at several guitar parts websites.

Here it is from GuitarPartsResource.com

Part No. EP 0080-010

And here it is from Stew-Mac

Part No. 1223

I've been looking over all my electronics catalogs trying to find the right impedances. Jensen makes just about the best, but they cost more than a pickup. I've found a few others that might fill the bill, but even they are $35 - $45. A bit too much for me to experiment with for something I'm in no rush to do myself.

The load should be constant. Sheilding depends on how much you spend. The Jensens are, of course.

BTW - If you peruse the Jensen website, and look over all the "white-papers" and application sheets, there's some really great info there as it relates to guitar isolation, impedance matching, and so forth. The webpage is worth looking over.

 

[Artie]

Re: Dual concentric pots?

A little update:

For "true" total isolation, modify the wiring to this:

Click here for full size.

 

[Kent S.]

Re: Dual concentric pots?

I was going to point that out, the shared grounds, but thought I was just tired. Plus it looks like there would be a level difference between one primary/secondary, and two primaries/secondary ... This uses a different switch , but here's my take on it (bear in mind this is untested also).
Yeah, I got snazzy, I gave one pup a Gibson style '50's tone stage wiring, and the other a Fender style '60's tone stage wiring ... Just for fun ... :laugh2: Here's my take ...

 

[Artie]

Re: Dual concentric pots?

Looks interesting Kent. I'm not sure I understand what you're doing with the bottom of the 4PDT switch. Where is the "common" terminal supposed to go? Is that to adjust the output level if both p'ups are selected?

We'll have to buy a couple transformers, and see how this whole thing works.

 

[Kent S.]

Re: Dual concentric pots?

Looks interesting Kent. I'm not sure I understand what you're doing with the bottom of the 4PDT switch. Where is the "common" terminal supposed to go? Is that to adjust the output level if both p'ups are selected?

We'll have to buy a couple transformers, and see how this whole thing works.

The upper half of the switch shunts the pup's hot to it's cold side, while at the same time shunting the hot and cold of it's corresponding primary (no signal, signal, no noise, no inductive coupling, no muss, no fuss, no problems ... LOL) when that pup is to be off.
The lower half of the switch (speaking in pairs that is),
grounds the center tap to effectively halve the secondary, since twice the signal is induced with two primaries operating ( a doubling of the voltage ... if assummed linear) ... This bumps it back down. Thing is, transformers aren't my *thing*, so I can't remember off hand the P/S ratio as to which is greater and which should be lesser ... as in step-up or step-down ... the intent was to step down the voltage when both primaries are active; However I may have that backwards. Another problem would be the looming question of what should the primary Z be ... 1 Meg each would be nice, and what should the secondary's Z be (CT and Full). Plus even if you found a transformer that was small enough, and spec'ed, I wonder what it would do to the frequency response ... like you said about the high end.
It does raise some interesting questions ... Things like this are when I would just call the transformer manufacturer and say, hey ... ya got something that will do this? :laugh2:

 

[Artie]

Re: Dual concentric pots?

Thing is, transformers aren't my *thing . . .

Yeah, me too. Where I work, I have a plethora of electronics catalogs at my fingertips. All the transformers that are listed as "audio-grade" are generally 600 ohm input/output, and, they're designed for communication work. As in voice/modem apps. Even those tend to be in the $35 - $45 range. Too expensive for casual experimentation.

The Jensen transformers will fill the bill, but at $75 - $85, way beyond practical consideration.

It was an interesting academic exercise, but probably not much more than that.

As soon as I get the "bugs" worked out, I'll send you diagram of my upcoming "multi-mode matrix switching system."

 

[Kent S.]

Re: Dual concentric pots?

Yeah, me too. Where I work, I have a plethora of electronics catalogs at my fingertips. All the transformers that are listed as "audio-grade" are generally 600 ohm input/output, and, they're designed for communication work. As in voice/modem apps. Even those tend to be in the $35 - $45 range. Too expensive for casual experimentation.

The Jensen transformers will fill the bill, but at $75 - $85, way beyond practical consideration.

It was an interesting academic exercise, but probably not much more than that.

As soon as I get the "bugs" worked out, I'll send you diagram of my upcoming "multi-mode matrix switching system."

Oh, and yeah I did leave off the ground for the center tap, as far as the trun ratio that should keep the output the same level ... I think ... :question:
Plus I don't know if the primaries need to be terminated or not. Anyway, here is the corrected schematic, and cool deal on that M. M. S. System, sounds a bit like my series super plus layout ... Anyway here's the corrected schematic ...

 

[Artie]

Re: Dual concentric pots?

. . . and cool deal on that M. M. S. System, sounds a bit like my series super plus layout ...

Thinking up these names is half the fun!

The "multi-mode" part of my switching system is just that it will be an active switching system, but in the absence of power, automatically reverts back to "ordinary" guitar functionality - so that the guitar could be carried to a friends house to use.

I did find some inexpensive audio transformers that might be worth experimenting with. ($2 or $3 each.) They're available from Mouser under the name HiQ Magnetics. I'm going to order a couple of these later this week, and see how they perform.