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Post by newey on Dec 17, 2021 14:20:41 GMT -5
For years, as far as anyone knew, no such part existed. A few years back, mention was made of ordering ones from China through Alibaba or whatever. But still pretty much rara avis. But now Bourns has them, readily available at Mouser.com. They have both 500K and 250K, with knurled shafts (they may have straight shafts as well, I didn't look further). These are A taper. I ordered a pair without really having a plan to use them, they'll go in the parts bin for future reference.   |
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Post by gckelloch on Dec 17, 2021 15:57:53 GMT -5
Cool. Can you tell if the sweep is the full range of each pot, or does it end in the middle so it can be used as a blend without loading the pickups in the middle?
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Post by newey on Dec 17, 2021 16:09:32 GMT -5
The sweep is the full range. There is no detent. It's just a regular dual-gang pot, not a blend or pan pot. JohnH's "Strat with 2 Volumes" uses a dual-gang tone pot as a "master" tone, so as to isolate the individual volume controls, that type of application is one of the main uses, and having the DPDT added just opens up more possibilities. I'm using one (without needing a P/P one, just a dual-gang pot) in my long-dormant stereo Tele build, so as to isolate the 2 channels from one another but still have a single knob to turn (it's a Tele, so real estate on the control plate is at a premium). Of course, one could wire this up with one gang reversed from the other so as to make it a sorta-kinda blend pot, but as you note, resistance in the center is the downside. EDIT:Another thought is that of using a regular pot to, for example, blend a neck pickup into a bridge pup (as opposed to a blend pot blending one out as the other is blended in). Here. with 2 gangs and a DPDT switch to play with, I can envision wiring one gang to blend the neck into the bridge, wiring the other gang to blend the bridge into the neck, and using the P/P to switch between the two. Or maybe we blend the neck into the output of the 5-way switch with one gang, blend the bridge in with the other, and switch between the two wirings. Just spitballin', y'understand?  |
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Post by gckelloch on Dec 17, 2021 17:09:26 GMT -5
The sweep is the full range. There is no detent. It's just a regular dual-gang pot, not a blend or pan pot. JohnH's "Strat with 2 Volumes" uses a dual-gang tone pot as a "master" tone, so as to isolate the individual volume controls, that type of application is one of the main uses, and having the DPDT added just opens up more possibilities. I'm using one (without needing a P/P one, just a dual-gang pot) in my long-dormant stereo Tele build, so as to isolate the 2 channels from one another but still have a single knob to turn (it's a Tele, so real estate on the control plate is at a premium). Of course, one could wire this up with one gang reversed from the other so as to make it a sorta-kinda blend pot, but as you note, resistance in the center is the downside. EDIT:Another thought is that of using a regular pot to, for example, blend a neck pickup into a bridge pup (as opposed to a blend pot blending one out as the other is blended in). Here. with 2 gangs and a DPDT switch to play with, I can envision wiring one gang to blend the neck into the bridge, wiring the other gang to blend the bridge into the neck, and using the P/P to switch between the two. Or maybe we blend the neck into the output of the 5-way switch with one gang, blend the bridge in with the other, and switch between the two wirings. Just spitballin', y'understand? Sounds good. I made a wiring schema that offers that blend/swap option using a single gang P/P pot. The pickup swap option utilizes one rack of a Super Switch. |
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Post by stevewf on Dec 18, 2021 15:25:01 GMT -5
If these pots are like the dual-gang Bourns that I've seen, then the resistance curves are really "A" and "Reverse-A".
That's because wafers are facing each other with the sweepers in between them.
One wafer (the one closest to the knob) will give you an A curve when sweeping from 0 to 10; the other wafer will give you an A curve when sweeping from 10 to 0.
Application: for that reason, I like to use the "RA" wafer for a bass cut control. Or, it can be replaced by a linear wafer if that's needed.
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Post by reTrEaD on Dec 18, 2021 19:56:01 GMT -5
If these pots are like the dual-gang Bourns that I've seen, then the resistance curves are really "A" and "Reverse-A". I suspect both elements are A-taper. But in any case, newey should be able to verify this for us by rotating to the midpoint and measuring resistance. If both elements are A20%, the resistance between wiper to CCW should be approximately 100k and from wiper to CW should be approximately 400k, on both sections. If one element is RA20%, the resistance on that section between wiper to CCW should be approximately 400k and from wiper to CW should be approximately 100k. |
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Post by newey on Dec 18, 2021 21:55:21 GMT -5
OK, I'll check 'em tomorrow. My matress is plaintively calling me at the moment.
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Post by Yogi B on Dec 18, 2021 22:04:10 GMT -5
I suspect both elements are A-taper. I suspect that, externally, both gangs appear to be A taper, but this doesn't take into consideration that orientation of the actual elements. As stevewf noted: [The] wafers are facing each other with the sweepers in between them. If you took a regular "A" taper and flipped it upside down and reattached it to the same shaft, you've reversed the directions of CW and CCW relative to the wafer. Therefore, if installed in the lower (upside down) position, a normal "A" taper element would give an apparent "reverse-A" (AKA "C") taper. Likewise, in order to get an apparent "A" taper when installed upside down, the taper of the actual element (that would be revealed if installed in the more usual orientation) must be "reverse-A". If both elements are A20% The "20%" given in the description is the tolerance (meaning ±20%, rather than being the total tolerance range given by ±10%). "A2" from the part number is the taper, but corresponds to 10% as per Bourns nomenclature (which counts in 5% increments). (AFAIK the only dual-gang pots that Bourns offer as standard with a duplicate of the same element (i.e. opposing apparent tapers) are their 'true'-blend pots, which have the ChrisK-preferred M/N taper.) |
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Post by reTrEaD on Dec 21, 2021 7:23:02 GMT -5
The "20%" given in the description is the tolerance (meaning ±20%, rather than being the total tolerance range given by ±10%). "A2" from the part number is the taper, but corresponds to 10% as per Bourns nomenclature (which counts in 5% increments). oic In that case the midpoint of rotation will result in 50k on side and 450k on the other side. Hopefully newey will confirm whether the 50k from wiper to CCW is on both gangs. |
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Post by frets on Dec 21, 2021 19:32:06 GMT -5
I’ve been using them for years and get mine at a wholesale cost from CE Distribution but they also can be found at Antique Electronic Supply for $7.95 a piece. I don’t know if that’s cheaper than Mouser.
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Post by newey on Dec 21, 2021 21:52:48 GMT -5
frets: $5.53 USD at Mouser, plus tax. Measurement of the pots has been delayed by the need to acquire a new multimeter, the old one having exited the mortal meter coil . . . So, $37 later at Home depot, I got this one:  Commercial Electrics brand, which is (I believe) Home Depot's house brand. It is much more rugged than my prior meter, although bigger/heavier, but that's OK, I don't really carry it around much. It also has AAA batteries instead of the tiny button cells my old one used, a big plus when batteries need changing. And, although advertised as just an "auto-ranging multimeter", it also has a capacitance measurement function and a diode forward-bias voltage function. Anyway. here's the skinny: I first measured the total resistance across the outer lugs, top gang and bottom gang, to see if there was any significant variance. These are nominally 500KΩ, 20% tolerance. The top gang measures 460KΩ, the bottom gang is 464KΩ, so no significant difference and both within the mfr's tolerances. (P.S.- the switch works, too). At 50% rotation, on the top gang, between the CCW lug and the wiper, I get 24.96KΩ. Between the wiper and the CW lug, 432KΩ At 50% rotation, bottom gang, CCW to wiper is 23.97KΩ, from wiper to CW lug is 437KΩ These are the "dime-sized" 17 mm pots, and it's a bit difficult to be exact as to where 50% rotation is- I figured it as accurately as I could using the split in the shaft as a guide. Nonetheless, I was probably a mite off, looking at my measurements. But I trust that answers the question . . .
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Post by reTrEaD on Dec 22, 2021 8:57:14 GMT -5
But I trust that answers the question . . . It does. Thanks, newey . |
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Post by sumgai on Dec 22, 2021 15:38:17 GMT -5
But I trust that answers the question . . . Yes, in one degree, but it does raise another question. As alleged above, the wafer might be "inverted". From your results, one might surmise that both wafers are facing in the same direction (say perhaps, track and wiper facing towards the switch). Can you verify this to be the case? Additionally, do you think that one could open the unit and invert the wafer so as to achieve something akin to a blend pot? With only 5% of the total resistance element at the 50% rotation point, such would introduce very little resistance into the signal path... sumgai |
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Post by newey on Dec 22, 2021 19:06:49 GMT -5
From your results, one might surmise that both wafers are facing in the same direction (say perhaps, track and wiper facing towards the switch). Can you verify this to be the case? I can't tell from an external view, with the 17mm footprint, the thing is mighty tiny. It is held together by fold-over steel tabs, so I suspect it could be fairly easily disassembled, but whether the element could be removed and fipped, I don't know, I'd have to (potentially)sacrifice one to look. I'm thinking it might not be do-able, given that the shaft has to hold the gangs while also moving up and down with the switch mechanism. |
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Post by frets on Dec 23, 2021 13:09:10 GMT -5
Newey,
Thanks for the Mouser price. I’m really interested in what you’re final decision will be going forward with using the dual gang pots.
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Post by stevewf on Feb 13, 2022 1:01:44 GMT -5
I should have mentioned that I've opened up at least one two-gang Bourns pot (not the "MN" blenders... which I've also opened, by the way). The type I've opened, called PDB182, do have the wafers in opposite orientation, with the wipers sharing a single carrier. The wafers are otherwise identical to one another. The type I've disassembled had two "A" curve wafers (probably the only type available). The result is that the top wafer (nearest the knob) exhibits an "A" curve and the bottom wafer a "C" curve. Another result is that the wafers cannot be flipped, since the wipers, mounted on their shared nylon carrier that's driven by the central shaft, will always be located between the wafers. Again, the ones I've opened do not have both two-gang and the DPDT, and therefore are not identical to the pots mentioned in the original post. However, I imagine that the two designs have the same construction for the pots. Ignoring the presence of the DPDT in the photo, the pot section sure looks the same as the ones I've dissected. Almost certainly, the two designs share as many components as possible, if only to keep production costs down. How-To: They are pretty easy to take apart. The metal fold-over tabs can be coaxed straight, releasing three sections from each other (the bushing, the pot, the switch). The shaft slides through the bushing and through the sweeper carrier. Its T-shaped tip moves the switch by hooking into a plastic block that slides up & down. The shaft turns the sweepers using its D-shaped cross section. It can all be disassembled and reassembled pretty easily, if you remember to "pull" the switch before disassembling (other wise you have to somehow pull the plastic block without the use of the shaft). Do keep fingers off of the traces, treat the wipers carefully, and don't remove any lubricating/damping grease. The tabs bend back into place, though they'll certainly work harden if they're bent too many times. I didn't take photos of the PDB182 as I took it apart; however I did take photos of a PDB183 (one-gang) that I modded.  Here you can see two wafers; the one closest to the camera is a "dummy wafer". Were it a real wafer, the trace would not be visible anyway, as it's facing inward. The curious can see how I bashed that PDB183 one-gang with another Bourns pot to make a two-gang with a 4PDT here. The one-gang into two-gang was fairly simple, but the 4PDT was hard, and I don't think I'll be doing it again. |
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Post by stevewf on Feb 13, 2022 1:16:51 GMT -5
...and then, there was the Bourns "blender" PDB182-GTRB that I added a DPDT to. That was also pretty hard, and yielded less-than-great results. That's because the detente mechanism in the blend pot doesn't work well with a push-pull shaft; I had to break the copper detente ring to get the shaft through it. As it is, I can barely feel the detente, and I don't know if it would last very long before breaking. It's not in any guitar right now.
Modding pots is something I used to do when I had a lot of spare time, which is no longer the case.
Incidentally, the blender pot, like the other two-gangers by Bourns, has the two wafers facing each other (i.e. opposite orientation) with the sweepers between them. The two wafers (with a resistance curve that Bourns calls "MN") are otherwise identical. That's how they get an "M" curve on one wafer and an "N" on the other. If they were consistent, then their "A" wafers could instead be called "AC" wafers.
I digress from the thread -- I couldn't resist posting this bit -- so I stop here.
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Post by stevewf on Feb 13, 2022 1:45:05 GMT -5
Newey, Thanks for the Mouser price. I’m really interested in what you’re final decision will be going forward with using the dual gang pots. As for me, so far, I've only used the two-gangs for two things: - In a Strat, adding a tone pot to the bridge pickup. I used a dedicated tone pot for the bridge, and the two-gang for the middle and neck together. Using a two-gang enables the use of a single knob while maintaining separate circuits for the neck and middle; if instead they shared a pot, then they'd be tied together (always both on or both off, together). In the tone knob (aka "treble cut"), a "B" curve (linear) is ok, so I use a pair of "B" wafers, and I don't have to worry about the response being uneven between the two pickups as I turn the knob. For this, of course, I have to wire the bottom wafer "backwards" (i.e. swapping the two outer lugs), since its effective curve is a mirror image of the top one. They're a mirror because the two wafers are facing each other.
- In any guitar, getting a 1MΩ "C" curve pot. They're hard to find (impossible? Anyone? * ), so I use a 1MΩ "A" curve in the bottom wafer of a two-ganger, leaving the top wafer unused. I use this for a so-called bass-cut control; I don't think a linear 1MΩ wafer sounds right, with the "nothing, nothing, EVERYTHING" response as the knob's turned that's typical of the wrong curve. Using a straight "A" is even worse in my case.
* I wrote to Bourns a few months ago, begging them to make a 1MΩ "C" pot, and also to make their wafers available separately, pointing out that the population of modders is multiplying rapidly these days. So far, no response.
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Post by frets on Feb 13, 2022 10:03:09 GMT -5
Hi Steve😺,
Thanks for your input on this subject. I use the Bourns dual gang push pull frequently (worried they’ll discontinue it). I too use the dualie for adding a bridge and neck tone usually with a Series/Parallel on the switch. I’m always interested in how guys are using this pot.
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Post by stevewf on Sept 13, 2022 20:36:00 GMT -5
Here, perhaps is a resolution of conflicting evidence concerning Bourns dual-gang pots. On one hand, I've used Bourns 2-gangs to get a "Reverse audio" taper from a normal "Audio" wafer; on the other hand, newey measured normal Audio taper response from a Bourns 2-gang pot. How can both be true? I first measured the total resistance [...] These are nominally 500KΩ, 20% tolerance. At 50% rotation, on the top gang, between the CCW lug and the wiper, I get 24.96KΩ. Between the wiper and the CW lug, 432KΩ At 50% rotation, bottom gang, CCW to wiper is 23.97KΩ, from wiper to CW lug is 437KΩ Same readings on both gangs... so that would invalidate the (my) theory that the 2nd wafer is reverse. And actually, it's not just a theory - I really have gotten a C-taper on the 2nd gang by using an A-tapered wafer. So what gives? I must have made an error somewhere along the way. The wafers are otherwise identical to one another. That could be the error - on closer inspection, specifically at the other side of the wafers, I now see that one wafer has an "A" where the other has a "C". "C" is sometimes used to describe Reverse audio taper, so maybe that's it. Both wafers read "10A500K" on the outside of the wafer. Outside meaning the side without the resistive trace on it.  I see the differing lettering on the inside face of the wafers.  I must have made a custom dual gang pot by taking the wafer from a single gang 1M Ω pot and putting using that wafer, replacing the "C" wafer from a normal dual gang pot. This would have required destroying the signal gang pot - which I certainly remember having done in the past - in order to harvest its wafer. In Bourns pots that I've messed around with: - Pots with Push-pull switches may be "cleanly" disassembled - both wafers may be removed/replaced without any permanent damage to the pot. - Pots without p/p switches may be partially disassembled without damage - the 2nd gang wafer may be removed/replaced, but the 1st wafer is stuck. It's the way they make 'em - they stake (aka "smash") the end of the shaft. Single gang pots also have the wafer staked in place. The staking mark can be seen in the 1st photo above - circular dent in the end of the aluminum shaft that's visible in the hexagonal center of the nylon piece. - Single gang pots also have staked shafts; to harvest the wafer, the pot must be destroyed. I did that with a dremel in order to scavenge a wafer (destroying a single gang 1M Ω pot), and used that wafer in the 2nd gang position to build my 1M Ω Reverse-audio pot.So, maybe Bourns has two versions of their audio taper wafers - one version for simple pots and for 1st gang, and another version for 2nd gang. Mystery solved? |
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