Pot taper...

[4real]

My recent strat project...everything works ok except..for some reason all three push pull pots seem to be an abrupt almost on/off function on the first portion of the things.

Strange as they are the same pots i've used in a few things...including the recent LP that used 4 and work perfectly...infact remarkably good taper to them, particularly the tone controls are effective.

I really use my volume control, so that's a downer...amy ahve done something wrong...is there a way of adjusting things...replacing the internals or just a matter of having three bad pots..which seems to be unlikely from the same 12 bag from china.

I had thought also that perhaps the pot for the "spin-select" was a bit much too...it might be the same pot problem...but it basically is reacting as full split on "0" and full HB on about "2"....is it possible to put a resistor across it and change the value perhaps...or the taper?

They are rated at 500k...

[JohnH]

Pete - I've also had inconsistent results from bags of Chinese pots. I bought enough to change all the sliders on our mixer with a few to spare and ended up not having enough good ones for the job.

But the spin-select is maybe as expected. When I use a 500k pot for single/Hb selection, in my case integrating that function with the tone pot, the change happens almost instantly between 9.5 and 10 at the sharp end of a log pot, or if its at the other end, about 0-2 as you found. If one were using a pot to give the best smooth transition from Hb to single, based on bypassing one coil, I think the ideal type would be about a 100k log taper, with the track cut so it goes to infinite at 10 for full Hb.

Álthough resistors can sometimes be used to adjust pot taper, I dont think there is anything you can do with a fixed resistor to flatten the slope of a pot in this case, without also compromising its ability to get to the full Hb sound, but others are welcome to speculate on this...

John

[4real]

Cheers...as I thought....

I have worked out a way in the past to take them apart and replace them with the guts (the carbon strip bit) of a compatible non-p/p and I may have some around. I used them in my tele and particularly the sustainer that uses a 1k 'drive' pot...and the tele's volume control is 1M (though I might have overdone that because it is so bright...but the taper is smooth!)...

I had a feeling that something a lot less would be more appropriate for the spin-select control...it's not bad that it is more of a 'switch' between split and full HB...but I think there might be a little more to be gained from it if there was a little 'range'.

The tone control too I thought I must have messed up as it is extreme in the lower numbers and does nothing after 2...so all or nothing...

It's a little odd that these pots all worked beautifully in the LP with just random selection...then all pots in this one are suspect tapers...but that's the weird thing about randomness I suppose...got a cluster there!

It would be interesting to hear what people think about the resistor thing for the split...how is this resistor wired btw...I figured a solution for a standard pot might be worth while and the 'taper' isn't that important for the spin select control I would think.

...

Does anyone know a brand and supplier for really good push pull pots/tapers...perhaps even something like a 100k pot...but just general pots that are reliable to save me bodging things together (its doable but a bit of a PITA) or for the future.

Thanks for the input though john, I did kind of suspect them...might try some mixing and matching but a future source would be good to know...

[4real]

I was wondering....

Cant seem to find any 100K push pull pots...how would 25K pots work for the spin-a-select control do you think? Should they be audio or linear ideally. With some trouble I could perhaps make a different value from the existing pot and the carbon strip of something compatible.

Otherwise any suggestions on pot brands and suppliers for quality 500k pots...and I guess...for an HSS strat, what value tone cap would people suggest for the single tone pot...and perhaps for a treble bleed components?

[JohnH]

Pete - if the 25k is used as a 2-lug variable resistor to bypass one coil of a series humbucker, then my guess is that it will go from fully single coil, almost to full humbucker but not quite get there. 25k represents the range from 0 to about 1.5-2 on a low end of a 500k log pot, and our experience would support that. I think it could be a good option (probably a 25k linear) if it is of a type where you can crack open the pot and get to the track, then cut the track at the upper end so you can get it to infinite for fully Hb. The trouble is, where to get a pp pot where you can do that without wrecking it? I have only used one type, which I would not want to try this on.

For treble bleed, you probably saw my recent thread on this. I concluded that for 'vintage' type humbuckers and 500k pots, 150k and 1nF was the best choice. That would be my basic suggestion, but you can investigate further if you want:

You have your LP build, which I think has 220k and1nF - which was my previous suggestion. If you have a listen to it in single coil mode and Hb, it will fairly well represent the sounds of an HSS from the point of view of treble contral at lower volume. The difference in going to 150k and1nF will be a bit more low end weight at lower volume, with 150k.

The other option is, if let me know all the relevant details of your HSS build, I can put them in my spreadsheet and suggest some custom treble-bleed values to best suit your guitar. Its very easy to do so Id recommend this just for interest, even if the answer turns out the same. The info needed is:

Pickup types (need to know or guess the pickup inductance, which in the likely absence of actual numbers, we can do roughly based on resistance and whether it is a 'hot' or 'vintage' type)
Switching combinations (will you have series wiring?)
Pot values
Your preferred length(s) of guitar cord
How you use your volume control. eg , with a normal log volume pot, do you mostly use it in the range 6-10 for smallish reductions? or 2-4 to clean up with a high gain? or full range?
Do you actually want the tone to stay consistent at lower volume, or do you want it to get a bit brighter or a bit darker?

The queaions are because the best values are a bit of a compromise, which can be targetted at the most important use of the volume control in your case.

cheers

John

[4real]

Thanks a lot john...will put a bit of thought into it and perhaps a bit of experimentation...I'm not entirely sure that out of all that I had, these last three that ended in this guitar are all weird tapers.

I have previously been able to take them apart and another pot and changed the 'value' and of course in doing so would be able to do some track cutting perhaps.

Being on an island, it's a 100km trip to the nearest place that sells electronics components...LOL...you will see how you are living in the country...and need to work with what I have boxed up after the last move...the LP worked perfectly as far as the pots and tone controls went.

I have a different brand (perhaps alpha) 250K push pull pot and might try that in the volume slot. Fortunately the gutiar is back routed and so it is possible to tinker a bit in there without messing the wiring completely and play the thing a bit.

The pickups are a seymour duncan JB HB...I imagine there is data available on this model or you might know...the 'singles' are stacked noiseless "hot JB's" by fender. They seem to use 250k pots with these apparently.

I do use the volume control and it is bugging me on this guitar. An 'even tone' would be ideal I suspect...on my tele I quite like that it takes the edge off of the sound, but then it has a 1Meg pot in it! On a strat I would do volume swells as well..but at the moment impractical.

On the LP the bleeds make things brighter and this is a good thing and the specs you gave work perfectly to clean and brighten slightly over powered HB's and then turn up to compensate for loss when split...so I'd continue with that recommendation in such an application.

I use about a 10 foot lead but I may need to go a bit longer and I am noticing the dullness when I do increase the length.

However, since I have you about...been doing some "research" and it looks as if bourns then alpha are the best push pulls available (guitar electronics. allparts, etc) and prepared to pay $15 for a properly working volume control. Probably get sucked into some mojo infused tone cap while I am at it...perhaps something in orange LOL.

...

However, since I have you about......Have been thinking that perhaps I should go "active". I routed a secret battery compartment behind the trem block so that isn't a problem. I have a few DIY preamps about I think....nothing 'special', opamp things. There seem to be a few commercial units about as well...I see for instance that GFS has a tiny tone pot board that seems to be a preamp/active tone control...tricky, but perhaps I could mod my pots to work this kind of thing into the tone control after teh controls and perhaps address the cable capacitence and all. There are similar things from artec, so am thinking of seeing if I can source something from them even...their EXP or other boards seem remarkably similar and use a push pull pot for bypass (so I could rewire to keep the phase switch.

www.guitarfetish.com/Neovin-PRE-1-Active-preampEQ-Board-install-kit_p_546.html
www.artecsound.com/pickups/index.html

More likely though, a decent control with an 'active' option built in after the controls in a manner similar to what you have worked on might be the go...maybe a slide switch on the back to go to passive mode and save power while still being plugged in...just in case.

My reading seems to suggest that your experience is that the treble bleed is better left of with active systems?

...

On the pot thing for the 'spin select'...I've dug out some old pots and will try and fiddle about perhaps today and see if there is something that will work better. Most push pull pots seem to be audio tapers unfortunately and 100K seem hard to find...so making one might be the go...25K at a pinch.

On the track cutting thing...I did see someone suggested as an alternative, to use nail varnish. If you were able to get a bit of nail varnish over the track it mingt even be possible without taking it apart. It dries fast and is pretty tough, and worse case is that if it wore out...you'd be back to a standard pot again...LOL...or perhaps the worst is that you glue the pot up while trying.....still it is "an idea".

...

The "singles" are stacked designs and supposed to be quite "hot" and they do sound good and noiseless...but there is a significant lack of power compared to the HB even when split (which surprisingly is almost as loud split as full on!). I've adjusted them as close as I can to the strings and all. It can even be 'useful' with this scheme in a way...there is a graduated increase in volume between the neck setting moving to the N+B in the centre and the three further selections that utilize the bridge...but it would also be nice to have a comparable rounder neck pup sound. I even got out the old volume pedal to experiment with pre-amping and using that to have a more 'on the fly' control over it...but really the solution might well be with a decent volume control on the guitar to work with it's quirks...


Anyway...thanks again for your time and knowledge on this...

[JohnH]

Just a brief reply so far (gotta get more paddocks slashed, kitchen built, fencing done etc...)

Those JBs seem like high output, with high inductance, as can be seen by the high dc resistance suggesting many turns etc. Heres a couple of data sources on them:

www.seymourduncan.com/products/redesign/specifications/

Heres some measurements from a chap on SD (cap values look way too high though)

www.cons.org/music/pickup-data.txt

So all that suggests that the output from this puppy may relatively more sensitive than most to loss of treble due not only to cord capacitance but also loading from pots. Does that correspond to your experience? If having and keeping the higher frequencies is a practical issue, then short cords, and high value pots, particularly the tone pot could be good. My pure guess for pots would be a 500k volume pot and a 1M tone pot, or a no-load tone pot of 500k.

The usual 1nF and 150k treble bleed seems like a good option again for this. but I think you might be very pleased to hear an active option with this pickup - it should reveal alot of high-end detail that might usually be lost. In this case, as you note, treble bleed is not needed nor wanted.

My opinion is that the clearest most tranparent active circuits are just the simplest no-gain JFET buffers. They run on almost no power (like <0.5mA) and just preserve the natural pickup signal with nothing taken away. Once its running, cable length is irelevant and you can even plug straight to a mixer line-in. The simplest version uses one JFET, one resistor and one capacitor (based on the buffer cable ciircuit, but built -in). You could have it switched out, or have two jack sockets, one active and one passive. See my buffer thread in the schematics section.

cheers

John