Low-z circuit matching

[Stilts]

Hi all,

I've just built myself a low-/medium-z humbucker that came out around 1.8k DCR, and apart from a booster before output, I'd like to have a passive volume, blend and tone control to go with it. What sort of pot values should I be using with this pickup type?

Thanks

[Rick Turner]

Try 50K or 100K. Not sure where you're going to get the right kind of blend control for this, though. The righteous ones are essentially stacked center-tapped pots with a log section and an antilog section; they are like pots that are full on at half-way up rotation, and they are easily available in 250 and 500 K values...I get them from AllParts. A 250K will work for you, but the taper may be a bit weird.

This is one of those things where trying and listening are better than using formulas, though you can use as a rule of thumb the general kind of DCR ratio/multiple used for pots with Fender single coil and standard Gibson-style humbuckers..

You'll want a fairly substantial cap, too...like a .1 mfd. Once again, try and listen, try and listen.

[Mike Sulzer]

Hi all,

I've just built myself a low-/medium-z humbucker that came out around 1.8k DCR, and apart from a booster before output, I'd like to have a passive volume, blend and tone control to go with it. What sort of pot values should I be using with this pickup type?

Thanks

1.8 K with which wire size?

[bbsailor]

Try 50K or 100K. Not sure where you're going to get the right kind of blend control for this, though. The righteous ones are essentially stacked center-tapped pots with a log section and an antilog section; they are like pots that are full on at half-way up rotation, and they are easily available in 250 and 500 K values...I get them from AllParts. A 250K will work for you, but the taper may be a bit weird.

This is one of those things where trying and listening are better than using formulas, though you can use as a rule of thumb the general kind of DCR ratio/multiple used for pots with Fender single coil and standard Gibson-style humbuckers..

You'll want a fairly substantial cap, too...like a .1 mfd. Once again, try and listen, try and listen.

Hello All,

My general rule of thumb is to make the load resistor/pot value to be near 40 times the DCR of the pickup. This works well with low Q pickup coils with little added inductance by the cores. But, with larger or more inductive cores I would up the ratio to 50 times the DCR to be better in the ball park.

If the sound is too shrill, lower the pot or load value by about 25 percent and listen again. Try again if still too shrill. Listen with the same length (assume 10 ft) of cable you will be using between the guitar and amp, because the longer/cheaper cords add more capacitance, like installing a permanent 350pf to 500pf capacitor across the output. But, at this low impedance, this should not be too much of a problem. Most of the equalization should be able to be done by the amplifier since this medium impedance pickup has fixed (1) lower resonance amplitude or Q and (2) a higher (but broader) resonance frequency. Your active EQ should be able to fine tune it. If not, wind pickup coil(s) again in another impedance range and repeat.

I hope this helps?

bbsailor

[Rick Turner]

bb and I are pretty much in agreement here. 1.8 x 40 = 72 K...a very inconvenient value for real world available pots, and 50 K may load the pickup too much though it will work...kind of. 1.8 x 50 = 90 K...close enough to 100 K to go for it.

[Enzo]

If the value of the pot is critical, you can fudge pot values with parallel resistors.

Go over to geofex.com,and under Tech Tips find the Secret Life of Pots. Scroll down to the material on pot tapers and such. Perhaps it could be useful in making a 72k pot out of a 100k pot.


Also, pots are notorious for being of loose tolerance, if you measure your pots from the bin, you may find a 50k pot that already measures 72k.

[Rick Turner]

And this is indeed an issue which begs the question: "How important are potentiometer tolerances? Or cap values, for that matter?" Let's say you had a Les Paul and all four pots were a negative 20% on resistance lug 1 to lug 3. And the next guitar you wired just happened to have pots all in the + 20% range. Well, you've just wreaked havoc on all your careful pickup winding... Here we are getting the turns count exactly right to within .1%, and I, for one, match coils to +/- 2%. And then you use real world passive components between the pickup(s) and the amp, and it all goes to hell. Four 500 K pots present a 125 K load to two pickups in a Les Paul...unless they're actually 400 K pots. Or 600 K pots... And that's not counting the amp or stomp box impedance load. I know that's an exaggeration, but not by much. You would not accept that much tolerance swing in your pickups, I dare say.

[bbsailor]

I agree with Rick.

Remember the old Gibson days when they used a special 300K ohm set of pots in their Les Paul humbucker guitars to somewhat tame the high end. Even a 250K pot in parallel with a 1 meg ohm amp input impedance represents a 200K ohm load on a single coil pickup and represents a 400K ohms load when using 500K pots on a humbucker. Now add the 300pf cable capacitance and you are starting to cut off the upper harmonics if, (1) your amp and speaker can produce them and (2) if your hearing is good enough to hear it. As pickups evolved into being louder (more turns), there was a need to return to 500K pots to retain more high end and let the higher inductance pickups breath.

bbsailor

[Rick Turner]

I'd suggest that you can't judge pickups (high Z at least) nor do adequate QC at all unless the comparisons..."scientific" as well as "subjective"... are done with an absolutely known impedance load. That probably means no pots and a switchable verified set of load resistors with no pots or caps in the way. OK, so put a bunch of caps on another switch. Maybe we should come up with a MEF standardized pickup loading box and a protocol for testing. Easy enough to wire a pickup selector switch directly to an output jack and then use a specified cable into "the box" and out to "the amp"...which should be standardized as well with regard to input impedance. Maybe the damned thing should even be buffered so we know that the load is 250K or 500K or 1 meg or whatever.

There isn't anywhere else where standards are likely to be set than here. I just don't think you'll get Larry DiMarzio agreeing with Seymour and whomever at Gibson and whomever at Fender or Rob Turner or the whomever at Music Man or Hartley Peavey, or especially John Hall at Rickenbacker, etc.

They can't even fucking agree on color codes...

The pickup business is really screwed up compared to microphones or loudspeakers...

[Stilts]

Thanks for the insight everyone, I have a few different value pots on hand that I can have a fiddle around with, so I'm sure I'll find something. Very good points about the wide tolerances of parts in comparison to the design of the pickup, so really to me that says trial and error is the best way to go to find what I like the sound of - the pickups are only for a personal project anyway, and now I have a ball park to work within.

1.8 K with which wire size?

32 AWG I think, if that makes any difference now

[Rick Turner]

I think this thread points out that a pickup is merely part of an entire system, and that is particularly true right up to the first stage of buffering/preamplification no matter whether that is in the instrument or downstream at the amp. The interactivity of pickup, pots, tone control caps or inductors, interior cables, and guitar cable is known, understood, and yet seems to be left out in a lot of discussions of pickup tone.

One might want to carefully document pot and cap values in classic Les Pauls, Teles, and Strats as well as the minutia of the pickups themselves if vintage tone is the goal.

[bbsailor]

Thanks for the insight everyone, I have a few different value pots on hand that I can have a fiddle around with, so I'm sure I'll find something. Very good points about the wide tolerances of parts in comparison to the design of the pickup, so really to me that says trial and error is the best way to go to find what I like the sound of - the pickups are only for a personal project anyway, and now I have a ball park to work within.



32 AWG I think, if that makes any difference now

Stilts,

1.8K of AWG 32 is 11,108 feet of wire. I suspect that you are using a much thinner wire to fit on a pair of humbucker bobbins. You are probably using a tightly packed AWG 38 or a more loosely packed AWG 40 to arrive at your DCR for two bobbins in series.

bbsailor

[Rick Turner]

It's pretty important to keep track of all the details, especially the ones that are easy to jot down...wire gauge and source, insulation type and build, number of turns, etc. You can certainly wind pickups with little more than a crank, some surplus wire and hopefully, an Ohm meter, but if you don't track how and what you make, how can you ever reproduce the results if you like what you hear?

[Stilts]

Stilts,

1.8K of AWG 32 is 11,108 feet of wire. I suspect that you are using a much thinner wire to fit on a pair of humbucker bobbins. You are probably using a tightly packed AWG 38 or a more loosely packed AWG 40 to arrive at your DCR for two bobbins in series.

bbsailor

I pulled the wire off some old Dimarzio split jazz bobbins from the 80's, so my estimate could very well be wrong - I don't have any particularly accurate measuring gear. The design is actually a quad coil humbucker, basically two split jazz pickups wired together. I've also just realised that the 1.8k was only for one pair of coils, oops
Incidentally, the turn count was about 1800 each coil for the bridge side and about 1500 each coil for the neck side of it, so overall it came out about 3.5k DCR in series

It's pretty important to keep track of all the details, especially the ones that are easy to jot down...wire gauge and source, insulation type and build, number of turns, etc. You can certainly wind pickups with little more than a crank, some surplus wire and hopefully, an Ohm meter, but if you don't track how and what you make, how can you ever reproduce the results if you like what you hear?

I did jot down all the specs, it just took some digging out And as far as the crank goes, my DIY one wasn't very good so I just wound it all by hand - good thing I wasn't making a standard guitar pickup haha

Edit: Must have had a total brain fart on this - the wire gauge should read something more like 42 rather than 32, sorry for the confusion. This week has been more tiring than I thought...

[Rick Turner]

In the kindest possible way, I'd like to suggest that before anyone posts questions here about a pickup they've made, that the winder be prepared to provide as many of the pertinent facts and specs as possible. Only then can the rest of us possibly chime in with advice, solutions, or suggestions. Accurate turns count, wire gauge, and DCR are the bare minimum of the important specs. Then things like magnet type, magnet circuit type, and inductance would be nice. And then an idea of resonant frequency, Q, and all that would really nail things down better.