Bad taper w/ Q-tuners PUs & 1 Meg-Ohm Pots

[stubbsonic]

Almost done with my crazy rewiring project (see below if you are interested). One problem remains. I can't get the taper of the pots to work right. 1-Meg-Ohm pots are recommended for the Q-tuner pickups. I bought two linear taper pots (recommended by a tech on this site), and two audio taper pots (recommended by a local bass tech). I tried both and had the same problem. The pot comes on very suddenly during the first 15% of the knob's throw. It ramps up pretty gradually after that. I tried both audio & linear taper. I'm using a treble bleed cap, and tried with a 100K resister (in parallel) and without. No noticeable difference. Eerg.

Here's some more details. It's an insanely cool project. Took my Ibanez 5-string, put on q-tuners, shielded everything, added coil tap switches, and added a transformer so the rig is switchable between true low-z (or high-z) balanced and high-z unbalanced.

Believe it or not, everything works GREAT!!! The bass sounds awesome and is really quiet even on single coil settings (though not perfectly quiet). The volume pots are the only thing that doesn't work.

[greenboy]

Can't help you on what to do there - I'm just running my Q-Tuners through a switch and on to the jack in both my Five and Six, and do all my control with my V-Bass. I love 'em more and more, especially since I'm often jumping around to different tunings down to F#0 and often big variations in gauge; here the tonal and string-balance setup that is possible with Q-Tuners reigns supreme.

They do low fat strings really well, really integrates those troublesome sub-E pitches nicely. I also like the extended and smoother top they provide, as some of those tunings are a little guitaristic on the skinniest strings.

[walterw]

Originally Posted by stubbsonic

... I can't get the taper of the pots to work right...The pot comes on very suddenly during the first 15% of the knob's throw. It ramps up pretty gradually after that.

hmm. the linear tapers might do that (jump up quickly from "off"), but i would have expected the audios to have the opposite issue, dropping off fast from "10".

the treble cap and/or the resistor will both exacerbate the first effect, as they leave either more treble (cap) or more everything (resistor) in the signal as the pot is turned down.

could your built-in direct box be changing something? maybe it would be worth hard-bypassing that circuit to see what happens.

[stubbsonic]

I think you are onto something, Walter. I have a bypass switch built in. When I flip the switch, I get both problems (jump up quickly from "off" and dropping fast from 100% on)

I hadn't really checked out the pots in every mode (i.e., with TRS cables, transformer in or bypassed, and TS cable transformer in or bypassed). As it turns out, I am getting all kinds of problems in the various modes. Back to the drawing board.

I need to do some more trouble-shooting. It's a true rat's nest inside that bass! I can barely get the cover on!

At this point, I'm considering keeping the balanced internals (for no reason other than it's already wired that way)-- but getting rid of the transformer. I do want to know where I messed up! I'm going to cry.

I've been very careful about following directions, and downright anal about my combination of the various ideas I've put together in to one super bass. However, my own lack of experience is biting me in the ass.

I appreciate the advice on this forum. Good folk here.

[BassicJohn]

You might have the audio taper pots wired backwards which would create something like you described. Try reversing the the two outside connections to the pot.

[stubbsonic]

The pots both go CW for up and CCW for down. As I look at the pot (from inside the bass with the lugs "on top") I have ground on the left, input in the center and output on the right. It used to be wired as the diagrams indicate, but I had no independence between the pots. If one was off, they both were off. Someone suggested swapping the wires so the input was in the center. It fixed the issue of no independence. But is that causing this other issue? Hmmm.

[stubbsonic]

Ok. I bypassed the transformer. Now the neck volume works right, the bridge pickup shuts off when the neck volume is down (but not vice versa). That's the problem I had before when I was advised to wire the input to the center lug.

I want to mention that I have been really careful about wiring this up. So there weren't any sloppy mistakes. It's just a complex little switching scheme (which works perfectly).

Getting the volumes to work is turning out to be trickier than expected.

[stubbsonic]

Ok. I did some more tests.

When I'm running unbalanced TS into an amp, the symptoms are described in my last post.

When I run TRS (balanced- but high-z) into a mixer input, the results are more symmetrical. There is a lack of independence between the two pots. And the taper is fine at the bottom part of the travel, but comes on very suddenly in the last 5% of the throw.

Because I have +/- separate and running through dual pots, it is causing unexpected loads that might run contrary to the simple hook ups that Erno (q-tuner guy) is expecting when he recommends 1 meg-ohm pots.

Also, my misguided quest for a balanced out has created even more unnecessary confusion.

Ultimately, I may need to back off of all these things (except the switching, which I really like)-- ooof. What a colossal waste of time & effort!!

I'd appreciate some help picking up the pieces.

[walterw]

my vote?

ditch that quixotic balanced idea entirely, two volumes (pickups both have to go to the center lugs for independent operation) tone(?),and your coil-splitting switch. there's something to be said for a minimal signal path for purity of tone.

at that point, try the linear volumes with no caps or resistors on them.

[stubbsonic]

Consider it ditched. Currently, the negative lead is shorting to ground at the jack (when the ring & sleeve are shorted by an unbal cable. That doesn't seem to fix anything.

I had linear pots in there and had pretty severe treble loss in non-full-up positions. Perhaps that won't be as bad if I'm rid of all the balanced business.

FYI, here's the diagram (which I also posted over on my other thread).
Disregard the transformer and that 4PDT switch. The coil/pickup selecting
switch scheme comes from www.1728.com

http://www.bubbastubbs.com/kurz/MyBalancedRig2.gif

FWIW, apart from the problems with the pots, the tone has been clean, quiet and very pleasing.

[SGD Lutherie]

Are those dual ganged pots? Do the tapers run in the same direction on both decks? For instance, blend pots have one side running the opposite.

And why are you running each coil to a volume pot? Just switch the coils before the pots, and use standard pots.

Your two decks of 1M is making them look like 500k pots anyway. Add them all together and you have a 250k load on the pickups.

[stubbsonic]

dual pots for balanced out (as mentioned on the other thread).

Each coil is not going to the pot, the final output of the coil selectors is going to the pot.

Thanks for your point about the cumulative load of all the pots on the circuit. That's probably a major factor, but because I've complicated matters beyond recognition, I'm not sure it will be easily resolved.

[JackANSI]

When I get to this point in an experiment, I walk away for a while.

When I come back I break it down into the stages I need and the stages I want.

I would guess you need a working bass but you want balanced out.

Wire up the simplest approach, just volumes (buy new 1meg audio taper pots to be sure you got the right ones!), and give it a try. (If your switch arrangement is working 100% and not causing the problems, keep it) When you get that working, treat it as a single block. Then wire up your balancing transformer like it should be and connect the output of your finished stage 1 block. (I never used a transformer inside a bass, I went with a balanced line driver IC, so I'm of no use there)

Working with everything all a once is complicated, simplify until you can understand each piece before you pack them together as a whole.

[SGD Lutherie]

Originally Posted by stubbsonic

dual pots for balanced out (as mentioned on the other thread).

I think that's your problem right there. You really can't get a balanced output from a pickup like that. Microphones have a balanced output, but that's from the transformer or preamp, and they don't have volume pots.

Balanced outputs are for noise cancelation in the cables.

My suggestion is to use standard pot wiring. You can still use 1M pots if you like, but by nature of the way guitars and basses are wired, they aren't balanced.

[stubbsonic]

Originally Posted by JackANSI

When I get to this point in an experiment, I walk away for a while.

...

...break it down into the stages I need and the stages I want.

...Wire up the simplest approach, just volumes

... (If your switch arrangement is working 100% and not causing the problems, keep it)

...When you get that working, treat it as a single block.

...Then wire up your balancing transformer like it should be and connect the output of your finished stage 1 block.

...Working with everything all a once is complicated, simplify until you can understand each piece before you pack them together as a whole.

This is VERY helpful advice (for life, too). What tripped me up was the fact that the pots add (or subtract?) load from the entire circuit in ways that could not have been predicted by those who were recommending those values. How could Erno (from q-tuner) know I was going to try all these balanced shenanigans.

Because the pots ARE the problem, I might decide to eliminate them (or have a master volume post everything-- though I suspect I may still run into this problem until I can determine what value of pot will work best as a post-everything pot.

With the switches, I can get a variety of blended sounds pretty quickly.

[stubbsonic]

Originally Posted by SGD Lutherie

I think that's your problem right there. You really can't get a balanced output from a pickup like that. Microphones have a balanced output, but that's from the transformer or preamp, and they don't have volume pots.

Balanced outputs are for noise cancelation in the cables.

... by nature of the way guitars and basses are wired, they aren't balanced.

I would like to quote from the naiant website where I got this idea:

"A guitar pickup is essentially similar to a dynamic microphone coil. For decades, dynamic microphones have been wired with the voice coil attached to the primary of the microphone's transformer, and not referenced to ground ('floating'). .... ...By and large, dynamic microphones are very quiet devices as a result of the combination of transformer isolation and balanced, floating transmission lines throughout, as well as shielded, humbucking coils....

[and]

Fortunately, it isn't necessary to use two coils (humbucker with a coil tap, etc.) and ground reference everything. It thus also isn't necessary to use the DPDT switch to go between balanced and unbalanced output. Simply float the pickup, and when a TS plug is connected, the guitar's TRS jack will ground reference one side just fine, no user input required. The same TRS jack will work balanced or unbalanced, depending on the cable that is connected. Backwards compatibility is maintained!"

The q-tuners are super quiet, so I can't really attest to an A/B comparison where the balanced signal was quieter than the unbalanced. The gain structure and impedance are so different that any comparison was not very practical. I will say though that I got a very hot signal that was very clean and VERY quiet!!

If the neg lead from a pick-up is shorted to ground, then half the voltage differential is given up. The signal-to-noise on a bass or guitar is very good and the inputs are designed to make it work just fine. In my semi-ignorance (the most dangerous kind), and encouraged by the Naiant schematic, I set out to combine the super-seven switching and the naiant balanced idea. The pots were an unexpected complication. They seem so innocent!

[walterw]

the thing is, that entire "balanced" idea looks like a solution in search of a problem. if the whole point was to reduce "noise", then what noise are we talking about?

i doubt it would do anything about hum produced by the pickup itself, which is coming through the air right into the coils.

in practice, 15 feet of shielded guitar cable between the bass and its first destination doesn't add any appreciable noise.

so now we're running pickups through all sorts of extra tone-robbing wire, pots, transformers and whatnot to "fix" a problem that isn't there to begin with.

the point of balanced microphones is to allow for literally a hundred feet of cable between the mic and the mixer, as well as multiple splitting of that signal, without appreciable loss or noise induced in the cable.

on top of that, it strikes me that the whole point of the q-tuners using 1 meg pots is to have as little "stuff" between the pickups and the destination as possible!

[SGD Lutherie]

OK, as I mentioned before:

1) Microphone cartridges attach to a transformer before leaving the mic. That's why they are balanced. The floating ground comes from the center tap. If you just attached the cartridge up to the XLR it wouldn't work properly.

2) Microphones don't have a volume pot attached after the cartridge, or the transformer. It wont work.

3) Your amplifier does not have a balanced input. If you don't have one side of the pickup grounded, it wont work.

If you do want to do it, the easiest way is the way EMG does it. Take an op amp. One side of the pickup goes to (+), the other end goes to (-), and the connection between the two coils is the ground. Since humbuckers are differential in nature, that would give you the plus and minus swing.

And you probably wouldn't hear a difference. There's very little reason to balance the signal right from the pickup.

Humbuckers are already differential, that's how they cancel hum. Mics are balanced because they have VERY little signal. The coils are about 10 Ohms. The internal transformer steps that up and makes it balanced. This is to kill hum induced in the mic cable, not the mic. It has little to do with the signal voltage swing.

And still they need a preamp at the end. The coil doesn't pick up much noise partly because it's low impedance.

As far as:

The q-tuners are super quiet, so I can't really attest to an A/B comparison where the balanced signal was quieter than the unbalanced. The gain structure and impedance are so different that any comparison was not very practical. I will say though that I got a very hot signal that was very clean and VERY quiet!!

Q-Tuners are just humbuckers. They aren't even shielded. The sideways coils help a little, and they have very little ungrounded metal in them. There is nothing in the design that makes them quiet.

The real test is to sit in front of your computer monitor... do you hear a buzzing noise? That's the lack of shielding. But shielding wouldn't look good in a clear pickup.

The gain structure and impedance of Q-Tuners is not all that radical. A BL-4 is either 12k or 14k. That's actually on the high impedance end of passive pickups.

The reason for this is they use air coils that don't have metal cores, so the inductance is lower. That's what helps them have the extended top end. But the lower inductance also means the output would be lower than a pickups with metal cores in the coils, so they have to wind them hotter. But you can wind pickups hotter with neo magnets without them getting muddy, especially with low inductance coils.

The neo magnets also make up for the low inductance, and don't contribute any inductance of their own. You will notice that the pole pieces don't touch the neos. This prevents the top end from being over the top by knocking it down a notch.

The other aspect of the Q-Tuner is the "side winder" setup of the coils. This gives them more of a single coil tone. The old Bill lawrence L-250 Strat sized pickups are made like that, but they only have the single blade pole in the middle.

So Q-Tuners are a very nice design, I like them, but nowhere as radical as an Alumitone or Transsensor. They don't even have coils, except for the small built in step-up transformer.

Obviously I have some experience with neodymium magnets and coil arrangements. And you can see everything going on inside a Q-Tuner. I wont show what's in mine though, but you can sit in front of a computer monitor with no buzz. Shielding isn't pretty however.

[SGD Lutherie]

Originally Posted by walterw

the thing is, that entire "balanced" idea looks like a solution in search of a problem....

the point of balanced microphones is to allow for literally a hundred feet of cable between the mic and the mixer, as well as multiple splitting of that signal, without appreciable loss or noise induced in the cable.

on top of that, it strikes me that the whole point of the q-tuners using 1 meg pots is to have as little "stuff" between the pickups and the destination as possible!

+1.

You typed this up as I was typing mine.

It's no fault of stubbsonic though... you just have to watch what you read on the internet. The guy writing that is missing the point that guitar pickups put out a lot more voltage, and aren't running 100 feet of cable before they get to the mixer (think of those mic snakes).

[greenboy]

Originally Posted by SGD Lutherie

Q-Tuners are just humbuckers. They aren't even shielded. The sideways coils help a little, and they have very little ungrounded metal in them. There is nothing in the design that makes them quiet.

The real test is to sit in front of your computer monitor... do you hear a buzzing noise? That's the lack of shielding. But shielding wouldn't look good in a clear pickup.

{...}

So Q-Tuners are a very nice design, I like them, but nowhere as radical as an Alumitone or Transsensor. They don't even have coils, except for the small built in step-up transformer.

Obviously I have some experience with neodymium magnets and coil arrangements. And you can see everything going on inside a Q-Tuner. I wont show what's in mine though, but you can sit in front of a computer monitor with no buzz. Shielding isn't pretty however.

Funny, I never noticed my Q-Tuners being noisy when I'm sitting at my computer, unlike many other pickups I've had. So I just cranked my amp and put my bass right up against my 19" CRT (that's right, old tech for better color accuracy in the price range, at the time I bought it anyway), and moved it to every practical orientation. I really wasn't hearing much that wasn't there before when it was 6' away.

Perhaps it's my shielded pickup routes and cavity, and the Q-Tuner's combination of elements including the air coil design, but I'm glad Erno didn't shield the top of the pickup because I've heard the effects of that before on other humbuckers: tone rob.

I really don't care if they are the MOST radical pickup ever devised, they really supply tone that works for me where others have not, and practical elements I get use out of like the three rows of adjustable hex heads ferinstance. I'm not ready to write them off simply because they aren't Bass Bars, or yours ; }