Mixing two pickups

[Mike Sulzer]

You said it's the same, buffered or not...

No. What I said was that the effect of one pickup loading another identical one does not change the frequency response of that pickup. The inductance is halved in the system, and the frequency response of the system changes because the effect of the cable capacitance interacting with the changed inductance. The analysis of the initial question, whether or not adding passively is like adding with buffers still has to be completed.

But you have not answered my question. Do you think that Rick's mental model of a pickup as mostly just a resistor is correct? If so, how do you justify that belief when there are so many measurements and theoretical discussions that show that to be untrue?

What about you, Brad. Are you willing to disagree with Rick when he is obviously wrong?

[RedHouse]

...What about you, Brad. Are you willing to disagree with Rick when he is obviously wrong?...

Well Mike with all due respect I'm hardly interested in mathmatically modeling the guitar/pickups/amp system or continual engagement in ongoing debate about what model type would things need to be, or what equations or theorums to apply. That's for you and a couple others here who enjoy that kind of conversation, I find it passingly interesting and often boring, no disrespect intended.

The rubber meets the road when one plugs-it-in, turns-it-on and gets after it musically.

Over the past 35 years I have in fact tried most all combinations of pickups, wiring, polarities (electric & magnetic) low and high impedance, buffered and unbuffered, high and low capacitance transmission cable etc ...ad infinitum, ad nausium.

No matter what part of the system, and lets make no mistake that tone is in fact created by the system and not one piece or it's parameters. Whether it's a treble-bleed circuit (which works regardless of the pickup and cable parameters) or a buffered pickup mixing system, each has it's own tone and then it's purpose. Interaction between elements of the system is what creates/causes tone, there's just no getting around it.

Yes I've tried buffered coils and found buffering pickups/coils prior to the mixing/volume/switching parts of the system works very, very, well. It has a different tone and definately if not completely removes the negative interaction between pickups/coils compared to when they are passively mixed as per Gibson/Fender style or Rick/JazzBass style.

Further staying away from the electrical modeling state of mind, the results of pre-ctrl buffering IMHO has the purest tone, whether this is what the user/player/musician desires is another thing.

Most bass players embrace this as do many of the more modern thinking guitar players, but many older guitar players and players who are trying to do a vintage tone vibe thing are seeking that tonal interaction between pickups/controls/cable/amp/speakers so that also is a valid recipie for tone, and really doesn't need any further diagnostics it's a tried-n-true effect that only needs further tweaking to dial-in the player to his tone.

What I absolutely do agree with is Rick's statement above "listening first and searching for explanations after". Sometimes the circuits that would seem right when brainstorming don't sound as good as basic or elementary circuits. As David mentioned already in a post above, the Alembic Strat-o-blaster circuit isn't exactly a prime example of preamp engineering, but the damn thing works and works great, as does the Don Tillman one too, and the Jack Orman mU amp is my favorite to drive the front end of a JTM45 with KT88's.

Back to your question Mike, what's wrong? Ricks articulation of your modeling debate? and BTW what's the obvious part?

[Rick Turner]

I do NOT believe that the resistance of a parallel coil/pickup is the only factor in the alteration of the frequency response of a pickup in a real world circuit with an amplifier, but I KNOW...simply by listening...that it's the more important factor and to use Mike's word, the most obvious one.

All any of you has to do is the very simple experiment that I proposed, and forget about your 'scope or LCR meter or textbook. Just plug the damned thing in and listen. Then go figure out why. Until Mike or any other disbelievers (who seem to number just about zero here) actually listens to this whole thing, this is not a real debate, it's a dialog in fantasy land where what I can only assume is misunderstood book knowledge is being supported over simple raw audio evidence.

Do the parallel pickup (away from strings) and like resistance resistor experiment and learn something.

[frankfalbo]

I had this conversation with Mitch Gallagher at Sweetwater recently because he was trying to quantify the net effect in the center position on a Les Paul with, say, a 250k pot on the neck and a 500k chosen for the bridge. In that case, the other pickup's load usurps the net load differential from the combined pot values. The pot value's net effect on the tone in the center position is nearly inconsequential by comparison. I could agree with the notion that the resistive load is the primary differentiator, and that a buffer in front of the sum rather than after makes a huge difference, again primarily replicable by adding resistive loading. But I'm not much for fancy book lernin'.

[Rick Turner]

Frank, absolutely...

Look, I can hear the loading effect of just one 500 K pot on a humbucking pickup as a 500 K shunt to ground. Drop that shunt resistance down to the equivalent of another pickup and the effect is quite dramatic.

The pots shunt thing is one of the reasons I like to put in push pull pots with controls bypass function. The first guitar I did the bypass on was a Tele that had been rewired and that the client wanted re-rewired back to close-to-stock, but there was this extra hole in the front plate. What could I do with that that would NOT affect the Tele-ness of it all. So I thought...just put in a pots bypass and see what happens. Well, what happened was that my client (Dorian Michael) played a gig and when it came time for him to rip a solo, he hit the switch and his bass player's head snapped around thinking that Dorian had just kicked down on a new stomp box. Nope, just a silly little toggle switch that took two 250 K pots out of the picture. The 125 K worth of shunt being gone brought up the sparkle and volume in a very noticeable way.

You simply have to listen to pickups, wiring, etc. to get it. Then go searching for the reasons.

This isn't even getting close to some of the stuff we deal with...magnets, for instance. Talk to magnet experts...they have a very hard time believing that we can hear the difference between Alnico II, Alnico IV, ceramics, etc., etc. They'll quote you Gauss and retentivity and every other damned thing, and it doesn't come close to what we deal with as far as what I call the "magnetic" signature tone of pickups. Science hasn't gotten there yet, but our ears and brains have.

[Marko Ursin]

Whoa, this discussion is so hot I'm afraid my potting wax is going to melt away from the coils sooner or later
Thanks for your comments.
I don't even try to understand all this theory behind pickups loading each other or not. I hope (and believe) I can make the combined pickups sound more like they really sound by buffering them. I assume that buffer before volume pot takes the effect of volume pot away from the sound. I mean does the pickup sound closer the same like when wired straight to the output jack? If I put volume pot before buffer the sound is closer to what I get with passive volume.
Marko

[Rick Turner]

If you want to hear how pickups really sound...with a given load...try wiring one direct to a jack and use a very short cable to an amp. Yes, you'll still have a bit of capacitive loss of highs from the cable, but what you'll hear will be close to the truth. An alternative is to use a very high quality unity gain buffer mounted as close to the pickup as possible, and then you can use a longer cable.

Anything you do to the signal path before that first stage of buffering, whether it's outboard or on-board, will affect the sound of the pickup. A volume control, a tone control, excess cabling, particularly if it's coax (think Gretsch hollow body or Gibson 335/355) will affect the tone of the pickups.

The only way to get away from it is to buffer each pickup and then actively combine them, and then, for the very cleanest system, use a line driver/buffer after any controls to drive the signal down to the amp.

BUT...this is just one way to do it all. Many guitar and bass players have gotten entirely used to the way passive volume and tone controls interact with pickups and pickups interact with one another. So all this becomes a set of artistic choices, NOT an absolute "this way is better than that way" kind of thing. I mean are you really going to argue with Peter Green's tone from the early Fleetwood Mac days where he was passively mixing out of phase pickups? Or can you dis any of the great guitar or bass sounds that have resulted from what we're debating here?

It's all about how it sounds, not about what some electronics textbook says is right or wrong. The science is there to help explain the art, not rule it.

I personally am a fan of the sound of pickups wired in series and then buffered. Big, fat, and then the buffer will preserve the sound. I once did a rotary pickup selector circuit for a two pickup guitar that went:

1) pickups in parallel, out of phase
2) pickups in series, out of phase
3) bridge pickup only
4) both pickups in parallel, in phase
5) neck pickup only
6) both pickups in series in phase

And with a 4th deck on the switch, I was able to compensate the gain of the preamp fed by the pickup selector switch so all the switch positions came out a very close to the same output from the guitar. That was intentionally taking advantage of the odd interactions between pickups in the passive realm, and then buffering the resultant signal so nothing else would be altered or lost. Worked great, it's just that guitar players hate rotary pickup selector switches, so I gave it up. Might look back at it though, using one of the 5 position Strat super switches.

The trick is in knowing what you gain and what you lose in both the passive world and with buffered pickups. Then you can choose to go one way, the other, or combine the two worlds to get interesting tone.

Just don't forget the digital tone controls, though...

Five digits on each hand...

[Rick Turner]

One other thing...

Try wiring a 5 meg pot as a shunt between hot and ground, and listen to what happens when you change the load resistance on the pickup. Yes, you'll be messing with the volume somewhat, but if you can compensate for that, you'll hear how changing the load changes the resonant peak of the pickup. You may find a sweet spot. When you do, disconnect the pot and measure the shunt resistance that you liked. That may be an ideal load for that pickup which you could achieve at the front end of a buffer/preamp.

I do loading tricks with piezo pickups, too, though with them being capacitive in nature, the lower the load, the higher the low frequency cutoff point. But just as audiophiles find "perfect" loads for phono cartridges, so to can we play with this in the pickup realms.

[David Schwab]

No. What I said was that the effect of one pickup loading another identical one does not change the frequency response of that pickup. The inductance is halved in the system, and the frequency response of the system changes because the effect of the cable capacitance interacting with the changed inductance. The analysis of the initial question, whether or not adding passively is like adding with buffers still has to be completed.

And what did that have to do with the talk about buffering pickups to prevent them from loading one another? Does a buffer load another buffer? That's the question, since buffered pickups don't "see" each other as far as impedance, etc.

But you have not answered my question. Do you think that Rick's mental model of a pickup as mostly just a resistor is correct? If so, how do you justify that belief when there are so many measurements and theoretical discussions that show that to be untrue?

I think pickups are both resistive and they are obviously inductors. Would putting a resistor in parallel simulate the two pickups? It probably gets close. Would putting an inductor do something similar? We know what you get when you put a resistor in series with a pickup, and when you use one in parallel. It's a common way to alter the tone by loading the pickup down. This is even used in some commercial guitars, like the PRS Santana model.

What I do know is that Rick has been doing this stuff for a long time.

We really weren't discussing why pickups load each other, we were discussing how to prevent it using active mixing. The rest is pedantic.

[Rick Turner]

David, rather than being pedantic, I think that the thread just took an interesting left turn. Perhaps much of this discussion would be better in a different thread, but here we are.

Much of this is difficult to unravel...for instance, inductors have DC resistance, too. Much of what we theorize about pickups is nearly impossible to separate out. For instance, is the mode of operation of a pickup nothing more than moving magnet? Or in a humbucker, is the string a moving magnetic shunt? (It sure is with the micro humbuckers that Roland uses for their synth pickups...) Or does the string disturb the magnetic flux thereby inducing current in the coil? What it is is all of the above... There is no one simple explanation of how pickups work, and different designs work through different mixtures of modalities.

To go slightly left of center again, one of the big breakthroughs for me was rewinding classic coil forms...humbucker, Tele, Strat, P-Bass, J-Bass, Guild/Hagstrom
Starfire bass pickups...as low impedance pickups wound with 7 x 44 Litz wire. The frequency response and resonance of the coils is completely out of the audio picture with these...yet there's still an essential quality to each pickup that is there in the standard high impedance versions. There's a signature tone that comes from the exact dynamic three dimensional geometry of these classic pickups that is independent of the LCR filter of the high impedance coil(s). That stuff is not in any textbooks on electronics that I know of, yet it is as true as can be. There was even stuff going on in the low end...which I did not expect...with "merely" going to low impedance coils. The bottom end is tighter...I'd even dare to say faster...and cable guru George Cardas explained it to me in terms of improved group delay...yes, phase response down in the lower regions. I know we don't generally think of magnetic pickups as being bandpass filters, yet they are.

[David Schwab]

I once did a rotary pickup selector circuit for a two pickup guitar that went:

1) pickups in parallel, out of phase
2) pickups in series, out of phase
3) bridge pickup only
4) both pickups in parallel, in phase
5) neck pickup only
6) both pickups in series in phase

And with a 4th deck on the switch, I was able to compensate the gain of the preamp fed by the pickup selector switch so all the switch positions came out a very close to the same output from the guitar. That was intentionally taking advantage of the odd interactions between pickups in the passive realm, and then buffering the resultant signal so nothing else would be altered or lost. Worked great, it's just that guitar players hate rotary pickup selector switches, so I gave it up. Might look back at it though, using one of the 5 position Strat super switches.

I remember reading about that trick with the compensated gain. Slick idea.

I always liked the six position rotary switches, like on the L6-S, but it is nice to have a toggle to switch out of that to the bridge pickup. I've done that on a few guitars.

[Rick Turner]

The other thing about doing the rotary switch that way was that it went very logically and intuitively from the thinnest sound...pickups in parallel out of phase...to the fattest...pickups in series in phase. You didn't have to intellectually know what was going on to thin out or fatten up your sound. With a switch like that on the passive side of the electronics followed by a preamp (with or without EQ and doodads), you can get the best of both worlds if that rings your bell. I found it very useful on my own guitar. Maybe I'll do it on the Model T I'm building for myself and do it with the double horseshoe pickup combined with one of those vintage Tiesco pickups that I truly love.

[Mike Sulzer]

OK, Rick, I did your test, and now by your own rules (listen first, explain later) you have to listen seriously to my explanation. This test is easy for me to do because I have a guitar I made where it is easy to remove a pickup out the back and let it hang without disturbing anything. (I made my first guitars, a bass, including the pickups, back in the early sixties when I was in high school; so I have lots of experience with the technical stuff, and I have learned the theory since then. This guitar I made a few years ago.)

Results:

1. Pickup with hanging pickup in parallel: The sound compared to the pickup alone has the thin sound that experience shows is the result of raising the resonance to a higher frequency than one usually wants it.

2. Pickup with resistor equal to its resistance in parallel: First, the level is way, way down. When the level is adjusted back up, the sound lacks highs compared to the pickup alone.

The sounds are totally different. No one could say they are remotely similar.

I have explained the first result above. No reason to do it again.

The second result is obvious. The impedance of a pickup is approximately equal to its resistance at very low frequencies. But it goes up with frequency, that is, it becomes inductive. The magnitude of the impedance becomes many times that of the resistance over most of the range and increases even faster as the resonance is approached. Therefore, when you put the resistor across it, you attenuate a lot, with the higher frequencies attenuated the most.

There could not be two situations that are more different. Seriously now, have you actually done the test that you urge others to do?

[Rick Turner]

Mike, how can you possibly imagine that I've not done the experiment? You just made my whole point...pickups loading one another changes the sound (OK, that could be said "frequency response") of each pickup, and the results you heard are exactly what I described. Resistive loading of high impedance pickups is a real game changer, and one simply has to be aware of it in order to deal with it. You can't think if it as a balancing act where one factor negates the other. These are wacky LCR networks, and if you change one factor, you've made a major change to the whole thing. If you change two or three, it's a whole new ballgame as far as tone is concerned.

Back to the OP...yes, if you buffer each pickup before any controls whatsoever, and then properly combine them, you'll not get the change of sound that loading produces...for better or worse. And you can mess around with resistive loading perhaps to find a tonal "sweet spot" for each pickup, and then combine them. You'll still have some tone changes as you'll have different harmonics of the strings going in and out of phase with one another with two pickups on. It's like having two mics on one source...you're going to get phase cancellation somewhere in the audio spectrum. There's no free lunch here, folks...

There is no right nor wrong with any of this as long as you understand that each approach has plusses and minuses. I've worked this game in about as many ways as it can be done, and I don't have an absolute that I stick to. Passive? fine... Active pickups? fine... Passive combining with subsequent active? fine...

The only times I pretty much always stick to active combining is when I've got a piezo and a magnetic pickup circuit to blend. The passive requirements are simply not compatible, and piezos suffer such capacitive loss in cable that you pretty much have to buffer them at least. The ceramics can kind of drive cable, but it's a major compromise.

[Mike Sulzer]

Mike, how can you possibly imagine that I've not done the experiment?

Because you said the two effects were nearly the same, when in point of fact they are very different.

I do not think I need to quote exactly what you wrote. It is clear to everyone what you are doing now.