that’s exactly the same principe than passive hum-cancelling actually 
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At some points, yes, there are operationnal amplifiers and gain stages embedded. Minimal preamps.
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Right! That’s why the hum canceling works.
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This exact circuit must be pretty linear actually
Also I know that EMG changed the opamp quite early on their early pickups, because the first one had too much of a battery drain. But they don’t sound the same. That’s why Leland Sklar uses the very first EMG P’s on his dual pickups Franken-P.
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What’s the filter at C3/R6 doing? 1µF seems too large to be bass tone. Is that simply routing off excess power?
C3 is a coupling capacitor, used to remove the direct current offset (the 4.5v that comes from R4/R5 to the non-inverting input). R6 brings back a reference to ground and is also used to bring a resistive load to the opamp.
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Ahh ok, so the parallel out then just gets roughly the pickups hum-canceled AC signal and C3/R6 are sending the remaining DC from the battery to ground? Cool.
The use of the inverting and non-inverting inputs, in respect with the phase of the coils, is a clever way to build a summing amplifier that will effectively add the two coils to create one signal.
C3/R6 does not really “send the DC to ground”. In fact C3 removes completely the DC reference of the signal. It means that before C3, the signal oscillate around 4.5v , and after C3 this is just a floating signal without reference. Then R6 brings back a reference to ground. But C3 removes the DC offset by itself. And nothing of this offset goes to ground.
To understand this, you can see a DC offset as a low-frequency of 0 hertz. C3 blocks this, whatever is its capacitance, even really large.
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Oh ok. So the grounding is just to provide a common reference for the AC so it’s not floating?
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It could have been done differently but yes, it’s just to make the signal oscillate around the ground, like every pickup. The ground of the power supply (9v battery) and the output signal must be the same, otherwise you can’t cut the supply with a stereo jack.
And also R6 sets the resistive load of the op amp, which determines the output current. R6 sets effectively the output impedance.
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I really need to spend some time and get back in to electronics at some point, it’s been a really long time and I have forgotten too much. I would have guessed R7 set the output impedance 
Oh I see - R6 is the dominant factor there in the impedance between the output and ground, nevermind. It has to be.
R7 is just a protection in case of short circuit between the output and the ground. Without it, the op amp could be damaged because the output current would be too high.
Finally the effective output impedance is set by a network of resistors :
- R6
- R7 + the volume pot in series (all that in parallel regarding R6)
- the input stage of the amp (or pedal) (parallel again)
But the output impedance of the pickup itself is set by R6.
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Yep thanks! It all made sense when I realized what R6 was doing.
Super interesting, and I’ve clearly forgotten too much basic stuff 
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I don’t understand most of that, but I understand enough to get the gist and it is very interesting in regard to how the pickups and signal actually work.
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In the nutshell EMG use current to reverse the 60 cycles hums on their active pickups so their single coils can sound like single coil without any hums.
Their passive sounds a bit more robust but balanced. That’s what I like about the Geezer it’s very in your face presence but civilized. My Relentless is not it’s up closed and very personal I tamed it with a tape wound.
I’m doing 3 mods this coming week all are going to be around EMG drivetrains but all will be guitars not bass. This will be a fun one. At least one will be on a music video someone is shooting in August.
I’ll do my best to document this.
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Me:
WTF?
But I really like where this discussion went!
@Al1885 - do you think that the Relentless sounds similar to the DP126? I mean, there must be a reason to name a PU “relentless” … and the other just “DP126”…
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@terb & @howard - I just gave my girlfriend the daily summary of “what happened last night on BassBuzz” … and she asked: "Do they know both the DiMarzio DP126 and the EMG GZR first hand, from their own experience? "
Good question - do you?
The relentless is/are actually the DP307N. No they are not similar, the relentless are much hotter. That aside the shape and design of the pickups is what awesome about the relentless. Billy Sheehan talked about his collaboration in designing the pickup. I attached the video to one of your thread before you bought the DP126.
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Yeah! I tried EVERYTHING to get the Relentless here in Germany, based on your input.
Also cause you could get it in chrome, which would have been much cooler on Pink’s Hot.
But at that time (perhaps even now) you could not get the Relentless anywhere over here (except in some kind of ivory colour).
With the knowledge I have now I would have installed the GZR on both basses.
Or I would have pursued the idea of converting one of them to double Humbuckers - but that would have driven me crazy!
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