Active Pickups Anyone?...

[Wired]

Hi all,

haven't posted for a few years, but I've been coming and lurking a bit on and off...

Have any winders around here ever thought of experimenting with active designs?

I mostly work on basses these days, and rarely wind anymore, but lately I've been puting prototype mini pre's in under pickups. This way I can blend actively, I have no lengths of Hi Z wiring more than a few cm, and I can use a differential input design so neither side of the coil is earthed. I gig a lot too here in Melbourne, and have several basses that are completely unshielded, have el cheapo pickups, with active EQ, no string earth, etc etc that are free of hum.

So I was thinking of making some micro pre's available to techs and pickup makers to experiment with. Still thinking through the issues at the moment, but they would be small enough to place in most guitars without extra routing, or for winders, actually incorporated/potted into pickup designs (think EMG, Basslines etc). The gain and input Z would be adjustable and they'd be compatable with the 25k pots that are around...

Maybe there's no interest, or there's already something on the market that does this job so I'd be wasting my time...

Any thoughts are welcome...


Cheers!

[David King]

If they're small enough to send in an airmail envelope to other continents then I'd be interested in playing with them. The EMG pots are nice but I'm not sure how many they be willing to sell off before they got suspicious. Ideally these circuits could still be bypassed and 100K pots would work either passive or active for simplicity. What about an open source design?

[David Schwab]

I was making low Z active pickups for a while. I kept the preamp external to the pickup however. I also didn't use a differential setup so that I could switch the pickups from series to parallel. My preamp had a trim pot for gain, and would put out enough signal to drive a power amp, if that's what you wanted.

With my pickups, the output was too low to use them without the preamps, since they were actual low Z windings (unlike EMGs) so that was the reason for having them active. I already fully shield them, so I didn't have to use that for noise reduction.

I'd be interested in checking out your preamp design. I haven't make any active pickups in a number of years, but keep thinking I'd like to explore that area again.

[Wired]

If they're small enough to send in an airmail envelope to other continents then I'd be interested in playing with them. The EMG pots are nice but I'm not sure how many they be willing to sell off before they got suspicious. Ideally these circuits could still be bypassed and 100K pots would work either passive or active for simplicity. What about an open source design?

they'll be tiny. Small enough to put in the pickup itself.

Not sure what you mean about EMG getting suspicious about pots... There's plenty of 25k pots suitable for guitar out there - stewmac, ebay.... I suppose Active/passive is an option, you would use regular 250k or 500k pots, between the coils and the pre, but they wouldn't be connected to earth until passive is selected. I have done this in a bass. Works fine. Sort of defeats the purpose of a micro pre with a diff input...

[Wired]

series/parallel is still an option with a diff input, depending on the pickup- whether the earth wire is wired internally to a coil or not. These days most commercial pickups have 5 conductor wiring so even if the coils are potted in epoxy, you can still use a diff input. You have to run the wires to the switch though of course, so it partly defeats the purpose of a tiny pre that can be nice and close to the coils...

as for noise reduction. I've noticed that a lot of fully shielded basses with active eq's still buzz. This is from earth loops. if the hum can't make it to the earth rail in the first place, it won't be looped and turned in to a buzz.

diff pre schematics are pretty easy to find. Unfortunately I make part of my living with my pre's so I'm not going to share my version, but google on instrumentation amplifier and that'll get you started if you want to design your own.

I was really trying to gauge if there was interest and understanding around the place for this stuff. Its hard stuff to understand, and I'm not sure I have the time to answer tonnes of emails if I put something like this into market...

Anyone have experience selling pre's or even maybe a funny pickup design that needed special sort of wiring schematic or something? I would imagine that aguilar and bartolini etc etc get heaps of emails from people asking questions. I've had to rewire quite a few mucked up installations from some pretty reputable luthiers over the years. And I'm not sure I would want to wade into that scene...

[David Schwab]

I've noticed that a lot of fully shielded basses with active eq's still buzz. This is from earth loops. if the hum can't make it to the earth rail in the first place, it won't be looped and turned in to a buzz.

My experience has been that the grounding or shielding on these basses is not all that good. That's where the buzz comes from. It's easy to fix also.

I'm also of the opinion that you can't have a ground loop in a bass because it only has one ground, at the output jack.

The rest of the wires are pretty much at the same ground potential. Ground loops occur when you have two paths to ground, which is not possible when you only have one ground. The little bit of current that might form between ground wires inside the instrument are inconsequential.

All my instruments are dead quiet, and I use the standard daisy chained grounds to the pots, as well as them sitting on copper foil. I don't get any buzz.

[bea]

But the active/passive option leaves You with the dependence on the cable capacity which i think is undesirable as soon as You invest efforts in active electronics.

As to the potentiometers i would actually prefer 10k to 25 k from arbitrary suppliers, preferrably not from those specialised on music stuff with their phantasy pricing.

[Wired]

Are you talking about passive wiring?

[Wired]

the problem with most pots from electronics stores is that they only have 6mm of thread. Fine for scratch plates, but not long enough for most through-face guitars. Also PCB pins can be a bit of a PITA compared to eyelets to solder to.

Some people like the loaded sound of pickups. That's why my pre would have an adjustable input Z.

[Wired]

Anyway, I think we are getting off topic.

Really just wanted to see if any winders out there were interested in producing active pickups but didn't have the electronics knowledge to follow through... Active/passive, and series/parallel switching and cable capacitance and loading etc are interesting topics, but not really what this particular pre would be aimed at...

[Mike Sulzer]

Some people like the loaded sound of pickups. That's why my pre would have an adjustable input Z.

You mean variable capacitor loading? It is the cable capacitance that matters in a passive setup.

[MrCandy]

You mean variable capacitor loading? It is the cable capacitance that matters in a passive setup.

That it is and I agree, but if pickup have failure frequency response originally nothing will help to make it sound.
For example if pickup have good attack characteristic originally(easy cut out of flageolets), than pickup will be fine with any load.(flageolets will sound as they sound with any load)
We can take EMG81, it seems that everything is fine, but we can rarely make the flageolets happen anyway

[Mike Sulzer]

That it is and I agree, but if pickup have failure frequency response originally nothing will help to make it sound.
For example if pickup have good attack characteristic originally(easy cut out of flageolets), than pickup will be fine with any load.(flageolets will sound as they sound with any load)
We can take EMG81, it seems that everything is fine, but we can rarely make the flageolets happen anyway

Not sure what you mean, but if you are saying that a good passive pickup sounds good with any load, I am not convinced.

[MrCandy]

Not sure what you mean, but if you are saying that a good passive pickup sounds good with any load, I am not convinced.

The idea was that pickup with well selected frequency response when it was made will sound better than pickup with failure frequency response
under equal conditions(cable capacitance).
About pre input capacitance I can say that it must be minimal and it is better to not touch it, you can model frequency response with coil winding
and it is better that way.
We have already given an example of bad pickup sound modeling with the help of preamp and Rin dances in previous post

[Mike Sulzer]

About pre input capacitance I can say that it must be minimal and it is better to not touch it, you can model frequency response with coil winding
and it is better that way.

Not it is not. There is no way you can wind enough wire on a standard bobbin so that it will have the save resonant frequency directly into a pre amp as when operated into a guitar cable. You need at least about 500 pf. You have to add some.