Pickup activating preamp

[Koreth]

This idea been bouncing about in my head these past few week as it's been taking form.

So one has normal passive pickups, which tend to have high(-ish?) output impedance, and are loaded down by the guitar's controls, the cable to the amplifier, and any effects pedals one is running. This results in a pickup that interacts with the aforementioned such that tone tends to get darker as the volume knob gets rolled down, the cable length increases, or one accumelates various effects pedals. For some people, this is a good thing, for others it is a bad thing.

Then you have active pickups, which contain an onboard differential preamplifier. This allows for a stronger output signal that one can more easily overdrive an amplifier with, better noise cancellation than with a standard passive humbucker, and a higher output impedance that is not loaded down by controls, cables, or effects, Tone is consistent no matter what happens with the controls, pedals or cable. Again, this is good or bad, depending on the players preference.

From what I've seen of pickups on this market, it seems to be an either/or proposition. But why can't we have aspects of both? Wouldn't it be cool to have your favorite passive pickup, but with a miniature differential preamp circuit such that you can have very low noise, and a low output impedance that doesn't get loaded down no matter how many pedals are on your pedal board? It seems to me that this doesn't have to be an either/or thing. Could you not simulate a cables's impedance on the input of the preamp, such that it sounds like you're always playing into your favorite 10' Mogami cable, no matter the cable you're actually using? Active pickups don't *all* have to be high output modern-voiced things. An active pickup with PAF-like tones because it's wound with PAF coils would be rather cool.

Is this a crazy line of thought that others have attempted before and failed? Or am I on to something potentially useful here?

[Mike Sulzer]

Yes, of course you can make the input to an onboard active preamp have the same input impedance as the combination of controls, cable and amp so that you can have the same sound as all passive, all controls on 10, or whatever you want. I doubt that very many designers bother to do this.

[dwmorrin]

Maybe you're thinking of the same thing RG Keen calls "Magic Loading." http://www.geofex.com/FX_images/Onboard_Preamp.pdf
Are you thinking of putting some RC "magic" within an active pickup's casing?

[Mike Sulzer]

Maybe you're thinking of the same thing RG Keen calls "Magic Loading." http://www.geofex.com/FX_images/Onboard_Preamp.pdf
Are you thinking of putting some RC "magic" within an active pickup's casing?

If Keen considers a resistor and a capacitor "magic", what must he think of a smart phone, the ultimate in extreme wizardry?

[dwmorrin]

If Keen considers a resistor and a capacitor "magic", what must he think of a smart phone, the ultimate in extreme wizardry?

I'd say the cell phone is pretty extreme wizardry! You'd definitely get burned at the stake if you showed up with a cell phone in the dark ages.

[Koreth]

I can't tell, does that circuit have differential inputs? Part of my hope for such a design was to have the preamp's inputs be differential, so it gets the noise-cancelling benefits.

I'm pretty sure some people like the sound of the loading the controls provide when turned down from ten, and I'm wondering if it wouldn't make sense to try to put some of the controls on the input to the preamp somehow.

[dwmorrin]

I can't tell, does that circuit have differential inputs? Part of my hope for such a design was to have the preamp's inputs be differential, so it gets the noise-cancelling benefits.

No. For differential inputs, you would use an opamp like shown here: ElectroSmash - EMG81 Pickup Analysis.

I'm pretty sure some people like the sound of the loading the controls provide when turned down from ten, and I'm wondering if it wouldn't make sense to try to put some of the controls on the input to the preamp somehow.

If you want to simulate a volume pot at "9", you would just stick two resistors in your preamp in a fixed attenuator configuration.
A tone control can be simulated by just a series resistor and cap to ground.

Loading the input doesn't seem to be the challenge.

Making the output perfectly mimic the tone and "behavior" (for lack of a better word) of a passive output is what I would think is tricky.
By "behavior" I mean plugging a passive guitar directly into a tube amp input tends to sound a bit different than plugging an active guitar directly into a tube amp. The designer might say... oh you just got to turn this knob blah blah... but the type of guy/gal who favors passive pickups doesn't want to hear any of that.

If you had active pickups that had no "artifacts" of being active... that would fool a passive pickup enthusiast... maybe then you've got something there.

[bbsailor]

This idea been bouncing about in my head these past few week as it's been taking form.

So one has normal passive pickups, which tend to have high(-ish?) output impedance, and are loaded down by the guitar's controls, the cable to the amplifier, and any effects pedals one is running. This results in a pickup that interacts with the aforementioned such that tone tends to get darker as the volume knob gets rolled down, the cable length increases, or one accumelates various effects pedals. For some people, this is a good thing, for others it is a bad thing.

Then you have active pickups, which contain an onboard differential preamplifier. This allows for a stronger output signal that one can more easily overdrive an amplifier with, better noise cancellation than with a standard passive humbucker, and a higher output impedance that is not loaded down by controls, cables, or effects, Tone is consistent no matter what happens with the controls, pedals or cable. Again, this is good or bad, depending on the players preference.

From what I've seen of pickups on this market, it seems to be an either/or proposition. But why can't we have aspects of both? Wouldn't it be cool to have your favorite passive pickup, but with a miniature differential preamp circuit such that you can have very low noise, and a low output impedance that doesn't get loaded down no matter how many pedals are on your pedal board? It seems to me that this doesn't have to be an either/or thing. Could you not simulate a cables's impedance on the input of the preamp, such that it sounds like you're always playing into your favorite 10' Mogami cable, no matter the cable you're actually using? Active pickups don't *all* have to be high output modern-voiced things. An active pickup with PAF-like tones because it's wound with PAF coils would be rather cool.

Is this a crazy line of thought that others have attempted before and failed? Or am I on to something potentially useful here?

Koreth,

Buffering the guitar at the output will eliminate the typical 1 meg ohm amp input impedance as well asthe cable capacitance leaving the only load being the on-board volume and tone controls. This can be done by installing a few parts in the guitar plug and a few more parts at the amp end to power the FET on the guitar end of the cable. See this web link: FET Preamp Cable

Use a a large metal .25 inch plug to house the FET and a few .125 watt resistors on the guitar end of thre cable. Then, mount the capacitor, other resistors and power connection on the amp end of the cable. I made one of these many years ago using a 9V wall wart power supply with a 1/8 plug and jack piggy backed on the amp end plug to either power it by a 9V battery or wall wart. This allows any guitar using this device to
function as an active pickup with a higher resonance and less dulling of the tone when the volume is turned down.

If you don't mind putting this in the guitar along with a 9V battery, wire it before the volume controls to minimize all loading but many guitarists don't want to modify vintage electric guitars so the active cable version produces about 90% of the benefits of the internal version.

Joseph J. Rogowski

[Koreth]

No. For differential inputs, you would use an opamp like shown here: ElectroSmash - EMG81 Pickup Analysis.

Indeed, the reverse engineered schematics of the EMG 81 I found when I started to wonder 'just how do actives actually *work*?' is part of what sent me down this path.

Making the output perfectly mimic the tone and "behavior" (for lack of a better word) of a passive output is what I would think is tricky.
By "behavior" I mean plugging a passive guitar directly into a tube amp input tends to sound a bit different than plugging an active guitar directly into a tube amp. The designer might say... oh you just got to turn this knob blah blah... but the type of guy/gal who favors passive pickups doesn't want to hear any of that.

If you had active pickups that had no "artifacts" of being active... that would fool a passive pickup enthusiast... maybe then you've got something there.

That is more what I"m aiming at. I don't think it's practical to fool every passive pickup enthusiest if I want to catpure the low output impedance and noise cancellation benefits benefit of active pickups. For some people, the consequences of high output impedance being loaded by cables and pedals, or more noise are an integral part of Tone. The interaction between fuzz pedals and a passive pickup's high output impedance and the control loading comes to mind. But I'd like to come close if I can.

If you want to simulate a volume pot at "9", you would just stick two resistors in your preamp in a fixed attenuator configuration.
A tone control can be simulated by just a series resistor and cap to ground

Loading the input doesn't seem to be the challenge.

But it seems to me that the loading of the coils, and how that loading changes as the guitar's controls are manipulated, is important to the behavior of passive pickups. Setting an RC network on the input of an opamp to simulate the volume being set at 10, is nice and simple. But what about when the volume control is turned down? The load faced by the coil has changed. If I recall correctly from my SPICE simulations of a pickup interacting with the tone controls (which I don't have to hand at the moment), the more a pickup is loaded down, the more the pickup's resonant peak is dampened, having the effect of sounding like the highs are rolling off at the same time. If there was a way to capture this effect as the volume was turned down, or at least having the option to, I think that would be ideal.

As soon as I can get some circuit diagramming tools to hand, I'll start sketching out my ideas. Though perhaps the design of the preamp itself should go in the amplifiers forum?

[J M Fahey]

Really, if the active mimics exactly the passive behaviour, then dispense with it and just stay passive.

Same with people who prefer passives (fine with me), "just use them"

Unfortunately, this seems to be important for us old timers, used to the old ways.

By practical experience, every weekend onstage I find "kids" (16 to 28 y.o.) meaning people who *started* listening to Rock and playing at most 14 years ago (and a majority just the last 5 or 6 years) who don't care or even have a clue about the old way to do things, (plug a guitar straight into an amp and dime it or add a relatively simple boost/distortion pedal or play Blues controlling everything by pick pressure ) or care about vintage amps, NOS tubes, etc.

90% I see put a huge pedalboard in the floor, plug the guitar there with a short cable, select one of the 256 or 1024 presets and chime away , using whatever amp on stage (it'd better be a Marshall, of course, but just because it's an Icon ) just as a reamp.

So all these subtle differences we care about are not even noticed.

Oh well.

[Koreth]

You wouldn't find a pickup that has that single coil chime (because it *is* a single coil), but also lacking the hum, buzz, and other environmental noise (because there's a differential preamp involved) to be useful?

[salvarsan]

If Keen considers a resistor and a capacitor "magic", what must he think of a smart phone, the ultimate in extreme wizardry?

Sarcasm doesn't propagate well via text. Assume that anything R.G. Keene wrote was accompanied by a chuckle.

In the same way, he knows his primary audience is hobbyists rather than the numerically fewer physical scientists.

You could enlighten us about his buffer amp with a little commentary on current mirrors.