active instruments

Started by zerohero, August 21, 2006, 12:13:25 PM

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zerohero

hi all,

i was wondering if it is possible to take a passive instrument and make it active. my first thought was just to add one of the small buffers in it, is this correct or is there more to it? ive also read that some have active pickups, are these special pickups or can you mod normal ones to get the same effect?


thanks

chunks717

pretty sure a buffer/ small gain amp is all that makes it active......some thing to drive the cable.
not sure how the p'ups would be any different, I don't think they should have to be.

Ardric

Yup.  The biggest hassle is figuring out how to power it.

Check out the Don Tillman active guitar cable.  It puts a buffer in the cable plug at the instrument end, so you get some of the benefits of active pickups with whatever you plug it into.  http://www.till.com/articles/PreampCable/index.html

The EMG pickups have small magnets and coils that would be really weak without active help.  They're very good at rejecting hum and noise, and the small magnets reduce the magnetic drag on the strings, so the guitar sustains longer.

If you've got that guitars control cavity open anyways, it may also be helpful to shield and rewire it.  http://www.guitarnuts.com/wiring/shielding/shield3.php

Pushtone

I highly reccomend the Strat-o-Blaster for an onboard preamp.
AFAIK, that's how it started life, inside a guitar.

It has a full sound with great low-mids.
The PCB layout over at GGG is even shaped to go into a cavity EZ, long and narrow.
The batt is actually bigger than the PCB.

Build it with a 100K resistor instead of a pot for unity gain.
Or a toggle that selects the 100k for unity or a 50k for a little onboard booster.

The GGG buffers are even smaller but sound more sterile (too perfect) to my ear.
It's time to buy a gun. That's what I've been thinking.
Maybe I can afford one, if I do a little less drinking. - Fred Eaglesmith

zerohero

thanks so much guys, really appreciated

Cliff Schecht

One of the main uses of active electronics is that they can drive longer cable lengths because of the lower output impedance (about 25 ohms). I use active setups in my 2 main guitars (one has EMG's and the other has passive pickups with a preamp). It really makes a difference when running through big pedalboards and lots of cabling.

Ge_Whiz

All of the above, plus my tuppence worth:

1. The basic principle, yes, is to incorporate a preamp / buffer / booster with a low impedance output that will drive long cables with less hum and noise and give a brighter sound, as the capacitance of the cable has less effect. Note, however, that this can cause problems with certain effects pedals that rely on interaction with the higher impedance normally observed - an example is the Fuzz Face, which tends to give a very limited fuzz range with a buffered input.

2. Yes, you need to include one or more batteries to power it. Often, two PP3s for 18V give much improved performance and headroom. Ideally, you need to be able to change them quickly if they fail. The current drain is usually tiny, but this only means they'll give out when you least expect it. I always include a pullswitch pot for volume or tone which when pulled out, bypasses the whole active shebang for emergencies (and also overcomes the problem highlighted in (1) above).

3. A further refinement is an enhanced tone control circuit that offers treble and bass boost/cut, or treble-bass and mid-range peak controls, or a tunable mid-range filter, or nine-band graphic EQ... Remember that all tone stacks, however designed, reduce the signal level, and you'll need one or more gain-recovery stages, before or after the tone controls, to get back to reasonable volume.

4. Op-amp systems are more versatile, but often greatly increase current drain over a transistor or FET design, plus they usually need a bipolar supply (probably two PP3s again).

5. Plan what you want, and make absolutely sure that (a) it does what you want and (b) it will fit in the guitar before you start attacking the guitar. Try to reign in your enthusiasm to incorporate treble boost, fuzz, overdrive, autowah, delay... Remember, more parts, more to go wrong!

Good luck. Converting a passive guitar to active circuitry can really have a positive benefit on your style and tone.

Mark Hammer

Read my 1979 article here: http://hammer.ampage.org/files/Device1-12.PDF   I haven't really changed my stance much since then (although my writing has improved considerably).

Situating active electronics in the instrument itself has pros and cons.  The articles walks through a lot of them.