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Active And Passive Together? Is It Too Much Of A Hassle?


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Hello all,

I think I've going too need a special wiring setup. For my school project I've researched a specific setup I'm after but since found it's going to be quite impractical. If anyone could help me with a few questions I'd really appreciate it.

Bridge [Active EMG-81] - Middle [Passive Gibson 498T] - Neck [Passive Seymour SH4]

Active and Passive pickups can't be wired together am I right?

After asking around what I think I've sort of understood is that what I could possibly do is have two different groups of wiring, and use a stereo input jack with two seperate connections to the input lead.

Question one, is this as simple as it sounds to solve or is it going to be a VERY big hassle, I don't mind a bit of work but not an insane amount.

Question two, running the two together, I was hoping to be able to run the 498T and EMG together at the same time, if I manage to solve the active-passive problem, what pickup selector options do I have to allow this. Will a simple 5 Way selector work and is it possible to wire it so each pickup has an on/off switch?

Question three, there isn't going to be a wiring clash due to brands or anything?

Question four, sort of the same as Q2 except in relation to volume and tone controls.

If anyone could give me a hand by answering some of these or even going as far as providing some basic wiring options etc then I would really appreciate it.

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If you want to wire them as separate systems, yeah, it's as easy as it sounds, but that doesn't allow for any mixing of the two systems.

If you want to mix the two systems, you CAN'T just wire the outputs together. You can't use a normal selector. It won't work right. You would have to add an active preamp that takes the two signals (from the active system output and passive system output) and combines them. This could be in the guitar or it could be a pedal.

Different brands don't matter for wiring or volume/tone, what does matter is combining active/passive. If you want to wire them to separate outputs, or a switched output that doesn't combine them, then no problem. If you want to combine them before the amp, it means some kind of extra preamp. Period.

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Ok I understand what you're saying.

I certainly don't want to have it setup outside of the guitar, so what is involved in wiring a preamp, and also can you explain how a preamp works and what it does if it's not too much bother, as I said it's a senior project and I've never built a guitar before, I've done basic wiring and soldering but that's also as far as I go with electronics, I plan to fix that when I hit university :D

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Well, the EMG pickup will already be using EMG's preamp, so it will have a buffered output. If I were doing it, I would make a little circuitboard (pretty easy- you need the copper clad board material, a laser printer, a sharpie, and some crazy chemicals) with a dual opamp. The first opamp section would be set up as a simple voltage follower on the passive channel output. This would give the passive pickups buffered output. I'd use the second opamp section of the chip to make a summing amplifier (http://www.ecircuitcenter.com/Circuits/opsum/opsum.htm) which would just take three resistors (or three resistors and a potentiometer, if you want variable gain). You'd need some little capacitors as a part of the power supply, and maybe a resistor or two. If you used surface mount components, it would be smaller than a postage stamp. You would want to select an opamp with decent audio-frequency performance, low noise, low idle current, and power supply of 9V or less.

I've noticed that some guitarists/guitar builders complain about opamps and want to use transistors, but I've built enough audio equipment with opamps that sounds great that I'll go with what makes more sense to me :D.

It's not particularly hard if you've done it a few times but it's not trivial if you haven't.

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Buffering the output will change the sound, but only to a small degree. Actually, it'd be more accurate to say it un-changes the sound :D. There are some frequency-variable signal losses inherent in the volume and tone controls (even turned all the way up) as well as the guitar cable that buffering the output eliminates.

You could actually do the preamp stuff just on perfboard without even making a real circuit board, it'd just be bigger. The real problem would be troubleshooting it if something went wrong.

If you're really wedded to the passive/active thing, the easiest thing to do would be to have the passive output and active output go to an on-on selector switch which chooses between them and can't blend. There's also the stereo plug setup you mentioned, which would require either a special Y-cable which splits the TRS (tip ring sleeve, or stereo) plug to two mono plugs, or a stomp box which would take the stereo in and have two mono plugs out. I rate this as slightly more complicated because it requires special equipment outside the guitar to work right.

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Nah sounds too complex, I'm still figuring out how to make the body, I don't need to screw around with this stuff too. I'll just buy the EMG-HZ model which is passive and have a 5 Way selector. Thanks for all the help! I might try it on another guitar I make or maybe once my project is done I'll go back and muck around with it.

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Hmm... I guess if you put a preamp on the output of the passive channel you might not need a summing stage... I wonder how well it would work. Lovekraft knew a lot more about this stuff than I do, so I imagine it'd work fine.

Edited by jnewman
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