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Hi,

I have on the bench an Epiphone Explorer with EMG active humbuckers and what looks like the standard EMG control harness. It all seems to work fine, now that I have replaced the switch, but I am noticing something I never saw before: the tone cap comes off the center tap of the tone pot and is attached to the hot lead on its way to the jack, not to ground as usual. The junction does not look "factory", but I don't like to assume too much, and of course, EMG's website is not responding today. Any ideas?

thanks,

David

Tags: EMG, active, capacitor, electronics, path, signal, tone, wiring

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The added cap is there to boost the mids and highs when you lower your volume.  As you increase resistance in the signal path, the cap lets the higher frequencies "sneak past" the pot.  The human ear is non-linear, and as as you lower your volume, midrange seems to drop out more than the lows.  Do a Google search on "equal loudness" or "Fletcher-Munson" curves.  Interesting stuff!

Tom,

Thanks for your response. Are you speaking of a cap across the in and the out of the volume pot, aka treble bleed? I don't think that's what is happening here, but since i don't know, i'm asking.

The circuit is as follows: 2 emgs (85 neck and 81 bridge), to two volume pots, to a 3 way toggle switch, and the output of the switch goes to the tip on a ring-tip-sleeve jack. On the way to the jack, the cap is tied into the output and the other end goes to the center lug of the tone pot. In other words, the path to the tone pot is THROUGH the cap. One outside lug of the tone is open, the other is grounded. That's the only capacitor in the system. Is it acting as a tone cap AND a treble bleed?

I know 'if it works don't fix it', but I'd like to know why it is that way, and if it is standard on EMG systems.

thanks,

David

What is the value of the cap?

104k is stamped on it, so .1 mF?

Yes, 104 is 0.1 mf

Sorry, I visualized the circuit incorrectly.  After re-reading, it's not what I thought.  I'd have to see a schematic and look at the actual circuit.  I'm an amp guy for the most part, and don't do a lot of guitar wiring these days.  What you're describing is still a tone circuit, although not the kind I usually see.  In the configuration that you're describing, the signal always has a path to ground through the cap, and adjusting the pot attenuates the signal passing through it.  It's a capacitor and a resistor is series.  Depending upon the value of the cap, with the sweeper of the pot turned all the way to ground, it probably sounds muddy, and with the pot in opposite position, you're still filtering some highs out.

 

As you said, if it "works" (AND you're satisfied with the sound), you can just leave it the way it is.

Some times, the output jack gets loose & the player turns the nut to get it tight, if the jack also turns (which it often does) it will twist up the wire inside the control cavity to the point that something breaks.  This is also the case with loose pots, they turn & things break. If the wire to the cap broke from this, & someone re-soldered it, that might explain the non-factory look. They may have not soldered it where it was originally, look close at the solder joints for evidence.  And as all say "if it ain't broke, don't fix it".

harrison,

you are correct. sir. it was broke, and now i have fixed it. standard signal path sounds a lot better, it turns out. thanks to you and Tom.

I called EMG but they haven't yet called back. They may not call me down here in New Zealand. :)

The circuit i would expect to see would be

I just thought maybe it was something specific to their systems that they wired it that way. Unfortunately, all the diagrams on their website seem to refore to more recent solderless circuitry. Maybe they figure, they sold the whole harness as one, why do you need to know how it goes? And anyway, they've moved on?

I'm not satisfied with the sound but i rarely am with EMG anyway. heat up the soldering iron and try it the other way...

It's only another way of achieving a tone circuit. You can either :

-hot>cap>middle leg of pot>right leg of pot>ground

-hot>middle leg of pot>right leg of pot>cap>ground

It's most of the time the way Fender or Gibson does it : http://www.dominocs.com/Gibson/WiringLibrary/wiringModern.jpg

Hi Pierre-Antoine,

It was as in your first example. But it sounds better as in your second example.

Had not seen Fender do it that way (first example), but there is always more to learn.

Thank you for your information.

David

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