Got a 2 channel EQ, but it has RCA jacks...

[MikeH]

I just got an older, 2 channel, 10 band MXR EQ off of ebay, that I believe is supposed to be used for home audio or studio mixing type situations, but I thought it would make a good distortion eq for bass (At 12 bucks it was worth a shot).  One channel for the input EQ to boost the favorable frequencies, and a second for the output EQ to bring it all back around.  The only problem is that it has RCA plugs, not 1/4 inchers.  I want to replace them with 1/4 inch jacks, but I don't really know anything about RCA plugs, but I'm sure they're the same deal as 1/4 inch plugs, so which is the hot and which is the ground?  Can you just swap them out, or is there any problems in doing so?

[Mark Hammer]

The inner connector is always hot (= jack tip) and the other connector is ground.

[R.G.]

Radio Shack sells RCA to phone jack adapters...

[Ben N]

You may have level or impedance matching issues.

Ben

[MikeH]

Yeah, I cracked it open and the RCA jack are pcb mounted along the back along with a bunch of other components.  And I couldn't swap out the jacks without some serious modifications, so I'll just use some adaptors or RCA to 1/4 adapters.

What sort of impedence issues might I have?  And how would I notice?  Low output?  Crappy Tone?

[Meanderthal]

What sort of impedence issues might I have?  And how would I notice?  Low output?  Crappy Tone?

Yes.

It may be designed for line level signals, and the wimpy signals from a bass may require a preamp or at least a buffer. Or, it may(if you're lucky) be the same as a 1/4 in. version I seem to remember from way back when(it's black with wood sides, right?). Try it and see... might be fine, might not.

[MikeH]

Yeah, wood sides, that's totally the one.  I'll get some adapters and try it out.  Throwing a booster in there would be no problem though, I'm planning to have this in a bypass loop with some fuzz/dist/etc.  When Impedance is an issue, is it best to boost the signal going in (to the EQ or other low(?) impedance device), or on the output side?  Imedance is something I've not had to deal with before.

[R.G.]

Yeah, I cracked it open and the RCA jack are pcb mounted along the back along with a bunch of other components.  And I couldn't swap out the jacks without some serious modifications, so I'll just use some adaptors or RCA to 1/4 adapters.

Here's another thing you could do - just drill yourself some 3/8" holes and mount 1/4" jacks somewhere inside the box. Then run a wire from the RCA jack hot pin to the signal lug on each 1/4" phone jack, and hook up all the grounds. Now both jacks are in parallel, and whatever is plugged in goes onto the board. It gives you some physical mounting freedom.

What sort of impedence issues might I have?  And how would I notice?  Low output?  Crappy Tone?

Hifi stuff is often as low as 10K input impedance. Used with a guitar directly on the input, this loads down the pickups and causes treble loss. It sounds dull. You can fix this by putting a high impedance buffer in front of the inputs. Or... if you can find or trace out the input circuits, these things often have an opamp buffer as the first thing at the input jacks. You could jigger the existing buffer to have a higher input impedance and not load. Note this is only a problem if the guitar goes directly into the input. If you have any effect in front of the inputs, the effect output is usually so low an impedance that it's not a problem.

Usually.

When Impedance is an issue, is it best to boost the signal going in (to the EQ or other low(?) impedance device), or on the output side?

It's best to buffer the input with an opamp follower.

Most hifi gear is intended to run from 0.775Vrms signals, about +/-1V peak or a bit more. Guitar signals are about 1/10 of that, about 70mV rms, but with BIG peaks from humbuckers. It may work fine just as it is. Try it before you start hacking.

The worst problem you'll have with feeding it too low a signal is that you may get more noise than you want. But usually hifi stuff is pretty quiet.