Phasing Issue When Connecting Two Amps

[lefty007]

I'm having some out-of-phase issues. I have two 4 Ohm cabs, so I use one head for each. I've been using a Y-cable to split the bass signal in two, then feeding each amp (using two G-K MB200), and that works fine. But when I use one MB200 and a TC electronic RH450 in the same fashion, they sound out of phase.

I tried taking a line out from the RH450 to the input of the MB200, but that also yields and out of phase effect.

I've been looking at splitter box (Whirwind) and Radial, but I can't seem to find a proper splitter.

Can anybody offer a solution for this?

Thanks!

[Lo-E]

Make yourself a 'turnaround' cable. Wire up a speaker cable with one connector reversed. Use it when you use the TC head. Cheap. Simple. Just make sure you label it well so you don't accidentally use it when you don't need a turnaround.

[JHAz]

Originally Posted by Lo-E

Make yourself a 'turnaround' cable. Wire up a speaker cable with one connector reversed. Use it when you use the TC head. Cheap. Simple. Just make sure you label it well so you don't accidentally use it when you don't need a turnaround.

Yep. One amp inverts the signal at the output, the other is noninverting. You just need to switch one around so that they match. Do mark the cable well and as permanently as you can, or you'll cause yourself a problem in 5 years when you find it in a box o' stuff and try to use it with identical amps, should that ever occur . . .

[DigitalMan]

Radial JDV can invert phase on a per output basis. It can also benefit the quality of your input signal to either amp significantly. Definitely worth considering for your situation.

[lefty007]

Thanks, all, great tips!

[walterw]

also try running the line out or "preamp out" or "effects send" from the one amp into the "power amp in" or "effects return" of the second; that'll bypass a bunch of extra preamp stuff, maybe the polarity-flipping stage too.

[lefty007]

Originally Posted by walterw

also try running the line out or "preamp out" or "effects send" from the one amp into the "power amp in" or "effects return" of the second; that'll bypass a bunch of extra preamp stuff, maybe the polarity-flipping stage too.

I tried every connection option possible and nothing worked. But the explanation that one of the amps reverses the polarity at the output stage (by design) makes a lot of sense...

[walterw]

in that case yeah, a polarity-flipping cable is the answer.

i'm inclined to suggest a reversing speaker cable, since there's no real "hot" or "ground" driving the speaker, just "+" or "-". as such, reversing it doesn't cause any ground hum issues or loops or whatever.

i don't suppose either amp or cab uses a banana plug does it? if so, just reverse it and you're done.

[nrbxbuev]

It can also benefit the quality of your input signal to either amp significantly.

[seamonkey]

The rh450 has DSP and some phase shift of it's own. It may not be 180 degrees.
You may have checked this already, but feed both amps after the preamp where the DSP is.

Take the "Post" output from the RH450 and feed it to the power amp in on the MB200
The post part is what's sent the the RH450 internal amp, and you should feed this to the MB200

[lowfreq33]

Google Little Labs IBP.