Minimax preamp,inverted polarity question


I'm wondering if the sub I'm running is out of phase with my main speakers.

I have a Minimax preamp that inverts polarity,my Quicksilver Mid Mono block power amps,do not invert polarity.

So,at my speakers,I'm currently running them red on black, black on the red of the speaker.

Now, I also run a B&W powered sub,I run the sub off the Minimax pre (it has two sets of outs)

Question: is my sub in phase with my main speakers.Im running it plus to plus Neg to Neg..

It would seem maybe not,seems to sound OK............??

Should I reverse the rca at the sub?????

Comments welcome

Reversing the RCA won't work.You would need to go inside the sub and swap +/-.With your set-up and the sub being self-powered,this nay be necessary.
The pre does invert so you compensated by reversing the speaker leads which is good. That should put them in polarity if the sub does not invert polarity. If you are still concerned get a test CD that has a tone near the crossover frequency. Try your speaker connections both ways and the one that is louder at the listening position is the one you want.

However, you also have the issue of the subs possibly being a different distance from you than the speakers. So even if they are in phase at the drivers they won't be when they reach your ears. Not completely inverted polarity but out of phase by some degree. No easy cure for this other than getting the distance as close as possible or using some type of digital delay.
Question: is my sub in phase with my main speakers.Im running it plus to plus Neg to Neg..

Mcgarick, not sure what you mean by this. It sounds like you are running a line-level signal via an unbalanced interconnect, with rca connectors, between preamp out and sub line-level in. Is that correct, and if so do you mean rca hot/center pin to rca hot/center pin, and rca ground/shell to rca ground/shell, rather than plus to plus and negative to negative?

And does the sub have inputs for both channels, which it sums together, or only for one channel, and if it is only one, how are you handling that?

Also, I think your post may be misleading Herman. If you have inverted preamp outputs feeding a non-inverting sub, and separately feeding a non-inverting power amp, and you have + and - interchanged on the main speakers, then your main speakers and the sub will indeed be out of phase.

Finally, if by "reversing the rca at the sub" you mean rewiring it so that the cable's center conductor is going to the ground shell, and the shield is going to the center pin, that would not be a good idea even if it were possible. You would be connecting the preamp's "hot" signal output to the signal ground of the sub, which would short the preamp output to ground if a path existed between sub ground and preamp ground (such as via their ac safety grounds if they both have 3-prong power plugs).

Then again, perhaps it is me who has been misled by your post :) In any event, clarifications of the questions I have raised would be helpful. And Herman's suggestion about checking volume levels with tones that are in a range of frequencies that would result in significant output from both main speakers and sub is an excellent one.

-- Al
Good catch, I missed that one. If it is all inverted out of the pre then you need to hook the speakers up black-black red-red so both they and the sub are being fed the same inverted polarity. That is unless you have a polarity switch on your sub and you can invert the sub with it and the speakers by hooking black-red.
Everybody,thanks for the input on this..

Ok, what if I remove the woofer on the sub and switch the wires around there????

What do ya think? Would that work??

There's a Phase switch on the back, it says "0 OR 180"
I don't even know what that means..or what it does..
When I switch it, the mid bass gets bumped up,I keep it at 0
Yes and yes!

The 0/180 switch is undoubtedly the polarity switch function that Herman referred to in his last post, and setting that to 180 should get your sub in phase with your main speakers. If that results in excessive mid-bass, then the other settings on the sub (such as the one called "low-pass filter"), and/or placement in the room, need to be optimized.

Good luck!
-- Al
Gee, all that pondering,and all I had to do was flick a switch!