Does Monster Cable MPA-3250/2250 Invert Phase?

5farms

Member
2020-02-03 3:00 am
First post and a real newb. I have both the Monster Cable MPA-3250 and -2250 amplifiers I want to use to power my Infinity Epsilon speakers. The woofer servo unit requires that the amp for the subs match the phase of the servo unit. The phase of the servo unit can be switched to match the amp. While I could flip a coin, I’ve read that a mismatch of phase would cause the amp to go into full power oscillation, jeopardizing both amp and speakers. Obviously the manual or other on-line searches have come up empty. Any information would be greatly appreciated, thank you.
 

5farms

Member
2020-02-03 3:00 am
It doesn't matter whether the amplifier inverts or not. You can correct it by simply reversing the speaker wires.

Yes, but I want to avoid finding out that I guessed wrong by sending the amp into oscillation and potentially damaging speakers or the amp. Once I know if the amp inverts phase, I can place the phase switch on the back of the servo unit to its proper setting.
 

AllenB

Moderator
Paid Member
2008-10-18 11:31 am
Posting this in case it helps.
 

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5farms

Member
2020-02-03 3:00 am
Posting this in case it helps.

Yes, thank you. That is pretty well described in the manual. The manual also describes, “ The signal phase of the SCU’s electronic woofer servo control circuitry must match that of the woofer amplifier.”

WARNING: The SCU’s phase switch must be correctly set for the amplifier in use. Incorrect setting of this switch can lead immediately to woofer and/or amplifier failure.”
 

AllenB

Moderator
Paid Member
2008-10-18 11:31 am
Does your amp have a volume control? I'm wondering whether it would be viable to turn that down, and to momentarily touch a 1.5V cell across the input terminals (one channel, correct polarity). See whether the woofer cone comes out or goes in. Make sure you know which way the woofer is wired as well.

This may not be conventional, or the best way but if I were stranded on a desert island with only the battery, I'd do it. Be careful not to damage the woofer and if you are unsure, don't do it.
 

5farms

Member
2020-02-03 3:00 am
If its that easy to destroy they should include a phase checker!

I bought these speakers used, but they are from the 90’s. And, replacement parts are difficult to come by and expensive.

Does your amp have a volume control? I'm wondering whether it would be viable to turn that down, and to momentarily touch a 1.5V cell across the input terminals (one channel, correct polarity). See whether the woofer cone comes out or goes in. Make sure you know which way the woofer is wired as well.

This may not be conventional, or the best way but if I were stranded on a desert island with only the battery, I'd do it. Be careful not to damage the woofer and if you are unsure, don't do it.

No volume control on the amps. I asked the question here because I found a different discussion here about this amp. It’s a Richard Marsh design and that thread mentioned he sometimes posts on this forum. As far as knowing which way the woofer is wired, that’s an added challenge since the speaker has to be dismantled to get to the drivers...the front drill cloth is fixed and not removable. Yeah, such joys, but I do appreciate everyone’s suggestions.
 
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5farms

Member
2020-02-03 3:00 am
Well, I flipped a coin and took a shot. Guessed the amp was in phase and I got it working with the speakers. I experimented with the center channel in the -3250 for just one side, figuring if I roached an amplifier, I could lose the unused center channel (independent power supply per channel). Thanks everyone for your replies/suggestions.


First post and a real newb. I have both the Monster Cable MPA-3250 and -2250 amplifiers I want to use to power my Infinity Epsilon speakers. The woofer servo unit requires that the amp for the subs match the phase of the servo unit. The phase of the servo unit can be switched to match the amp. While I could flip a coin, I’ve read that a mismatch of phase would cause the amp to go into full power oscillation, jeopardizing both amp and speakers. Obviously the manual or other on-line searches have come up empty. Any information would be greatly appreciated, thank you.