[Matthewnz]

Hello To All,
I recently received a pair of M225 monoblocks a week ago and have enjoyed their performance this week.  The stereo image is sometimes quite different from the stereo amp they replaced which leads me to this question: Do the M225s invert polarity?  If so, how do I manage the use of subwoofers that use a high-level input?
I currently have the positive leads to the subs on the (+) terminal of the amp and grounded to a screw on the back of the chassis. 

[danielgk]

If at all possible I would recommend using the low level inputs on a subwoofer amp.  (AVA's digital preamp has both RCA and XLR outputs so this would be easy to do).  If you insist on using the high level inputs, I'd connect them as you have described.  If you are using the M225 chassis as the ground (black) connection to the subwoofer amp be sure you have the ground lift switch on.

I looked at the only schematics I have of a subwoofer amp (a Dayton from Parts Express) and found that the negative high level connection input is tied to ground thru a 100 ohm resistor.  While the M225 could probably drive this without any problem, the resistor is a small wattage and would probably burn up if the M225 were cranked.  Fairly easy to guess that in the case of the Dayton you won't damage a bridged amp by connecting both outputs, but it is not intended to work that way.

Most subwoofer amps have a polarity switch so there would be no need to connect with opposite polarity, but if you have to connect with reverse polarity just connect the M225 black output (-) to the subwoofer red input, keeping the M225 chassis ground connected to the subwoofer black (-) input.

The M225's do not invert polarity but your system / speakers might have enough phase shift that a subwoofer amp sounds better (louder) when it is connected "out of phase".  Most do in my experience.

Finally, your mention of image bothers me.  If the image is great, wonderful, better than the old amp in most every way then that agrees with most of the reviews the M225 has gotten.  If you feel the image is lacking you should be sure to try inverting one of the speaker connections just in case one of the M225's accidentally got wired out of phase (they are hand built).


Dan

[Matthewnz]

Thanks Dan for your timely response,
My query is based on what I perceived as the stereo image having reduced depth, relative to the previous amp and extended lateral imaging, again relative to the previous amp. 

I have heard this effect before when playing a mono recording that had inverted polarity reversed with the image rather than being between the speakers extended somewhat lateral to the speakers.

I would not say the stereo image is lacking in any sense.
I don't think what I'm hearing has to do with one channel being out of phase having experienced that in the past, there is no perceived suck-out of bass notes or other weirdness. 

Perhaps what I'm hearing is that these amps simply throw a wider soundstage.  So far I am positively impressed by overall tonality and timbre of these amps (a gross understatement) and they seem to work well with the room and associated equipment.

At this point I will keep the system as is for another 50 hours of use and then recalibrate speaker positioning and subwoofer levels if needed. 

Thanks again for your informative reply.

[RonN5]

If you are talking about a REL sub, then they will likely suggest you treat the M225 like a class d amp assuming Dan confirms that it isn’t using earth ground as one of its xlr legs… that there is voltage in each of the legs which doesn’t work with the REL for its standard 3 wire hook up.

https://m.youtube.com/watch?v=5JDd623pbN8&embeds_referring_euri=https%3A%2F%2Frel.net%2F&source_ve_path=Mjg2NjY&feature=emb_logo

https://m.youtube.com/watch?v=-uIL84DWoCE

[peter4jc]

My query is based on what I perceived as the stereo image having reduced depth, relative to the previous amp and extended lateral imaging, again relative to the previous amp. 

Perhaps what I'm hearing is that these amps simply throw a wider soundstage.  So far I am positively impressed by overall tonality and timbre of these amps (a gross understatement) and they seem to work well with the room and associated equipment.

At this point I will keep the system as is for another 50 hours of use and then recalibrate speaker positioning and subwoofer levels if needed. 

Thanks again for your informative reply.

I've noticed this as well, having a wider soundstage being interpreted as lacking depth, but I don't think that's what happening and it's more how our brains perceive the sound.  Almost like the sound seemed deeper before because it wasn't as wide... it took some time for my ears/brain to become accustomed to the new amps (I have the same monoblocks).

[Matthewnz]

Ron & Peter,
Thanks for your input, mu semi-long winded response was lost due to an "error"