Digital Amplifier Questions

G.,
The M525 is used; however it only has approximately 60 hours on it. In a couple of days I will post my thoughts.

That's exciting Richard.... You basically got an essentially brand new M525 for the priced of a used one! Let us know how things develop. G.

G.,

There are a few things that were obvious from the beginning that I can address:

Overall stage and image sizes: compared to the A21, image size appears to be the correct height/size with the M525...the A21 is relatively flat and images appeared below eye level, as if I was looking down. One of the most significant difference is the overall stage...this is where the M525 really shines, outstanding separation of instruments, with the best front to back placement of instruments that I've ever heard in my system

Authority-very hard to explain because the A21 and M525 are very different, I need more time to provide honest feedback

Transients distortion and speed- M525 has a lower noise floor, where music emerges out of a completely dark background

treble sweetness in complex passages-the A21 was closed in and lacking detail compared to the M525, cymbals sound so real and natural with the M525

Guido,

Well, I finally tested my amps for RF interference today; sorry it took so long.

The only FM radio I had for testing was my bedroom alarm clock. I tuned it to an FM station that had very good reception and then positioned it within 2 inches along each amp's sides, top, front and back. I then increased the distance, to a distance of about 6 inches and then multiple distances trying to find any location where the signal was affected. I even tested my class A/B bass system amp even though I knew there should be no RF interference/leakage on a non-class D amp.

The results indicated there was absolutely zero affect on FM radio reception on any of my amps at any position or distance I tested. I understand your comment that, even if there was some RF interference/leakage from an amp, it would not affect the sound quality produced by the amp.

I was still pleased with the lack of RF interference, however, since I consider this a validation of the amps being well designed and the designers' attention to details. As a reminder For anyone interested, the 3 amps I tested were the following:

D-Sonic M3-600-M mono-block amps
ClassD Audio SDS-440-CS stereo amp
Emerald Physics EP-100.2-SE stereo amp

I highly recommend all 3 of these amps for sound quality. Not having any apparent RF leakage issues is just a bonus for those concerned.

Guido & Noble100,

Why an FM radio? I would expect that an AM radio would provide a much more sensitive and potentially more meaningful test.

As you probably realize, FM is inherently vastly more immune to RF interference than AM, since the audio that ends up being reproduced corresponds to frequency variations in the airborne signal rather than to amplitude variations. Also, in contrast to the AM broadcast band the 88 to 108 MHz frequencies of the FM band (and even its 10.7 MHz IF frequency which follows down-conversion within the radio) are vastly higher than the bandwidths of any audio component, and are therefore much less likely to be relevant.

I suspect that if an FM radio audibly responds to airborne RFI generated by an audio component it is likely not what is picked up by its built-in antenna that results in the audible interference, but rather what is picked up by downstream circuitry within the radio that operates at much lower frequencies. That response probably being much less sensitive than an AM radio's response would be to interference picked up by its antenna.

FWIW, my guess is that you'll hear significant interference when an AM radio, preferably tuned near the low end of the band (e.g. 540 kHz), is placed close to the amp. But what will be of interest is how quickly the interference drops off as the distance increases.

Best regards,
-- Al