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Class D multichannel amps — mixing and matching


Feb 18, 2020
Hi all, im currently running a 9.1 Dolby Atmos home theater system using a Marantz receiver. Five of the nine channels (LCR and 2 of the surrounds) are driven by a NHT Power5 amp that I’ve owned since 2008. It’s one of the early class D ICEPower amps, containing 2x 500ASP and 3x 500A modules, all tied to a common power rail, plus a buffer stage. The other 2 surround and 2 height channels a driven by the Marantz receiver itself.

Here are some measurements for the NHT Power5

I’ve been thinking that class D has come a long way since those early ICEPower modules, and perhaps I could buy a 2nd 5 channel amp containing latest generation Purifi, Hypex, or IceEDGE modules, use this in place of the NHT Power5 to power the LCR channels, and move the 4 channels currently driven by the receiver onto the NHT. Besides the benefit of using superior class D amplification modules on the main channels, a secondary benefit will be that once all of the speakers are being driven by external amplification, I can switch the Marantz into power saving mode which will shut down the internal amplifier stages so that it runs cooler and lasts longer.

My question is, what specs/measurements if any should I match or otherwise pay attention to when mixing two different multichannel amps to drive the various channels in a HT setup? Should the gains be the same or similar? The wattage? The frequency rolloff points? Should the distortion curves match (which would defeat some of the purpose of switching the main channels to Purifi or Hypex modules)? Should the input impedances match (which has more to do with the buffer stages)? On the Marantz I use Audyssey calibration, which I hope would be able to compensate for different gains and rolloff points.

Thanks in advance for any suggestions you have regarding matching two multichannel amps in a HT setup.


Active Member
Jan 5, 2023
About the only thing that should be compensated for when switching amps is the different gain between the old and new amplifiers. The rest is not of concern as far as the switchover goes, or WRT compatibility issues.


Major Contributor
May 27, 2021
The wattage should probably be "similar" but it doesn't matter if you aren't using all of the available power. You don't want any of the amps to be clipping (and you don't want to burn-out speakers).

Usually the front channels are the "loudest" but I don't know if there is a "rule" for that and the surround-channel peaks may be just as high.

The frequency rolloff points? Should the distortion curves match
Almost all amplifiers have flat frequency response over the audio range and distortion below audibility unless over-driven into clipping. Sometimes noise is audible.

Should the input impedances match (which has more to do with the buffer stages)?
Input impedance is rarely an issue. Line input impedance should generally be 10K Ohms or greater but in reality most line-outputs can drive 1K.


Active Member
Forum Donor
Jan 4, 2023
Seattle Area
Your NHT amp sounds great, no current replacement amp will sound better in your system, improvements are in the inaudibility region. If your amp has the same "ECO" mode as the Denons, you can use that mode now and given how little power is probably being used by the surrounds, it will be in the ECO mode most of the time anyway. Be happy, get some more music, maybe another sub...
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