So another problem that keeps popping up is soon finally addressed: I never have enough space in my AV rack for all my gear, and I continuously run out of amplifier channels for my expanding HT Atmos setup that went from 5.1 -> 7.1 -> 7.2 -> 5.2.4 -> 7.3.4. This is likely where it will remain with room size and other constraints.
Aside from the critical amplifiers needed for the main front stereo speakers, I need minimum 9 channels for the remainder of centre, rears, sides and overheads.
However, I only have 8 channels of surround amplification, shown here as DIY projects:
https://www.avforums.co.za/threads/diy-6ch-power-amp.85141/
https://www.avforums.co.za/threads/amp-restoration.107495/
The last one is used for the centre speaker and despite being gloriously overkill, it's bridged for just that bit of extra juice and therefore leaves a 2ch deficit. I suppose I could have just built/bought a stereo power amp but who knows what comes next (e.g. active speakers) to leave me yet again with the same headache.
Because of space and cooling, size and low idle power were critical parameters and therefore DIY (again) was the solution. For chassis I opted for a custom design made of powder-coated 1.6mm steel since imported ones need just too much rework and are never the optimal dimensions. Width was kept as the standard 430mm and height minimized, arriving at 53mm total height including lid. Looks are rather utilitarian but I have something in the works to vajazzle the fascia. Slots are cut in the sides of the lid to allow a very quiet Noctua fan built into the side of the AV rack to provide minimal inaudible airflow in HT mode that keeps everything perfectly cool. Not needed but why not and it extends component lifespan which will anyway be rather extensive with the overdesign and part quality used.
Since I was anyway doing it, I decided to double up and build two of these to give me 8 channels total in a very compact space if stacked. I have no immediate use for the second one but the costs & efforts are just so much less when combining.
Design was as always a mix of new designs and new stuff. For the amplifier modules themselves, I used the same ICEPower 400A2 stereo module as used in the centre amplifier, but the rest including the assembly is quite different. Firstly I mounted everything on a single 3mm plate as a substrate and primary heatsink to easily wire and test/debug, then bolt it with thermal paste to the chassis bottom for final chassis integration.
AC power enters into a switched & fused IEC module with a little standby circuit for monitoring a trigger input. Two triggers jacks are provided to allow a passthrough from a single source with a rear override switch. Front panel will have a single power LED. When trigger or override is on a 16A relay switches power to the rest using strands taken from Supra LoRad 2.5mm silver cable.
Switched AC goes to a massively overkill linear PSU with dual regulation stages, mostly copied from my DSP project design. It provides +-12VDC extremely quiet power for the input buffers as well as auxiliary power for the amplifier modules.
The main power supply is a 800W SMPS with exceptional performance and efficiency. Its auxiliary +-15V output (actually destined for opamps etc. but unused since I already have my own linear PSU) is instead filtered with a complex multi-stage ripple filter and then regulated down to 12.7V for the gate drive voltage of the amplifiers. The +-62VDC power outputs are filtered with a basic snubber and a CLC pi filter that nicely reduces the ripple a bit further but with the inductors being sufficiently oversized not to cause problems.
Input buffer is the latest version of my current reference design (at least using opamps instead of some class-A affair) for lowest noise and distortion. Component quality got upgraded somewhat and XLRs are now from the improved Neutrik D-series. Initially there were some further controls provided but since they all proved unnecessary during testing they all got removed for simplified wiring.
Placement/wiring is always a critical consideration and it worked out well here. Where there is any overlap of high and low-power wiring deliberate clearance is kept with 90degree crossings. The black wiring is mainly for control and low-power DC, thin white wire is actually balanced silver Teflon coax between amp and buffer. Speaker cable is tightly twisted pure copper and other DC cables a mix of silver-coated copper and pure copper.
Output terminals were changed to Neutrik Speakon simply because it's easier and safer than lots of banana plugs. Despite the Speakons being 4pole and therefore capable of even more convenience of 2ch/plug, I preferred to use only 2 poles to keep the internal wiring tidy.
Performance was not really surprising since all the components have been used before albeit not in the same iteration, combination or layout. With the output voltage of the SMPS being a little lower than optimal, each amplifier channel produces 350W into 4Ohm, which is really enough for whatever can be thrown at it. Distortion is incredibly low and noise is horn-friendly. Crosstalk is nearly immeasurable. With all four channels driven the maximum sustained power will be a bit lower given the 800W limit of the PSU but that never happens, especially for surround media. I'll overall compare it very favourably to the Purifi 1ET400A I used in a different design but both need careful attention to sound & measure their best. Anyone with a Purifi-based NAD amp is welcome to come visit to verify this claim.
I also compared it to the 6ch version and each has strengths and weaknesses: the 6ch's input buffer is not as sophisticated (maybe one day I replace it..) and its noise and distortion is higher due to the modules having integrated PSUs. However, each channel pair is capable of 500W sustained so it is definitely capable of more power. I haven't done serious stereo A/B comparisons but I'm almost convinced this one will come out tops and is actually massively overkill for just surround duty. I design all my amps (unless specifically required for a purpose) for a total gain of 26dB so despite having 3 different amps now for surround they all have the exact same gain for an easy and convenient joined setup without offsets in the processor.
Power usage is not bad, with <1W in standby and 39W in idle. This is not bad for four channels and could have been even less had I not used the linear PSU. As expected the bottom is the only that gets only mildly warm.
Photo below is basically the end result; final pictures shall be shown once everything is ready. Overall I'm extremely pleased, I got 8 channels of extremely good quality in a very compact size that needs very little cooling and that I'd happily put up against any multichannel Rotel or similar; even a Trinnov Amplitude (latter as I had one for comparison once..)
Aside from the critical amplifiers needed for the main front stereo speakers, I need minimum 9 channels for the remainder of centre, rears, sides and overheads.
However, I only have 8 channels of surround amplification, shown here as DIY projects:
https://www.avforums.co.za/threads/diy-6ch-power-amp.85141/
https://www.avforums.co.za/threads/amp-restoration.107495/
The last one is used for the centre speaker and despite being gloriously overkill, it's bridged for just that bit of extra juice and therefore leaves a 2ch deficit. I suppose I could have just built/bought a stereo power amp but who knows what comes next (e.g. active speakers) to leave me yet again with the same headache.
Because of space and cooling, size and low idle power were critical parameters and therefore DIY (again) was the solution. For chassis I opted for a custom design made of powder-coated 1.6mm steel since imported ones need just too much rework and are never the optimal dimensions. Width was kept as the standard 430mm and height minimized, arriving at 53mm total height including lid. Looks are rather utilitarian but I have something in the works to vajazzle the fascia. Slots are cut in the sides of the lid to allow a very quiet Noctua fan built into the side of the AV rack to provide minimal inaudible airflow in HT mode that keeps everything perfectly cool. Not needed but why not and it extends component lifespan which will anyway be rather extensive with the overdesign and part quality used.
Since I was anyway doing it, I decided to double up and build two of these to give me 8 channels total in a very compact space if stacked. I have no immediate use for the second one but the costs & efforts are just so much less when combining.
Design was as always a mix of new designs and new stuff. For the amplifier modules themselves, I used the same ICEPower 400A2 stereo module as used in the centre amplifier, but the rest including the assembly is quite different. Firstly I mounted everything on a single 3mm plate as a substrate and primary heatsink to easily wire and test/debug, then bolt it with thermal paste to the chassis bottom for final chassis integration.
AC power enters into a switched & fused IEC module with a little standby circuit for monitoring a trigger input. Two triggers jacks are provided to allow a passthrough from a single source with a rear override switch. Front panel will have a single power LED. When trigger or override is on a 16A relay switches power to the rest using strands taken from Supra LoRad 2.5mm silver cable.
Switched AC goes to a massively overkill linear PSU with dual regulation stages, mostly copied from my DSP project design. It provides +-12VDC extremely quiet power for the input buffers as well as auxiliary power for the amplifier modules.
The main power supply is a 800W SMPS with exceptional performance and efficiency. Its auxiliary +-15V output (actually destined for opamps etc. but unused since I already have my own linear PSU) is instead filtered with a complex multi-stage ripple filter and then regulated down to 12.7V for the gate drive voltage of the amplifiers. The +-62VDC power outputs are filtered with a basic snubber and a CLC pi filter that nicely reduces the ripple a bit further but with the inductors being sufficiently oversized not to cause problems.
Input buffer is the latest version of my current reference design (at least using opamps instead of some class-A affair) for lowest noise and distortion. Component quality got upgraded somewhat and XLRs are now from the improved Neutrik D-series. Initially there were some further controls provided but since they all proved unnecessary during testing they all got removed for simplified wiring.
Placement/wiring is always a critical consideration and it worked out well here. Where there is any overlap of high and low-power wiring deliberate clearance is kept with 90degree crossings. The black wiring is mainly for control and low-power DC, thin white wire is actually balanced silver Teflon coax between amp and buffer. Speaker cable is tightly twisted pure copper and other DC cables a mix of silver-coated copper and pure copper.
Output terminals were changed to Neutrik Speakon simply because it's easier and safer than lots of banana plugs. Despite the Speakons being 4pole and therefore capable of even more convenience of 2ch/plug, I preferred to use only 2 poles to keep the internal wiring tidy.
Performance was not really surprising since all the components have been used before albeit not in the same iteration, combination or layout. With the output voltage of the SMPS being a little lower than optimal, each amplifier channel produces 350W into 4Ohm, which is really enough for whatever can be thrown at it. Distortion is incredibly low and noise is horn-friendly. Crosstalk is nearly immeasurable. With all four channels driven the maximum sustained power will be a bit lower given the 800W limit of the PSU but that never happens, especially for surround media. I'll overall compare it very favourably to the Purifi 1ET400A I used in a different design but both need careful attention to sound & measure their best. Anyone with a Purifi-based NAD amp is welcome to come visit to verify this claim.
I also compared it to the 6ch version and each has strengths and weaknesses: the 6ch's input buffer is not as sophisticated (maybe one day I replace it..) and its noise and distortion is higher due to the modules having integrated PSUs. However, each channel pair is capable of 500W sustained so it is definitely capable of more power. I haven't done serious stereo A/B comparisons but I'm almost convinced this one will come out tops and is actually massively overkill for just surround duty. I design all my amps (unless specifically required for a purpose) for a total gain of 26dB so despite having 3 different amps now for surround they all have the exact same gain for an easy and convenient joined setup without offsets in the processor.
Power usage is not bad, with <1W in standby and 39W in idle. This is not bad for four channels and could have been even less had I not used the linear PSU. As expected the bottom is the only that gets only mildly warm.
Photo below is basically the end result; final pictures shall be shown once everything is ready. Overall I'm extremely pleased, I got 8 channels of extremely good quality in a very compact size that needs very little cooling and that I'd happily put up against any multichannel Rotel or similar; even a Trinnov Amplitude (latter as I had one for comparison once..)
