HPA-nxV200 R2 based  dual mono amplifier Configuration: Dual mono (2 x 500 VA), separate supplies for input stage (2 x nx Volt One) and output stage (90.000 uF per channel). The amp was easy to build and worked as expected “out of the box” The nx Volt Ones needed adjustment, but if you give them a proper input voltage, they behave exactly as described. The questions I had during building were promptly answered by Anthony. And had I bought the right secondary trafos right away, I would not have needed his support at all. Listening Impressions To set my personal bias straight: I have been passionate about Hi Fi for + 40 years, I have heard a lot of gear, including top of the line amps from Audio Research, Naim, McIntosh, Classe, PassLabs,  etc– and I am lucky enough to have a pair of very capable speakers (Audiovector SR6AA), so...

HPA-LSP40seThe first big decision was one case or mono blocks? After 5 min of thought, mono blocks it was.Listening to these amps is very pleasing to the ear. They certainly have that 'wow' factor.No background noise and very detailed sound. Low & mids are very powerful and highs are clean.When married up with the correct speakers and pre amp you can quite easily create a live sound stage sound.Have tested these amps on speakers ranging from $1.5K to $8K with very impressive results.The only problem with these amps is that they show up any weakness in the rest of your system. I had to upgrade my pre amp to realise the full potential of these mono blocks and what a difference it made!The final problem you'll have after building these amps is kicking your friends out.....Well done Anthony.Next project HPA-nxV500.Regards,AnthonyMelbourne, Vic

Firstly, what I am hooking the amp up to? The pre-amp is based around Rod Elliot's project 88 pre-amp that uses the Burr-Brown OPA2134 op amps. My speakers are also home made using Scan-Speak units, 18W8456 Kevlar bass unit and D2905 treble unit and a 4th order Linkwitz-Riley cross over (Volt air-cored inductors and Expotus capacitors).The amp itself is built using the SPS-80 switch mode power supply from ColdAmp electronics, set at ± 75v. The mains input is filtered and all connections are gold plated, obviously. The box is just a 2U rack mount case, and looks pretty empty.Lets start with the silence. Switch off the pre-amp so that the input is shorted and stick an ear into the bass cone. Nothing, not a sound. I guess it would be surprising if there was any mains hum from the ColdAmp PSU, but I have to check that I have switched...