Conclusions

Q&A's

Q: Have you reached your original performance requirements?
A: Yes. To the best of our knowledge (and we would be happy to find out that we are wrong) an amp of this performance level was never built before. We are proud of reaching this level of performance without using any Diamond Shaped Cristallized silver wires with Reflown Teflon insulation, or coils wired and blessed by Tibetan monks, $25/pc. teflon capacitors pulled from the USSR army NOS or absurdly expensive "sound neutral" electrolytics.

Q: Ok, but how does it sound?
A: The idea to build such an amp was the same as behind climbing Mount Everest - because it is there and because it should be possible. This amp is, before anything else, a wonderful piece of engineering. As of the sound: right now, to the extent we are able to evaluate, it sounds precise and pure as a swiss engine, extremely dynamic and totally transparent. In a word (to our taste) it sounds great. As soon as we'll have the amp cased and ready to go (most likely by the end of 2007) we will conduct extended audition tests among audiophiles and professionals here in Toronto. We will update these pages as soon as we will have more results and testimonies on audition tests.

Q: Ok, you did it, now what?
A: No, we are not done yet. See below for a short synopsis on what's on the drawing board.

Q: How much would it cost to build this puppy?
A: Our estimate is of about $150-$170 per channel, in parts and PCBs. A full stereo amp (including power supply, heatsinks and case) could be built most likely for well under $1000. A brand name amp with measured performances in the same class currently sells for $40,000! However, the mandatory one-time investment in test equipment (which is well into the thousands range) is a different story, EBay should be your friend... Your investment in knowledge and experience: priceless!

Q: Are you selling PCBs, parts or any other hardware components?
A: No, you are on your own. We believe that this amp was build using fairly standard parts, in current production, so you should be able to source them yourself. We are though willing to offer design and support services for any entity that believes in our view of high performance audio. Contact us if you are interested!

Q: How can I find more about your work?
A: Contact us. We would be happy to respond your questions. Bear in mind though - there are only so many hours a day and our families are yearning for some more attention...

What are we currently looking into? Beyond finalizing the last construction details (a better power supply (probably dual mono) and the case) we are looking into a balanced input stage. Unfortunately, because of the current architecture of the whole amp, it would be very difficult to build the amp input stage balanced. What's left is a balanced input to single ended converter - which is fairly simple (although not trivial to build, if it is to conserve the amp performance). Also, the front end is currently at version 0.01 in schematic and 1.1.2 in PCB layout and altough it's working great some improvements (both in schematic and the PCB layout) are on the design board.

Secondly, we are aware that HEC may not have many fans out there. The simple fact that it needs a helipot and adjustment work to tune the ultimate performance looks unappealing. Then some experts prefer to look at the HEC as just another negative feedback loop, applied to a base amp that has the open loop gain increased by yet another (positive) feedback loop. Which raises quite a question about the whole concept being worth the complexity involved... Therefore, we are looking into combining prof. Cherry's NDFL with the concept of Transitional Miller Compensation (or shortly, TMC) the expected result being an amp that has (multiple) negative feedback loops only. While, if possible, keeping the same level of performance as we got here.

Third, we are still looking for ways to protect the amp without interfering with the performance. A sonically transparent protection circuit will open the possiblity to use vertical MOSFETs or bipolar devices in the output stage.

Fourth, such a power amp needs a matching preamp. Another design and implementation challenge... Would it be possible to build an unconditionally stable preamp with gains of 10-1000 (or more) while keeping the THD20 and IMD distortions under 0.0001% in all circumstances?

And then who knows? However, if you still have any doubts, no, we are not planning to build any zero feedback amps.