Sadly our listening impressions are inconclusive. It was a very busy trip and jc and Dr. Bae, our wunderkind layout engineer, were only able to finish the prototype preamp in time for us to give it a 30 minute listening at 11PM the night before we left.I'll await what Andrew can tell us on the test bench and Joe's impressions of the Silbatone trip
Everything, every stage in this preamp is "new" so we cannot be sure what we were listening to. The unit had fantastic dynamics, an incredible 3-D effect that was kind of shocking, but, alas, a tiny bit of electronic glaze to go along with the radical detail. It was very encouraging but a project needing bench time and adjustments. A few days burn in would also help.
It might not be the FETs causing the coloration and jc thinks it isn't. We are using silver LCR chokes, a new kind of silver alloy wire in the 437A output/interstage transformer, and an output stage using a 6900 and a FET in a freaky new configuration. In other words, the whole project is a leap into the unknown at every solder connection.
To my ear, the negative effect we experienced could be RF. The prototype is still an open faced sandwich of PCBs on a metal plate, naked jumper wires and an outboard step up trans.
Then again, one grid stopper might fix the questionable glaze factor. The 437A in the post-EQ gain recovery stage is quite a hotrod, high gain x bandwidth product tube. Maybe more attention needs to be focused on implementation here.
While it was playing, jc and I just looked at each other puzzledly. The overall presentation was so very different from what we are used to that we haven't a clue which element contributes what to the sound.
I hope that the silver EQ chokes aren't the reason for the crazy 3-D because then that would be another stupid expensive part that we all have to buy to be "state of the art."
Here's a pic of the breadboard prototype. On the left is the silver RIAA module with relay switching for various phono EQs, then a pr of big 5k transformers for the 437A, audio board with D3a/437A/6900, and finally a complex power supply with lots of regs and whatnot.
I am sure it will turn out interesting but we don't know enough yet to predict the end result. That why they call it Research and Development... a.k.a. learn as you go.
Surely jc would have other things to say but that is my perspective. He might be flying back to Seoul to work out the details so we can play this box at the Munich show.
