Continued from prior post…
I can’t say this sounds any better or worse than the stock components, as I have no way to make that comparison. However, I find the results sublime!
The burn in time was extensive, possibly due to the use of automotive grade hybrid polymer bypass caps. Likely an unnecessary change.
CAUTION! The Bypass Capacitors in this amplifier are NOT electrolyte capacitors! These are extremely low ESR
polymer capacitors and are critical to the sound of this amplifier. The use of even expensive high grade audiophile
electrolyte capacitors will ruin this amplifier! If in doubt leave them alone!
I have settled on E2A3 tubes and zero negative feedback as my favorite. This is with 10 inch full range lii Audio drivers in diy BLH enclosure. No crossover or baffle step correct circuit—output transformer coil directly to speaker coil. I also tried very sensitive two way horn speakers but found the sound, while excellent, was less controlled—less engaging without negative feedback. for me the two way horn speakers sounded better with negative feedback engaged. Again my favorite was the full range without negative feedback
While not necessary, I back this up with REL sub connected at speaker level. I have tried other subs and other connection methods and this to me is by far the most musical.
Kaisei Caps are tight fit. Had to leave leads long on one resistor and one diode and bend out of way. If you’re doing the build and look at the board it will be evident which ones.
Using a modern 2 volt source I cannot imagine running this amplifier with a preamp even in negative feedback selected. In zero negative feedback mode, you will likely need to reduce the source level through Roon or similar software.
As I am primarily using zero negative feedback and don’t particularly care for roon’s digital volume control I elected to add a voltage divider circuit in front of the volume pot. This is a personal preference and not unique to this amplifier. I have done it with others.
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These are Vishay naked Z foil resistors. (Note: the jumper posts are cut on input(top)…look very closely. This actually allows you to use less of the carbon trace on the volume pot (turn control higher) which In theory provides a cleaner signal. Hard to say there is an audible difference, but it certainly does no harm to the signal and greatly improves the functional range of the volume control. I used 67K ohm inline with signal and 24K Ohm to ground (bottom side). If you are using the negative feedback mode, or have a low voltage source, you may not want to do this. Delicate procedure, and difficult to undo if you do not like the results. I did breadboard experiments at the inputs with cheap resistors first. This is delicate work, and certainly not for everyone.