There have been several massive hurtles on this journey. The biggest was noise, which I have done a great job of limiting (-90dB at full volume, drop the input volume to 50% and the noise is -110dB). Second was the EQ section. The EQ was strangely way more difficult to get perfectly integrated than I expected. It would cause self oscillation at extreme settings and with the knobs centered the response was not flat. There was also an 18kHz roll off regardless of knob positions. I tried so many different EQ circuits with no success before finally getting smart. After finally getting some software to run EQ simulations I was able to design an EQ that is perfectly flat in response when the knobs are centered, offers a good amount of boost and cut, and does not cause self oscillation at any setting. I started with the "James" EQ, which is a passive version of the Baxandall circuit. That circuit is not perfectly flat with the knobs centered, so I had to modify it. The circuit still oscillated at extreme settings, but thankfully I came up with a mod that resolved this issue. I got it worked out really good. The other element of the EQ equation is the amplifier section that drives it. The EQ has its own tube, which is out of circuit when the EQ is bypassed. Its a 6922 cathode follower circuit with some negative feedback around it to create a super clean low impedance output to drive the EQ. It sounds stupendous! The EQ adds a bit of THD when engaged, but its not over the top. It sounds very warm and musical.
Next week I'll do some thorough tests measurements for the Trinity page. Next step is to build a production model. Thanks to the high cost of prototyping it will have to wait a little bit.