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For tubes we get two Baldwin-branded factory-matched 6SN7 at the outputs. Those may be rolled with 6N8S, 6SN7GT, 5692 or CV181 but be aware that the taller variants of the latter won't fit inside the tube cage held down with four bolts. There are also two 6N6P drivers and two EZ35 rectifiers. Those rectifiers could become 6C5S, CV574 or 6X5GT replacements if you wanted to experiment.
The stepped attenuator's main design goal was to match the DAC's gain with a preamp where 12:00 equals a standard 2Vrms and 3:00 becomes 4.2Vrms but it can of course also serve amp-direct connections. To learn more required an email to designer Gregor.
On USB and why not: "During our endless experiments whilst developing the TAD-1, we established that fitting any kind of switching device—electromechanical or semi-conductor-based logic chip—just ahead of the dual-mono DAC chips to create an I²S connection with a built-in USB module changed the final sound and not for the better. There's also the ongoing 'battle' in computer audio to develop separate USB interfaces as the ultimate for sound quality once used with separate DACs. None of the newest—some of them excellent-sounding—OEM designs we tested became any definitive answer in our quest for best sound. Hence the choice became to design, develop and build our own high-end USB-I²S bridge as a completely different product which in the near future might be superceded by newer USB audio chip developments; or leave the choice of external USB interface to the customer."
On everything else or rather not: "I established to myself that the same DAC chip can be 'pushed' to sound average, good or very good depending on circuit design and associated parts.One can design an audio DAC using an industrial chip which will sound exceptionally good or one can spoil the sound despite using a chip that was designed specifically as an audio part.D/A converter chips are very analogue in that regard and respond very much to the fine-tuning of parts and circuitry.The TAD-1 is crafted and engineered by hand. It combines the best old valve circuit design with modern digital design techniques in our special chassis. I understand how people might want to know more regarding component selection and circuit topology and thought long and hard about what to share. I hope prospective customers will appreciate that this product truly is the result of burning the midnight oil for many years so its IP will remain protected."
On the company: "We are a small creative team working within our own company. The team consists of me as chief electronics engineer and production designer; of artist/teacher Jacqueline as company secretary; of Sabih, ex BBC sound engineer and journalist as our product manager; of Dylan as electrical and Matty as mechanical engineers in production; and of two more employees for other production/packaging requirements. We all are dedicated music lovers and critical listeners. As for this project,
I'd reached a point in my life when I had time to fulfil my ambition to really focus on creating a DAC to my own specification.The aim was the best Redbook CD playback whilst accepting 24-bit resolution and higher sample rates with an analog valve output stage. I wanted complete satisfaction when listening.My love for audio engineering and sound is shared by friends who belong to the same 'club'. Chief among these is Sabih Tasoz.After listening to the prototype at our place, Sabih took it to his own place for more prolonged listening.He concluded that it was too good to keep to myself and had to be shared with others. And that's how the TAD-1 was born as a commercial product." With this you now know as much or little about the circuit or any specific sonic goals for the DAC under review as I did.