Tag: 01a preamp

01a Preamp Gen2: Build (Part 2)

Spent this afternoon building a compact modular base for the UX-4 sockets, a custom tag strip and the filament bias resistor array. Given the very low power dissipation on the filament resistors they can be placed below the valve socket board to minimise space. The actual size of resistors is a killer, but I have a stock of these lovely wire-wound ones:

Also the gyrator boards were mounted on top of the output teflon capacitors, again to minimise space. The trimpots to set the anode voltage are located at the top for handy adjustment if necessary:

01a Preamp Gen2

The return of the 01a stage

SX201a in actionI remember my first 01a pre-amplifier to be one of the best sounding ones I ever had. The uniqueness of its tone, detail and clarity was astonishing. Perhaps it is due to the warm tone it provides and I guess this is the reason why Thomas Mayer branded his design as the “sound processor”.  I fell in love with the sound of a CX-301a and the joy of listening to this stage was so great that I found a fantastic excuse now to re-build this stage. My Starlight Discrete DAC has a very low output due to the step down transformer it has. I can only get 500mV as maximum output level. Not enough to drive my system to full level.  This was a perfect argument for me to look at building a simple amplifier stage that could add the sonority of the 01a in my system.

Continue reading “01a Preamp Gen2”

01a preamp (revisited 2013)

CX301a DHT preampLooking at improving the CX-301a preamp with cathode follower output I modified the gyrator load by replacing the DN2540 by a LND150 and 2SK170 which have a lower capacitance and will improve the performance. Likewise, the tail CCS now has low-noise audio transistors such as the KSC1845 and KSC3503. Bias point is roughly the same, a bit lower than before. Overall distortion in the simulation is great: THD<0.005% @ Vo=16Vpp and loading 100K and 330pF (cable load representation).

U2 could be 6Z52P, D3a or PC86. The latter will require and adjustment as the filament is 3.8V and not 6.3V.

I think is time for building and listening to a potential great preamp…