01a Preamp Gen2

No Gravatar

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


HY1269 curves

No Gravatar

HY1269 I’m a big fan of the thoriated-tungsten filaments and I value them not just because they do look very cool, but fundamentally due to how they sound in a single-ended stage. I hope to build a nice push-pull amp with these type of valves soon.

I found a pair of HY1269 valves recently. This valve is not well-known amongst the used ones out there but they do have some interesting characteristics as a directly heated tetrode that would be interesting to consider it for a plate-to-grid (Schade) feedback configuration.  With its 30W of anode dissipation capability, it’s a good candidate for an output stage. However, it’s quite likely that you will have to drive it in A2 to get the most out of this valve. Like designs using 811a and similar transmitting valves, the HY1269 can be operated in class A2 even with no signal on the grid.

As per my “Robustiano” design using the 6P21S, it would be nice to see extracting 6W or more out of this  transmitting valve. I’m sure that the thoriated-tungsten touch will provide a lovely sound if properly implemented.

Continue reading


Starlight Discrete DAC Festival – London 2014

No Gravatar

A lot was already said about this fantastic day at Jon’s. The Starlight CD + Discrete DAC festival didn’t go as planned but we had a wonderful time. I had the chance to bring my own Starlight and sounded nice in Jon’s system despite the ground loop issue. Not clear what it was, despite it played well at low AVC levels but not when volume was increased. Perhaps was the load? Anyway, lots of tests from differential DACs to cathode follower outputs and Tom’s bipolar version.

I have to admit that the transformer coupled DAC sounded very transparent and detailed. The valve output gave a warmer tone and even harmonic contribution. The 6N1P implemented as cathode follower was very well received.

Tom’s bipolar DAC implementation is very promising. Clearly the tiny DC bias saturated the AVC and bass wasn’t good. Once we added the coupling PIO it came back to life with a subtle sound I enjoyed very much. Some challenges aside with the ESL resonances which I hope Jon can sort out soon.

Food and hospitality were superb in another unusual warm September day.

Most of all, a great day with fantastic company.

Thank you all





6P21S tetrode curves and model

No Gravatar

6P21STime ago I generated the tetrode curves for this great directly heated tetrode using my analog curve tracer. I originally used this tetrode in triode-mode. Although it’s a good candidate for a SET amplifier with its 21W in triode-mode, I always wanted to find out how it will perform with Schade-type anode to grid feedback. Building an accurate beam-type tetrode model was key. Luckily now, Derk Reefman has developed an accurate model for these type of valves.

I also worked with Ronald Dekker and insisted him to build in the “Schade” feedback capability in the uTracer using software rather than hardware:

Continue reading