01a Preamp Gen2: Build (Part 3)

The preamp build is progressing, albeit slowly. I tried a new breadboard construction approach. A nice Ikea chopping board was used to build the front and back wooden panels. A pair of aluminium squared section rails are used to provide support and hold a pair of top plates for the power and audio connectors. As a bonus given the low power consumption of the filaments, I will use these rails as the heat sink for the Rod Coleman filament regulators as well 🙂

All in a very compact design as I literally ran out of space for further equipment in my living room!

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: Build (Part 1)

The first step in the building process of this preamp has been to get the active load boards ready. A reasonably quick assembly process this afternoon:

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01a Preamp Gen2

The return of the 01a stage

I 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.

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SX-201a Sylvania

I have a pair of Sylvania’s SX-201a which sound superb. My preferred ones for 01apreamps. I’m looking at revamping my 01a line-stage shortly. Here is a trace of the anode curves for one of them:

The uTracer is a fantastic tool clearly. Well done Ronald!

Improving the CX301a DHT pre-amp

An idea discussed with Rod Coleman, Andy Evans and others in DYIAudio forum which still is evolving. The purpose is to increase the output driving capability of this preamp using a cathode-follower stage. A bonus is to provide the filament bias using the cathode-follower valve filaments:

01a DHT preamp updated

Updated this superb preamp. See here for details
Enjoy
Ale

26 preamp (gen2) article

For those who are keen on the 26 preamp in filament bias and OT, here is my latest incarnation of this great pre-amp.

New modular preamp 26/01a and 4P1L

Today made some progress in building the modular pre-amp using my latest design on the 26. I’m planning to make this preamp a modular one to enable quick changes and replace pair of valves and OT. This will enable to use 01a and 4P1L as well…

I used a floor plank I found around as the base. The front is a simple aluminium piece that holds the stepped attenuator. Both 4-pin sockets are standing with the rubber suspensors that DHTRob kindly sent me. The two resistor arrays for filament bias are placed between the valves and the OPTs.