Tag: 2P29L preamp

DHT Audio Shootout @ London

Here’s the summary of the shootout day we had yesterday at my place with  Tony Rees and Andy Evans

Test Music

For testing the pre-amps Andy suggested the following 2 tracks:

  1.  Ravel Feria (Cleveland/Boulez)
  2. Janacek The Cunning Little Vixen Act 3 Scene 7 “A vixen’s running through the woods” Prague Theatre/Gregor


The Ravel is orchestrated for a large orchestra and percussion, and listening was particularly for the timbre of strings, brass and woodwind and the clarity of the percussion. The Janacek is for several different voices and chorus, and listening was for the tone and character of the voices and how well they were differentiated from each other. In both cases the overall clarity, life and crispness was considered.

Andy Evans

Although I wasn’t familiarised enough with these 2 tracks myself, I found them to be an excellent choice and a reflection of Andy’s musical experience and knowledge as musician. 

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2P29L DHT Preamp – final build

Finally I managed to build a stable version of the 2P29L preamp. The wooden modular version inspired on DHTRob designs paid off. Here it is:

The result is fantastic. The 2P29L is a superb DHT, quiet and it sounds amazing. The circuit is similar to the original one but with a slightly different operating point due to the valves themselves:

I’m still running them at 20mA. This time the anode voltage has to be increased to 150V to achieve this. Consistent across the 2 valves used.

C2 was modified to fit a gift I received from my friend Vyacheslav. Instead of the usual 220nF, I fit a bigger 470nF FT-3 version which improves the LF response.

The frequency response is very good, as I published before.  For the curious ones, here are some further pictures of the build:

 

 


I can’t say more than what I said before. This is a fantastic DHT, it provides a great detailed sound and is quiet. No microphonic noise and the dynamics are great. One of my favourite clearly.

 

2Ж27Л / 2Z27L DHT Preamp

Back in 2012 I did some experiments with this Russian valve.  The 2Ж27Л / 2Z27L is a fantastic valve. I discovered that if I run it hot, it’s extremely linear and non-microphonic. Bingo! With its highish μ of about 16, it’s ideal as preamp stage or driver. 

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2P29L DHT Preamp

The Mule saga continues and it was time to modify the 3B7 preamp and to test the 2P29L valve. This was quite easy as they both have loctal sockets. I had to modify the Rod Coleman filament regulator to set the filament current down to 120mA. Then a bit of wiring work, and in less than an hour a new preamp was ready. Job done, this is why I built the Mule:

The circuit is quite close to my original design time ago. I modified the filament resistor to use an existing Russian NOS wirewound part I had in stock and suit this preamp quite well. Added grid and screen stoppers as well:

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