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. 

Here is my implementation for an DHT preamp (as usual with the gyrator load):

This is very similar to the 2P29L which is described here. You only need to change a resistor on the Rod Coleman regulators and you’re done. It took me 15min to do the upgrade, I wish a mod in a preamp could be done every time like this. The loctal pinout is the same. The anode voltage is reduced to about 116-120V to push the valve to the maximum cathode current which is about 4mA. 

The result is great, check out the distortion profile:

2Ж27Л / 2Z27L THD @ 2Vrms output
2Ж27Л / 2Z27L THD @ 5Vrms output
2Ж27Л / 2Z27L THD @ 10Vrms output

Distortion is mainly H2 and below 0.03% for a 10Vrms output. This is very nice.

When you tap hard the valve you get some microphonic noise at about 2.5kHz. Surprisingly, when I built it on my Mule preamp, no noise is picked up! It’s extremely quite for a 24dB DHT stage! Nice discovery.

The frequency response is good, see below:

Flat from 5Hz to 170kHz (-3dB points). Expect worse response when fully loaded. The only disadvantage of this valve is the 4mA maximum current. If you need, you will have to add a FET follower at the output to drive more demanding capacitive loads. 

How does it sound?

I will have to get back to this a couple of weeks later when I manage to spend some proper time to listen to the stage. The initial impressions are (after listening Freddie Hubbard’s Open Sesame record for some time:

  1. Treble is very clear and sharp
  2. Tone is very detailed and clear – I like this valve
  3. Bass not as powerful as a VT-25/10Y, well what can you expect with only 4mA through the BSH111BK FET 🙂

What a great valve…

Will report back in some weeks.

3 Replies to “2Ж27Л / 2Z27L DHT Preamp”

  1. Despite it measures really well and sounds great, I found it a bit tiring after listening to it for some time. There is something in the treble that I don’t like. Specially when listening to any brass arrangements. I did not measure any significant H3, so am puzzled. Well that is why listening tests provide the ultimate veredict!

    I still think it would be a nice valve for a final stage in a RIAA preamp though.

  2. I’m suspecting something similar in the treble with 2P29L. Can’t put my finger on it, but with my amorphous core OPTs everything comes through in the treble. Sounds like you didn’t hear it with the 2P29L if you listened to that for weeks. The 2P29L treble is remarkably clear – maybe there’s a peak somewhere. Anything that sets my tinnitus off is suspect for me – usually I’m used to it but peaky treble sets it off and I hear the hissing more clearly. I did notice that if I tapped the chassis I got a high pitch ring. I haven’t grounded pins 2 and 6 – maybe I should. Just wondering if there’s a common factor with these aluminium encased tubes. Maybe they need rubber tube dampers even….Andy

    1. Hi Andy,
      To me the 2Z27L sounded really different to the 2P29L. The 2P29L was very detailed and clean to me. Now I have adapted the Mule to the 4P1L which is sounding fantastic with the new gyrator board (IXTP08N100D and BSH111BK). I do like this combination very much. Luckily, I’m running a pair of Svetlana early 1950s 4P1L which are not microphonic at after several hundred hours of playing.
      I will build another Mule probably so can do further tests in parallel

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