{"id":6515,"date":"2017-06-23T21:23:06","date_gmt":"2017-06-23T20:23:06","guid":{"rendered":"http:\/\/www.bartola.co.uk\/valves\/?p=6515"},"modified":"2017-07-08T07:53:33","modified_gmt":"2017-07-08T06:53:33","slug":"2%d0%b627%d0%bb-2z27l-dht-preamp","status":"publish","type":"post","link":"https:\/\/www.bartola.co.uk\/valves\/2017\/06\/23\/2%d0%b627%d0%bb-2z27l-dht-preamp\/","title":{"rendered":"2\u041627\u041b \/ 2Z27L DHT Preamp"},"content":{"rendered":"

Back in 2012<\/a> I did some experiments with this<\/a> Russian valve.  The 2\u041627\u041b \/ 2Z27L is a fantastic valve. I discovered that if I run it hot, it’s extremely linear and non-microphonic. Bingo! With its highish \u03bc of about 16, it’s ideal as preamp stage or driver. <\/p>\n

Here is my implementation for an DHT preamp (as usual with the gyrator<\/a> load):<\/p>\n

\"\"<\/a><\/p>\n

This is very similar to the 2P29L which is described here<\/a>. 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. <\/p>\n

The result is great, check out the distortion profile:<\/p>\n

\"\"<\/a>
2\u041627\u041b \/ 2Z27L THD @ 2Vrms output<\/figcaption><\/figure>\n
\"\"<\/a>
2\u041627\u041b \/ 2Z27L THD @ 5Vrms output<\/figcaption><\/figure>\n
\"\"<\/a>
2\u041627\u041b \/ 2Z27L THD @ 10Vrms output<\/figcaption><\/figure>\n

Distortion is mainly H2 and below 0.03% for a 10Vrms output. This is very nice.<\/p>\n

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.<\/p>\n

The frequency response is good, see below:<\/p>\n

\"\"<\/a><\/p>\n

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. <\/p>\n

How does it sound?<\/h2>\n

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 <\/a>record for some time:<\/p>\n

    \n
  1. Treble is very clear and sharp<\/li>\n
  2. Tone is very detailed and clear – I like this valve<\/li>\n
  3. Bass not as powerful as a VT-25\/10Y, well what can you expect with only 4mA through the BSH111BK FET \ud83d\ude42<\/li>\n<\/ol>\n

    What a great valve…<\/p>\n

    Will report back in some weeks.<\/p>\n","protected":false},"excerpt":{"rendered":"

    Back in 2012 I did some experiments with this Russian valve.  The 2\u041627\u041b \/ 2Z27L is a fantastic valve. I discovered that if I run it hot, it’s extremely linear and non-microphonic. Bingo! With its highish \u03bc of about 16, it’s ideal as preamp stage or driver. <\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[12,911,156,67],"tags":[1055,918,1032,1056,258,625,864,982,186,888,1057],"class_list":["post-6515","post","type-post","status-publish","format-standard","hentry","category-dht-valves","category-gyrator-pcb","category-pre-amplifier-valves","category-thd","tag-2j27l","tag-2p29l","tag-2p29l-preamp","tag-2z27k-preamp","tag-2z27l","tag-bartola","tag-bartola-gyrator","tag-bsh111bk","tag-dht-preamp","tag-gyrator-board","tag-russian-dht"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p2r2tK-1H5","jetpack_likes_enabled":true,"jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/6515","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/comments?post=6515"}],"version-history":[{"count":1,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/6515\/revisions"}],"predecessor-version":[{"id":6521,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/6515\/revisions\/6521"}],"wp:attachment":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/media?parent=6515"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/categories?post=6515"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/tags?post=6515"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}