{"id":6303,"date":"2017-03-24T20:35:01","date_gmt":"2017-03-24T20:35:01","guid":{"rendered":"http:\/\/www.bartola.co.uk\/valves\/?p=6303"},"modified":"2017-07-08T07:53:34","modified_gmt":"2017-07-08T06:53:34","slug":"cx-112a-dht-preamp","status":"publish","type":"post","link":"https:\/\/www.bartola.co.uk\/valves\/2017\/03\/24\/cx-112a-dht-preamp\/","title":{"rendered":"cx-112a DHT preamp"},"content":{"rendered":"

Introduction<\/h2>\n

\"\"<\/a>This was one of my first DHT preamps. I found a quartet of NOS CX-112a <\/a>Cunningham (globe) back in Buenos Aires many years ago and built one of my first DHT preamps. I loved it. I played with it before I moved into the 26 and then started the long exploratory journey with DHTs. <\/p>\n

The CX-112a can be easily fit in an existing 01a preamp<\/a>. Take a look at what Thomas Mayer<\/a> recently blogged about this valve, worth reading it. <\/p>\n

Well, you can get more current drive than 01a (nearly double) but no thoriated tungsten filaments. Anyhow, the gain is slightly higher but is very easy to adapt to my gyrator-based circuit, that I couldn’t resist to take the quartet out of my valve stash and make them sing again after so many years.<\/p>\n

<\/p>\n

The circuit<\/h2>\n

Again, an easy drop in without modifications. If you want to learn more about this circuit then I suggest you read the 01a blog posts. In summary, here it is:<\/p>\n

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

I used my existing 01a, however I tried newer PCB boards<\/a> with the IXTP08N100D top MOSFET as well as slight variation of the components as shown int the diagram. I like the fact I can drive it at 8mA, better Slew Rate and deeper bass as the BF862 transconductance is higher. <\/p>\n

Performance<\/h2>\n

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

This is an outstanding preamp. I have to admit that I was even impressed with the bass, closer to the VT-25<\/a>. It has good dynamics but probably the level of detail not as close as the 01a. I think it’s really good and is worth listening for some time. I will leave it running as I enjoy it very much. <\/p>\n

The measured performance is great. Let’s have a look at the frequency response:<\/p>\n

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

Flat response from 3Hz up to 700kHz. High-bandwidth, clear treble and strong bass. A real contender amongst the DHTs<\/p>\n

Distortion can be as low as 0.005% for 1V output to 0.11% for 10V swing. The harmonics haven’t  got the best cadence when at full tilt, however, at normal levels they are great:<\/p>\n

\"\"<\/a>
THD @ 4Vmrs<\/figcaption><\/figure>\n
\"\"<\/a>
THD @ 10Vmrs<\/figcaption><\/figure>\n

I don’t know how easy are the CX-112a to get these days, but certainly they are worth using. The sound of the preamp stage is great. Detailed and with strong bass and clear treble. I feel at this early stage is a good contender to the 01a as well as the VT-25.<\/p>\n

i will play it for a while. Boards and preamp overall needs some break-in time. <\/p>\n

Cheers<\/p>\n

Ale<\/p>\n

 <\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

Introduction This was one of my first DHT preamps. I found a quartet of NOS CX-112a Cunningham (globe) back in Buenos Aires many years ago and built one of my first DHT preamps. I loved it. I played with it before I moved into the 26 and then started the long exploratory journey with DHTs.  … Continue reading “cx-112a DHT preamp”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_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}},"categories":[12,911,156,67,5],"tags":[10,1017,1021,1020,1022,777,1019,1018,186,287,875,1023,554,275,118],"class_list":["post-6303","post","type-post","status-publish","format-standard","hentry","category-dht-valves","category-gyrator-pcb","category-pre-amplifier-valves","category-thd","category-valves","tag-01a","tag-112a","tag-112a-dht-preamp","tag-112a-preamp","tag-ale-moglia-gyrator","tag-bf862","tag-cx-112a","tag-cx112a","tag-dht-preamp","tag-filament-bias","tag-gyrator-pcb","tag-gyrator-pcb-bf862","tag-lcr-impedance-bridge","tag-rod-coleman","tag-vt-25"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p2r2tK-1DF","jetpack_likes_enabled":true,"jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/6303","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=6303"}],"version-history":[{"count":1,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/6303\/revisions"}],"predecessor-version":[{"id":6310,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/6303\/revisions\/6310"}],"wp:attachment":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/media?parent=6303"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/categories?post=6303"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/tags?post=6303"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}