{"id":7722,"date":"2019-02-03T11:15:52","date_gmt":"2019-02-03T11:15:52","guid":{"rendered":"http:\/\/www.bartola.co.uk\/valves\/?p=7722"},"modified":"2019-04-13T11:41:38","modified_gmt":"2019-04-13T10:41:38","slug":"hybrid-mu-follower-aka-gyrator-rev08-pcb-update","status":"publish","type":"post","link":"https:\/\/www.bartola.co.uk\/valves\/2019\/02\/03\/hybrid-mu-follower-aka-gyrator-rev08-pcb-update\/","title":{"rendered":"Hybrid Mu-follower (aka Gyrator) Rev08 PCB Update"},"content":{"rendered":"

It’s been far too long since I last posted on this blog. With the limited spare time I’ve got these days, I concentrated in setting up the new workshop and system since we moved back to our place. I’m nearly there, so now it’s time to get back to work<\/p>\n

I made some updates to the “gyrator” PCB. I’ll stop referencing it gyrator from now on, since the name is misleading. However, it got popular that way. Nevertheless, it’s a hybrid mu-follower circuit but if only if you take the output from the anode, it behaves like a “gyrator” from a frequency response perspective. If you’re interested in this circuit in more detail, please read the lecture I gave last year at ETF.18. You can download it from here<\/a>.<\/p>\n

Back to the board, here are the few changes made:<\/p>\n

    \n
  1. Moved the trimpot P1 for easier fixing of the board with the M3 standoffs.<\/li>\n
  2. Added a gate stopper resistor (R9) to avoid oscillation at low anode current (<10mA) when using high-gm MOSFETs in the lower position J4. This was evident with devices like BSH111BNK<\/li>\n
  3. Added an LED (D4) indicator and a series resistor (R8) at the drain of M3. This enables indication of:\n
      \n
    1. Normal operation subject to \u00a0value of R8<\/li>\n
    2. Source current into load (e.g. like in A2 operation) subject to value of R8.<\/li>\n
    3. Short output to ground. Depending on duration and current limitation of power supply, this may prevent damaging M3 MOSFET. Not guaranteed, but in some scenarios will work.<\/li>\n<\/ol>\n<\/li>\n<\/ol>\n

      <\/p>\n

      Here is the circuit diagram for reference:<\/p>\n

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

      Of course you can continue using jFETs in the board. However, I found that the BSH111BK\/BSN20BK and other high-gm perform really well in this circuit. They are still plenty and available out there, not like the BF862. Unfortunately this one is EOL (see lecture for replacement options).<\/p>\n

      Here is a sample test of the 01a preamp stage with this new board:<\/p>\n

      \"\"<\/a>
      REv08 PCB board tested with the 01a preamp.<\/figcaption><\/figure>\n

      In this case with the use of an IXTP3N100D2 and BSH111BK operating at 3-4mA the frequency response is flat to nearly 380kHz. Same combination of FETs in a Rev07 board will oscillate at LF due to the lack of gate stopper.<\/p>\n

      With a Rev07 IXTP08N100D and BF862 board, the response only gets up to 150-180kHz depending on the valve. This is not a limitation whatsoever in audio band, let’s make this point clear.<\/p>\n

      A snapshot of a completed board:<\/p>\n

      \"\"<\/a>
      Rev08 PCB completed<\/figcaption><\/figure>\n

       <\/p>\n

       <\/p>\n

      in the following picture you will see the three new components added so you can compare to the previous Rev07 version. Also note that this is a prototype version so it doesn’t have an ENIG Gold board finish:<\/p>\n

      \"\"<\/a>
      Rev 08 PCB: the new components added to the circuit<\/figcaption><\/figure>\n

       <\/p>\n

      The new boards were tested on my 01a preamp. They sound amazing, as good as the previous ones. Interestingly enough, I made a mistake during breadboarding and the LED turn on really brightly with 100mA shunted through the output. The FETs survived this time thanks to the limiting resistor and the current protection I have on my bench power supply.<\/p>\n

       <\/p>\n

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

      It’s been far too long since I last posted on this blog. With the limited spare time I’ve got these days, I concentrated in setting up the new workshop and system since we moved back to our place. I’m nearly there, so now it’s time to get back to work I made some updates to … Continue reading “Hybrid Mu-follower (aka Gyrator) Rev08 PCB Update”<\/span><\/a><\/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":[911],"tags":[864,1195,982,1189,1190,875,1194,652,1196,1193],"class_list":["post-7722","post","type-post","status-publish","format-standard","hentry","category-gyrator-pcb","tag-bartola-gyrator","tag-bartola-hybrid-mu-follower","tag-bsh111bk","tag-etf","tag-etf-18","tag-gyrator-pcb","tag-gyrator-rev08","tag-hybrid-mu-follower","tag-ixtp3n100d2","tag-rev08"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p2r2tK-20y","jetpack_likes_enabled":true,"jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/7722","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=7722"}],"version-history":[{"count":2,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/7722\/revisions"}],"predecessor-version":[{"id":7853,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/7722\/revisions\/7853"}],"wp:attachment":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/media?parent=7722"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/categories?post=7722"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/tags?post=7722"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}