{"id":1448,"date":"2013-04-20T09:41:19","date_gmt":"2013-04-20T08:41:19","guid":{"rendered":"http:\/\/www.bartola.co.uk\/valves\/?p=1448"},"modified":"2013-04-20T09:41:19","modified_gmt":"2013-04-20T08:41:19","slug":"push-pull-fascination","status":"publish","type":"post","link":"https:\/\/www.bartola.co.uk\/valves\/2013\/04\/20\/push-pull-fascination\/","title":{"rendered":"Push-Pull fascination"},"content":{"rendered":"

I love the sweetness of my 45 SE amplifier, but you know what? A great push-pull (PP) amp has a fantastic presence, bass and dynamic response. Whenever I listen to a good PP amp, I get to the conclusion that I need to have different amps ready to be played depending to the music I want to listen to! My last two years have been devoted to what Morgan Jones calls in his book “single-ended madness”. \u00a0And yes, my 4-65a SE in class A2<\/a> is slowly coming to life and when ready so then I will be properly mad.<\/p>\n

6C4C amps I listened so far made a great impression both in SE and in PP. Owning all components required, I embarked on refining a full DHT push-pull design and again, cap-less (excluding the power supplies of course).<\/p>\n

<\/p>\n

Two pivotal components in the design are the OT and the IT. I have a pair of LL1682PP<\/a> and an LL1660\/20mA which can be used as phase splitter in Alt-V mode. The driver is the beloved 4P1L in filament bias which is powered from a CCS and VR array which provides isolation to the raw power supply, being this a great thing to keep the signal path around the VR:<\/p>\n

\"6C4C<\/a>The 4P1L is biased at 20mA and 210V which provide sufficient headroom to drive the output stage. A 6e5P option may be attractive as well in this position.<\/p>\n

The output stage has a hybrid bias arrangement. It’s mainly fixed bias using a Rod Coleman regulator which generates a stable and quiet reference voltage across a resistor (R6) and the offset balance adjustment between valves is provided by small feedback provided by two 5 ohm filament resistors. This will help us compensating different valves.<\/p>\n

I looked at various bias points for 6C4C and I found about 300V\/50mA being quite good in terms of reduction of H3 component. Higher bias points will increase the H3 level significantly.<\/p>\n

The LL1682 is an 8K8:8 transformer so each valve will see Zaa\/2 or 4K4:<\/p>\n

\"6C4C<\/a>Now, how this circuit is expected to perform:<\/p>\n

\"6C4C<\/a><\/p>\n

The distortion pattern is as expected in an PP amplifier. The odd harmonics ratio is high nearly to 50%. THD is about 0.22% for 4W of output power. The driving signal at full tilt is about 130Vpp and you will need to use this amp with a preamp to provide at least 16-18Vpp input:<\/p>\n

\"Grid <\/a>
Grid drive voltage and grid current <\/div> <\/div> <\/div>
\"Power <\/a>
Power supply current <\/div> <\/div> <\/div> <\/div> <\/div>\n

The supply current is 136mA average due to the 100mA bias current of the two 6C4C plus the driver CCS (36mA). You can see that the peak current goes up to 156mA in each cycle as a normal operating mode in a PP amp. Each valve will suck additional current whilst the other will use less in\u00a0counter-phase. The bias point is responsible for the 20mA difference in the peak that the supply needs to provide.<\/p>\n

A promising design which will need testing as usual…<\/p>\n

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

I love the sweetness of my 45 SE amplifier, but you know what? A great push-pull (PP) amp has a fantastic presence, bass and dynamic response. Whenever I listen to a good PP amp, I get to the conclusion that I need to have different amps ready to be played depending to the music I … Continue reading “Push-Pull fascination”<\/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":[5],"tags":[782,286,217,382,383,387,385,386,384],"class_list":["post-1448","post","type-post","status-publish","format-standard","hentry","category-valves","tag-4p1l","tag-4p1l-driver","tag-6c4c","tag-6c4c-pp","tag-6c4c-push-pull","tag-ll1660","tag-ll1684","tag-ll1684pp","tag-push-pull-madness"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p2r2tK-nm","jetpack_likes_enabled":true,"jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/1448","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=1448"}],"version-history":[{"count":5,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/1448\/revisions"}],"predecessor-version":[{"id":1458,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/1448\/revisions\/1458"}],"wp:attachment":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/media?parent=1448"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/categories?post=1448"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/tags?post=1448"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}