{"id":8091,"date":"2019-11-10T20:37:46","date_gmt":"2019-11-10T20:37:46","guid":{"rendered":"http:\/\/www.bartola.co.uk\/valves\/?p=8091"},"modified":"2019-11-10T20:37:53","modified_gmt":"2019-11-10T20:37:53","slug":"6e6p-dr-hp-amp-part-3-measurements","status":"publish","type":"post","link":"https:\/\/www.bartola.co.uk\/valves\/2019\/11\/10\/6e6p-dr-hp-amp-part-3-measurements\/","title":{"rendered":"6e6p-dr HP amp \u2013 part 3: measurements"},"content":{"rendered":"\n

As I promised, I took the HP amp back to the workshop for a bit of abuse on the bench. Here are some interesting measurements which correlate with some of my listening impressions so far. <\/p>\n\n\n\n

I added a set of 300\u03a9 dummy loads at the output to simulate the HPs. Firstly I tested the optimal circuit which has the Sowter 8665 output transformer in Parafeed mode (4:1) to drive the load. You can get a very clean and flat response across the audio band from 3Hz up to +90kHz. There is a minor hump to be tuned due to the RLC circuit formed by the parafeed circuit. I used a 4.7\u03bcF Mundorf EVO oil cap. It’s pretty flat to me, so will leave it there.<\/p>\n\n\n\n

The performance of the circuit is amazing. Distortion is very low, up to 0.07% at 100mW (which is VL=5.47Vrms): <\/p>\n\n\n\n

\"\"
6e6p-dr Headphone Amp performance @ 100mW output level<\/figcaption><\/figure><\/div>\n\n\n\n\n\n\n\n
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Sowter 8665 output performance of the HP amp @ 100mW (maximum power)<\/figcaption><\/figure>\n\n\n\n

Harmonics from H3 onwards are very low level and distortion is primarily driven by H2. This measures as good as it sounds. Great stage.<\/p>\n\n\n\n

Well, let’s look at the stage with the 100\u03bcF Mundorf EVO oil cap instead. This is a completely different beast. We are asking the hybrid mu-follower to drive a 300\u03a9 which is pretty tough. The stage has low output impedance and current drive. The maximum current drive for 100mW will be around 18mA. Anyhow, the load will be steep and a tough one for this stage without the output transformer. Although the sound is very nice at low level, I could easily prefer the Sowter circuit during the listening tests. Lets see why.<\/p>\n\n\n\n

As you can expect from the hybrid mu-follower topology, the frequency response is very good:<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

However, distortion is significantly higher: THD is 1.7% for 100mW in 300\u03a9 (5.47Vrms). You should expect 0.5% or less at normal listening levels though. <\/p>\n\n\n\n

<\/p>\n\n\n\n

<\/p>\n\n\n\n

<\/p>\n\n\n\n

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

As I promised, I took the HP amp back to the workshop for a bit of abuse on the bench. Here are some interesting measurements which correlate with some of my listening impressions so far. I added a set of 300\u03a9 dummy loads at the output to simulate the HPs. Firstly I tested the optimal … Continue reading “6e6p-dr HP amp \u2013 part 3: measurements”<\/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":[33,5],"tags":[605,865,960,31,1234,965],"class_list":["post-8091","post","type-post","status-publish","format-standard","hentry","category-headphone-amp","category-valves","tag-6e6p-dr","tag-bartola-valves-gyrator","tag-headphone-amp","tag-headphone-amplifier","tag-sennheiser-hd650","tag-sowter-8665"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p2r2tK-26v","jetpack_likes_enabled":true,"jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/8091","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=8091"}],"version-history":[{"count":5,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/8091\/revisions"}],"predecessor-version":[{"id":8101,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/8091\/revisions\/8101"}],"wp:attachment":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/media?parent=8091"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/categories?post=8091"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/tags?post=8091"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}