![\"\"](\"https:\/\/i0.wp.com\/www.bartola.co.uk\/valves\/wp-content\/uploads\/2020\/03\/IMG_1284-rotated.jpg\")
<\/a>I wanted to revisit as a first preamp, the old and beloved RE-084\/A-408 DHT which I never had the chance to share. This is a great valve. I had a decent stash of Valvo pairs which sound like angels. Here was my previous incarnation:<\/p>\n
I used filament bias and also a source follower as was driving directly the 4P1L output stage. Performance was great as it was the way it sounded:<\/p>\n THD only rises to 0.03% at 20Vpp showing how linear this valve is!<\/p>\n I also played with an unbypassed cathode resistor instead of filament bias:<\/p>\n <\/p>\n My latest version is very similar and went back to filament bias, but with SiC diodes instead. I love the sound of these diodes. I biased the valves at lower voltage but will likely push them up to 6mA\/150V as before:<\/p>\n I tested the new mini-gyrator PCBs<\/a> based out of SMD devices. They work brilliantly!<\/p>\n <\/p>\n <\/p>\n","protected":false},"excerpt":{"rendered":" It’s been a while since I experimented with preamps again. I settled as a permanent setup with my 01a\/ER801a which I love. However, I wanted to continue with my experiments so I built a new Mule, let’s call it “Mule 2” for now. It’s based out of multiple PCBs which simplifies the construction process and … Continue reading “The return of the Mule (RE084)”<\/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":[1179,156,67],"tags":[1310,625,875,1312,1311,1062,1172],"class_list":["post-8291","post","type-post","status-publish","format-standard","hentry","category-pcb","category-pre-amplifier-valves","category-thd","tag-a408-tube","tag-bartola","tag-gyrator-pcb","tag-re084-tube","tag-re084-valve","tag-source-follower-pcb","tag-valvo"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p2r2tK-29J","jetpack_likes_enabled":true,"jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/8291","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=8291"}],"version-history":[{"count":1,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/8291\/revisions"}],"predecessor-version":[{"id":8300,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/8291\/revisions\/8300"}],"wp:attachment":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/media?parent=8291"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/categories?post=8291"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/tags?post=8291"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a>As \u00a0you \u00a0can see below, the frequency response is impacted at LF with the increased reflected impedance at the anode due to the unbypassed cathode resistor. Gain is also reduced a tad. This can be sorted with the increase of the gyrator capacitor C1 which I left at 100nF:<\/p>\n<\/a><\/p>\n<\/a><\/p>\n