{"id":8778,"date":"2013-11-04T17:25:21","date_gmt":"2013-11-05T01:25:21","guid":{"rendered":"http:\/\/rustybolt.info\/wordpress\/?p=8778"},"modified":"2014-01-01T16:43:02","modified_gmt":"2014-01-02T00:43:02","slug":"2013-11-04","status":"publish","type":"post","link":"https:\/\/rustybolt.info\/wordpress\/?p=8778","title":{"rendered":"2013-11-04 Audio Preamp, Two Transistor"},"content":{"rendered":"<p><a href=\"http:\/\/rustybolt.info\/wordpress\/wp-content\/uploads\/2013\/11\/IMG_20140101_142155.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"alignright size-medium wp-image-9122\" alt=\"IMG_20140101_142155\" src=\"http:\/\/rustybolt.info\/wordpress\/wp-content\/uploads\/2013\/11\/IMG_20140101_142155-300x248.jpg\" width=\"300\" height=\"248\" srcset=\"https:\/\/rustybolt.info\/wordpress\/wp-content\/uploads\/2013\/11\/IMG_20140101_142155-300x248.jpg 300w, https:\/\/rustybolt.info\/wordpress\/wp-content\/uploads\/2013\/11\/IMG_20140101_142155.jpg 800w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a>This was in a schematic from the 1960s, the days of silicon transistors, before low noise op amps.\u00a0 The 2SC369 is old and very likely to be no longer available.\u00a0 The replacement transistors could be any low noise small signal, such as the BC550C or 2N5088.\u00a0 The supply voltage shown is 34 VDC, but this can be reduced by reducing the 10k resistor to 1k for example, and increasing the 100 uF.\u00a0 For best low noise performance, the resistors, especially the 100k and 270k, should be low noise metal film type.<\/p>\n<p>External to the circuit, there was a rotary switch on the front panel which switched the input between phono, tuner, etc. and also the corresponding N.F.B. to the output.\u00a0 Following the circuit there were volume and tone controls and then the power amplifier.<\/p>\n<p>I digitized this and posted it Jan 1, 2014.\u00a0 It was probably drawn in the 1980s.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>This was in a schematic from the 1960s, the days of silicon transistors, before low noise op amps.\u00a0 The 2SC369 is old and very likely to be no longer available.\u00a0 The replacement transistors could be any low noise small signal, such as the BC550C or 2N5088.\u00a0 The supply voltage shown is 34 VDC, but this<a href=\"https:\/\/rustybolt.info\/wordpress\/?p=8778\"> <\/p>\n<p> (Read More&#8230;)<\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[8],"tags":[],"class_list":["post-8778","post","type-post","status-publish","format-standard","hentry","category-audio"],"_links":{"self":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/8778","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=8778"}],"version-history":[{"count":8,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/8778\/revisions"}],"predecessor-version":[{"id":9121,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/8778\/revisions\/9121"}],"wp:attachment":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=8778"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=8778"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=8778"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}