{"id":390,"date":"2020-03-04T23:25:25","date_gmt":"2020-03-04T20:25:25","guid":{"rendered":"https:\/\/tomorrow82.ru\/?page_id=390"},"modified":"2020-03-04T23:25:25","modified_gmt":"2020-03-04T20:25:25","slug":"the-feedback-network","status":"publish","type":"page","link":"https:\/\/tomorrow82.ru\/?page_id=390","title":{"rendered":"The Feedback Network"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\">Figure 1 shows a block diagram of the amplifier with the feedback \nnetwork connected to it. At audio frequencies, the parallel combination \nof C6 and C7 is a short circuit while C8 and C9 are open circuits. \nFeedback is taken from the loudspeaker output through R17 and R18 to the\n inverting input of the diff amps. The fraction of the output voltage \nfed back to the diff amp is R19\/(R17 + R18 + R19). The gain of the \namplifier is approximately equal to the reciprocal of this ratio, which \nis 21 (26.4 dB) for the values specified.<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"\"><tbody><tr><td class=\"has-text-align-center\" data-align=\"center\"><img loading=\"lazy\" decoding=\"async\" width=\"540\" height=\"207\" class=\"wp-image-392\" style=\"width: 540px;\" src=\"https:\/\/tomorrow82.ru\/wp-content\/uploads\/2020\/03\/fdbknet.gif\" alt=\"Figure 1. Amplifier block diagram showing feedback network.\"><\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\">Figure 1. Amplifier block diagram showing feedback network.<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">At frequencies above about 150 kHz, C8 and C9 become short circuits. \nThis causes the feedback to be taken from the driver stage instead of \nfrom the output. By splitting the feedback into two paths in this way, \nstability from hgh-frequency oscillations that can be induced by load \ncapacitance is improved. Below 1 Hz, C6 and C7 become open circuits \ncausing the amplifier to have 100% feedback at dc. This improves the \nstability of the bias currents and voltages. With 100% dc feedback, the \ndc gain of the amplifier is unity.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">C6 is an electrolytic capacitor. C7 is a film capacitor which is used\n in parallel with C6 to improve its high-frequency characteristics. The \ncircuit board layout provides an option to use two polar capacitors in \nseries for C6 or a single non-polar capacitor. If a non-polar capacitor \nis used, a short circuit jumper must be installed to complete the \ncircuit. One builder who accidentally left the jumper off was distressed\n because his amplifier had very poor bass response. Without the jumper, \nthe lower cutoff frequency is 1.4 kHz rather than below 1 Hz.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Figure 1 shows a block diagram of the amplifier with the feedback network connected to it. At audio frequencies, the parallel combination of C6 and C7 is a short circuit while C8 and C9 are open circuits. Feedback is taken from the loudspeaker output through R17 and R18 to the inverting input of the diff&hellip; <\/p>\n<p><a class=\"moretag\" href=\"https:\/\/tomorrow82.ru\/?page_id=390\">\u041f\u0440\u043e\u0447\u0438\u0442\u0430\u0442\u044c \u0441\u0442\u0430\u0442\u044c\u044e \u0446\u0435\u043b\u0438\u043a\u043e\u043c<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-390","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/tomorrow82.ru\/index.php?rest_route=\/wp\/v2\/pages\/390","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/tomorrow82.ru\/index.php?rest_route=\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/tomorrow82.ru\/index.php?rest_route=\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/tomorrow82.ru\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/tomorrow82.ru\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=390"}],"version-history":[{"count":2,"href":"https:\/\/tomorrow82.ru\/index.php?rest_route=\/wp\/v2\/pages\/390\/revisions"}],"predecessor-version":[{"id":393,"href":"https:\/\/tomorrow82.ru\/index.php?rest_route=\/wp\/v2\/pages\/390\/revisions\/393"}],"wp:attachment":[{"href":"https:\/\/tomorrow82.ru\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=390"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}