{"id":641,"date":"2016-01-10T21:05:15","date_gmt":"2016-01-11T02:05:15","guid":{"rendered":"https:\/\/billthompson.us\/bt\/?p=641"},"modified":"2017-12-28T15:06:20","modified_gmt":"2017-12-28T20:06:20","slug":"simple-clean-mic-preamp","status":"publish","type":"post","link":"https:\/\/billthompson.us\/bt\/simple-clean-mic-preamp\/","title":{"rendered":"Simple, Clean Mic Preamp"},"content":{"rendered":"<p><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-643 size-medium alignnone\" src=\"https:\/\/billthompson.us\/bt\/wp-content\/uploads\/2016\/01\/mic-pre-8-300x151.jpg\" alt=\"\" width=\"300\" height=\"151\" srcset=\"https:\/\/billthompson.us\/bt\/wp-content\/uploads\/2016\/01\/mic-pre-8-300x151.jpg 300w, https:\/\/billthompson.us\/bt\/wp-content\/uploads\/2016\/01\/mic-pre-8.jpg 640w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/p>\n<p>This isn&#8217;t exactly new. I started this preamp project when I was just getting into digital recording in 2001 and still very active in Ashly Audio but I&#8217;m still using these preamps unmodified to this day. I wanted a very clean, neutral preamp with absolutely no unnecessary bells and whistles.<\/p>\n<p><center><!--more--><\/center><\/p>\n<h2>A Simple, Clean Microphone Preamplifier:<\/h2>\n<p><strong>Features:<\/strong>:<\/p>\n<ul>\n<li>Very low distortion<\/li>\n<li>Reasonable noise performance<\/li>\n<li>Accepts high levels without overload<\/li>\n<li>Simple enough to package 8 preamps in a 1u rack enclosure<\/li>\n<li style=\"text-align: left;\">Reliable and easy to service<\/li>\n<li>Wide range gain adjustment without complexity<\/li>\n<\/ul>\n<p>With all this in mind the design took the following form:<\/p>\n<p>A high quality 1:3 Jensen input transformer was used. This provides a bit of impedance matching from the mic to the first amplification stage helping to minimize noise without specialized electronics and it also gives great inherent RF and ground loop immunity,<\/p>\n<p>A dual op-amp provides two amplification stages with the gain control between the stages. A linear taper control increases or reduces the gain of both stages simultaneously giving wide adjustment range and good repeatability for all channels.<\/p>\n<p>A DPDT switch and 4 resistors are used to produce a switchable constant impedance 20dB pad to accommodate very high input levels.<\/p>\n<p>The power supply is external so there&#8217;s no AC in the preamp chassis. This way there&#8217;s no chance of any hum.<\/p>\n<figure id=\"attachment_642\" aria-describedby=\"caption-attachment-642\" style=\"width: 640px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-642 size-full\" src=\"https:\/\/billthompson.us\/bt\/wp-content\/uploads\/2016\/01\/micpre03.jpg\" alt=\"micpre03\" width=\"640\" height=\"401\" \/><figcaption id=\"caption-attachment-642\" class=\"wp-caption-text\">1 of 8 channels in the 8 channel 1u mic preamp<\/figcaption><\/figure>\n<p><center><b><a href=\"https:\/\/billthompson.us\/bt\/sch\/micpre03-1280.jpg\" target=\"_blank\" rel=\"noopener\">Larger schematic &#8211; opens in a new tab<\/a><\/b><\/center><\/p>\n<figure id=\"attachment_920\" aria-describedby=\"caption-attachment-920\" style=\"width: 640px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-920 size-full\" src=\"https:\/\/billthompson.us\/bt\/wp-content\/uploads\/2016\/01\/mic-pre-8-1.jpg\" alt=\"Internal view of 8 channel preamp in 1u rack chassis\" width=\"640\" height=\"323\" srcset=\"https:\/\/billthompson.us\/bt\/wp-content\/uploads\/2016\/01\/mic-pre-8-1.jpg 640w, https:\/\/billthompson.us\/bt\/wp-content\/uploads\/2016\/01\/mic-pre-8-1-300x151.jpg 300w\" sizes=\"auto, (max-width: 640px) 100vw, 640px\" \/><figcaption id=\"caption-attachment-920\" class=\"wp-caption-text\">Internal view of 8 channel preamp in 1u rack chassis<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<figure id=\"attachment_921\" aria-describedby=\"caption-attachment-921\" style=\"width: 640px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-921 size-full\" src=\"https:\/\/billthompson.us\/bt\/wp-content\/uploads\/2016\/01\/micrack-1.jpg\" alt=\"micrack\" width=\"640\" height=\"480\" srcset=\"https:\/\/billthompson.us\/bt\/wp-content\/uploads\/2016\/01\/micrack-1.jpg 640w, https:\/\/billthompson.us\/bt\/wp-content\/uploads\/2016\/01\/micrack-1-300x225.jpg 300w\" sizes=\"auto, (max-width: 640px) 100vw, 640px\" \/><figcaption id=\"caption-attachment-921\" class=\"wp-caption-text\">(3) 8 channel preamps with (2) 12 channel Echo A-D converters &#8211; the current 24 track recording setup<\/figcaption><\/figure>\n","protected":false},"excerpt":{"rendered":"<p>This isn&#8217;t exactly new. I started this preamp project when I was just getting into digital recording in 2001 and still very active in Ashly Audio but I&#8217;m still using these preamps unmodified to this day. I wanted a very clean, neutral preamp with absolutely no unnecessary bells and whistles.<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"categories":[9],"tags":[],"class_list":["post-641","post","type-post","status-publish","format-standard","hentry","category-projects"],"_links":{"self":[{"href":"https:\/\/billthompson.us\/bt\/wp-json\/wp\/v2\/posts\/641","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/billthompson.us\/bt\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/billthompson.us\/bt\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/billthompson.us\/bt\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/billthompson.us\/bt\/wp-json\/wp\/v2\/comments?post=641"}],"version-history":[{"count":0,"href":"https:\/\/billthompson.us\/bt\/wp-json\/wp\/v2\/posts\/641\/revisions"}],"wp:attachment":[{"href":"https:\/\/billthompson.us\/bt\/wp-json\/wp\/v2\/media?parent=641"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/billthompson.us\/bt\/wp-json\/wp\/v2\/categories?post=641"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/billthompson.us\/bt\/wp-json\/wp\/v2\/tags?post=641"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}