{"id":2842,"date":"2018-06-09T12:53:50","date_gmt":"2018-06-09T17:53:50","guid":{"rendered":"http:\/\/pugix.com\/synth\/?p=2842"},"modified":"2018-06-09T14:58:40","modified_gmt":"2018-06-09T19:58:40","slug":"befaco-abc-noise-fix","status":"publish","type":"post","link":"https:\/\/pugix.com\/synth\/befaco-abc-noise-fix\/","title":{"rendered":"Befaco A*B+C Noise Fix"},"content":{"rendered":"

\"\"<\/a>Befaco A*B+C<\/strong> turned out to have a noise floor issue.\u00a0 Befaco issued a schematic diagram with the fix.\u00a0 I’ve done this modification and confirmed that the noise level is no longer a problem.<\/p>\n

AB+C_V1.0_Schematic_FIX<\/a><\/p>\n

Since the schematic is a little hard to read, I’ve listed all the changes here.\u00a0 (If you’ve bought a full kit of parts, be sure to double check that you have received the latest parts values.\u00a0 Otherwise you’ll have to source the correct parts for yourself.)<\/p>\n

It’s fairly easy to work on the module.\u00a0 Just remove the single screw holding the boards together and separate them.\u00a0 Most of the rework is on the main PCB.<\/p>\n

If you are building it fresh, simply omit the following resistors from the Control PCB.<\/p>\n

Cut off from Control PCB<\/h3>\n

R102, R103, R104, R105, R106, R107, R110, R111<\/p>\n

Change to the following new values.<\/h3>\n

If you are changing these parts, fortunately the PC board markings that identify the parts are still visible after the parts are installed.\u00a0 The PC board is good quality and should not be damaged by rework.\u00a0 I used a good quality solder wick to help remove the parts.\u00a0 Then I cleaned flux from the board with isopropyl alcohol before soldering in the new parts.<\/p>\n

R1, R37 -> 12K<\/p>\n

R2, R36 -> 10K<\/p>\n

R5, R33 -> 100K<\/p>\n

R6, R32 -> 10K<\/p>\n

R7, R20 -> 10K<\/p>\n

R8, R30 -> 100K<\/p>\n

R12, R26 -> 100K<\/p>\n

R13, R19 -> 100K<\/p>\n

R14, R24 -> 47K<\/p>\n

R17, R31 -> 10K<\/p>\n

R18, R25 -> 10K<\/p>\n

C2, C13 -> 10 picofarad<\/p>\n

Options<\/h3>\n

R11, R22 -> Either a bare wire or 1K.\u00a0 I used 1K so as not to have a jack connected directly to an input pin of the AD633.\u00a0 Using the 1K will reduce the signal by about 1%, which doesn’t really matter because the maximum gain is 2X.<\/p>\n

R27 -> 4K7 or omit if you don’t want to mix the top section into the bottom one.\u00a0 I chose to omit.<\/p>\n

Modifications<\/h3>\n

Use an ohmmeter to verify which end of R12 and R26 to lift.<\/p>\n

R12 – Lift the end going to R14 and connect it directly to IC1 pin 13.<\/p>\n

R26 – Lift the end going to R24 and connect it directly to IC4 pin 2.<\/p>\n

 <\/p>\n

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

Befaco A*B+C turned out to have a noise floor issue.\u00a0 Befaco issued a schematic diagram with the fix.\u00a0 I’ve done this modification and confirmed that the noise level is no … Read More<\/a><\/p>\n","protected":false},"author":1,"featured_media":2499,"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":[161],"tags":[71],"class_list":["post-2842","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-eurorack","tag-diy"],"yoast_head":"\nBefaco A*B+C Noise Fix - Richard Brewster's Electronic Sounds<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/pugix.com\/synth\/befaco-abc-noise-fix\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Befaco A*B+C Noise Fix - Richard Brewster's Electronic Sounds\" \/>\n<meta property=\"og:description\" content=\"Befaco A*B+C turned out to have a noise floor issue.\u00a0 Befaco issued a schematic diagram with the fix.\u00a0 I’ve done this modification and confirmed that the noise level is no ... 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