{"id":7363,"date":"2022-11-14T19:54:48","date_gmt":"2022-11-14T17:54:48","guid":{"rendered":"https:\/\/www.tonmeister.ca\/wordpress\/?p=7363"},"modified":"2022-11-14T19:54:48","modified_gmt":"2022-11-14T17:54:48","slug":"keep-your-needle-clean","status":"publish","type":"post","link":"https:\/\/www.tonmeister.ca\/wordpress\/2022\/11\/14\/keep-your-needle-clean\/","title":{"rendered":"Keep your needle clean"},"content":{"rendered":"\n

One of my jobs at Bang & Olufsen is to do the final measurements on each bespoke Beogram 4000c turntable<\/a> before it’s sent to the customer. Those measurements include checking the end-to-end magnitude response, playing from a vinyl record with a sine sweep on it (one per channel), recording that from the turntable’s line-level output, and analysing it to make sure that it’s as expected. Part of that analysis is to very that the magnitude responses of the left and right channel outputs are the same (or, same enough… it’s analogue, a world where nothing is perfect…)<\/p>\n\n\n\n

Today, I was surprised to see this result on a turntable that was being inspected part-way through its restoration process :<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

Taken at face value, this should have resulted in a rejection – or at least some very serious questions. This is a terrible result, with unacceptable differences in output level between the two channels. When I looked at the raw measurements, I could easily see that the left channel was behaving – it was the right channel that was all over the place.<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

The black curve looks very much like what I would expect to see. This is the result of playing a track that is a sine sweep from 20 Hz to 20 kHz, where the signal below 1 kHz follows the RIAA curve, whereas the signal above 1 kHz does not. This is why, after it’s been filtered using a RIAA preamp, the low frequency portion has a flat response, but the upper frequency band rolls off (following the RIAA curve).<\/p>\n\n\n\n

Notice that the right channel (the red curve) is a mess…<\/p>\n\n\n\n

A quick inspection revealed what might have been the problem: a small ball of fluff collected around the stylus. (This was a pickup that was being used to verify that the turntable was behaving through the restoration – not the one intended for the final customer – and so had been used multiple times on multiple turntables.)<\/p>\n\n\n\n

So, we used a stylus brush to clean off the fluff and ran the measurement again. The result immediately afterwards looked like this:<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

which is more like it! A left-right channel difference of something like \u00b1 0.5 dB is perfectly acceptable.<\/p>\n\n\n\n

The moral of the story: keep your pickup clean<\/strong>. But do it carefully! That cantilever is not difficult to snap.<\/p>\n","protected":false},"excerpt":{"rendered":"

One of my jobs at Bang & Olufsen is to do the final measurements on each bespoke Beogram 4000c turntable before it’s sent to the customer. Those measurements include checking the end-to-end magnitude response, playing from a vinyl record with a sine sweep on it (one per channel), recording that from the turntable’s line-level output, […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","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":[66,4,32,65],"tags":[],"class_list":["post-7363","post","type-post","status-publish","format-standard","hentry","category-analogue","category-audio","category-bang-olufsen","category-measurements"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p48hIM-1UL","_links":{"self":[{"href":"https:\/\/www.tonmeister.ca\/wordpress\/wp-json\/wp\/v2\/posts\/7363","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.tonmeister.ca\/wordpress\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.tonmeister.ca\/wordpress\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.tonmeister.ca\/wordpress\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.tonmeister.ca\/wordpress\/wp-json\/wp\/v2\/comments?post=7363"}],"version-history":[{"count":1,"href":"https:\/\/www.tonmeister.ca\/wordpress\/wp-json\/wp\/v2\/posts\/7363\/revisions"}],"predecessor-version":[{"id":7370,"href":"https:\/\/www.tonmeister.ca\/wordpress\/wp-json\/wp\/v2\/posts\/7363\/revisions\/7370"}],"wp:attachment":[{"href":"https:\/\/www.tonmeister.ca\/wordpress\/wp-json\/wp\/v2\/media?parent=7363"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.tonmeister.ca\/wordpress\/wp-json\/wp\/v2\/categories?post=7363"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.tonmeister.ca\/wordpress\/wp-json\/wp\/v2\/tags?post=7363"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}