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In Reply to: RE: 28KHz anomaly, different album downloads. No 28KHz blip digitizing my own L.P. posted by Tony Lauck on July 13, 2014 at 08:47:58
Are there tape machines in existence using signals in the 28kHz range, such as one might expect to find in a typical switching power supply? I figured all tape machines are so old they probably all use old school rectified, filtered, transformer isolated 60Hz supplies.
I'd be more inclined to suspect the digitizing machinery.
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It's not uncommon to find PC power supplies switching in the 25KHz range but there's no set rule and it depends on the design. Switching power supplies can have a switching frequency upwards of 1-MHz.
I doubt that the old tape machines used switching power supplies. I was thinking it could be the tape bias frequency but I believe those were up around 400KHz.
No rule for sure but it makes passing emissions easier to keep frequencies down.
Unlikely to be digitizing machinery at least not in the Waltz for Debbie. That used the Pacific Microsonics ADC. It's unlikely that such a highly regarded device would have spuria that are 40 dB greater than spuria on my $150 juli@ sound card.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
I didn't see many details but am wondering what type of power supplies that Pacific Microsonics device uses. Undoubtedly it meets it's quoted specs but the question becomes how does any analog gear connected to it react to any emissions it may produce? especially old school analog gear which in it's day didn't require much immunity to perform well.
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