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The Electronic Miracle of Rochelle Salt |
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Graham Slee
Admin Group Retired Joined: 11 Jan 2008 Location: South Yorkshire Status: Offline Points: 16298 |
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Posted: 13 Aug 2017 at 5:34am |
I didn't know that rochelle salt comes with its own built-in RIAA equalisation! Perhaps a chemist could comment?
Rochelle salt, or potassium sodium tartrate tetrahydrate as it is chemically known is used to make the crystal of a crystal cartridge. They play records academically flat (not perfect but close enough). I know a forum where people are saying it gives a -6dB per octave frequency response. A crystal cartridge is called a constant amplitude device, so therefore a constant amplitude device has a falling frequency response? Eh? Your amplifier is also constant amplitude because it has a flat response, but not any longer! It now has a falling response of -6dB per octave to fit an argument that is so obviously wrong. Either that or it looks like National Semiconductor got it all wrong in their 1980 Audio/Radio Handbook! Looks like you can't trust the big semiconductor manufacturers? I have only one comment for people dragging out the rubbish about RIAA EQ: go away! A magnetic cartridge is a constant velocity device. Its output increases at +6dB per octave. So, now a question for you, if the record's output increases at +6dB per octave (forgetting the flat portion between 500Hz and 2122Hz for the moment) to suit the -6dB per octave "opinion" regarding crystal cartridge reproduction, then the output from a record using a magnetic cartridge must increase at +12dB per octave?? Yes? Therefore a phono stage that falls at -6dB per octave would not EQ the record! You know that to be a lie. Fact: potassium sodium tartrate tetrahydrate does not have a built-in RIAA filter! Neither does lead-zirconium titanate which ceramic cartridges are made from. So is there something else in the cartridge that does RIAA EQ? Take one apart and see. Two slivers of crystal (make stereo). Wires attached at each end. A blob of silicone sealant holds it all in place. Perhaps silicone sealant does the RIAA EQ?? Or perhaps it's a property of diamond or sapphire... The record cutting electronics were developed by long dead engineers. Unfortunately we cannot talk to them. Those who make them today copy what those engineers did, and might make circuit modifications, but it seems nobody actually understands how the recording EQ works. There is always a chance however that National Semiconductor, and hence I, got it totally wrong. |
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