Are there any designs on the forum for a reverse RIAA circuit? I did a quick search and didn't see any. Ultra accurate not required, but I have a couple of phono pre-amps I want to check.
EDIT: I see Rod Elliot has a design, hopefully that will do.
EDIT: I see Rod Elliot has a design, hopefully that will do.
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Thank you all. Yes, that would have been better. Fortunately I have already discovered those links by accident. The Rod Elliot version will probably suit me, for a simple check. I should have all the components for that. I presume polystyrene caps will do?
Patrick Turner on Turner Audio had a very good one too, but you can try two or three different ones...you don't need fantastic precision with riaa.I was able to replicate 20khz square waves with two different filters, way more than what you really need .What you really look after is the response under 500hz .
I am changing valves in the phono stage of a pre-amp at the moment. I just need to compare the new and old responses to check if there is any change. Great accuracy not needed at the moment, but of course it wouldn't hurt. Simplicity of construction is needed though.
unfortunately there's no simplicity of construction with anti-riaa filters.You need to get the exact values in picofarads.Mica, polystyrene, pps capacitors, low noise precision resistors...but parallel/series resistors and parallel capacitors will get you any value.
Luckily I have plenty of polystyrene caps and can test them. Resistors the same. I just wanted to be sure that the styrenes would be OK.
They are specifically good for this kind of applications...but some say that they are prone to modify their values a bit after soldering so remeasure them after soldering.I never had a problem though...
It feels good to get 0.1dB accuracy but you would be hard pressed to find a cartridge where 5% (+-0.5dB) values would matter.
I know what you mean...Actually i remember there was a study showing that people aren't able to hear riaa nonlinearities up to 6db...but we're here to show we're more catholic than the Pope, aren't we?
It's more important than absolute accuracy to get the same performance for both channels.
Best regards!
Best regards!
I made up the Rod Elliott circuit, and the revised pre-amp seems OK. There was a bit of wild swinging at 50Hz, but it doesn't sound though the system playing music, so I suspect it is a lack of screening on the reverse RIAA circuit. I used a 5mV signal, from 20-20kHz.
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