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Capacitors for RIAA Circuit
Capacitors for RIAA Circuit
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Old 11th September 2019, 11:22 AM   #41
dmills is offline dmills  United Kingdom
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I have been working on a board for use in a record CUTTING chain that is going to be using C0G (Which has rightly taken much of the polystyrene market). These are NOT your high K ceramics (Which are unsuitable for use in filters), and are in fact excellent.

It is interesting to note that the classic German recording lathes used at best 5% components in their equalisers back in the day (Also, they generally had an extra pole or two up in the low ultrasonic to deal with stopping the inverse RIAA curve rising at 20dB/Decade into the AM radio band)...

I discovered the other day that COG extends out to 1uF these days (at a price, but still pretty amazing, I remember when a couple of hundred pF was the upper limit).

One hint if doing the low K ceramic thing (And there is little reason not to), above about 0805 in size, get the soft termination ones, more likely to survive less then ideal soldering practises without cracking.

Regards, Dan.
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Old 11th September 2019, 11:36 AM   #42
Johnny Canuck is offline Johnny Canuck  Canada
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Capacitors for RIAA Circuit
Quote:
Originally Posted by WntrMute2 View Post
Thanks guys. I've ordered the Kemet ones and am trying to reach the LCR guys without success. I'm in the US and they don't seem to have a distributor here.
HifiCollective in the UK carries LCR and some generic types as well.
Polystyrene Capacitors | Hifi Collective
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Old 11th September 2019, 12:03 PM   #43
craigtone is offline craigtone  United States
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Has anyone used the KEMET Goldmax in RIAA applications?
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Old 11th September 2019, 12:04 PM   #44
blu_glo is offline blu_glo  England
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Quote:
Originally Posted by DF96 View Post
No, the Central Limit theorem says that if you combine lots of 5% tolerance components then you are more and more likely to get a result which is much better than 5%.
…....
Thankyou, now I remember, and stand corrected!

hmmm, but if eventually the result statistically tends towards the nominal, then the distribution is not really random.....???
in a truly random scenario the result should still be within the 5% tolerance..


XD

Last edited by blu_glo; 11th September 2019 at 12:18 PM.
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Old 11th September 2019, 12:38 PM   #45
Mark Tillotson is offline Mark Tillotson
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Quote:
Originally Posted by blu_glo View Post
IIRC this is not quite correct.
The tolerance of any number of randomly selected 5% capacitors in a network produces a bulk capacitance of same 5% tolerance.
Doesn't work that way, cancels just like noise for the reason component variation is a kind of noise.

However there is a caveat, which is you have to assume the 5% parts are unbiased, ie about 50% are over-value and about 50% are under-value.

If you can assume parts are chosen by binning after measurement, this is a valid assumption.

However that's not always how components are made. The production line can have continual feedback to keep the output components close to the desired value. Typically this means 5% components have much closer grouping than the 5% suggests, but perhaps with a gap in the middle where the 1% components are selected out.

It makes sense to try to make all 1%, and the rejects go to the 2% or 5% bin. If the demand for 5% is high, then excess 1% components are demoted to the 5% line (noone's going to complain!).

Basically you can't quite assume the 1/(sqrt(N)) improvement in precision when using multiple devices, but if you SOT then you'll get much better than that anyway.
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Old 11th September 2019, 12:51 PM   #46
RajkoM is offline RajkoM  Bosnia and Herzegovina
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Why a bunch of unnecessary theory.
Buy very cheap great Russian teflons, open the iron case, unwrap teflon and alu foil and make the capacitor you want for your RIAA preamp.

It will be unbeatable, surely.
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