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Old 6th February 2004, 03:18 PM   #1
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Default Another Simple RIAA preamp ?

Hi there.

I was recently browsing some old AA & AudioXpress issues, when I came upon the schematic of a RIAA preamp in the readers' mail. I reproduce it here (hope there's no copyright infringement). It is authored by Mr Eddy Folkers, and was apparently publicated in "Hifi News & Record Review, Sept. 1984" by M.J. Hawksford (the same Hawksford as the "cascode" one ?). It is mentionned that the two input transistors should have low gain (typ. 100), beta matched, and the four other BJTs should have a beta > 300.

Just wanted to know what you guys think of it, or if someone has already built it, or listening impressions form anyone ?
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Old 6th February 2004, 07:00 PM   #2
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Default Re: Another Simple RIAA preamp ?

Konnichiwa,

Quote:
Originally posted by CheffDeGaar
Just wanted to know what you guys think of it, or if someone has already built it, or listening impressions form anyone ?
Looks very interesting. Symmetrical folded casode, no loop feedback. Like it.

Sayonara
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Old 6th February 2004, 07:44 PM   #3
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yeh, interesting.

Gain depends on the impedance of the RIAA network.
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Old 7th February 2004, 06:38 PM   #4
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On first glance, is this MM or MC? The input impedance is pretty low and the rec for using low beta makes it sound like the input current noise does not matter. In fact the input impedance looks like around 400 Ohms or so. Bipolars right on the input are bad for RFI and the huge electrolytics there might not please some people.
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Old 7th February 2004, 08:18 PM   #5
SY is offline SY  United States
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Hey Scott, any chance I could get you to post the FET design you're using for MM?
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Old 9th February 2004, 01:48 PM   #6
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Quote:
Originally posted by scott wurcer
On first glance, is this MM or MC? The input impedance is pretty low and the rec for using low beta makes it sound like the input current noise does not matter. In fact the input impedance looks like around 400 Ohms or so. Bipolars right on the input are bad for RFI and the huge electrolytics there might not please some people.
Well, quick sims showed a rough 50dB gain @ 1kHz. So should be MM. But I agree that the input impedance is low, < 1kOhms with most of the BJT models I used for my sims. RIAA response is rather good (see pic). Dunno about PSRR, or how the whole thing could be improved. Will surely tried to breadboard one to "see" how it measures and sounds...
BTW, thanks all for your enlightening comments.
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Old 10th February 2004, 05:34 AM   #7
Werner is offline Werner  Europe
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Think FETs and suddenly the front-end + RIAA look vaguely like
JC's Vendetta. Sort of.
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Old 10th February 2004, 10:34 AM   #8
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>by M.J. Hawksford (the same Hawksford as the "cascode" one ?)
The same

>is this MM or MC?
Hifi N & RR paper was about MC

>rough 50dB gain @ 1kHz. So should be MM
30-40dB will be MM
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