Another Simple RIAA preamp ?

CheffDeGaar · 6th February 2004, 03:18 PM

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 ?

ThorstenL · 6th February 2004, 07:00 PM

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

robo7 · 6th February 2004, 07:44 PM

yeh, interesting.

Gain depends on the impedance of the RIAA network.

scott wurcer · 7th February 2004, 06:38 PM

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.

SY · 7th February 2004, 08:18 PM

Hey Scott, any chance I could get you to post the FET design you're using for MM?

CheffDeGaar · 9th February 2004, 01:48 PM

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.

Werner · 10th February 2004, 05:34 AM

Think FETs and suddenly the front-end + RIAA look vaguely like
JC's Vendetta. Sort of.

dimitri · 10th February 2004, 10:34 AM

>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

7th February 2004, 08:18 PM	#5
SY diyAudio Moderator Join Date: Oct 2002 Location: Chicagoland Blog Entries: 1	Hey Scott, any chance I could get you to post the FET design you're using for MM? __________________ If there's a sucker born every minute, where do the rest of them come from?

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6th February 2004, 07:44 PM	#3
robo7 diyAudio Member Join Date: Dec 2003 Location: Kir-on	yeh, interesting. Gain depends on the impedance of the RIAA network.

7th February 2004, 06:38 PM	#4
scott wurcer diyAudio Member Join Date: Jan 2004 Location: cambridge ma	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.

10th February 2004, 05:34 AM	#7
Werner diyAudio Member Join Date: Jan 2002 Location: Belgium	Think FETs and suddenly the front-end + RIAA look vaguely like JC's Vendetta. Sort of.

10th February 2004, 10:34 AM	#8
dimitri diyAudio Member Join Date: Oct 2002 Location: retired	>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