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Carl
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Joined: Sep 11 2005 - 12:57am
Nagra SF

Michael wonders why the choice between the standard wide -bandwidth RIAA or the 1976 IEC curve which rolls of the response below 50 Hz and is (only ?) useful for rumbly turntables.

I think Aalt Jouk van de Hul gives an excellent answer (http://www.vandenhul.com/userfiles/docs/Phono_FAQ.pdf)
A: There are several reasons for this effect (woofers constantly moving in and out with a big amplitude):
1. The bottom end of the frequency range of your phono amplifier is not limited to say 10 Hz, but runs deeper to e.g. 1
Hz or less. So here an internal modification is necessary to produce a stop at around 15 Hz. There is no music
around 15 Hz and an extended frequency response only produces problems for the rest of the equipment. Here a
subsonic/rumble filter is the correct message for your technician.
2. Your phono amplifier does not produce this 2 - 5 Hz by itself, but gets the signal from your cartridge/arm
combination. So the first question here is: Is the cartridge/arm resonance frequency to low? Normally the value is
around 10 Hz (see Appendix 2). When the cartridge has a too high compliance and/or the arm is too heavy (effective
mass around 20 grams and more) then the resonance frequency drops from around 10 Hz (which is standard) to 5
Hz or less (also see 36). So remove weight from your arm by e.g. taking a lower weight headshell or by removing
weight as much as you can. You can also ask your friend if you can try his cartridge in your arm to see if the same
happens again. Assuming that your friend has a different brand of cartridge.
3. What also helps to produce an unhealthy subsonic output is the uneven surface of your records. With uneven and/or
unpolished stampers (see 164), the vinyl pressing result is also uneven. When you still like to listen to such records,
use your pre-amplifier

dcstep
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Re: Nagra SF

Good points all, BTW, where'd did the onboard SFs all go???? If you had trouble you pushed a button on my old Bryston 1B. Seems to me if you're going to build a "complete" phono-pre that it'll include a SF. Oh well...

Thanks for the report.

Dave

Carl
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Re: Nagra SF

The site of Aalt Jouk van de Hul is well worth reading Dave!

By the way I always wondered why you can not get phono stages with a SF and a simple notch filter. I have got a lot of records in pristine condition but my wife loves old Dutch cabaret. I often find those records but those treasures can use a notch filter.

Somehow high end is not always very practical. I hope for a reaction from Michael.

KBK
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Re: Nagra SF

Introducing a filter at the INPUT of a phono pre, where a rumble or Subsonic filter might be placed, is very detrimental to the quality of a tiny phono signal. The SF would have to be at the output end of the phono section.

IMHO, the inclusion of a subsonic filter makes a $2000 phono unit sound like a $500 one.

The short answer is you can have sonic quality... or some desired switches. But not both.

Carl
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Re: Nagra SF

I had a Chord phono stage at home for some time. The differences with or without SF were really very small.
I have not compared a phono stage with SF switch and a stage without SF switch. To hear the difference you have to built two near identical stages. I do not think al lot of people had a try but may be Michael or John ???
Personally I do not believe that men (or better you Americans ) can sent a rocket to Mars and are not be able to make a phono stage with a switch you can not hear when it is on "of" position.

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