MM Input Stage working in inverted mode - not to find; why ??

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tiefbassuebertr

tiefbassuebertr

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Joined 2005
tiefbassuebertragung.de
#1
MM Input Stage: RIAA Equalization with Shunt Feedback - not often to find; why ??

For such input stages the 47k load works in serial mode to the cartridge inductors.
Main disadvantage is probably the not sufficient signal to noise ratio cause the large resistors.

But I have heard, that the peaks by scratches on records much less aubible.

Are there experiences concerning this topology ?
Some links in this matter
http://audioqualia.prophpbb.com/topic60.html
http://www.diyaudio.com/forums/solid-state/29772-overload-considerations-riaa-preamps.html
http://www.vinylengine.com/library/john-linsley-hood/1450.shtml
http://www.diyaudio.com/forums/analogue-source/249557-riaa-amp-using-shunt-feedback.html (post #40)
 
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#2
any news?
fig. 2b on page 4 under
http://www.ti.com/lit/an/snoa586d/snoa586d.pdf
shows such a topology.
On page 3 of this PDF I read follow:

The primary handicap of the inverting configuration is its noise performance.
The 47k resistor in series with the source adds at least 4 µV of noise.

OTOH - a RIAA preamp isn't so critical than a microphone preamp, because the inherent noise of the record itself is the dominant source of total noise - so I think.
Therefore I want to know, where are opamp based projects like this
http://phonoclone.com/diy-pho4.html
but only for MM cartridges.
The most interesting approach comes from Musical Fidelity - go to
http://www.markhennessy.co.uk/mf_a1/technical.htm
scroll down to "PHONO-PREAMP".
 
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#4
I use an inverting RIAA stage, but it's buffered by a flat non-inverting amp with a gain of 3 or so. The resistors on the first stage are lower than you might expect, for low noise, which is no problem because the signal amplitudes are low too. That first stage lets me drive fairly low values on the RIAA stage as well. Works very well and the curve is perfect as can be, regardless of source impedance. Using inverting for the first stage doesn't seem wise.
 
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#5
lcsaszar said:
The cartridge impedance (series L-R) adds to the 47k, causing the gain drop at HF.
Click to expand...
No, the cartridge frequency response will be exactly the same. It sees 47k whether this is a shunt resistor to ground at the input of a non-inverting stage or a series resistor to the virtual ground at the input of an inverting stage.

The reason that inverting inputs are not generally used for MM is that the thermal noise from the 47k resistor is not shunted by the cartridge. Also, current noise from the opamp sees MM+47k rather than MM||47k.
 
#6
Holfi Batt2riaa

I have heard, that this modell under
www.avmentor.gr - Reviews: Holfi Batt2riaa phono preamplifier
operates in this kind. Who can upload the schematic ?
DF96 said:
No, the cartridge frequency response will be exactly the same. It sees 47k whether this is a shunt resistor to ground at the input of a non-inverting stage or a series resistor to the virtual ground at the input of an inverting stage.

The reason that inverting inputs are not generally used for MM is that the thermal noise from the 47k resistor is not shunted by the cartridge. Also,
current noise from the opamp sees MM+47k rather than MM||47k.
Click to expand...
What happens by this solution?
http://www.markhennessy.co.uk/mf_a1/technical.htm
(scroll down until "Phono preamp")
schematic from post #40 under
http://www.diyaudio.com/forums/analogue-source/249557-riaa-amp-using-shunt-feedback-4.html
looks a lot like the preamp in the a1
the article is to find here:
http://www.keith-snook.info/wireless-world-magazine/wireless-world-articles.html
 
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#7
What happens by this solution?
Musical Fidelity A1 › Technical
(scroll down until "Phono preamp")
Click to expand...
That is a different circuit, using a preamp before the main opamp.

schematic from post #40 under
RIAA amp using shunt feedback
looks a lot like the preamp in the a1
Click to expand...
That is not the classic inverting circuit, so my comments do not apply. In orer to talk about a circuit, we need to be clear which circuit we are talking about.
 
#8
DF96 said:
That is a different circuit, using a preamp before the main opamp.


That is not the classic inverting circuit, so my comments do not apply. In orer to talk about a circuit, we need to be clear which circuit we are talking about.
Click to expand...
For me there is no substantial difference between both circuits.
The only difference is at inverted input, in one case the 47K input resistor (go also to fig.2 under http://audioqualia.prophpbb.com/topic60.html )
and in the other case the one-transistor transconductance amp instead the 47K input resistor for better SNR.
lcsaszar said:
The cartridge impedance (series L-R) adds to the 47k, causing the gain drop at HF.
Click to expand...
Interesting to read under this URL (go to post # Fri Feb 14, 2014 2:06 pm) is follow:
Interesting in this system is the presence of a nearly ideal noise reducer which cleans up LP surface noise along with the preamplifier's input 47kOhm thermal noise.
This circuit is very effective in reducing both vinyl and cassette tape noise
So that means, not the SNR from the phono/RIAA preamp itself (without playing records) is crucial while listening tests.
Is this estimate right ?
 
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#14
URL collection for active RIAA equalizing in the inverted mode (shunt feedback)
RIAA amp using shunt feedback
JLH "Liniac" RIAA
How to get good dynamics in phono stage (post #20)
Overload considerations in RIAA preamps
Shunt feedback in phono preamplifiers - audio qualia
http://vkaudiotest.co.uk/Audio Inverting Amplifier.htm
http://www.angelfire.com/az3/dimitri/images/riaa.pdf
https://linearaudio.nl/sites/linearaudio.net/files/JLH_LINIAC.pdf
http://www.keith-snook.info/wireless-world-magazine/Wireless-World-1971/The Liniac - John L Linsley Hood.pdf
https://web.archive.org/web/2014070...rld-1971/The Liniac - John L Linsley Hood.pdf
https://www.americanradiohistory.com/Archive-Electronics-Today/90s/Electronics-Today-1992-04.pdf (page 17)
http://www.ti.com/lit/an/snoa586d/snoa586d.pdf (page 3 and fig. 2b on page 4)
 
#15
Using shunt feedback on a MM RIAA is very suboptimal. As already mentioned, you have the 47k resistor Johnson noise and the amplifier noise current to deal with - especially so if using a bipolar input gain stage. Shunt feedback offers no advantages in processing clicks and pops from the record surface - good overload margins and all-active RIAA equalization is the best way to deal with that issue.

The problems with shunt feedback RIAA MM EQ amplifiers have been thrashed to death in numerous articles and by various luminaries in the field so I am struggling to see why you’ve even started this discussion. They are suboptimal. Period.
 
#17
Bonsai said:
Using shunt feedback on a MM RIAA is very suboptimal. As already mentioned, you have the 47k resistor Johnson noise and the amplifier noise current to deal with - especially so if using a bipolar input gain stage. Shunt feedback offers no advantages in processing clicks and pops from the record surface - good overload margins and all-active RIAA equalization is the best way to deal with that issue.

The problems with shunt feedback RIAA MM EQ amplifiers have been thrashed to death in numerous articles and by various luminaries in the field so I am struggling to see why you’ve even started this discussion. They are suboptimal. Period.
Click to expand...
Even if you and probably most other are that conviction, that can be wrong anyway.
Please note: Even if everyone agrees, everyone can be wrong (Bertrand Russell)
Check out Post 33 under
https://www.diyaudio.com/forums/ana...a-amp-using-shunt-feedback-4.html#post3791369
and my reply so as the link from post 8 here in this thread.

There it is completely different opinion that convinces me more than your opinion. But I don't know exactly, which of both opinions is right.

For this reason I started this discussion. But in the meantime, I see that I have to examine it myself.
 
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#19
well stated, df96.
:up:
at this point, folks just need to build some hardware using a couple of different approaches, measure and listen, then decide what THEY like.

mlloyd1

DF96 said:
You asked a question. We answered it. You don't like the answer, so you are seeking alternative answers. Fair enough, but please excuse us if we don't sit here ready to rebut all possible alternative answers. In the end it is not your opinion or my opinion which matters, but what happens to be true.
Click to expand...
 
#20
IMO the best use of an inverting MM input stage is to create near zero input impedance and do away with external series resistance altogether. Using cartridge impedance to create a filter pole, albeit not a particularly useful one. Then tackle f compensation arising.


Not all cartridges cope well, but those that do work very well indeed, IME.


My stuff on this is well documented. Aurak I called the prototype version that I still use as my listening preamp. Hans did a balanced version that I'm yet to test, but the SE version does fine for me.

LD
 
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