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Old 1st November 2012, 10:17 PM   #1
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Default 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
Overload considerations in RIAA preamps
http://www.vinylengine.com/library/j...ood/1450.shtml
RIAA amp using shunt feedback (post #40)

Last edited by tiefbassuebertr; 5th September 2016 at 04:32 PM.
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Old 5th September 2016, 02:46 PM   #2
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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 V 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".

Last edited by tiefbassuebertr; 5th September 2016 at 03:05 PM.
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Old 5th September 2016, 05:44 PM   #3
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The cartridge impedance (series L-R) adds to the 47k, causing the gain drop at HF.
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Old 5th September 2016, 05:49 PM   #4
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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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Last edited by Conrad Hoffman; 5th September 2016 at 05:52 PM.
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Old 6th September 2016, 11:01 AM   #5
DF96 is offline DF96  England
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Quote:
Originally Posted by lcsaszar
The cartridge impedance (series L-R) adds to the 47k, causing the gain drop at HF.
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.
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Old 7th September 2016, 02:49 AM   #6
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Default 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 ?
Quote:
Originally Posted by DF96 View Post
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.
What happens by this solution?
http://www.markhennessy.co.uk/mf_a1/technical.htm
(scroll down until "Phono preamp")
schematic from post #40 under
RIAA amp using shunt feedback
looks a lot like the preamp in the a1
the article is to find here:
http://www.keith-snook.info/wireless...-articles.html

Last edited by tiefbassuebertr; 7th September 2016 at 03:09 AM.
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Old 7th September 2016, 10:05 AM   #7
DF96 is offline DF96  England
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Quote:
What happens by this solution?
Musical Fidelity A1 › Technical
(scroll down until "Phono preamp")
That is a different circuit, using a preamp before the main opamp.

Quote:
schematic from post #40 under
RIAA amp using shunt feedback
looks a lot like the preamp in the a1
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.
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Old 27th September 2016, 02:21 PM   #8
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Quote:
Originally Posted by DF96 View Post
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.
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.
Quote:
Originally Posted by lcsaszar View Post
The cartridge impedance (series L-R) adds to the 47k, causing the gain drop at HF.
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 ?

Last edited by tiefbassuebertr; 27th September 2016 at 02:41 PM.
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Old 27th September 2016, 04:35 PM   #9
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Quote:
For me there is no substantial difference between both circuits.
The issue is whether the circuits think they are different, not whether we think they are different.
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Old 27th September 2016, 07:27 PM   #10
Koifarm is offline Koifarm  Netherlands
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I do not get it. Output noise -63db. My tube preamps do much better -82db or more. Distorsion is very low 0.001%. So what do you mean, better noise or better distorsion?
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