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Old 7th June 2014, 05:44 PM   #53561
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Now to continue to drive everyone nuts, let us start the next round! (SY you're back in.) If we think that noise versus distortion is a trade off in low level amplifier design using ICs, then can we apply some engineering skills to balance this.

Some might say the record noise is above this so don't worry about it. Others might insist on a double blind test to see if it matters. JC just compares one preamp to another to see if he can hear a difference.

Now Pavel would say use a buffer, which is one approach, but let's see if we can apply some perception research to get a better balance.

One item of interest would be masking. If we have a pure sine tone 100 db below the noise level it would not be perceived by humans. There is reasonable evidence that with the noise level equal to the tone it would be an issue.

Somewhere around 20 to 30 db of masking would hide the tone. So we now have a target of designing for the distortion to be 20 db below the noise level.

An audio engineer would also know that the resonant frequency of our hearing is around 3,500 to 5,000 hertz.

The distortion of an LME49990 is around .00001% in this range as long as we stay well away from clipping. (15 volt rails 2,000 ohm load, 3 volts out.)

So the first question is what noise bandwidth should we use as a design value for a second harmonic distortion of a 4,250 hertz fundamental?
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Old 7th June 2014, 06:13 PM   #53562
SY is offline SY  United States
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Quote:
Originally Posted by simon7000 View Post
(SY you're back in.) If we think that noise versus distortion is a trade off in low level amplifier design using ICs...
If I don't accept that axiomatically, does that mean I'm back out?
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Old 7th June 2014, 06:18 PM   #53563
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If I don't accept that axiomatically, does that mean I'm back out?
Can you play nice and answer the question?
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Old 7th June 2014, 06:19 PM   #53564
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Have you established the premise?
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Old 7th June 2014, 06:29 PM   #53565
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Quote:
Originally Posted by simon7000 View Post
Now we are almost there! The next question should be easy, what is the impedance of the phono cartridges? Or in other words how many nv/sqrt(Hz) will the cartridge produce?
Re arguments (*)

Re noise
Ed see att.1.
SY is right (L affect cartridge noise a lot) but I see your point at post #53555.
I would be with you but as Iíve said, for me this noise is of no importance (**) when a cartridge is reading a groove.
Rest attachments (pls see the broadband spectrum, not the 50Hz related peaks): DENON DL103 plus a 23.5dB head pre (***), plus Hagerman Buggle RIAA pre (40dB/1kHz), plus passive volume control. 0dB=1.286Vrms

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(*) Socrates was
an outlaw , illegally practicing a midwifeís art to give birth to the latent knowledge (he was himself son of a midwife)
a serial killer, murdering wrong assumptions
an anarchist doubting and putting under examination long held beliefs
a man married to Xanthippe

(**) Not only due to itís low amplitude compared to record surface noise but due to itís smooth spectrum. Our head (mine at least) doesnít notice it.
I would consider it a problem when it starts to modulate, that is when the cartridge sees a heavily varying preamp input impedance. This leads to my third pre amp criterion Stable input impedance. See how Dimitri is dealing with this problem for the last 25 years or so
http://www.angelfire.com/az3/dimitri/images/riaa.pdf
Supply Bootstrapping Reduces Distortion In Op-Amp Circuits | New operational amplifiers optimized for high-performance audio and ultrasound applications combine extremely low total harmonic distortion plus noise (THD+N), -130 dB, with large output vo
JFET Follower Amplifier Cancels Distortion | Analog content from Electronic Design

(***)
Quote:
Originally Posted by gpapag View Post
Attached Images
File Type: jpg 1 Answer.JPG (91.4 KB, 170 views)
File Type: jpg 2 Cart on rest arm.JPG (146.9 KB, 169 views)
File Type: jpg 3 Cart on stationary groove.JPG (148.4 KB, 167 views)
File Type: jpg 4 Cart reading unmodulated test groove.JPG (149.0 KB, 166 views)
File Type: jpg 5 Test rec lead-in.JPG (150.5 KB, 166 views)
File Type: jpg 6 Ravel lead-in.JPG (151.6 KB, 21 views)
File Type: jpg 7 Orf lead-in.JPG (152.1 KB, 23 views)
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Old 7th June 2014, 06:37 PM   #53566
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Quote:
Originally Posted by gpapag View Post
Re arguments (*)

Re noise
Ed see att.1.
SY is right (L affect cartridge noise a lot) but I see your point at post #53555.
I would be with you but as I’ve said, for me this noise is of no importance (**) when a cartridge is reading a groove.
Rest attachments (pls see the broadband spectrum, not the 50Hz related peaks): DENON DL103 plus a 23.5dB head pre (***), plus Hagerman Buggle RIAA pre (40dB/1kHz), plus passive volume control. 0dB=1.286Vrms



(**) Not only due to it’s low amplitude compared to record surface noise but due to it’s smooth spectrum. Our head (mine at least) doesn’t notice it.
I would consider it a problem when it starts to modulate, that is when the cartridge sees a heavily varying preamp input impedance. This leads to my third pre amp criterion Stable input impedance. See how Dimitri is dealing with this problem for the last 25 years or so
http://www.angelfire.com/az3/dimitri/images/riaa.pdf
Supply Bootstrapping Reduces Distortion In Op-Amp Circuits | New operational amplifiers optimized for high-performance audio and ultrasound applications combine extremely low total harmonic distortion plus noise (THD+N), -130 dB, with large output vo
JFET Follower Amplifier Cancels Distortion | Analog content from Electronic Design

(***)
Great stuff george, now, what would cause a phono stage to not have a stable impedance ..?
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Old 7th June 2014, 06:48 PM   #53567
gpapag is offline gpapag  Greece
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Originally Posted by a.wayne View Post
what would cause a phono stage to not have a stable impedance ..?
For the esoterics (engineering details) see Dimitri’s elaboration.
Acc to my simple mind, it is mostly the interaction of the RIAA feedback network with the cartridge.
A buffer solves this problem (see an MC head amp. Also the first buffer with a passive RIAA scheme for a MM cartridge)

George
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Last edited by gpapag; 7th June 2014 at 06:53 PM.
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Old 7th June 2014, 07:24 PM   #53568
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George,

The issue of distortion increasing with loading in IC op amps shows up in any low level circuit.

But you are getting too far ahead. The issue at hand is noise masking. Right now it is easier to look at flat FR masking before getting into vinyl noise and EQ. Now since the example is JC's work he uses passive eq, placing more emphasis on the first stage preamp.

(Distortion if you look carefully actually begins to rise above 2 volts into 2000 ohms.)

So the question on the floor remains. For design values what should the noise bandwidth be?
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Old 7th June 2014, 07:36 PM   #53569
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Quote:
Originally Posted by SY View Post
Have you established the premise?
I am aware of the bandwidth you chose. Would JJ pick the same?
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Old 7th June 2014, 07:59 PM   #53570
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Quote:
Originally Posted by simon7000 View Post
I am aware of the bandwidth you chose.
For what?

Quote:
Originally Posted by simon7000 View Post
Would JJ pick the same?
For what?
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