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Old 27th December 2012, 07:05 PM   #11
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Super nice job!!

Let me know when its available as a kit or PC board.
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Old 27th December 2012, 09:27 PM   #12
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Quote:
Originally Posted by Joachim Gerhard View Post
Here we go.
Thanks Joachim, looks great. You are right, the servo would not be needed, for the reason that servo on OPENAMP1 board would do the job.

How is your real experience with noise of your circuit?
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Old 27th December 2012, 09:40 PM   #13
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I hope some of you might appreciate the measurement I am posting now, as measurements like this are almost never shown, for understandable reasons. It is the noise of the preamp with real cartridge at the input. The cartridge is Shure M35X, turntable output cable connected to the input of the phono preamp. The tonearm is above the vinyl record. 0dBFS = 2Vrms.
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Old 27th December 2012, 09:48 PM   #14
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You are right Pavel, the noise of this structure is not the lowest.
Around 1.4nV/qHz. In praxis the noise is of a very benign character.
The cartridge has to have an output of better then 0.5mV though.
The noise can be reduced by 6dB when we parallel 4 LMEs for a total of 8 per channel.
The circuit has other advantages. It has no common mode distortion and it is totally hum free because it is balanced. I also like that the feedback of this semi discrete INA is not connected to ground.
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Old 27th December 2012, 09:57 PM   #15
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Quote:
Originally Posted by Joachim Gerhard View Post
Around 1.4nV/qHz. In praxis the noise is of a very benign character.
This is fine, Joachim. I completely understand the advantage of the balanced MC input. Just a small question, are there enough cartridges that do not have connected "ground" of one of the coils to the metal case of the cartridge?
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Old 27th December 2012, 10:40 PM   #16
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Most good MC cartridges have a " floating" construction. Benz, Lyra, Ortofon, to name a view.
Some tonearms make a connection of one of the pins of the cartridge to the tonearm wand though, like Rega. I think that is false but it can be rewired.
Optimum is when the cartridge pins are brought out plus any " metal" part that the arm maker wants to be grounded. My turntable has a different " philosophy" altogether.
I have a Spiral Grove SG1 with Centroid arm. Here the turntable is made from metal ( aluminum and steel ) and the tonearm is made from carbon fiber. The metal parts of the turntable are connected to main earth. Anyway, even when you connect an unbalanced ( say not floating ) arangement to my MC head design the chance is high that hum will be suppressed.
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Old 27th December 2012, 10:44 PM   #17
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The optimum would be a 6 wire arrangement where 2 wires per channel are in a shield.
Any metal parts would then be a 7nth wire that goes to phono ground.
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Old 27th December 2012, 11:10 PM   #18
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Hello Pavel,
cool to see you back @ Audio !
A foolproof, reliable MMpre is a thing some of my
back to Vinyl Friends are looking for .
Btw,
very nice Board, close to my beloved Dispre II,
one of the most underrated Preamps i know.
Cant wait to mate em....
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Old 29th December 2012, 09:38 PM   #19
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Hello Benedetto,
thanks for your input. The preamp is really "foolproof". If assembled with recommended components without mistakes in soldering, it works at first attempt, without any adjustment. The DC output offset is below 1mV.
Regards,
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Old 29th December 2012, 10:22 PM   #20
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Quote:
Originally Posted by PMA View Post
I hope some of you might appreciate the measurement I am posting now, as measurements like this are almost never shown, for understandable reasons. It is the noise of the preamp with real cartridge at the input. The cartridge is Shure M35X, turntable output cable connected to the input of the phono preamp. The tonearm is above the vinyl record. 0dBFS = 2Vrms.
It might be nice to post spectra with the cartridge compared to shorted input- that way, you demonstrate that the preamp is not the limitation (assuming that's not the case!). What's the reference level for the noise graph?

Nice demo of how good an IC preamp can be.
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