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Old 5th December 2009, 12:38 AM   #301
Salas is offline Salas  Greece
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Where does the light blue trace go in the third picture at 20Hz -dB wise? Is it the combination of head amp and op amp loop Riaa 2nd stage?
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Old 5th December 2009, 12:41 AM   #302
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gain is 60dB with a 5 Ohm cartridge and the third plot on top shows input to output showing the 60dB gain in the in the noisefloor in the bass and the falling noise following the RIAA curve.
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Old 5th December 2009, 12:43 AM   #303
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if it whould fall to -130dB in the high treble it whould be noiseless
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Old 5th December 2009, 12:47 AM   #304
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at 20 Hz noise is -90dB/U RMS when the volume at 1kHZ is 0dB/U RMS (= 1V RMS, 2.82V P-P)
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Old 5th December 2009, 12:53 AM   #305
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it is the compleet MMP with OP amp RIAA stage plus servo
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Old 5th December 2009, 01:01 AM   #306
Salas is offline Salas  Greece
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Thanx.
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Old 5th December 2009, 01:10 AM   #307
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so what to do next ?
i plan to build the Salas shunts now. the powersupply i am now using is the LC Audio Low noise supply in double mono. seperate supplies for the input and outputstage. i have the input and outputstage in seperate boxes. i will ad the circiut diagramm of the LC regulator in the attatchement.
second i plan to do a High Z FET version and then i whould like to try the inductive RIAA.
By the way i have already specified the 25mH inductors. they will be wound in OFC copper by a german specialist on a low distortion closed ferite bobin. i plan to sell them in matched pairs with 1% tolerance measured on a Wane Kerr bridge and Brühl + Kjaer quality control. they will not be dirt cheap but i plan to sell them for 50,-€ a pair plus shipping. this does not cover my expenses because matchig ferrite coils is not easy. to wind the same number of turns is not enough because the permeabiity of the ferite bobbins strays a bit. low level resolution of that coils is excellent because there is no Barkhausen effect and magnetising probems at low volume in that ferrrite that happens in iron cores and gives the boundary of resolution. look at the latest Audio issue of Elektor for an extensive explanation of that effect.
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Old 5th December 2009, 01:14 AM   #308
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here is the lc audio supply
Attached Images
File Type: gif dcreg.gif (55.1 KB, 414 views)
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Old 5th December 2009, 01:31 AM   #309
Salas is offline Salas  Greece
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So good bobbins for pre filtering? Or there is added value interest for passive crossover use?
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Old 5th December 2009, 01:58 AM   #310
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no, this 25mH i will use in the inductive RIAA, of cause good idea they could be used for prefiltering too. they are 37mm in diameter and have around 6 Ohm so they can stand some power. in spaekers they could be used too, maybe i open up a coil bussyness !
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