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Old 3rd May 2011, 09:59 AM   #2211
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Quote:
Originally Posted by Joachim Gerhard View Post
In the latest Accuphase stage i have seen as much as 16 in parallel.
Only three in parallel (K370) at the MC stage input (Q1 etc), bulk is complementary differential BJT.
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Old 3rd May 2011, 10:18 AM   #2212
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The MC stage is bipolar. Shure, it is diffential. Still for me that are 16 plus 16 in parallel.
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Old 3rd May 2011, 10:35 AM   #2213
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Here is the basic circuit of the FPS from Linear Audio 0. The actual circuit is a bit more alaborated with more Opamps in parallel to drive the feedback of the first stage and a diffential servo around the second stage. RIAA precision is better then plus-minus 0.1 dB without any odd values but with selection of the caps to 1%. Distortion is mostly burried in the noisefloor and when it comes out is less then 0.001% up to high frequencies. The kit that Pilgham provides does not have the balanced to unbalanced converter at the output. It was put in for simulation. So it is also balanced out.
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Old 3rd May 2011, 11:05 AM   #2214
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Quote:
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MC stage input


(memo note, think again before pushing enter button)
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Old 3rd May 2011, 11:20 AM   #2215
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(: have you heard it ? it measures great but i think the concept is very conservative.
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Old 3rd May 2011, 01:19 PM   #2216
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Quote:
Originally Posted by Joachim Gerhard View Post
... As far as i can remember the S/N is -77dB flat to 20kHz.
How do you mean that "flat to 20kHz"? Noise distribution should have to follow the EQ curve.
I'm also interested in fully balanced phono , that's why I have a raised a question to you in relation of measurments.
Here are my meausrements to compare with yours.
Hagerman inverse riaa + Phono is connected on Left CH, Right channel is simple looked back to show the capability of the system.
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Old 3rd May 2011, 03:15 PM   #2217
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This are really excellent results. I whould be interested to see the circuit diagram. "Flat" noise of my stage was calculated by Sigurd Ruschkowski in Microcap so i have to ask him how he did that. To get the real measure of a phonostage i connect the cartridge to the stage and play a reference tone at 1kHz 5cm/sec from a record (red ). The Lyra Olympos cartridge i used has around 0.3mV output at that speed and an impedance of a bit less then 6 Ohm that adds to the noise as Johnson noise. I compare that to the noise of the stage with the arm lifted ( light blue and the other channel yellow). See an example of a single ended Fet stage with 4 x
2SK170 and 4 x 2SJ74. The blue line is the output of the Olympos to pink noise.
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Old 3rd May 2011, 03:17 PM   #2218
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You can see that the noise is much less over the whole spectrum then the noise it makes when the stone hits the plastic as Salas whould say. Maybe we got a bit neurotic about extremely low noise.
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Old 3rd May 2011, 05:00 PM   #2219
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Some missing details
Measurements made by a modified E-MU 1212, so the fullscale (0dB) is approx. +18dBu.
The Hagerman type inverse riaa was implemented (twice) fully differentialy, so its exit appears as a ~120R @ 60dB atten for phono. It isn't too optimal setup for a 4 pair of AD797.
The phono stage had in 60dB gain.
With 0R input termintaion and +66dB gain the calculated RTI noise is 31nV in audio band.
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Old 3rd May 2011, 05:18 PM   #2220
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I build balanced stages with the AD797 too. After 20 years it is till one of the lowest distortion and noise amps around. How did you modify the Soundcard ? I use an E-Mu 0202.
Does the Hagerman implement the Neumann "pole" and is this the reason for the rising response towards 20kHz ? I usually do not implement the Neumann. Most MC cartridges are a little hot up there anyway and are voiced with a standart RIAA.
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