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JFET input phono preamp for MM
JFET input phono preamp for MM
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Old 3rd August 2020, 11:57 AM   #101
billshurv is offline billshurv  United Kingdom
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JFET input phono preamp for MM
Quote:
Originally Posted by Hans Polak View Post
It now seems that the only purpose of starting this thread was to promote the product for genereating revenue.
Nothing wrong with that, but it should have been placed in the Commercial Sector.

Don't see it. Pavel's webpage still clearly says 'no sales since 2012'. Given how cluttered threads become starting one to post a specific topology for discussion seems completely logical even if some final details with held. Each person has a right to control their own disclosure even if others don't agree with it.
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Old 3rd August 2020, 03:17 PM   #102
Hans Polak is offline Hans Polak  Netherlands
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Hi Bill,
Of course, everybody has the right to not disclose.
But why then show a undocumented circuit diagram in the first place ?
Doesnít that mean that you want to keep some for yourself ?
The only reason to keep it secret that I can think of is that you either want to sell the design or still want to sell the product yourself.
Not producing any answers relating to inconsistancies, means that the thread was seemingly not intended to start a discussion either.
Itís all a mystery to me, but again, anyone is entitled to do what he or she likes but so is my good right not to believe that there are no hidden commercial intentions behind this all.

Hans

P.s. as a matter of fact, a BOM is the least Iím interested in, I was just pointing at only a few of several inconsistancies in graphs and data.
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Old Yesterday, 04:33 PM   #103
Hans Polak is offline Hans Polak  Netherlands
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Quote:
Originally Posted by PMA View Post
Sorry but it is the inductive impedance magnitude in parallel with 47k input resistor that makes the noise. Please let's not speculate about iron losses, if you put the circuit into Microcap you get the same noise rise. And Microcap knows nothing about iron losses in the ideal inductor used for the simulation.
I have put the generic model into LTspice, using 2SK170 and 2SJ74 for the input and 2SK1056 and 2SJ162 for the output.
A gave the input Fet's 1 mA bias each and the Mosfet's an idle current of 23mA.
With that setup, I was completely surprised by the very low noise level at the input.
With 50R at the input the equivalent A-weighted input noise for this Riaa amp gave 631pV/rtHz, that's adequate for almost all MC Carts !!
A 50R MC Cart would have a S/N of 75dB(A) ref 0.5mV@1Khz.

This of course under the premise that my LTspice models for both input Fets are correct.
But if so, it is the first amp that I came across that could be used for MC and for MM.
A second amp directly behind this amp with switchable gain could adjust for the overall required MM or MC gain, at the same time giving a low impedance output impedance, making the connection to a preamp less susceptible for EMF from outside.

The images below are resp. showing the unweighted input and output noise at 36dB gain for a 50R MC Cart in Red and for a 700mH/1.3K Orto Cart, terminated with 47K//125Pf in Blue.

Hans
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File Type: jpg Noise.jpg (339.0 KB, 67 views)
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Old Yesterday, 09:43 PM   #104
billshurv is offline billshurv  United Kingdom
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JFET input phono preamp for MM
That's very interesting. Thank you for doing the analysis Hans.
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