2. analog
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Dedicated phono-pre for MM only?

Hi All,
the subject of phono-pres, specifically 'adapted' to MM came up in some related postings.

IF, and only if, MMs are much to ones liking --- why spend your buck on some 'halve backed' 60dB plus, MC gain requirement, stage? Why not consider put the $$$ into a TOP 40dB gain stage of either SS or tube?

Raul had more thoughs on the subject as he mentioned before, and might share, why he knows that a TOP MM compared to MC stage circuit requirement might NOT be -one suit fits all-.

There could even be a nice argument to fit a tube gain stage only into an otherwise SS only system!?

Again, the $buck saved on the 20dB plus circuitry could be translated into the BEST circuit for an MM.
I realise, that most such stages were simply fitted inside some older TOP pre-amps, (e.g. Jadis...).
I have not come across a **dedicated** , current 40dB stage neither in nor outside a pre-amp.

Thank you,
Axel
axelwahl

Showing 2 responses by quiddity

quiddity
119 posts
 
Kirkus

I'm not sure I understand your point about dynamic capacitance of JFET vs V/T inputs, and if I do I'm not sure I agree with it.

Assuming that you are talking about junction thickness dependent capacitance varying with drain - source voltage, I thought this effect was pretty well analogous to Miller capacitance in V/Ts. In both cases cascoding reduces the variation in drain / source (read anode / grid for V/T) voltage.

Is there a secondary effect in JFETs I need to know about?

Mark Kelly
quiddity
119 posts
 

Kirkus

Thanks for that, I will have a more careful look at the design calculations for my MM only phono amp. The input stage is currently using 2SK389BL as diff amps with simple resistive loads (balanced inputs, there's no need for a feedback connection to the diffamp 'cos there isn't any feedback).

It will be easy enough to change these to cascode.

Mark Kelly
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