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-   -   Solid state phono preamp design philosophy (http://www.diyaudio.com/forums/analogue-source/122129-solid-state-phono-preamp-design-philosophy.html)

PMA 28th April 2008 10:18 AM

Solid state phono preamp design philosophy
 
Gentlemen,

I would like to open a discussion on this topic. MC phono preamp, solid-state.

- active/passive equalization
- discrete/opamp
- BJT/JFET, which position
- power supply, active PSU filter
- enclosure, shielding properties
- wiring, grounding
- SE/balanced

Jan Dupont 28th April 2008 11:37 AM

This will be interesting ;)

I we choose to go for an opamp version, then it must be active equalization with BTJ buffered balanced output.

Some kind af active PSU filtering is a must...

Regarding to shielding, wiring and grounding, maybe it better to take this up, when we know where we are heading ;)

AMV8 28th April 2008 11:54 AM

Hi

I guess I would choose a pre amp uilt from discrete devices.

I would go for passive equalisation. The only reason to avoid passive normally is that the pre amp sees a high input resistor, which means resistor noise, but that can be avoided by circuit design.

I have always had a preference for transistors - I simply prefer the sound. However fets do seem to transfer more detail on occasions. I would like to try both in an mc pre.

Don

richie00boy 28th April 2008 12:15 PM

No the reason to avoid passive EQ is because it massively wastes headroom and requires lots of gain.

AMV8 28th April 2008 12:38 PM

Richie

I do not agree with you.

Maybe it is better to simply give your views than to criticise the views of others.

This is a forum for all to enjoy. It is also audio and there are few/no absolutes except for what sounds best - which is again a personal view. In my case I am an engineer with over 50 years design and construct ( and listening and enjoying ) experience in audio.

Don

richie00boy 28th April 2008 01:54 PM

I did not intend to criticise, I don't know where that impression came from.

PMA 28th April 2008 03:24 PM

Jan,

there are examples of opamp phono preamp circuits with combination of active and passive equalization as well, divided into 2 opamp gain stages.

Jan Dupont 28th April 2008 03:51 PM

PMA;

I know, but if we going to use opamps why not then use full active equalization ?

GRollins 28th April 2008 04:21 PM

Quote:

Originally posted by richie00boy
No the reason to avoid passive EQ is because it massively wastes headroom and requires lots of gain.

Hmmm...another student who slept his way through RIAA 101. the choice of active EQ invokes the same gain loss as passive EQ--roughly 20dB at 1kHz. That's inherent in the RIAA curve. Headroom problems are a function of circuit design and are easily avoided. Go back to sleep, someone will wake you when the bell rings and it's time to go home for the day.

The phono stage I've been working on fits into the discrete/passive/balanced category. You can use a balanced circuit as single ended, but there's no way to use a single ended circuit as balanced unless you specifically add extra circuitry to generate the balanced signal. It'd be nice if cartridges had center taps on the coils, but we'll just have to do without. It can be done.
I've got a chip (AD797 and AD...something with a JFET front end, I forget the number...843?) single ended, passive circuit. Nothing exotic or weird about it. Somewhere around here I have a tube RIAA, but since I use moving coils it was noisier than I cared to live with. Could have gone hybrid and used a 2SK170 in the front end, but wanted to keep it all tube. Besides, you're wanting solid state, so I'll leave the tube dingus on the shelf. I'm not even sure where the silly thing is, anyway.

Grey

gain 28th April 2008 04:51 PM

just my opinion ...

- active/passive equalization
passive. less active components is less possibility for noise and less complexity.

- discrete/opamp
discrete. nothing wrong with op amps, just prefer to roll my own.

- BJT/JFET, which position
i like the sound of bipolar better. purely subjective choice.

- power supply, active PSU filter
linear regulated power supply is least noise. active PSU filter would be nice.

- enclosure, shielding properties
- wiring, grounding
- SE/balanced

like ACD says, cross those bridges when we come to them.


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