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Planning a jfet input phono preamp stage

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Hari Iyer

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My current phono pre-amp uses op-amp for the RIAA stage and is a very old-fashioned designed one which compress lows and mid-bass to much and has too screechy highs.

I recently used a cambridge audio azhur 651A phono stage and it was sounding quite different and good. But again its very very flat and does not have much life as per me. I would say its very neutral.

This is tempting me to built one jfet input stage + op-amp phono stage which hopefully would be able to remove the issues in my current phono-stage. The phono-stage is a very important part of the vinyl audio and any mess-up in that will ruin the entire sound stage of a turntable.

Keeping my fingers cross as of now.

Cheers,
 

omishra

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Use good opamp like AD823 or two LM49990 which has inbuilt JFETs at input stage.
 

Hari Iyer

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@ omishra - its a full discrete design and no Op-amp will be used.

@jsl
MM & MC both is configurable with internal 4pole dip switch.

If you need more pcb's let me know and i can get it built for you too.
 

Hari Iyer

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I will ask the pcb fabricator to make a total of 10 boards for the time being. Will update you after that.
Currently am travelling and should take another 10 days to get it in my hand.

Cheers,
 

Hari Iyer

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Done some mods in my Sony opamp based RIAA ckt - replaced by pass caps from electrolytic to MKP and found significant improvement in coloured highs with smoother highs.

Now this week end will be adding my jfet input stage which has a constant current source.

Will post a ckt if that works ok.
 

Hari Iyer

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Feb 8, 2010
Messages
3,165
Points
113
Location
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The phono pre-amp has a DC blocking capacitor 6.8uF MKP type. I am contemplating of by-passing this. The best coupling is to have no coupling capacitors. Will have to measure for DC at the output before i connect them to my amp.
 
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