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Old 7th June 2010, 02:09 PM   #1
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Default Magnetic-Pickup Phono Preamplifier

Hi,

Anybody tried making this simple circuit. This was taken from National Semiconductor application notes 32, page no. 34. Can I get some opinion about this circuit please?

Thanks
Renjish
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Old 7th June 2010, 04:54 PM   #2
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Looks good to me, although I might prefer using an op amp to make it easier to build. And to repair years from now, should that ever be necessary.
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Old 7th June 2010, 05:00 PM   #3
kevinkr is offline kevinkr  United States
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Not enough gain, you would need to follow this with another gain stage having 15 - 20dB of gain in order to have typical phono stage gain. The least I would consider would be 36dB and much more can be needed if you have a line stage with minimal or no gain.

In addition I think you would need to select fets for best performance and the power supplies would have to be extremely quiet.

I would look around a bit more. I suspect there are a lot of reasonably good discrete designs here if you search.

Tubes and op-amps are other good options. SY's design is particularly good and can be used with a conventional MM or HO MC if you don't use the specified input transformer.. It's output impedance is low enough that I suspect it would comfortably drive most solid state line stages. Take a look at SY's article: "His Masters Noise" His Master's Noise: A Thoroughly Modern Tube Phono Preamp
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Old 7th June 2010, 05:01 PM   #4
LAJ is offline LAJ  United States
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Its easier to build one from an LM387. There is a circuit for a preamp using this IC in the N/S Audio Radio book. Also included are the components values for the NAB curve in case you wanted to make a tape preamp (which is what I built). The only drawback is that it uses a relatively high supply (+24) which might be unavailable if you are building it inside other equipment.
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