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I'v found myself in need of a new preamp for my turntable (the one built into my power-amp went out with a bang and tripped the breaker!).

I'm using a moving magnet type cartridge with output around 5mv, I would like high gain to around 1v peak to peak, must include RIAA compensation and a simple and preferably cheap design with good sound that can be powered with a 'wall-wart' type mains adaptor.

After a little research I found a design by Boozhound Laboratories that is very simple and seems to have very good reviews/reputation.

This is the Boozhound Laboratories circuit (rev3):

boozhound labs preamp

So I copied the circuit into LTSpice to see how it would preform, swapping the 2sk170 for lsk170a as I'v heard original 2sk170's are tough to find.

my bhl ltspice

The circuit had less output than I wanted at only about 620mv from a 10mv input (peak to peak voltage) and fairly high distortion at 0.178% mainly all second harmonic.

So I changed the drain resistors to 4.7k witch increased output to 1300mv but also increased distortion to 0.249%:

fft of my ltspice mod

Unhappy with that amount of THD, I decided to try and do better with my own transistor based design:

my preamp

Output was good at over 1000mv and distortion was very low at 0.003%.

my amps riaa curve

My amps RIAA curve also looks about right?

My question is shall I go with the Boozhound labs design that has a good reputation, despite its high distortion and use fake jfets, or my own circuit that I'm really not sure on transistor noise, how it will sound and dislike the need for more caps (C1 and C2 for added gain).

I would also like to improve power supply noise rejection. Would a simple voltage regulator (like LM317), capacitors and perhaps a inductor be good enough?

Thank all!

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  • \$\begingroup\$ If I remember right you want about 47K input impedance for a phono preamp. The original circuit gives that, but your circuit has the 47K in AC parallel with (100K || 800K || Zin of the BJT. You might want to adjust the 47K up to compensate for that. \$\endgroup\$
    – John D
    Dec 26 '19 at 22:07
  • \$\begingroup\$ yes, 47k input impedance is what I'v heard too. I will change the 47k to 100k. Thanks John D \$\endgroup\$
    – G Frank
    Dec 26 '19 at 22:24
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    \$\begingroup\$ I'm not a big fan of asymmetrical source impedances in audio systems, so I see a problem with both circuits. Are you against global or local negative feedback (beyond degeneraion)? Also, what about a true class-A driver design? \$\endgroup\$
    – AnalogKid
    Dec 26 '19 at 23:13
  • \$\begingroup\$ not sure what you mean by asymmetrical source impedance's AnalogKid \$\endgroup\$
    – G Frank
    Dec 27 '19 at 0:05

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