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Old 1st February 2009, 10:55 PM   #11
Salas is online now Salas  Greece
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How much is your total gain at 1kHz? Bias current of Q5?
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Old 1st February 2009, 11:01 PM   #12
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I'm aiming for about 40dB at 1kHz, which matches up pretty well with the usual MM source. Bias current for Q5 is about 2ma.
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Old 1st February 2009, 11:07 PM   #13
Salas is online now Salas  Greece
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Yes 40dB is OK, no good to push the peak to peak on jfets for excess gain that is going to be thrown away on a volume pot. Why 16K Rload? Low inductance cart? A Grado?
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Old 1st February 2009, 11:10 PM   #14
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A Grado it is. I'm using a Grado Gold.
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Old 1st February 2009, 11:17 PM   #15
Salas is online now Salas  Greece
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A well balanced cart. On a good TT and arm is no slouch. What TT and arm? I also liked that little amp of yours with the shunt under the cathode instead of self bias or LEDs. I guess with efficient speakers, this phono combined with that amp is gonna sound very immediate and alive. Can it be driven directly from your phono with just a pot? Sensitive enough? You have the phono buffered already. Wishing you a great actual test with very little or no changes.
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Old 2nd February 2009, 02:10 AM   #16
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I'm using a Kenwood KD2055, which is ok, but nothing to get excited about. I have a KD500 with no arm, and some SME3009-R arms. I wanted to put one together using an aftermarket bronze bearing to replace the stock nylon bearing and a carbon fiber head shell.

Attached are some simulation results for my preamp second stage - much lower distortion than a simple common source stage for the same output level.
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File Type: gif fdbk_sim-res.gif (17.0 KB, 893 views)
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Old 2nd February 2009, 02:14 AM   #17
Salas is online now Salas  Greece
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Interestingly the 2nd is more than the 3rd but the 5th is more than the sixth, 7th more than 8th. Very low in total off course. Is it changing pattern along the way? Can that shunt output bias amp be driven without a preamp, with the 40dB of the phono?
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Old 2nd February 2009, 02:26 AM   #18
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I would only use the simulation results for indication purposes. The only thing I would conclude at this point is that the higher order products are likely to be low amplitude.

I could drive my little amp directly from the preamp, but I have no speakers efficient enough at this time to make the exercise worthwhile.
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Old 2nd February 2009, 02:38 AM   #19
Salas is online now Salas  Greece
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I would make a Hemp FR8 Mass loaded TL. Very easy, would add an affordable Tangband Ribbon above 10kHz for sparkle. 94dB after baffle step correction, easy 8 ohm load, no imp dips. Can be done in a weekend if veneering isn't required. Goes deep, great focus point source all over psycho acoustically critical bands. Great TT for restoration you got by the way. Proper speakers, your 500 and the rewired SME will really highlight your excellent electronics.

Click the image to open in full size.
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Old 2nd February 2009, 08:28 AM   #20
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Hi Wrenchone,
nice to see the journey proceeding!

What is your reasoning for chosing a current mirror as a ccs for the voltage reference zener? (as opposed to a fet or led/transitor based solution, for instance)
What is the bandwith and the noise performance of the regulator?

Thanks,
Rüdiger
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