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Old 6th September 2008, 04:16 AM   #61
Salas is offline Salas  Greece
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2N5459 would be nice for your gain goal as well. Good for noise, not best, but cheap, widely available, matches for many a batch, and not soon to be unobtanium.
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Old 6th September 2008, 04:17 AM   #62
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I have plenty of PN4303 on hand - better noise-wise....
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Old 6th September 2008, 04:23 AM   #63
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How many nV/SQRT Hz? 2SK goes 1.6 down low and 2N5459 about 10.
A 5534 op amp does about 4.
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Old 6th September 2008, 04:31 AM   #64
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I don't have my JFET book on hand, but it's better the the 5459, and not as good as the 2SK170. I ran a JFET SRPP setup using the 4303 in my system (even with the problems I acknowledged), and never had a noise prroblem using a Grado Gold cartridge. It sounded nice, even if it wasn't the most accurate pramp... This time around, I can get it right. If you're curious about the old circuit, search for the "JFET SRPP" thread - it's documented there.
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Old 6th September 2008, 04:37 AM   #65
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I will. I like SRPP in tubes too, if the load is right. Its essentially hidden push pull. Needs its 'best' load to shine. Anyway with 47K input load the input resistor's Johnson will much likely dominate. The 5534 circuits are pushed up to 10nV in practice. Anything in the 10 area will do for mm.
For low mc under 5 is good if you have over 92dB speakers. Its good to load such a wimpy mc with 47K too, but with 1K or under, and low ppm resistor you win on noise.
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Old 6th September 2008, 10:12 AM   #66
Salas is offline Salas  Greece
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Quote:
Originally posted by wrenchone
If you're curious about the old circuit, search for the "JFET SRPP" thread - it's documented there.
Read that. Nice work. Wanted to ask, did you find that 100R gate stoppers were mandatory in that by measurement? Did you see ringing? Also you had a Pacific?. Did you see need for gate stoppers there?
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Old 6th September 2008, 12:36 PM   #67
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on psu side ??

in the next 2week for 15$ ska-amp have discrete regulator 50ma max :40 dB better regulation than a LM317 at 10KHz and much lower noise.

Greg (ska-amp) stimate 90 dB from 100Hz -20KHz at 24V from a 28V unreg supply.

I will go for dual mono config , now I need a good unreg psu.....

I ask if can work at 40v...
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Old 6th September 2008, 01:07 PM   #68
Salas is offline Salas  Greece
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A 317 with 22uF bypassed adj leg resistor will get you to -80dB ripple rejection. You can build an R-C filter before the LM317 if you size your transformer's secondary voltage higher. Just use your DMM for current measurement, see your mA draw and size a resistor to drop 10V to the main filter capacitor. See that you can get 43V on LM's input. Size the setting resistors ratio (see data sheet online) for 37V out. That will add some extra dB rejection and will be damping the current draw from the bridge rectifier reducing power rail wide band switching noise.
In my circuit you will need around 13mA per channel. A 8k2 will drop 10.66V. If you use common supply, a 3k9 will drop 10.14V.
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Old 6th September 2008, 01:15 PM   #69
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I have read from Pedja that non feedback regulator:

"that more relaxed, also more natural or simply more "normal" sound is what it brings in my experience"
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Old 6th September 2008, 01:21 PM   #70
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True. But RC helps in that department too. Shunt regulator more open sound even. Depends on how far you want to push the tone performance. But what I suggested can keep you happy for a while.
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