Here are results with DN2535 jfet on input.
Distortion with cap 0.3% dropped to 0.04%, but gain of the preamp dropped significantly so i adjusted on the input to match the output.
Distortion with cap 0.3% dropped to 0.04%, but gain of the preamp dropped significantly so i adjusted on the input to match the output.
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Yet another Hamptone pre built. This time with J113. Distortion with the cap is 0.22%, distortion without cap is only 0.023%. Big drop in gain though, almost 20dB. But its the cleanest so far.
Definitely will finish in the box and compare to other pre.
Definitely will finish in the box and compare to other pre.
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One thing i need to mention. Previosly i blamed channel gain differences on variation in jfets.
While there is certainly a scatter of jfets in a bunch, there may be other reason.
See i am reusing older volume pots, some from cassette decks, or other amps.
On the volume board, comes with balance pot too, i noticed big differences in resistance between channels in various positions. The volume pot does not track well between left and right. Its a poor quality pot. This is certainly other reason for gain differences.
While there is certainly a scatter of jfets in a bunch, there may be other reason.
See i am reusing older volume pots, some from cassette decks, or other amps.
On the volume board, comes with balance pot too, i noticed big differences in resistance between channels in various positions. The volume pot does not track well between left and right. Its a poor quality pot. This is certainly other reason for gain differences.
Experimented a little with the cap. Depending on the value, it has some low fr rollof. You either use big value, like 330uF or 470uF and live with bigger gain and bigger distortion, or you use no cap and have lowest distortion and no rollof.
In all cases, distortion is predominantly 2nd harmonic.
In all cases, distortion is predominantly 2nd harmonic.
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Exactly as the tighter feedback (no cap) is applied, gain is decreased of 20dB and distortion also decreased of 20 dB. Exactly as it should be 🙂.
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Boden, i am analytical biochemist. Not EE. Sorry can't explain how that feedback works.
Perhaps you can find some answers in similar circuits.
https://blog.audioworkshop.org/simple-jfet-preamp/#.Wuen_eo5aUn
http://www.ciphersbyritter.com/RADELECT/PREJFET/JFETPRE.HTM
More reading here.
Better to read about cathode bypass capacitor in tube circuits.
https://tapeop.com/interviews/btg/37/diy-jfet-mic-pre/
Better to read about cathode bypass capacitor in tube circuits.
https://tapeop.com/interviews/btg/37/diy-jfet-mic-pre/
Cathode bypass cap role.
https://www.mojotone.com/blog/what-does-this-thing-do-cathode-bypass-capacitors
https://www.mojotone.com/blog/what-does-this-thing-do-cathode-bypass-capacitors
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Ok, i tested lu1014d, it did not work well. I guess biasing is not optimal.
I put j113 in the front instead. Now i have two well working j113 hamptones.
Reason? Well, if one sounds great, two in row should sound even better. At least such is theory. Secret of japanese audiophiles is to put two preamps one after another.
I have already asked that question, what are the pros and cons, and noone replied.
Anyway, i am here to learn, and put some more shades on mona lisa, like bimo and tillerson.
I put j113 in the front instead. Now i have two well working j113 hamptones.
Reason? Well, if one sounds great, two in row should sound even better. At least such is theory. Secret of japanese audiophiles is to put two preamps one after another.
I have already asked that question, what are the pros and cons, and noone replied.
Anyway, i am here to learn, and put some more shades on mona lisa, like bimo and tillerson.
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