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The Kuartlotron - keantoken's simple error-correction superbuffer
The Kuartlotron - keantoken's simple error-correction superbuffer
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Old 21st March 2014, 05:27 PM   #161
Joachim Gerhard is offline Joachim Gerhard  Germany
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I got the buffer back from Martina so i can try to trim for lowest distortion.
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Old 22nd March 2014, 01:50 PM   #162
keantoken is offline keantoken  United States
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Nice, let's see how it turns out.
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Old 23rd March 2014, 10:55 PM   #163
Joachim Gerhard is offline Joachim Gerhard  Germany
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The buffer can be trimmed for minuscule distortion.
The distortion cancelation can be even so high that i suppress 2nd harmonic in my analyser !
The best copy of the input signal is at 250 Ohm ( rather high, there was 1 56 Ohm before,
i only tested higher values but i will also try to lower the 56 Ohm ).
The best cancelation of the analyzer happens at 470 Ohm.
Attached Images
File Type: png Kean buff dist before trimming.PNG (221.8 KB, 768 views)
File Type: png Kean buff dist after trimming 480 ohm.PNG (419.6 KB, 753 views)
File Type: png Kean buff dist loopback copy 250 Ohm.PNG (551.2 KB, 733 views)
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Old 23rd March 2014, 10:58 PM   #164
Joachim Gerhard is offline Joachim Gerhard  Germany
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From left to right :
Kean buff without distortion trim, with analyzer cancelation, best copy of the input signal.
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Old 23rd March 2014, 11:22 PM   #165
keantoken is offline keantoken  United States
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Good! It is odd that you need such a high resistor. Can you use a multimeter to measure the Vbe of a few transistors from the same batch you built it with?
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Old 23rd March 2014, 11:30 PM   #166
Joachim Gerhard is offline Joachim Gerhard  Germany
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Sure, itīs odd and i will measure Vbe.
Installed now 270 Ohm in both channels and they measure very much the same.
Will listen tomorrow.
Could not find a trim with lower value.
Measured the TKD pot at -30dB and -70dB.
No distortion so this red herring is from the table.
Attached Images
File Type: png kean buff pot dist -30dB.PNG (393.9 KB, 693 views)
File Type: png Kean buff pot dist -70dB.PNG (399.9 KB, 479 views)
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Old 23rd March 2014, 11:31 PM   #167
Joachim Gerhard is offline Joachim Gerhard  Germany
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Vbe with or without the circuit under current ?
I did not trim the test point for halve voltage though.
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Old 23rd March 2014, 11:38 PM   #168
keantoken is offline keantoken  United States
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Measure transistors out of the circuit, with nothing else connected that could affect the measurement. That's why I said to measure other transistors from the same batch, not the ones in the circuit.
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Old 24th March 2014, 12:17 AM   #169
Joachim Gerhard is offline Joachim Gerhard  Germany
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OK
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Old 24th March 2014, 12:49 AM   #170
Joachim Gerhard is offline Joachim Gerhard  Germany
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BC550C 0.704V
BC560C 0.682V
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