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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 6th September 2018, 10:32 PM   #931
keantoken is offline keantoken  United States
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Cool.
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The Kmultiplier rail filter! -=- The Simple Kuartlotron Superbuffer!
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Old 21st September 2018, 10:13 PM   #932
silasmellor is offline silasmellor  Denmark
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The Kuartlotron - keantoken's simple error-correction superbuffer
Built up one of project16s boards tonight. Adjusted to 5v at TP but encountered something odd: r9 trimmer did nothing to the offset but I could dial it down with r1 trimmer. Is this normal?

Will measure fft with rew next but that’s for another day.
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Old 21st September 2018, 11:40 PM   #933
keantoken is offline keantoken  United States
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If you did it with the input grounded, then R9 will not do anything. It needs to be adjusted with the input open. R1 is for trimming distortion, not offset, although you could use it that way for small amounts of offset if distortion wasn't particularly important.
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Old 22nd September 2018, 01:42 AM   #934
silasmellor is offline silasmellor  Denmark
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The Kuartlotron - keantoken's simple error-correction superbuffer
Yep that will be it, I will try again with open inputs and then tune r1 after. Thanks!
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Old 22nd September 2018, 10:37 AM   #935
silasmellor is offline silasmellor  Denmark
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The Kuartlotron - keantoken's simple error-correction superbuffer
Ok, had another go at this. With open inputs the offset is 45mv, r9 is a 1M trimmer paralleled with 1.8M. I can adjust approx 10mv across its whole range. I suppose I need to change R9 to something else but I’m unsure what.

Vbe of 560s were 0.686 and 0.688 and 550s were 0.685 and 0.680.
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Old 22nd September 2018, 10:57 AM   #936
keantoken is offline keantoken  United States
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If you didn't use BC560C, the offset may be too large to correct.

Reset R1 to 56 ohms.
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Old 22nd September 2018, 11:37 AM   #937
Project16 is offline Project16  France
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Quote:
Originally Posted by silasmellor View Post
Ok, had another go at this. With open inputs the offset is 45mv, r9 is a 1M trimmer paralleled with 1.8M. I can adjust approx 10mv across its whole range. I suppose I need to change R9 to something else but Iím unsure what.

Vbe of 560s were 0.686 and 0.688 and 550s were 0.685 and 0.680.
Hello Silas

R9 is a 1M trimmer with a 1.8M resistor in series and not in parallel.

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Old 22nd September 2018, 11:56 AM   #938
silasmellor is offline silasmellor  Denmark
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The Kuartlotron - keantoken's simple error-correction superbuffer
Ok progress, I switched the 1M pot for a 5k one and jumpered the series resistor position and managed to get below 1mV. Not sure how to explain this, I clearly misread the schematic and thought r9 was 2k7...

Kean, they are 560CTA.

Last edited by silasmellor; 22nd September 2018 at 12:01 PM.
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Old 22nd September 2018, 03:57 PM   #939
silasmellor is offline silasmellor  Denmark
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The Kuartlotron - keantoken's simple error-correction superbuffer
Ok, using the 1M trimmer with the series 1.8M also works, so I suspect I’m just at the end of the travel for the pot, probably at low R. Would it make sense to try something even higher, like 2.2M for the Series resistor to R9? Is Avery low resistance for R9 a problem?
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Old 22nd September 2018, 08:44 PM   #940
Project16 is offline Project16  France
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The values 1M for the trimmer + 1.8M for the resistance correspond to the schematic.
If the trimmer is at its maximum value I think that a 2.2M should solve the problem but maybe it is at its minimum value and at that moment it is necessary to reduce the value of the resistance.
Keantoken may be a suggestion.
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