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Old 3rd August 2019, 07:37 PM   #461
jan.didden is offline jan.didden  Europe
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First batch is shipped.

Jan
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Old 3rd August 2019, 09:49 PM   #462
astromo is offline astromo  Australia
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First batch is shipped.

Jan
Fantastic!
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Old 7th August 2019, 11:15 AM   #463
jan.didden is offline jan.didden  Europe
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Default 20k Rin variant

Update 7 August 2019 - new 20k Rin variant!

Some of you who work mainly with tube equipment have asked for a version with a higher input impedance than the 10k for the stock MK II. Input impedance is a compromise between complexity of the attenuator and the frequency response as was the case with the 100k Rin of the initial version. That 100k required quite a complex calibration for flat frequency response.

The 10k MK II in contrast doesn't need any calibration and is flat to over 1MHz. But listening to you, I build up a unit with 20k input impedance, and tested it. I am happy to report that it has a flat frequency response out to over 600kHz in all settings, without any calibration.

The 20k input impedance version requires some different values for the attenuator resistors. To my surprise, it all fell so nicely together with existing E96 values that 8 less resistors are required, 2 positions on the board have to be shorted and 6 can be left open! Here is the BOM fragment for the 20K Rin variant. All other part values and designations remain the same.

Worst-case attenuation error is 0.1dB in any setting; Rin variation is 19.95k to 20.08k (calculated).

Linear Audio AR MK II Attenuation board Bill Of Materials variant for 20k Rin version only!

Jan
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Cable: a potential source of trouble interconnecting two other potential sources of trouble - Erik Margan
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Last edited by jan.didden; 7th August 2019 at 11:27 AM.
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Old 13th August 2019, 08:41 PM   #464
astromo is offline astromo  Australia
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Package received.

Thanks Jan.

Now I just have to warm up the soldering iron.
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Old 13th August 2019, 10:56 PM   #465
astromo is offline astromo  Australia
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Package received.

Thanks Jan.

Now I just have to warm up the soldering iron.

Jan - query regarding R48/R49 for the Attenuation PCB BoM. What's the required tolerance? You haven't nominated a recommended part, just a comment and a resistance value.


From looking at the board these resistor should just be straight forward through hole axial resistors, shouldn't they? Why make the comment, 0.4" pitch?

EDIT: Also, what's your take on "low" for temperature coefficient?

Last edited by astromo; 13th August 2019 at 11:12 PM.
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Old 14th August 2019, 12:37 AM   #466
astromo is offline astromo  Australia
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From looking at the board these resistor should just be straight forward through hole axial resistors, shouldn't they? Why make the comment, 0.4" pitch?

Answer to self - board hole spacing. Broke out a ruler and put it up against the board. Came up with 10 mm, which is close enough to 0.4". Got confused by the octopart BoM search function. The have a filter for "terminal pitch" which relates to SMD parts and the rest.
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Old 14th August 2019, 06:03 AM   #467
jan.didden is offline jan.didden  Europe
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Yes. These are run-of-the-mil resistors for biasing zenerdiodes. If they fit, they are OK, hence the 0.4in pitch ;-)
Same for R29 and R31.

Jan
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Old 14th August 2019, 10:01 AM   #468
astromo is offline astromo  Australia
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Yes. These are run-of-the-mil resistors for biasing zenerdiodes. If they fit, they are OK, hence the 0.4in pitch ;-)
Same for R29 and R31.

Jan
No worries.

I've defaulted to +/-1% tolerance and 100ppm/C, 'ish.
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