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Old 14th February 2018, 11:37 AM   #21
scottjoplin is offline scottjoplin  Wales
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It would help if you can trace the wiring. I think, judging by the number of resistors and the binary coding, and that the input resistance varies considerably that it must be arranged as a shunt volume control. Does the resistance input to output change?
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Old 14th February 2018, 11:45 AM   #22
IDM is offline IDM  United Kingdom
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Hi, Yes, the series resistance does vary. Again I haven't recorded every position but you will get the picture from this graph. Any thoughts?
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Old 14th February 2018, 11:53 AM   #23
scottjoplin is offline scottjoplin  Wales
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That's the same as the input resistance graph. What does "inf" mean? Also on the previous graph it shows output at zero for all settings. Your graphs don't make sense, what you wrote makes more sense.
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Old 14th February 2018, 12:17 PM   #24
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Inf was infinity or off the scale for resistance. I agree the values seem really odd. So odd that I repeated the testing and got the same result!

The output resistance was never zero, it was generally about 300 ohms for almost all settings, it just looks like zero due to the scale difference. If you turn the volume way up the output resistance eventually goes up to about 47K. But as in the graph most of the way it is no more than 300R!
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Old 14th February 2018, 12:28 PM   #25
scottjoplin is offline scottjoplin  Wales
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That is the nature of a logarithmic volume control at the bottom of it's scale. Measure the output resistance at around position 200 for example
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Old 14th February 2018, 08:37 PM   #26
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Right I have measure input, output and series resistance across the entire range by measuring every 5th position. The graphs shown below. Essentially the input resistance drops too low (as far as I understand it). Also when being used only the first 15-20 positions are of much use without it becoming ridiculously loud and the first position is too loud. Resistors need to be changed to spread the range of effective volume control. Any ideas?
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File Type: png input resistance 2.png (12.8 KB, 47 views)
File Type: png output resistance 2.png (11.1 KB, 48 views)
File Type: png Series resistance.png (10.5 KB, 48 views)
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Old 16th February 2018, 03:57 PM   #27
scottjoplin is offline scottjoplin  Wales
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I think you should trace the circuit, see what's going on exactly, otherwise it's all guess work
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