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!
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!
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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So I finally got around to testing/installing this volume control. At min and max it reads 1k6. I've built a 12SN7 buffer to drive it. Too many steps in mid volume, not enough at the ends. Still it works. I'm not sure if I like it better than a Chinese Alpha pot though. The pot need the buffer.
I can also confirm that there is bleed through at zero volume unlike a pot. I also noticed that the 50K pot specified was actually 20K, and both gangs are wired in parallel. I'm using an off board 10K single gang pot in lieu of the original pot. I also removed the 7812 and the input cap and drove it directly from 12V.
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I bought the volume control indicated in the first post and I installed it in my tube preamp. It work correctly except if I connect a phono in any of the inputs. In this case, I get strong spikes from the loudspeakers.
Anyone have any idea about how avoid this problem?
If anyone have the schematics of the volume control it would be really useful.
Regards, Francisco
Anyone have any idea about how avoid this problem?
If anyone have the schematics of the volume control it would be really useful.
Regards, Francisco
By "a phono in" I assume you mean an RIAA preamp? It's probably outputting a bit of DC. Check it's output caps to see if they are leaking. Otherwise, connect the volume control with a capacitor input.
Thanks for your response. Yes, I mean a "RIAA preamp". It's an EAR 834 that has a 2uF cap at the output. Attached is the schem.
View attachment 799842
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