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ESP P113 volume control problem
ESP P113 volume control problem
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Old 20th October 2020, 06:40 PM   #1
NealJ is online now NealJ  United Kingdom
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ESP P113 volume control problem
Default ESP P113 volume control problem

I've just built Rod Elliott's P113 HPA using my own PCB and have a problem with the volume control. I'm using 300ohm Sennheiser HD600 headphones.

The pot only really gives any output at the very last fraction of its clockwise turn. There is some sound before that, it stays relatively constant at a low level before kicking in. I had the board connected to an Alps RK27 20K log pot, I then swapped it out for an Alps RK09 10K pot but the result is the same. I've seen this behaviour mentioned elsewhere on the forum in relation to 'passive' preamplifiers and described thus:
It is the effect of turning the volume control and it stays really quiet until close to the end where all the power seems to be in the last "hour" of the volume control between 4 and 5 o'clock.
If I bypass the pot, the amp works fine and there is a nice gradual increase in volume when I use my source volume control (Samsung Galaxy S7).

Any advice please?

Last edited by NealJ; 20th October 2020 at 08:46 PM. Reason: wrong alps model corrected
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Old 20th October 2020, 07:51 PM   #2
Mooly is offline Mooly  United Kingdom
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ESP P113 volume control problem
Worth checking that you have used 22k for R1 and not something like 220 ohm.
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Old 20th October 2020, 08:29 PM   #3
NealJ is online now NealJ  United Kingdom
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ESP P113 volume control problem
Just checked, it is 22K in both channels.
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Old 21st October 2020, 07:13 AM   #4
Mooly is offline Mooly  United Kingdom
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ESP P113 volume control problem
Very strange then if it is not correct with a log pot fitted. As you designed your own PCB it is worth checking that you have the wiper of the pot connected to R1 and that you haven't transposed an end pin and the wiper.
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Old 21st October 2020, 08:43 AM   #5
NealJ is online now NealJ  United Kingdom
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ESP P113 volume control problem
You got it there.

The pot is mounted off board and I have it connected to the output, not the input. I'll swap it over after work.
Such a daft mistake, thank you very much for your help Mooly.
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Old 21st October 2020, 11:22 AM   #6
Mooly is offline Mooly  United Kingdom
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ESP P113 volume control problem
That's good It's an easy error to make.
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