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:
Any advice please?
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?
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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.
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.
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.
It's an easy error to make.
Hi sorry for reviving this somewhat old thread..
To the OP: so what is your experience with Rod's headphone amp so far?
I'm thinking to build a heaphone amp myself too, but not sure which design to choose yet...
Read some posts about CMOy but PCBs for it looks like they are unobtainable at the moment.
To the OP: so what is your experience with Rod's headphone amp so far?
I'm thinking to build a heaphone amp myself too, but not sure which design to choose yet...
Read some posts about CMOy but PCBs for it looks like they are unobtainable at the moment.
I think it's excellent, absolutely silent. I've listened to it quite a lot and I really enjoy it.
I can also recommend Richard Murdey's Sapphire HPA on this forum.
Nisbeth, also on this forum has some CMoy type boards that you can download from his site (the slowdiyer).