Cmoy Headphone Amplifier, part 2

Tonight I made significant progress on my Cmoy amplifier. It makes promising noises now but it’s noisy and generally is not super-awesome sauce. I think I’m going to lay out a PCB design for it and assume that most of my problems are due to my horrible assembly practices.  I’ve got enough parts for one more I think, so that should be ok to do without too much cost at Digikey.

When I put it down I was having a problem with one ear working only intermittently.  Today I start checking the circuit for symmetry and I found that the IN+ on the right side was reading 100K ohm but the IN+ on the left side was only reading 80K ohm (to ground, spec is 100K).  I desoldered the connection between the resistor and the DIP connector and when I reconnected it was reading 99.7K.  Given how jankily this whole point-to-point setup is, I’m pretty satisfied. That fixed most of the balance issues.  It’s still got a bit of an issue. I think it’s due to the power supply resistors that split the 9V battery voltage for the floating ground are not terribly balanced (junk-drawer-specials).

I also disconnected the volume adjustment pot. I think I smoked it’s case when I was hooking up the leads.  It just occurred to me that having something a 10K path to ground from the input will probably have a good effect on the pop and hiss even though I’ve decided that I don’t want volume control.  Better check out the junk drawer. EDIT: Yop, that was it.

One other modification I’d make if I were doing this again would be to add some sort of soft-start. When I flip the power switch a loud pop occurs as the cap’s fill up. Sounds like ass and can’t be good for my headphones either.

In conclusion, I want this project done, so I’m going to drill the front panel and mount this up. Hopefully I’ll revisit this again soon because I don’t think it’s going to perform very well at work with my nice headphones.

This entry was posted in Cmoy Amplifier, Projects. Bookmark the permalink.

Leave a Reply