Anyway Alexan doesn't have the OPA2134 but they do have the much worse (but still orders of magnitude better than the LM358!) TL072. About $1.50 apiece (67 pesos). Not so bad..
I use the "Gwado" design which is very similar to the CMoy but with lower gain and a series resistor to drive low-impedance cans. The Sennheiser is 32 ohms which is difficult to drive, more so with a lowly TL072. But, the TL072 is pin-compatible with the OPA2134, so if this is a success, I can get some of those and drop them in.
So far all I have is a protoboard layout. Because I don't have 3.5mm jacks, I can't pipe in a signal or pull out any output. All I can do so far is measure the DC offset. It's about 11mV on one channel, and 20mV on the other channel. Not small, but not fatal.
I'm using the virtual ground design with two 470uF capacitors, as in the original CMoy design. The clerk at Alexan failed to include any 0.1uF capacitors (which are power supply snubbers) and I didn't check. So I used some humongous 0.047uF, 600V (!) capacitors from one of my past photo-flash projects. These caps are even bigger than the 470uF electrolytics!
Once this build is validated, I will transfer it to an Alexan PC201 veroboard, which I've cut down to fit inside an HC101 plastic case.
1 comment:
this is nice. I'm also planning to do this same project so I was looking for a store that sells a kit. apparently it's not so sikat here in the philippines.
looking forward to you finishing this project!
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