J-Mo Mk II headphone amplifier

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Obviously still some wiring missing, but since I have tested the boards and they are working I though I'd show off anyway - my J-Mo clone is ready :D

I thought the design looked interesting but wanted to try out a different PCB layout (sorry Richard :) ) to be able to use different parts. I managed to shrink the boards a bit in the process, but that wasn't the primary purpose. I have just tested the amp very briefly in a bench setup, but it seems sound quite good.

/U.

Pics:

jmo-1.jpg


jmo-2.jpg


jmo-3.jpg
 

rjm

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Joined 2004
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Very nice, and no need to apologize: you haven't changed the name, or claimed the circuit as your own.

I'm surprised you didn't put the M-reg and J-Mo and diodes on the same board. It would have saved you having to wire a bunch of interconnects... screw terminals are not ideal as far as long-term reliability is concerned.
 

rjm

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Joined 2004
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Ah, that one. I remember it, but Boberly's site seems to have vanished so I'm copying the circuit from the ebay listing of the guy you got the boards from. I don't know who did what, but it is a similar to the Gilmore amp, though with a diamond buffer output stage. I recently touched on something similar.

Anyhow, should make for an interesting comparison. Push pull vs. single ended circuits and all that.
 

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sound is... amazing! :D

i worry first because cap output. but sound extreme detail and clear. very pleasant, too. thank you :D

i would like ask again, tho. the cap, i use 220uf with low imp phone, and as preamp. this affect frequency? even as preamp higher value cap better frequency response? thank you again :D

and is it possible increase h2 distortion with change resistor?
 
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rjm

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Joined 2004
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As a preamp, you could use a much smaller value, a 2 uF film cap for example. Larger values will not improve the frequency response unless you are driving a 600 ohm input or something. 220 uF is fine for most headphones, though I invite you to experiment a little: larger values can subjectively sound more "bassy", smaller values more lean or fast, so personal preference and matching the sonic characteristics of the headphone comes into play.

Basically, the higher the circuit gain the higher the distortion. The exact relationship between the resistor values and the performance is complicated as the bias currents as well as the gain are affected. It's someting that's best examined under simulation with LTSpice.
 
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