Been working on this board for a while, and just got it to the point where I am happy with the layout.
It is now 3 identical channels (except for gain of course), all using a single channel dip opamp, with a class AB discrete diamond buffer, with SOT23 input and SOT223 output transistors in its feedback loop, with precision ST50x jfet crd ccs for the buffers, and another ST50x crd for optional biasing of the opamp.
The board is going to be a very tight fit in the DN1, because of how short the internal height of the case is, so will not slide into the mounting rails, but rather be supported by the board mounted Alps RK097 pot, and switchcraft 3.5mm input and output jacks. It is actually tight enough that depending how the holes for the front panel are drilled, the plastic tops of the output transistors may sit on the bottom of the case.
I will probably still make a couple changes to the pcb, but it is pretty much how I want it now. The dimensions are currently ~60x38mm.
That should cover most of it, so here are the pictures of the board.
It is now 3 identical channels (except for gain of course), all using a single channel dip opamp, with a class AB discrete diamond buffer, with SOT23 input and SOT223 output transistors in its feedback loop, with precision ST50x jfet crd ccs for the buffers, and another ST50x crd for optional biasing of the opamp.
The board is going to be a very tight fit in the DN1, because of how short the internal height of the case is, so will not slide into the mounting rails, but rather be supported by the board mounted Alps RK097 pot, and switchcraft 3.5mm input and output jacks. It is actually tight enough that depending how the holes for the front panel are drilled, the plastic tops of the output transistors may sit on the bottom of the case.
I will probably still make a couple changes to the pcb, but it is pretty much how I want it now. The dimensions are currently ~60x38mm.
That should cover most of it, so here are the pictures of the board.
Major Update
Well, after looking at the routing and everything, I decided to use a dual opamp to drive both input and output grounds. Because of issues with nearly all opamps driving capacitive loads, I removed the pair of electrolytic caps sitting from rail-vgnd, so there is only the small bypass caps to worry about. I may add a pad for an optional inductor/ferrite that can be used to isolate the output of the input vgnd driver opamp from capacitive loads, which will be very easy to route. Also changed the routing a bunch again, so the groundplane has less cuts in it, and there are no vias at all now. Also, I removed the board mounted jacks, because the output jack must now be isolated from the input. Thats pretty much it, so bring on the criticism.
Well, after looking at the routing and everything, I decided to use a dual opamp to drive both input and output grounds. Because of issues with nearly all opamps driving capacitive loads, I removed the pair of electrolytic caps sitting from rail-vgnd, so there is only the small bypass caps to worry about. I may add a pad for an optional inductor/ferrite that can be used to isolate the output of the input vgnd driver opamp from capacitive loads, which will be very easy to route. Also changed the routing a bunch again, so the groundplane has less cuts in it, and there are no vias at all now. Also, I removed the board mounted jacks, because the output jack must now be isolated from the input. Thats pretty much it, so bring on the criticism.
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