MIDIbox

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====== MBHP_OPL3 module modifications, the 5V option ======

The [[http://www.ucapps.de/mbhp_opl3.html|MBHP_OPL3]] module originally has three TL074 op-amps, and a circuit that needs +/-12V bipolar power supply.

In Wilba and nILS [[sammichfm|sammichFM]], they use two OPA4348 rail-to-rail op-amps, that can be powered by 5V.

Sauraen suggested another 5V rail-to rail op-amp, the MCP6004, which is pin compatible with the TL074, and a way to modify the OPL3 module to use these.[[http://midibox.org/forums/topic/18492-mbfm-5v-option/]]

- Replace R5,R7,R10 and R13 with jumpers\\
- Bridge IC6 pads 1&3, 5&7, 8&10 and 12&14\\
- Leave out:\\ 
IC6\\ 
R4, R6, R8, R9, R11, R12, R14, R15\\
C15, C16, C19, C20, C23-C30\\
- Bridge C20 pads (to supply Ground for the op-amps)\\
- Leave out bridges to IC6\\
- Use MCP6004 for IC3 and IC5 (IC3 The op-amp, not the DAC, labeling error)\\
- Supply 5V to the +12V pin, and Ground to Ground\\

This way the second buffering stage is left out.

In the sammichFM, nILS designed a separate dedicated 5V supply for the DACs (YAC512) and the op-amps.\\
To modify the OPL3 module for this approach:\\

- Cut the trace between the 5V pin of the Oscillator and the DAC\\
- Leave out the middle horizontal bridge from IC1\\
- Connect the right pad of this bridge to the 5V pin in the middle of the board with a jumper\\
- Connect the left pad of this bridge to the 5V pin of the Oscillator with a jumper\\
- Two separate 5V voltage regulators, IN pins connected through a ferrite bead\\
- One 5V source to Core and J1 of OPL3 module\\
- The other 5V source to J3 of OPL3 module\\
- Ground ONLY to J3!\\

Tips:\\
- Starlike wiring (Ground from PSU to each module + Audio outputs)\\


I can vouch for these mods :)\\
My MIDIbox FM V1 has hardly any noise, and it has enough gain.



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