fluke

I can't see the ym2612 in the parts list for the DX7 II. The ym2612 is only 4 operator FM and the the DX7 is 6 operator FM anyways so it can't be the sound generator chip. Wouldn't it be easier to write a program to run on a megadrive to control the ym2612 than to try and source the chips and build custom hardware?

The Casio CZ series use Phase distortion synthesis which is a different concept to Frequency or Phase Modulation, though it did produce similar results. The main difference between FM and PM is that a DC offset in the modulator produces a pitch shift in the carrier with FM and only a phase shift with PM. This makes a PM synth more stable. See http://archive.cs.uu.nl/pub/MIDI/DOC/phase-mod for more information and some C source code.

The answer is - enough voltage to get 5mA flowing at the given resistance. ;) Have a look at http://www.midi.org/techspecs/electrispec.php for the MIDI electrical specification. MIDI in has an optocoupler (typical voltage drop of 1.3V for a 6N138) and a 220? resistor. So your MIDI out needs 2.4V to supply 5mA. If your supply is higher, add more resistance to drop the voltage. Eg an extra 120? if you're using a 3.3V part with a 3V minimum output high voltage or 380? if you've got a 5V part with a 4.3V minimum output high voltage. In the MIDI spec example (and the MIDIbox), they've been cautious and used 2 220? resistors (also 380? isn't a standard resistor value). My MIDISPORT 2x2 has a single 470? registor has its output. Speaking of which, the MIDISPORT 2x2 is a nice device to base a MIDI interface off. It uses the Cypress AN2131SC (same as the MBHP USB), an 8051 based microcontroller with hardware USB support. It downloads its firmware from the host computer so development cycles are fast. The stock firmware isn't class-compliant and doesn't work with Vista 64-bit. When i get some time i'll write new firmware for it, using the open source firmware for Linux (http://www.linux-usb.org/ezusb/) as a base.

I'm going to actually finish building my MIDIbox FM this year. I'm building it without a control surface, so i designed a stripboard layout for the Core, with banksticks and a 12pin connector to the OPL3 board. Then i had what i think is a really good idea. What if i move the OPL3 connection to other pins so that the hardware I2C interface on the PIC is freed up. Then i could connect the MIDIbox FM Core as an I2C slave to another Core that is being a MIDI Router without needing a PIC16F88 between them. And i could put my DB50XG in the same box for the complete 90s synth experience. :) Does this sound like a workable idea? I know i'd have to extend MIOS to support this, would it be a lot of work?

I find a small flat-blade screwdriver is the best tool for removing ICs. Just lever it in from from one end then the other 3 or 4 times, going up only a small amount each time so as not to bend the pins.

The SID is not a simple locked microcontroller. It is a full custom analog/digital IC, they can't even change feature size without needing a major redesign. Even if you do selectively etch away each metal layer to get a full layout of the SID, you'd still need them restart the 20 year old process that they originally used to make the SID to avoid needing a redesign. A better plan would be designing a SID clone either out of multiple chips (so hobbyist could make it and you wouldn't need analog and digital in the same chip) or a analog/digital FPGA.

512kbit = 64kbyte

The LM324 has lower bandwidth (1MHz vs 4MHz), is slower (0.5V/us vs 13V/us) and is probably noisier than the TL074. But they'll work, so have a listen and see how you like them. Just remember to socket them so you can change them later.

334 is the right code. I'm not sure of what exactly would have one, but something low tech with a design that hasn't changed in 10-20 years is more likely to have through-hole parts. Polyester or "greencap" capacitors are also suitable, you're more likely to find 330nF in those types than ceramic. Remember that it is also 0.33uF. If you really can't find that value, just substitute the closest value ceramic capacitor you can find. It's just a noise filter capacitor, so you could even get away with leaving it out. The construction is more important than the exact value here.

If i understand you correctly, you're referring to pins 2 (/IRQ) and 9 (TEST) of the YMF262 chip. If so, they can safely be left unsoldered as they have no connection. If you look at the PCB images, you'll see that the pads were only as large as the pins and didn't go anywhere.

The power supply will be noisy, leading to some noise on the audio signal. How much noise depends on the power supply filters, ripple rejection of the opamps, switching frequency (52kHz in this case), etc, etc.

That's a switch mode power supply, so it will be noisy. The one you posted is a +/-12V supply only, they also sell a +/-5V version which uses the same PCB, just different regulator chips, hence the confusion.

Without any rectification, the capacitors on the input side of the 7805 are simply acting as resistors to ground, with a resistance of -j/2?fC (ie 1/2?fC with 90° phase lag). So all you've got there is effectively 0.4? resistor to ground, which would explain the ripples.

MPLab does work under WINE for editing/assembling programs, but i couldn't get it to talk to a programmer. It did work under VMWare though.

I'm in NZ and pollin.de quoted me €22 + €3/kg for shipping. How did you get a rate of €7 to Australia? (Was it actually the rate to Austria instead? :) )