Powering OPL3 module from +-5V?

[Sauraen]

Is it possible to power the analog portion of the OPL3 module from +5 / -5 volts instead of +12 / -12 volts? The +5V power to the YMF262 and DACs would of course be unchanged.

[nILS]

Yes. You do wanna switch the opamps to some rail-to-rail opamps and adjust the gain set by the resistors. Or simply go with +5V only (like the sammichFM does).

[m00dawg]

Of note, I do find the output from the sammichFM quieter than any of my other synths so it requires more gain as a result. Something to consider before looking at lowering the voltage for the op-amps (since, correct me if I am wrong, that will also lower their output).

[nILS]

Yes and no. To voltage on the opamp limits the maximum input/output voltage they can reproduce without clipping the signal. If you simply lower the voltage from +-12V to +-5V you'll potentially clip 7V on either end of the signal. The resistors need to be adjusted, not to raise the gain, but to lower it.

[verpeiler]

Or simply go with +5V only (like the sammichFM does).

Cool! Didn't know that. Could you elaborate? Didn't found the sammichFM schematic (only the PCB layout) up to now. Are there information's about that anywhere online?

[nILS]

I most certainly can. Have a schem :flowers: This is only for one of the YACs, the other one is identical.

The DACs on the mbFM output a signal of 0..5V (what else could they do, they're powered by 5V). So it seemed only natural to simply buffer that signal and output it, rather than turn it into a bipolar signal (+-12V), which requires additional voltages. Since regular opamps can only have in/output voltages up to ~1.5V of their power rails, I went with a rail-to-rail amp, that lets the signal get very close to the rails. The voltage divider made up of R52/R56/R57 and R53/R58/R59 lowers the signal to roughly 0.4V - 4.6V, centered around 2.5V to prevent clipping.

sammichFM_base_rev1_output.pdf

[Sauraen]

I already have +-5V power rails in my build, so how about this: Output of DAC goes through 10uf coupling capacitor, becomes -2.5 to 2.5 volts. Run this through unity-gain buffer made from normal non-rail-to-rail op-amp powered from +-5 volts. I've been experimenting with the LF412 op-amp and it clips at +-4.17 volts when powered from +-5, so that should be enough. Does this sound good?

Also, do the sample-and-hold op-amps for the DAC need to go rail-to-rail? If so, I would need to make IC3 and IC5 on the MBHP_OPL3 board TLV2774 rail-to-rail op-amps powered from +5 volts, and then make IC6 a normal op-amp like LF347 powered from +-5 volts. And somehow insert the coupling capacitors between the two...

[nILS]

Yep, sounds good.

AFAIK the S&H should go ~0..5V (apparently 0.4V - 4.6V will do just fine, see sammich).