MD1 audio w/ mCD & 32x buffer amp circuit

Posted on Feb 5, 2014

Need some program to set it`s channels to the maximum level, or write the full scale to the DAC. Looking at the MD schematics, you`ll see that the audio is mixed together with relations of 0. 0431 for the PSG, 1 for the YM and 0. 0468 for the external audio sources (both 32x and CD) What I did with my audio amp was tapping all signals before going through the electrolithic

MD1 audio w/ mCD & 32x buffer amp circuit
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capacitors (and removing those caps, and everything after them, resistors, the sony amp, everything), Amp`ed the YM outputs by 28, and mixed them with the straight PSG and Ext audio, "without" amplification (actually there`s a trimmer to adjust the PSG level About the ADC filtering, a first-order low pass filter at 61kHz should be enough. It will give you 40dB attenuation for the 6. 1Mhz replica. This means that the spectral components around 6. 1Mhz (+/- 61kHz) will have a maximum of 7mV (ignoring noises and crap) They were powered by a linear 6Volt regulator (7806), completely separated from the MegaDrive logic and analog supplies, and draws about 30-40mA of current. Now I would do something different regarding the PSG: I would use separated opamps to fead each channel separately, even though their input would be the same: this reduces cross-signaling between audio channels. Oh yes there`s more stuff like control bits and bit inversion crap in this protocol. This means you have to do some signal processing between the ADC output and the SPDIF connector.

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