Posted By
MMS
on 2016-05-05
18:02:30
 |  Re: Modern sound chip for the Plus/4?
Wow, RobertB, you are fantastic! It is a very nice find.
Yes, it is exactly the same. The only difference between the C64 and the Plus/4 is where are the pins connected on the user port.
Even the PRG drive this (assembled, or anything) could be the same, just by changing the output address of the 8bit data, instead of CIA to ACIA.
UPDATE:
As I see, it is a stereo device (?)
You can check a real design in step by step, and how it sound in real life action, though the MOD player and the WAV players also requires REU due to big file size.
You can hear it in action from 5.20 onwards, it is an evidently clearer sound than internal SID (or TED):
https://www.youtube.com/watch?v=Gn1w9tJHtAQ
Although there is an existing C64MOD player, just need to be converted (http://csdb.dk/release/?id=58189&show=review#review)
As visible, it supports the playback via SID (4bits); the 8bit extension of SID(8bits) and the Covox (8bits)
So, the Digimax circuit on http://digitalaudioconcepts.com/vanessa fits to our needs, and almost there, but need to be conncted on different User Port pins on Plussy.
The C64 Pin9 (ATN) need to be connected on Plus/4 on same Pin9 (ATN), but C64 Pin8 (PC2 handshaking line) I am not pretty sure.
Maybe the Pin8 PC2 is equivalent to the Plus/4 PinD (RTS, Request to Send) ?
BUT the TI's tlc7226 is a little overshoot here and stereo output is more complex to program.
TI 7226 has 4 independent outputs channels, and you need to connect them properly. That's why it need those extra lines and a lot of extra components.
If you compare with a ZN428E-8 circuit, it is much simplier.
Price-wise: 4pcs of ZN428E-8 costs 10USD with shipping (probably I can find cheaper too) --> 2.5US/pc
http://www.aliexpress.com/store/product/4pcs-lot-ZN428E-8-DIP/1908244_32482071868.html
TI7226 5pcs of TI7226 costs 25USD + shipping --> 5.5 US/pc
(and the cost of extra components)
Still, the DIGIMAX has a proper layout diagram and schematics on the link RobertB provided, and a working protoype with step by step built instructions (pictures in the Youtube video), also a C64 (REU) program that can play MODs, and an other one that can play big WAV files.
More complex and expensive to build than the ZN428E Covox device, but already has some support.
OFF: while the heck the links in the < url > tags do not work?
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So, there was an OPL2 solution by Commodore itself, supported by Yamaha chip YM3526 with DX technology, and later almost the same implemented in Adlib on PC.
Called Commodore SFX Sound Expander.
It has 9 voices, two operators and works well with an external (midi?) keyboard too, or the below addon.
And proven work with Commodores. There are some videos controlling it with Arduino
There is a add-on keyboard ("Incredible Musical Keyboard") that works with the form of C16 too, and with that Sound expander would sound better (and higher polyphony) than the SID itself.
The sound it produces is very similar to the background music I remember from Dune2 on PC.
Incredible Musical Keyboard (plus a demo of Sound Expender at 7:30):
https://www.youtube.com/watch?v=RX4JfLCaBMU
Sound Expander demo from 2008
https://www.youtube.com/watch?v=jR5RcXSlKNU
Longer from 2015, and this guy told he can produce one for C64, just in case :-)
https://www.youtube.com/watch?v=FOKcDSakqt8
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