Possible Cave SH-3 stereo mod?

[DaveOrAstroDave]

Hi everyone,

I was looking at the datasheet for the YMZ770C (the sound chip on the Cave SH-3 boards),
and I found that the pins for analog audio left and right are #23 and #24.

Pin 23 appears unconnected, at least on Espgaluda 2.
Has anyone looked into this for a possible stereo sound mod?

I might just dig out the ole 'scope and have a look at what signal, if any, is on that pin...

Dave

[PC Engine Fan X!]

Hi everyone,

I was looking at the datasheet for the YMZ770C (the sound chip on the Cave SH-3 boards),
and I found that the pins for analog audio left and right are #23 and #24.

Pin 23 appears unconnected, at least on Espgaluda 2.
Has anyone looked into this for a possible stereo sound mod?

I might just dig out the ole 'scope and have a look at what signal, if any, is on that pin...

Dave

For Dave,

Your discovery sounds pretty intriguing...I wonder if the Cave SH-3 "Ibara" PCB can output in stereo as well?

Break out your 'scope and tells us what you find... ^_~

PC Engine Fan X! ^_~

[Stefan_L]

If the pin really is unconnected then it most likely don't have any sound coming from it or it has the same sound as coming from the other pin.

If both pins would be joined then there could be more of an possibility it really would output stereo if they where seperated.

[Dave_K.]

Welcome new Dave (thats makes about 4 or 5 Daves now). Great discovery, and anxious to find out if there is any signal on that pin. I don't know the specs on that chip, but you may need to gnd/raise one of the other pins to activate stereo, as the chip may be outputting mono (combined) on the one pin.

If the pin really is unconnected then it most likely don't have any sound coming from it or it has the same sound as coming from the other pin.

If both pins would be joined then there could be more of an possibility it really would output stereo if they where seperated.

No necessarily true, its entirely possible the chip can do both, but was wired for mono only since this conforms to the jamma spec. No reason to add extra wiring/parts if nobody is going to use it that way (which can turn into higher production costs over a large volume of boards).

[MKL]

If the pin really is unconnected then it most likely don't have any sound coming from it or it has the same sound as coming from the other pin.

If both pins would be joined then there could be more of an possibility it really would output stereo if they where seperated.

Obviously not: when a board has a mono volume pot (as is the case here) the merger of the left and right channels can only happen *before* the pot which is in turn before the amp.

[Stefan_L]

Obviously not: when a board has a mono volume pot (as is the case here) the merger of the left and right channels can only happen *before* the pot which is in turn before the amp.

Yes i know... i am only talking about the chip pins and not jamma or amplifier setup.

[MKL]

Obviously not: when a board has a mono volume pot (as is the case here) the merger of the left and right channels can only happen *before* the pot which is in turn before the amp.

Yes i know... i am only talking about the chip pins and not jamma or amplifier setup.

The point is that if a mono channel is fed into the amp it wouldn't make sense that the L and R pins on the amp were joined together. Compare for instance the MVS motherboard MV-1FZ which is the only MVS mono board that has a stereo amp: L and R are on pins 3 and 4 but 3 is unused since the amp is set to mono, no trace going to that pin.

[DaveOrAstroDave]

Hey guys,

Looks like I got you all worked up over nothing.
Pin 23 is active, but it seems to be outputting the exact same signal as pin 24.
I had a feeling that would be the case, but at least now we know for sure.
There is no stereo sound hidden somewhere on these boards.

The datasheet doesn't say anything about a stereo-enabling pin, though there might be a register on the chip which is accessible through software.
If anyone wants to look at the datasheet, it's at: (warning - japanese pdf)

http://www.yamaha.co.jp/product/lsi/pro ... 770c50.pdf

I suppose it's possible that there is a trace connecting the two pins together underneath the sound chip itself, but I'm not going to remove the whole chip just to get a look.
Yes, I am crazy enough to solder test leads onto my new PCB, but I'm not that crazy.

By the way, Dave K, I think I might know you from BYOAC? I used to post there around the time I was working on the AKI encoder...
Or maybe I saw you on KillerCabs? Anyway, it's always a pleasure to meet another Dave (or five).

[MKL]

As I said, *if* there are stereo channels they will merge together before the volume pot so it's pointless to check the amp which is after the pot. You should check the trace that goes to the inut pin of the pot and see if it splits somewhere.

[DaveOrAstroDave]

As I said, *if* there are stereo channels they will merge together before the volume pot so it's pointless to check the amp which is after the pot. You should check the trace that goes to the inut pin of the pot and see if it splits somewhere.

I haven't been looking at the amp. I've been looking at the pins on the YMZ770C, which is the sound synthesizer chip. If it's not stereo where the sound is generated, I don't see how it can be stereo anywhere else...

[MKL]

ah it's the sound generator, I thought it was the amp (I don't have these boards). Content yourself with mono then