SID Power Line vs Ground

[napierzaza]

Okay, so if the SID has a 5v, and a 12v (or 9v) input, AND two grounds... Which ground is which? I have no seen any info on this but I believe Wilba suggested having them seperate. In is design they are together though:

Can anyone shed a light on this?

[nILS]

There's an audio ground and a digital ground. Basically they are the same :-) It's just that the ground plane is split to isolate them from each other.

[napierzaza]

So... 14 is the regular 5v ground... and which is the audio ground?

I was told to seperate the 12v and the 5v ground, but I don't know where they should actually go. Or is it that the IC is completely 5v. But the the audio is 12v?

If I have two separate power supplies and wire it like that, there should be no issue?

[nILS]

Well, you have to have a common ground at some point obviously. AFAIK this point would ideally be in the PSU.

[napierzaza]

Herm, okay, I'll have to do this. I have two seperate transformers so ultimately I guess there is no really appropriate ground connection.

[Wilba]

SIDs have only one ground (Vss pin) and two supplies (Vdd and Vcc pins).

I connected the SID's ground pin to an "audio ground" instead of the "digital ground".

One experiment I did with my MB-SID (before MB-6582) which used custom SID modules was to connect the SID's Vss pin to the audio ground instead of the digital ground. I had two ground wires going to each SID module, the audio ground was used for the buffer section (the BC547 etc.), the digital ground was used just for the 74HC595. Originally the SID's Vss pin was connected to the digital ground and I broke the track and reconnected it to the analog ground. This appeared to reduce some noise, so I did the same thing with the MB-6582 PCB.

If you're building your MB-SID using modules or veroboard, it makes sense to do a similar thing, connect the SID's ground to the buffer section and the 5V/ground wires for the SIDs and buffer section should be separate to the 5V/ground wires for the rest of the modules (Core, DIN, DOUT etc.). The ground wires can connect up at some common point (like where you supply ground to the whole setup, near a voltage regulator pin). However, it's not really required; you can build a low-noise SID synth without doing all this extra work.

[napierzaza]

Thanks for the verbose answer Wilba. I really appreciate it!

I made my own double-PCB based on your designboard, and so my SID is on the audio ground. So far the design I made is going well, just trying to correct any mistakes I might have made before actually putting my 6581s inside. I don't want to damage them.

I'm using two transformers for my power, so the only connection between 12v and GND is through the SID. I was wondering whether something bad wound happen though considering that it's taking 5v and not grounded to the same level. I'm glad to hear that it will not be a problem, I will remove my ground pin jumper!