Commodore 64 (C64) Dual SID Fix (Save the data bus!)

A short mod on the Dual SID (SID2SID) board I recently added to my C64. This mod is required or you stand to damage the data bus on either SID at some point in future - only if both SIDs are using the same chip select and base address (dual mono, psuedo stereo).

Special thanks to Dave Curran for helping simplify this fix.

On a standard SID2SID board it's not configured in such a way there will be a problem.

#commodore #c64 #dualsid #sid #diy

[Bangulo]

Great work Gadget! This is probably my fav channel for repairs on youtube.

[DaveCurran]

Happy to have helped. I think I'll have to build myself one of these now.

[Reinier_]

Good to know, some weeks ago my DualSID (8580/6581) died or not working for some reason.
First it works great, but now SID2 side is not working and at the SID 1 I hear that some sid don't sound right.
First I was thinking my 8580 died, but with a second 6581 it don't want to work.

So I think it is the board, but now I want buy a new one.

[moshly]

This is more complicated than it needs to be.
All you need to do is tie SID2's R/W line low. (Always write)
None of the registers in the SID are R/W, they are all Read or Write only.
So when you read one of the readable registers, SID1 reads to the bus & SID2 writes to a nonexistent register.

[Plan-C]

Hi Thanks for this. Just etched and built a sid2sid from scratch to try and get a nano working properly with a partially dead 6581. Did I get it correct? you severed the rw connection between the 2 sids on pin 7 and just grounded the rw on the second did? Cheers.

[riskybusiness]

where does the lovely synth sounds come from in your intro, @0:08, thanks

[Silverfox]

i have a few questions please. i see in your mod you separated the CS lines and added the diodes. i cant understand, did you separate the R/W line that was connecting the 2 SIDs and send R/W#2 to GND i also noticed, you have an extra cap at the top and what are those thin black kaynar wires for.

[Eightbitswide]

Is there a way to do this with the standard SID2SID board where this might be selectable? This way you could have six separate voices when needed and psuedo stereo when not. Perhaps by added three or four switches?

[bwack]

Hi. I was reading the blog post related to this SID board. Remember the discussion about the swinsid that didn't perform correctly with an eprom pla ? I didn't know the DIS board has a gate on the #CS signal to SID2. This might be the answer to why SID doesn't perform well. Margins are tight, and adding propagation delay on the CS might tighten the timing margins further.. (?) I don't have the full picture so I can't tell :)

[ZendarHouseClassics]

I'll be using 2 x 8580 in my C64C when I have put together my SID2SID pcb, is this mod required in all situations?
Also I would appreciate if you could do a video on how to connect the SID2SID for switchable stereo and dual mono.

[MsMadLemon]

Fantastic video! I must have watched it a number of times throughout these few months lol... I've had a SID2SID board untouched for a good 8 months now I think, now's the time to bite the bullet and just have a go.

I'm needing to pick your brains about this, as you know I have a C64c and i'm wanting a switch between Mssiah stereo mode and pseudo stereo (hearing each SID on each stereo channel I believe?) . Am I correct in thinking it's as simple as having a switch on SID2's CS pin switching between the cart port pin and the CS of SID1? (of course with the diode and resistor mod you've just shown)

It's all the logic Pot XY etc talk which is throwing me slightly lol

Also about the power...i'm aware that the 6581 requires 12v, i'm figuring cutting the power trace on the SID2SID board and getting power from one of the capacitors on the motherboard (I believe one of them supplies 12V ) should be fine right?

[RETRONuts]

Can you make a video doing this on the C64C motherboard or is it the same, I would like to use the 6581 with my 8580 sid chip..?

[efrog]

That's a SID2SID, I thought it was a "DualSID"... ;-)