I’m a geek, you’re a geek, we’re all geeks
and geeks enjoy their old games and computers.
In the eighties, the commodore 64 used what was revolutionary at the time, the “Sound Interface Device” – SID chip, for short.
The SID chip is capable of playing 3 different voices simultaneously, and adding filtering to the outputted audio, which made for a remarquable audio quality, much more advanced than what was avaiable at the time.
But the chip is no longer being produced.
When building a new Commodore, or fixing one up, where can a geek get a replacement SID?
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This article follows a previous one about playing music on the 64The Sound Interface Device was revolutionary, but is no longer produced. When fixing up a Commodore 64 or building one, geeks may have to replace the SID chip. This generally means extracting a “new” SID from a donnor machine – or getting one of the modern equivalent chip.
Sadly, as no SID sounded the same even back then, modern equivalent cannot be 100% identical to the vintage chips. But they can be quite interesting and even offer new features.
We’ll explore some of the possible replacements.
SwinSID
Released in 2005, the original Swin SID was meant to replace the base functionality of a SID chip in a world where they knew the chip was becoming more and more scarce (and pricier at the same time) – the idea was to use an ARM microcontroller as a replacement before stock exhausts. It was designed by Swinkels – thus the SWIN name.
It can be made to replace the MOS 6581 (older) and MOS 8580 (newer) SID chip but doesn’t include analog inputs for the paddle or mouse inputs. – this means less gaming options, but also issues running diagnostics properly; mainly, any harnessed tests would fail control ports and declare a faulty CIA.
Audiowise, comments are that the chip sounds different than both the 6581 and 8580. The analog nature of the filtering included in the original SID chips makes it difficult to replicate fully, but the SwinSID has it’s own sound and plays perfectly.
Several variants has been made over the years, getting the Swin SID smaller and smaller, up to a point where the Nano SwinSID is about the same size as the original SID chip:
NOBOMI ARMSID
The ARM SID uses an ARM Cortex M4 at it’s heart (thus the name ARM) and is meant as a drop-in replacement for both the 6581 and 8580 SID chips. In addition, there is an AD8515 opamp for analog input logic; this means that the ARM SID can handle paddles and mouse, which the SwinSID cannot.
A configuration software can be run from the Commodore to change settings on the ARM cortex and personalize the audio experience, which makes this SID replacement very flexible. It even detects if there are more than one ARMSID chips at different addresses on the computer!
The developper for the ARM SID is Martin Lukasek. There are a few variations of these SID replacement. More information can be found (in english, and czeck) at nobomi.cz.
For anyone curious how it sounds, there is a video on the retro shack on the ArmSID.
BACKBIT BACKSID
The BackSID by BackBit is a rather new product, released in 2021.
BackBIT is still a startup, and BackSID is still new, so firmware development is still somewhat ongoing, which is a good thing. The collaborative nature of the BackBIT company makes for a great customer support and nice improvements of the BackSID.
The device auto-detects into which Commodore it is installed to properly adjust how to behave, and a configuration software ran on the Commodore helps with costumizing the settings or upgrade the firmware. It also has the analog portion of the SID chip for paddles and mouses.
More information can be found on BackBIT’s BackSID page.
A word from Evie, who created the BackSID – there on YouTube.
These a few of the possible replacement SID chips for the C64, there are others, but this gives a nice overview.
These are a nice way to bring back audio on a Commodore 64, they also bring some nice features, and are not overly priced.
Most of the C64-specific chips are slowly finding modern replacement, with the latest being the Complex Interface Adapter (CIA) chip. It is now possible to create a brand new C64 without using anything vintage. That’s progress!
Keep on geeking!
Related articles
Building a C64 in 2023 (wereallgeeks)
Playing Music on the C64 (wereallgeeks)
Swin SID (c64-wiki)
ArmSID (Nobomi)
BackSID (BackBit)
CIA chip replacement (wereallgeeks)
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