Quick answer: the 6581 is the original Commodore 64 SID sound chip (1982 to around 1986). It runs on 12V and has a warm, gritty, inconsistent filter that many classic game composers wrote for. The 8580 is the later revision used in most C64C machines. It runs on 9V, runs cooler, has a cleaner and more consistent filter and louder combined waveforms, but plays old sampled speech and drums very quietly. They are pin-compatible but not drop-in interchangeable, because the supply voltage and filter capacitors differ.
The SID (Sound Interface Device) is the reason the Commodore 64 still has a loyal music scene decades later. If you are buying a C64, replacing a dead sound chip or setting up an emulator, knowing the difference between the two versions matters.
A quick history of the SID
The SID was designed by Bob Yannes at MOS Technology in 1981 and launched with the Commodore 64 at CES in January 1982. Unlike the simple tone generators in most home computers of the time, it was effectively a small synthesiser on a chip, with three voices, ADSR envelopes, ring modulation, oscillator sync and an analogue filter. Yannes later co-founded the synthesiser company Ensoniq.
Time pressure meant some features did not behave exactly as specified, which gave the original 6581 its quirks. The 8580 revision, which appeared around 1986 and was made until about 1992, was revised to follow the specification more closely.
6581 vs 8580 at a glance
| 6581 | 8580 | |
|---|---|---|
| Years used | 1982 to around 1986/87 | Around 1986/87 to 1992 |
| Process | NMOS | HMOS-II |
| Vdd supply (pin 28) | 12V | 9V |
| Filter capacitors | 470pF | 22nF |
| Filter | Non-linear, varies between chips, distorts | Linear, consistent, cleaner, stronger resonance |
| Combined waveforms | Quieter, muddier | Louder, clearer |
| Old “digi” samples | Loud | Very quiet without a fix |
| Heat and reliability | Runs hot, more failures | Runs cooler, more durable |
| Found in | Original “breadbin” C64, C128, plastic C128D | Most C64C machines, metal-cased C128DCR |
Some 8580s are labelled 6582 or 6582A. These are the same chip as the 8580. The figures above come from the C64-Wiki SID page and the Wikipedia MOS Technology 6581 article.
How do they sound different?
The biggest difference is the filter. On the 6581, the filter’s cutoff behaves non-linearly and varies a lot from one chip to another, so the same tune can sound noticeably different on two 6581s. It also adds distortion, which gives bass lines and leads a raw, warm character. The 8580’s filter is cleaner, more predictable and can reach higher resonance.
Combined waveforms (where a voice plays triangle, sawtooth and pulse together) are louder and clearer on the 8580, and the overall output is less noisy.
Which is better? It depends what you are listening to. Most classic game music from 1982–1986, by composers such as Rob Hubbard and Martin Galway, was written on and for the 6581, so many fans feel it sounds “right” on that chip. Some later music was written with the 8580 in mind. Neither is objectively better; many collectors keep one of each, or use a replacement that can switch between both.
The sampled speech and drums problem
Many games and demos play digitised samples (speech, drums, sound effects) using a trick with the SID’s volume register. On the 6581 that trick is loud; on the 8580 it is very quiet, often almost inaudible. That is why some games’ speech seems “missing” on a C64C.
Later software often detects the chip and compensates, but older titles do not. The C64-Wiki notes a hardware fix: a resistor of about 330k ohms from the 8580’s EXT IN pin to ground makes old samples audible again. Only attempt this if you are comfortable soldering.
Why you cannot simply swap them
The 6581 and 8580 share a pinout, but the boards around them are different:
- Voltage: the 6581 needs 12V on its Vdd pin; the 8580 needs 9V. Putting an 8580 into a 6581 board exposes it to a higher voltage than it was designed for and risks killing it.
- Filter capacitors: the boards use different values (470pF for the 6581, 22nF for the 8580). The wrong capacitors leave the filter sounding badly off.
Adapter boards exist that convert the voltage and capacitors, but they must match the chip and board you have. If in doubt, replace like with like, or use a modern replacement designed for your board.
How to tell which SID your C64 has
- Look at the case: an original brown “breadbin” C64 almost always has a 6581. Most slimmer C64C machines have an 8580, but some early C64Cs used older boards with a 6581 inside, so check the chip itself.
- Open the case and read the chip: the SID is a 28-pin chip labelled 6581, 8580 or 6582. See our Commodore 64 deep dive for an overview of the main chips.
- Use a test program: several SID detection tools on C64 software archives identify the chip without opening the machine.
Always work with the computer switched off and unplugged, and take anti-static precautions when handling chips.
Signs your SID chip is faulty
SIDs, especially 6581s, do fail. Typical symptoms are no sound at all, one or more voices missing, a filter that does nothing, or loud buzzing. Before blaming the chip, check the sound cable, TV volume and audio connections, and the C64 power supply, because a failing supply can cause strange faults. Our guide to restoring a Commodore 64 power supply explains why an old PSU is worth checking or replacing anyway, and troubleshooting a C64 black screen covers other common faults.
Replacement options for a dead or missing SID
Original 6581 and 8580 chips are no longer made, so prices for genuine pulls have risen and remarked or fake chips appear on auction sites. Your options are:
- A genuine used chip from a reputable seller with returns. Be wary of “new old stock” claims and unusually cheap listings.
- Modern replacement boards such as SwinSID, ARMSID, FPGASID and SIDKick pico. These emulate or recreate the SID in a module that fits the original socket. Features and accuracy vary: some can switch between 6581 and 8580 sound, and some offer stereo with a second SID. Check each project’s documentation for compatibility with your board before buying.
- Emulation: if you just want the sound, modern emulators model both chips closely. Our C64 emulator guide explains how to choose. VICE, for example, lets you select the SID model.
If you are buying a SID replacement, check current prices on Amazon, but specialist retro stores are often a better source.
As an Amazon Associate, Retro Tech Lab earns from qualifying purchases.
Why real hardware still sounds different
The SID mixes digital and analogue circuitry, and the analogue filter differs from chip to chip. That is why emulators get very close but enthusiasts can still tell the difference, and why recording projects capture tunes from real chips. Our article on why chiptune audio sounds different on emulators goes into more detail.
FAQ
What is the difference between the SID 6581 and 8580?
The 6581 is the original 12V NMOS chip with a gritty, inconsistent filter. The 8580 is the later 9V HMOS-II revision with a cleaner, more consistent filter, louder combined waveforms and quieter sample playback.
Can I put an 8580 in an original C64?
Not directly. The original board supplies 12V and uses 470pF filter capacitors, while the 8580 needs 9V and 22nF capacitors. You need a suitable adapter, or a modern replacement designed for that board.
Which SID chip sounds better?
Neither is objectively better. Most early C64 game music was written for the 6581, so many people prefer it for classics; the 8580 sounds cleaner and suits some later music.
Why is the speech quiet on my C64C?
Most C64Cs use the 8580, which plays old volume-register samples very quietly. Some later software compensates; otherwise a resistor mod or a replacement that emulates the 6581 fixes it.
Is the 6582 the same as the 8580?
Yes. Chips marked 6582 or 6582A are the same design as the 8580 and use 9V.
Are new SID chips still made?
No. Original SIDs are no longer manufactured. Modern replacement modules recreate the chip, and used originals are sold second hand, sometimes as remarked or fake parts.