KILL C64 SID BUZZ - NOW!

Tonka · Post by **Tonka** » 02/07/2007 - 11:39

Hi all,

I know there are a number of people here who still like to record/listen to SIDS from a real C64 (Kenz, Waz - I'm looking at you), so I thought I would share this cable mod which I just made. It basically annihilates all SID buzz on ANY C64 to a practically inaudiable level!

You won't have to open up your C64, won't need to build weird and wonderful gizmos with extra chips, capacitors and filters and won't need to use software to remove the noise in post production (unless you're absurdly picky). Just make this ridiculously simple lead and enjoy noise free SID forever!

Now for my apauling diagram!

**NOTE - the diagram shows the MALE pins of the cable NOT the female pins of the C64 DIN input socket**

My previous lead has always just had the two connections before now - ground and audio out. It has (recently?) been discovered that the main cause of SID buzz is the audio in which remains open at all times - amplifying any residual noise to an irritating level. Just make sure that this particular pin on the connector is grounded too. I literally just blobbed some solder to join up pins 2 & 5 and that nasty SID buzz has almost completely gone.

Here are 2 examples before and after modding my standard lead - both from the same 1983 C64 with 6581 SID chip and at the same volume:

Before:

http://www.monotron.co.uk/Noisy6581.mp3

After:

http://www.monotron.co.uk/Cleaner6581.mp3

A final example with the modded lead:

http://www.monotron.co.uk/WizballHiScore.mp3

SID buzz, R.I.P.

Kenz · Post by **Kenz** » 02/07/2007 - 12:00

Blimey! That's worth a try - I shall 'solder blob' one of my spare C64 audio leads and will let you know what happens. (If you see a news item about an explosion in Malvern you'll know why).

Tonka · Post by **Tonka** » 02/07/2007 - 12:04

Kenz wrote:Blimey! That's worth a try - I shall 'solder blob' one of my spare C64 audio leads and will let you know what happens. (If you see a news item about an explosion in Malvern you'll know why).

LOL! Prepare to shit yourself with excitement. I still can't believe something so simple is so effective at removing that damned infernal buzz!

Let me know what happens (and upload a before and after if you can - I love those things).

Post by **LMan** » 02/07/2007 - 12:21

*hands out retro nobel price to Tonka*

Tonka · Post by **Tonka** » 02/07/2007 - 12:35

LMan wrote:*hands out retro nobel price to Tonka*

LOL! Sadly, I can't take ALL of the credit.

AFAIK, 'Alpha' made the whole 'audio in = SID buzz' discovery ( http://www.bigmech.com/misc/c64mods/noisereduction.html ), which he resolved in a number of slightly more complex ways, all of which involve opening up your beloved C64 and soldering bits and pieces to the mother board for grounding the audio in.

I've just dumbed the process down by doing it at audio cable level.

Analog-X64 · Post by **Analog-X64** » 02/07/2007 - 15:59

OMG!!! It took over 20 Years to figure this out????? hahahahaha.

As part of my job I make all sorts of cables for Industrial Robots to Tool Attachments like Weldguns and one of my enemies is Noise!!!

I'm always grounding contacts and shielding contacts to reduce noise.

The SID chip itself is not perfect and does have some noise, but I never knew that there was an Audio IN contact not being used and sitting there opened... Guess never paid too much attention to it.

Hmmm.... I should buy a whole bunch of these cables and de-noise them and sell them online

naaa.... wife would kill me with so many other projects I have to finish first.

Mayhem · Post by **Mayhem** » 02/07/2007 - 18:03

Wow... that really is a difference

Tron · Post by **Tron** » 02/07/2007 - 18:45

Signifficant difference indeed, Tonka. I'm almost embarassed that us geeks didn't figure this out sooner.

How about modding our 64s?
Drill a hole, cram in a simple switch that internally grounds the audio in, and label the switch "Vintage on/off".

Analog-X64 · Post by **Analog-X64** » 02/07/2007 - 19:13

Tron wrote:Signifficant difference indeed, Tonka. I'm almost embarassed that us geeks didn't figure this out sooner.

I've always used my 1702 Monitor and there was always some Humm but I always thought it was coming out of the Monitor. Never bothered to look further into it. I'm glad some people are tinkering with this stuff and noticed the problem.

Thanks Tonka for bringing this to our attention... so if I ever need to record directly off my C64 I now know what to do.

Razmo · Post by **Razmo** » 02/07/2007 - 19:18

I don't know about the C64 itself increasing the noise level becuase of a non-grounded Audio In pin, but I know, that the SID chip itself has the ability to process external audio signals through the filter, and that the chip has an EXT IN -> FILTER routing switch bit... and just switching the external input to go through the filter eliminates a lot of the noise... I guess it's set as routed AROUND the filter as default, and as very few see the need to change this on a C64, this may be why the noise is most present...

Also sound card like the HardSID has the Audio In pins grounded via a jumper to prevent extra noise...

By the way, if anyone is interrested in seeing how the SID looks under the magnifying glass, and "under the hood", then take a look at:

http://sid.kubarth.com/

A very interresting page with lots of insight for the initiated (you)

Kenz · Post by **Kenz** » 02/07/2007 - 21:57

Right, Tonka says this will be perfectly saf ...

BZZZT! ZZAP! FRRRZT! GLAAARGE!

Just kidding, works a treat!! I'll post a couple of comparison mp3s online tomorrow for you to check out. Nice work Tonk me old mucka!

Analog-X64 · Post by **Analog-X64** » 03/07/2007 - 4:42

The difference in these MP3's examples are amazing, but I wonder if the small bit of noise that is left could be completely reduced by placing a 100ohm Resistor between the pin and ground reducing the current flow, also shunting the Resistor with a small Capacitor wouldn't hurt. Something like this:

Code: Select all

      ____   
2 -+-|____|-+- 5
     100 ohm

Code: Select all

      10 nF
   +---||---+
   |  ____  |
2 -+-|____|-+- 5
     100 ohm

Tonka · Post by **Tonka** » 03/07/2007 - 8:00

Kenz wrote:Right, Tonka says this will be perfectly saf ...

BZZZT! ZZAP! FRRRZT! GLAAARGE!

Just kidding, works a treat!! I'll post a couple of comparison mp3s online tomorrow for you to check out. Nice work Tonk me old mucka!

LOL! I can't help wondering what was happening to you in the original picture to make you pull that face...

*Visualizes Natz in full bondage gear beating Kenz with a rubber chicken*

Yeah - up some empyfwee's M8. Let's have a listen!

Tonka · Post by **Tonka** » 03/07/2007 - 8:12

Analog-X wrote:The difference in these MP3's examples are amazing, but I wonder if the small bit of noise that is left could be completely reduced by placing a 100ohm Resistor between the pin and ground reducing the current flow, also shunting the Resistor with a small Capacitor wouldn't hurt. Something like this:
Code: Select all
      ____   
2 -+-|____|-+- 5
     100 ohm
Code: Select all
      10 nF
   +---||---+
   |  ____  |
2 -+-|____|-+- 5
     100 ohm

It certainly couldn't hurt, though it's not something I could do with my soldering 'skills'!

I think up to a point though, there will always be a degree of noise due to the fact that the chips are such old technology. I guess the best quality we could expect would be the same sort of noise level that the Hardsid gives out, but whether that's possible with a real C64 and all it's noisy old components (including the video output, which I'm sure is the next main culprit next to the audio in), I'm not sure...

Be interested to listen if you do it though...