Project: Making My PowerMac G4 MDD quiet

Noisy computer on my balconySome weeks ago I got my hands on an old PowerMac G4 (Mirror Drive Door). It’s no speed monster but two 1.25 GHz CUPs and 1 GB RAM it’s more than enough for my usage. There’s only one catch – The MDDs are really noisy. For a while I kept it on my balcony but that will only work when it’s not raining (and it rains a lot in Sweden) so I decided to make some modifications to get it quiet.

Computer specifications:

  • Power Macintosh G4 (Mirrored Drive Doors) – model number: M8570
  • 2 x 1.25 GHz G4 PowerPC (7455) CPUs (with ALU sink)
  • 4 x 256 MB (PC2700) RAM (max 2 GB)
  • ATI Radeon 9000 Pro (64 MB)
  • 1 x 120 GB HDD
  • FireWire 800
  • DVD Reader / CD-burner (combo drive)
  • USB 1.1 (I must get hold of an USB2 PCI card)


I started out with some research to find out if there were any existing modifications and found the following great articles:

This was a good starting point. Both for inspiration and information.

I tore apart the mac to find specifications for all my fans. I didn’t search for any disassembly instructions which I recommend you doing. The computer is a pain to work with. I put together data (airflow, noise levels, RPM, etc) for all original fans by reading data sheets from the manufacturers web sites and tried to find replacement fans with similar air flow capacity but with lower noise levels. The specifications for both the original and new fans are put together in this Google Docs spread sheet.

Time for Modding!

Standard thermometerWhen the fans were ordered I started to gather some temperature data with the original configuration (except for the speaker which was removed). I used the program Temperature Monitor to get the CPU and HDD. Since the MDD can’t measure other temperatures I used a standard indoor/outdoor thermometer to measure PSU, room, DVD and PCI temperatures. Just attach the fan with tape where you want to measure. Having some different data was really valuable (as comparison) to find out which fans that are necessary and not. I also measured the energy (Watts) the computer used for normal desktop use to about 120 W and 130 W when burning CDs using a (UPM PM300) power meter. I compared this data to a friend’s new computer (that was quite even though it consumed 200-250 W). I thought that if that computer is quiet mine can be as well.

I’ll describe the different configurations I tried below. All data is available in the following Google Docs spread sheet.

Test 1 – Original configuration apart from removing the speaker to let air flow through that.

One 92 mm fan replacing the 2 60 mm PSU fansTest 2 – I removed the two 60 mm Nidec fans from the PSU and replaced that with one 92 mm Zahlman fan running at 7 V that I attached (temporarily) using tape. The temperatures rose a bit, but not too much whilst the noise level was lower but still too disturbing.

Custom built connector cableTest 3 – I kept the 92 mm fan attached to the PSU (from test 2) and connected the DVD fan at 5 V (instead of original 12 V). To be able to attach the DVD fan to 5 V I built a connector cable using a standard connector socket. You can cut the cables to the fan and solder these on a standard 3 pin fan connector (or 4 pin Molex connector) if you want but I thought it was better to build the custom connector. I noticed a tiny temperature drop but no real drop in noise.

92 mm chassis fan (bottom front)Test 4 – I put the DVD fan back to 12 V and attached a 92 mm fan running at 5 V in the bottom front blowing air in to the computer. I hoped that this could help the CPU fan getting some cold air from outside the chassis and thereby letting it run at as low RPMs as possible (and thereby being quiet). This mod didn’t do any difference in noise or temperature.

Ultraslim 80 mm fan between chassis and CPU sinkTest 5 – When the 92 mm fan (from test 4) didn’t do any difference I wanted to try to put a fan between the CPU sink and the chassis. The idea was that this fan should draw hot air out from the box. I had ordered a slim (15 mm instead of standard 25 mm) 80 mm fan that I hoped to fit perfect. It didn’t. The RAM was in its way. I decided to try to use a Dremel and remove as much plastic as possible from the new fan. After a whole lot of cutting (in the fan) I could attach it (using stripes). I noticed a drop in temperature but no drop in noise. The CPU fan had to be removed.

Test 6 – The final mod! I kept the 80 mm fan (as in test 5). I replaced the 120 mm CPU fan with the PrimeCooler fan. And put back the original two 60 mm fans in the PSU. Since I had ordered a quiet 60 mm fan I replaced the original chassis door fan with that as well (even though it didn’t do any difference). I ran the computer for a while and found out that both noise and temperature was ok so I put back the speaker and crossed my fingers. After some hours I realized that this configuration was more than good enough! The noise level is ok. The computer is not quiet but it doesn’t disturb me anymore and that’s good enough. The temperatures are almost normal so I decided to stop here. For now at least.


It was a fun project to get this computer quiet even though it required about 10 h of work. I can’t really understand why Apple decided to make the computer so loud when it’s possible to make the “windtunnel” macs quiet. It’s like they wanted it to be noisy to make people feel that it was a really powerful computer or something.

If you aren’t into modding I would recommend you just changing the 120 mm Delta CPU fan with a new one and keep an eye on the temperatures. I think that would be enough. If it isn’t try to find a slim 80 mm fan that you attach between the CPU sink and the chassis as well.

Happy modding! Comments and questions are more than welcome.