Alesis MultiMix Hum

The following information addresses how to repair a power supply issue with the Alesis MultiMix. I first noticed the problem about a 7 months ago.

Symptoms are as follows:

  • Clip & Sig LED are on solid (FX section)
  • XLR Inputs hum
FX Section
Here are the LED’s lit up. If you try using the FX section, it hums.

The XLR input hum is the worst problem in my case. So after some Googling and reading, problem is that 2 of the power supply capacitors are blown. To change the capacitors is fairly simple. First thing is to remove the screws on the bottom and the back of the mixer as shown below.

Rear Screws
Remove all the screws on the bottom of the mixer
Three rear screws on the mixer.

Now that the rear plate is loose, disconnect the black 8 pin connector to the power supply, then disconnect the 2 pin SPDIF connection to the main bored on the right.

Disconnect the black 8 pin connector.
Disconnect the 2 pin SPDIF connector.

There should be enough room to get a fillips screw driver in there and remove the power supply bored. But first the connecting wires need to be disconnected.

From left to right:

  • Power Connector
  • Power on/off switch
  • Phantom Power switch
  • Main power to the the mixer
Next step is to remove the 4 screws from the power supply bored. You will need to pry off the components from the heat sink.
Right capacitor has the bottom blown right out of it & the left one is leaking at the top.

As many posts online have said, both capacitors are going to need changing at the same time. Here are the specs of the capacitors. Voltage doesn’t matter to much.

Right Capacitor – 1000uf @ 35V

Left Capacitor – 2200uf @ 35V

My local electronics shop had the right capacitor in stock but I had to use a 50V cap on the left one. It was a little bit bigger so my new cap sits a little sideways on the bored.

New capacitors are installed. You can see the left cap had to be a little to the left so the top part of the mixer would clear.

That is it. You have now successfully change the 2 capacitors causing the hum in your mixer. Follow these steps backwards to put your mixer back together.  Be sure to evenly apply pressure  to the heat sink. Also, when putting the base plate back in, be patient, it will slid in together easily.