Results 1 to 2 of 2

Thread: Soundcraft MFXi Mixer-Hum in the outputs

  1. #1
    Junior Member
    Join Date
    Jan 2013
    Location
    Picayune, MS
    Posts
    13
    Thumbs Up/Down
    Received: 0/0
    Given: 0/0
    Rep Power
    0

    Soundcraft MFXi Mixer-Hum in the outputs

    I have on the bench a Soundcraft MFXi mixer with 60hz hum in the main and aux outputs. There is nothing connected to the mixer except some headphones. Iíve plugged it into different outlets in different buildings and can still hear the hum in the headphones. Using the AFL buttons Iíve determined all the channels are clean. The hum is only present in the outputs.

    I disassembled the chassis. The switching power supply is mounted and grounded to the bottom half of the chassis while the rest of the circuits are in the top half. The two halves are only connected by the power supply output ribbon cable. When the two halves of the chassis are separated there is no hum. When they touch and the top half is connected to earth ground, the hum returns. Lifting the earth ground doesnít help either.

    Any ideas?

    0 Not allowed! Not allowed!

  2. #2
    Senior Member nevetslab's Avatar
    Join Date
    Apr 2010
    Location
    Burbank, CA
    Posts
    1,306
    Thumbs Up/Down
    Received: 369/1
    Given: 942/1
    Rep Power
    10
    I was curious to see what this was, and fetched a couple images off the internet for visual aids:

    Click image for larger version. 

Name:	mfx8_Mixer.jpg 
Views:	6 
Size:	54.2 KB 
ID:	52499 Click image for larger version. 

Name:	Power Supply-1.jpg 
Views:	6 
Size:	37.5 KB 
ID:	52500 Click image for larger version. 

Name:	Power Supply-2.jpg 
Views:	6 
Size:	34.4 KB 
ID:	52501

    When you have this opened up, does anything look like it's missing, or cable routing suspicious? Any hardware missing? Such as shielding that might have been in place to shield the RFI these switching supplies will generate? I've never been inside this model before. Also, somewhat odd that using the AFL monitoring, all the input channels don't exhibit the hum, while the buss outputs do. Now, buss amps can pickup stray fields and have lots of gain. Cable routing on the power supply from the SMPS to the system may be critical. There is lethal voltage on that power supply, so make sure it's not connected to the AC mains when trying to vary the lead dress in searching for the source of hum injection.

    0 Not allowed! Not allowed!
    Logic is an organized way of going wrong with confidence

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Lexicon Effects Fault on Soundcraft EFX8 Mixer
    By Peter gavin in forum Music Electronics
    Replies: 1
    Last Post: 08-29-2015, 10:36 AM
  2. behringer UB2442fx Pro mixer - clicking / popping noises on outputs
    By jnsomerville in forum Music Electronics
    Replies: 19
    Last Post: 03-21-2015, 08:32 AM
  3. SoundCraft Urei 1603 DJ mixer
    By km6xz in forum Schematic Requests
    Replies: 2
    Last Post: 03-12-2014, 08:20 AM
  4. Old Standel SI15b outputs
    By randomair in forum Maintenance, Troubleshooting & Repair
    Replies: 6
    Last Post: 09-25-2009, 07:40 PM
  5. MX3282A Aux Outputs
    By dawgpilot in forum Music Electronics
    Replies: 1
    Last Post: 09-25-2008, 01:28 AM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •