KRK Speakers \ M-Audio Fast Track Pro \ Apple Tower

Question

Level 1

112 points

KRK Speakers \ M-Audio Fast Track Pro \ Apple Tower

Apologies up front. I realise this is not the most appropriate place in the world to post this particular question ... but I've often found Logic users to have a lot of enormously helpful answers.

Just installed a set of self-powered KRK Rokit 6 speakers. Here is the peculiar thing happening:

The KRK's are plugged into an M-Audio FastTrack Pro ... which is plugged into a Mac Tower with Intel processors.

When I click (highlight) any audio file, say an AIFF, MP3 (Quicktime Player), I immediately get a medium high frequency hum in both speakers, that lasts about ten seconds, then stops.

When I actually PLAY the file the hum starts up again, and continues throughout the play.

If I don't click any audio file, the speakers are more or less quiet, no hum.

If I open Logic Audio, Garage Band, constant hum. Soundtrack Pro doesn't hum when idling, but if I try and play and audio track, hum.

THE SIGNAL STRAIGHT OUT OF THE MAC WORKS FINE.

THERE IS NO HUM ON MY M-AUDIO StudioPro4 speakers.

This is obviously an M-Audio problem.

I bought the speakers instead of an Apogee. Tsk, tsk. But I'd rather keep the speakers for now.

Any ideas would be most appreciated ...

All the best,

Ben

All the best,

Ben

MacBook Pro 2.16 Intel Core Duo, Mac OS X (10.4.11)

Posted on Jun 1, 2009 7:22 PM

Reply

Answer 1

Pancenter

Level 6

14,788 points

Jun 1, 2009 8:41 PM in response to Ben Low

1. Are you using different cables?

2. Are the KRK's plugged into the same wall circuit as the Mac (Tower you say?)

How were the M-Audio studio 4's powered? Were they plugged into a different power outlet or are they powered by a wall wart or the Mac? (usb powered)

pancenter-

Reply

Answer 2

Ben Low Author

Level 1

112 points

Jun 2, 2009 12:06 AM in response to Pancenter

Thank you Pancenter...

I think I got a bit hysterical too quickly. Very good questions you ask. Thank you. The problem was a too long cables between Fast Track Pro and speakers. So dumb. Shorter cable, no problem. I have to go out and buy a medium short cable in the morning to be absolutely sure. (I've got very very short cables, and very very long cables, no medium short ones...)

I should apologize to M-Audio for being snarky.

Thank you for a quick response. You were bang on. And I'm also going to redistribute the power bars I think. I wish there was a device to quickly analyze circuits and wall sockets (maybe there is, I'm a novice in the electrical department).

All the best,

Ben

Reply

Answer 3

Pancenter

Level 6

14,788 points

Jun 2, 2009 12:25 AM in response to Ben Low

Ben Low wrote:
Thank you Pancenter...

I think I got a bit hysterical too quickly. Very good questions you ask. Thank you. The problem was a too long cables between Fast Track Pro and speakers. So dumb. Shorter cable, no problem.

Are you sure it was just cable length, I was thinking you might be using unshielded cables, aka: speaker cables. With any type of powered speaker the cables need to be shielded, preferably a low impedance (TRS, XLR) connection.

So, if you're going out cable purchasing, be sure to get shielded cables.

pancenter-

Reply

Answer 4

Ben Low Author

Level 1

112 points

Jun 2, 2009 9:17 AM in response to Pancenter

You are absolutely right Pancenter, thank you...

I'm going to get a set of TRS cables. This very morning. Excuse my obvious ignorance, I've used XLR's forever, but TRS? The holes look like 1/4 inch or guitar-jacks to me ... if they are simply shielded 1/4 inch cables I've got a huge trunk of them, gold-plated tips, from the old days in the big studios.

??

Ben

Reply

Answer 5

Ben Low Author

Level 1

112 points

Jun 2, 2009 10:07 AM in response to Ben Low

Aha!

It appears I have a box just crammed full of specially made 'TRS' cables, from a studio I had twenty years ago. They work beautifully. No hum. Nada. Lovely sounding monitors. Time to play.

Thank you for your help Pancenter...

Ben

Reply

Answer 6

Pancenter

Level 6

14,788 points

Jun 2, 2009 11:34 AM in response to Ben Low

Ben Low wrote:
You are absolutely right Pancenter, thank you...

I'm going to get a set of TRS cables. This very morning. Excuse my obvious ignorance, I've used XLR's forever, but TRS? The holes look like 1/4 inch or guitar-jacks to me ... if they are simply shielded 1/4 inch cables I've got a huge trunk of them, gold-plated tips, from the old days in the big studios.

TRS are the 1/4" equvilent of low-impedance mic cables. Ground (shield) does not act as a signal carrier as it does in a regular 1/4" guitar cable. However... for this to work properly, both outputs and inputs must be wired for TRS, if not the cables will (usually) behave like standard 1/4" 2-conductor (shield/hot) cable.

pancenter-

Reply