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darcybaston · Nov 2, 2001, 02:48 PM

This is so strange, because it only does this with certain stereo components.

I've tried to use the audio outputs of the iMac to plug into various Sony receivers. The first is a 10 year old Sony STR-AV920, and the second a 1 year old Sony STR-DE435. Using the same cables and 1/8" to RCA converter:

920: no problems at all, works great!

435: all sound has around a >=63hz buzzing hum, loud.

I figured the 435 doesn't like the signal from the iMac and since the 920 doesn't hum, it may be filtering it. So, I decided to use the 920 as a pre-amp and go iMac-920-435 with the 435 as the end of the chain that would amplify the signal. Well, I discovered that the 920 doesn't filter the hum, it passes it along to the 435 as if the 435 was plugged straight into the iMac!

Grrr. I plugged the iMac back into the 435, observed the hum and left it on to see what I could plug/unplug to get this unclean signal thing to disappear.

Turns out that if you turn off the iMac, the hum is louder.

If you unplug the iMac from its power supply, the hum stops!

So the iMac is creating this hum itself, but the STAV920 amplifier doesn't receive it while the STRDE435 does....HELP!!! I need to kill this stupid hum!

Darcy
[email protected]

LeftWingLock · Nov 5, 2001, 03:29 PM

I had the same problem when I switched to a new Sony from my old Kenwood amp. What worked for me was a ground loop insulator. You connect it between the audio output from the mac and the cables from your amp. I got mine at Radio Shack for around $15. I'm at work now but I will post from home tonight with the part number.

[ 11-05-2001: Message edited by: LeftWingLock ]

iPaul UK · Nov 5, 2001, 04:07 PM

Left, is right.. It will be an earthing problem.. Old and new equipment are often earthed in slighly different ways. Plus different equipment has different input impedance's which can also drastically affect hum related problems.

The ground loop insulator should help, although often it's cheaper to experiment with disconnecting the earth lead on bits of equipment one by one until you found what is causing the problem. Although obviously this can create a safty issue! If it's at all possible, see if you can disconnect the earth/shield cable on the Mini jack that your plugging into your iMac. Might be a bit fiddly, but it might well fix the problem. (This does not pose a safty issue either)

cdhostage · Nov 5, 2001, 06:40 PM

I wonder why it's at 63 Hz... When I had humming problems with my iSub, it was always at 60 Hz, which I believe is the frequency of AC on American power lines.

iPaul UK · Nov 5, 2001, 09:37 PM

The frequency can vary a little (Not that it should). Besides, without proper audio test equipment, or an oscilloscope, it's very hard to tell if it really was humming at 63hz

darcybaston · Nov 5, 2001, 11:01 PM

That's right iPaul. My 920 just happened to have a 63hz band display and it was way up there when the hum occurs. It's easy to imagine a 3hz inaccuracy.

I don't feel like opening up the iMac or the Sony, but I'll try a ground loop insulator for sure. Thanks for that peice of information!

Darcy

LeftWingLock · Nov 6, 2001, 12:22 AM

Darcy,

The Radio Shack catalog number is 270-054, Audio System Ground Loop Isolator. I don't remember the exact price but it was under $20.

Good Luck

[ 11-06-2001: Message edited by: LeftWingLock ]

darcybaston · Nov 6, 2001, 12:59 AM

Thanks LeftWingLock! Did yours reduce or completely eliminate the problem?

LeftWingLock · Nov 6, 2001, 01:22 AM

Completely gone. I've got about 25 feet of cable between the iMac and stereo and there is no hum what so ever.

darcybaston · Nov 6, 2001, 08:56 PM

25' and no hum? Well done! I'm just looking to resolve 2' hehe.

darcybaston · Nov 9, 2001, 02:12 PM

Well, got the ground loop at Radio Shack that you suggested and SOLVED! Thank you SO MUCH. It works great, and came with a very handy Y-splitter which is much better than the one I was using.

It was $16.99 Canadian.

Darcy

LeftWingLock · Nov 9, 2001, 04:07 PM

Darcy,

Good, I'm glad that worked for you.

Chad

andymcdeee · Nov 9, 2001, 05:43 PM

awwww, just ready all that makes me feel all gooey inside.

What a happy ending...sniff....

darcybaston · Nov 10, 2001, 12:03 PM

*sniff sniff* I know! People really do like me...

LOL!

omarv · Apr 13, 2002, 05:03 PM

the ground loop insolatore worked for me too. thanks

beetleboy · Apr 18, 2002, 03:04 PM

Thanks!!! The ground loop isolator works perfectly for me too!!! The radio shacl folks were very nice too!

Beetleboy