Using Low Impedance Headphones

Question

Using Low Impedance Headphones

I have a pair of Stax electrostatic Earspeakers (headphones), which are driven from an interface box (totally passive and un-powered) to drive the earspeakers. The interface box is normally connected to an amplifier using the speaker output connection (4/8 ohm). They require a reasonable amount of power to drive them to useful listening levels. Later models of this interface box are mains powered with line inputs, but mine are self powered and operate directly from the speaker outputs of the amplifier and loads the amp as would a pair of speakers.

Is it possible to connect such a low impedance device (the interface box) to the audio output socket on the iMac? I have the previous version (24in intel core duo).

I have on order a small stereo power amplifier which I know will work (15W/per channel) and I am planning to use that.
The other option I am considering is using the Fubar USB converter to line audio to then drive this amplifier.

I cannot find any technical details on the output (impedance) capabilities of the audio output for the iMac.

So, my original question stands. Can the iMac drive the interface box (8ohm input)directly from the audio outconnector?
Regards
Steve Bruhn

Two iMac 24in Intel Core2 duo, G5 iMac, Intel Mac Mini, variety of screens., Mac OS X (10.6)

Posted on Nov 15, 2009 5:18 PM

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Answer 1

den.thed

Level 10

91,216 points

Nov 15, 2009 6:34 PM in response to Stephen Bruhn

Hi Steve

It should work just fine, the 24" iMac's have an Internal 24-watt digital amplifier that supplies full Line Level Output. The only thing you may need is a 3.5mm to RCA adapter or Y-cable if your sound system only has RCA inputs.

The following adapter and Y-cable are examples that can be found at any electronic's retailer.
http://www.cablestogo.com/product.asp?cat%5Fid=118&sku=40645
http://www.cablestogo.com/product.asp?cat_id=2009&sku=40422&relatedItem=true

Dennis

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Answer 2

Nov 15, 2009 7:18 PM in response to den.thed

Hi Dennis,

Thanks for the reply. My main question was in relation to the audio output ability to drive 8ohm speakers, rather than line out levels, or higher impedance headphones. Yes, I realise the iMac has that 27W amplifier, but not sure if this power is available at that audio out socket. Seems a lot of power to try and pump through a 3.5mm plug, if you get what I mean. Normally speaker connections are via screw terminals even on low power amps (current is quite high at these power levels, especially at 4ohm).

I am getting the feeling that the iMac digital amp is mainly designed to drive the internal speakers at that power level, rather then trying to put 27W to external speakers through the 3.5mm audio out socket.

Thanks for the quick post. Much appreciated.
Best regards

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Answer 3

den.thed

Level 10

91,216 points

Nov 15, 2009 7:29 PM in response to Stephen Bruhn

Good point, you would surely get better results from a pre amp or stereo receiver!

For more info scroll down in the > [Audio Product-Specific Details|http://developer.apple.com/legacy/mac/library/documentation/Hardware/Co nceptual/HWTech Audio/Articles/Audioimplementation.html] article and have a look in the iMac section for the full details.

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Answer 4

Nov 15, 2009 11:51 PM in response to den.thed

Hi Dennis,

Thanks so much for the link! This is an excellent reference. Didn't know it existed.
Yes, it has answered my question.

Best Regards
Steve

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Answer 5

den.thed

Level 10

91,216 points

Nov 16, 2009 3:53 PM in response to Stephen Bruhn

Your welcome!

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