Driving headphones from the speaker output. What do you reccon?
Aug 22, 2002 at 12:37 AM Thread Starter Post #1 of 11

Ian Milton

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When I had my naim nap 250 and before they had a headphone amp the dealer told me you could drive headphones by wiring up the speaker outputs to a female jack socket thus allowing the power amp to drive the phones.

I have a very good stereo amp now and wondered how this arrangement would work in the real world, and if it would be as good or bettr than a dedicated head amp.

Any comments?

Ian
 
Aug 22, 2002 at 1:59 AM Post #2 of 11

Hirsch

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If you're not careful, you'll need a new set of headphones. Antique Sound Labs makes an adapter, the UHC-Signature, that allows connection of headphones to a speaker amp. You can also rig an attenuator circuit into the cable between amp and headphones, basically just a couple of resistors (I've got a diagram of one designed by Joe Grado somewhere). Bad idea to hook up the headphone directly.

A good speaker amp will also sound good driving headphones, if precautions are taken to make sure the headphone isn't overpowered.
 
Aug 22, 2002 at 3:52 AM Post #3 of 11

dougli

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Hirsch, this is probably a stupid question, but what are the advantages of having a separate headphone amp for driving headphones, versus using the UHC-Signature and a "decent" speaker amp? I realize it depends on which headphone amp versus which speaker amp, but just in general terms, what are the pros and cons? It seems like everyone uses headphones amps, and no one uses the UHC, so there must be some good reasons...
 
Aug 22, 2002 at 5:29 AM Post #4 of 11

Hirsch

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I've only used the UHC-Signature once, and it sounded very good to me. However, usually you'll want to run speakers from your speaker amp as well. That means a second set of speaker cables...one to run from the amp to the UHC-Sig, and a second to run from the UHC Sig to the speakers. Impossible for me, as my speaker cable is internally biwired...and my cable runs about $500-$600 anyway, so at that price it's almost easier to buy another amp than run a second cable pair. Further, there may be some degredation of the sound to the speakers caused by having an inline device...I didn't get the chance to explore this as fully as I would have wanted.

So, one advantage of the headphone amp in my speaker system is that I can run it off of a tape loop, so it doesn't interfere in the signal path to my speakers at all. However, most of my headphone systems are just that: headphone systems. No real need for a speaker amp to drive headphones (AKG-K1000 excepted, of course), and, without the need to generate the amount of power needed for many loudspeakers, the amp designer can usually (not always) give better quality sound for less money by focussing on a headphone-specific product (with correspondingly small wattage demands).
 
Aug 22, 2002 at 12:55 PM Post #6 of 11

Anders

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Many years ago I had a Stax electet phone with an adapter box for connection to speaker output. A technician modified it and added an output for ordinary phones. It didn't work well with the tube amp I had then. Recently, I found this thing deep in my drawers and tested it with my Krell 300i (150W in 8 ohm). It worked surprisingly well. No problem with hiss on Sennheiser HD600 but a little hiss on the more sensitive Audio Technica W11R. On the later I found the sound in some aspects better than on my Headroom MOH, a little warmer and better ambience.
I wondered what would happen if I could get an optimized adapter box. I think there is some resistor in the box that could be optimised for the AT, and change to better cables and plugs than the simple ones in the box.
 
Aug 22, 2002 at 8:00 PM Post #7 of 11

Budgie

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All you really need is a 100 to 150 ohm resistor in series with the hot lead of each side of the headphones.
 
Aug 22, 2002 at 8:29 PM Post #8 of 11

jopi

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Depends on the amp.

With some amps it makes sense to put an 8 Ohm resistor across the speaker terminals to fool the amp into thinking it got a regular speaker load.

You should just try it and hear how it sounds.

Make sure those resistors have high wattage and you may need some heat sinks on top of it.
 
Aug 23, 2002 at 12:25 AM Post #9 of 11

Ian Milton

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Thanks for your comments lads. The amp I have has a massive external power supply, its extremely fast but the volume control is st up in such a way that you have a lot of control between 6 and 12 oclock and does not bite until 3 oclock. I can run it at full volume if I wish too. Do you think this would nullify the need for resistance?

Ian
 
Aug 23, 2002 at 2:40 AM Post #10 of 11

Hirsch

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This is Joe Grado's adapter to use a speaker amp with the HP-1000:

gradospk.jpg
 
Aug 24, 2002 at 12:30 AM Post #11 of 11

Budgie

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On the amps I have tried it on, I usually don't notice any difference loading the amp with 8 ohms, but it certainly can't hurt and may help some amps stay stable. That Grado hookup is interesting, but you may need to fiddle with the 20 ohm resistor value depending on your headphones.
 

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