Amp/Headphone Impedance Matching
Mar 13, 2002 at 8:39 PM Thread Starter Post #1 of 6

Ross

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I'm not quite sure where this question belongs, so I'll post it here.

In the Headroom forum, Tyll mentions that the new 9v Airhead, designed for headphones of 150 ohms+, will work with Grados and other low impedance headphones with the 120 ohm adapter available with the Porta Corda.

Does this mean that any headphone amp designed for headphones of 250 ohms or more (and I have several of these) will work with Grados using a 120 ohm adapter?

What is the ideal resistance of an adapter for this purpose? Is there a formula? Is it simply a question of adding the headphone impedance to the adapter resistance (e.g. Grado + adapter = 152 ohms)?

What happens if you use 32 ohm headphones on an amp designed to drive 250 ohm headphones? Whenever I've tried this, it sounds okay. Is there damage being done to the amp? Does it detrimentally affect the sound?

Any help with these questions would be appreciated.

Ross
 
Mar 13, 2002 at 9:29 PM Post #2 of 6

danny

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Ross,

Tyll DID NOT say that the 9V airhead needed a 120 ohm adaptor to drive low impedance phones. That was a repeat of a question by Joe Bloggs. None of the versions of the airhead need an adapror to drive low impedance phones. As far as the other issues, I will let Tyll, Todd, or Mike address them. But I will repeat, NONE of the Airheads need an adaprot to drive low (or high) impedance phones.

Hope this helps.
 
Mar 13, 2002 at 11:48 PM Post #3 of 6

Ross

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Thanks, Danny, but I'm still a bit confused. I don't understand why the 9v Airhead is recommended for 150 ohm headphones.

I also don't understand what happens when you use low impedance headphones with an amp designed to drive high impedance headphones, and whether this degrades either the amp or the sound quality.

I would also like to know whether it is possible to use some kind of adapter to use low impedance headphones on an amp designed for high impedance headphones.

I'm hoping there are enough people on the forum with the technical expertise who can answer these questions.

Ross
 
Mar 14, 2002 at 12:19 AM Post #4 of 6

slindeman

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My limited understanding:

Setting aside sensitivity for the moment, higher impedance headphones require more voltage swing, while lower impedance headphones require more current. The 9V battery obviously provides more voltage to the opamps than 3 AA batteries (4.5V) would, but the 3 AA batteries have more mAH for a longer battery life. So, if you are just using Grados, which use a lot of current and don't require much voltage swing, you are better off going with the 3 AA battery version, because the amp would work longer before you would need to change batteries, and the sound would likely not improve by feeding the opamps the extra voltage that the 9V provides. Using the 3 AA version with high impedance headphones like HD600 would be like driving your HD600 with a portable source (low voltage swing capability) and would probably sound kind of lifeless.

My suggestion would be to get the 9V if you want it to drive all sorts of headphones, the 3 AA if it is only for low impedance or very high sensitivity headphones. And I think it is a good thing they are eliminating the DC-DC converter of the old models.
 
Mar 15, 2002 at 10:10 PM Post #5 of 6

danny

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Scott,

A very good answer, especially as none had been shipped when you wrote it. However, all of the new models of the airhead not only have an LED
biggrin.gif
, but they can take up to a 15V DC supply for their external supply. So the people who use low impedance phones when traveling, and want to use the high impedance phones at their house/work etc., can get the 4.5 Volt version, and plug into a 15V wall wart, and get the best of both worlds.

Please note, that the external supply can be up to 15 Volts, any DC supply between 5 Volts and 15 Volts will work just fine.
 
Mar 16, 2002 at 7:21 AM Post #6 of 6

Driftwood

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wow! those new airheads sound really cool!

very versatile... and the addition of an led seems like it will be a very welcome addition.

I like that there are a couple different versions, now you can get what suits you best.

Driftwood
 

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