[Sugano-san]

As I am not a technician, I would appreciate some expert feedback on the following:

When driving headphones with the power amp of your home rig, what measures are required/indispensable (besides a proper connection) and why? Isn't it sufficient to be very, very careful with the volume pot when using a power amp to drive headphones? What role (if any) does the headphones' impedance play? What's the purpose (if any) of add-on transformers in this context?

Specifically:

The AKG K-1000s are headphones that were originally designed to be connected to power amps. It says so in AKG's manual (notwithstanding that there are dedicated headphone amps that yield very good results, such as the SAC K-1000 amp or the RKV MkII, which, after all, are only small power amps that are designed to work well with an impedance above 100 Ohms). It works. I've tried it.

I have confirmed the aforementioned claim by hooking up my K-1000s to (i) a 2 x 20 W EAR V20 tube amp, and (ii) a Musical Fidelity Nu-Vista Integrated amp, which delivers in excess of 250 Wpc into 8 Ohms. (I am aware that the K-1000's impedance is 120 Ohms and that because of that the available power from the amp is considerably lower than into 8 Ohms.)

Now I see this product from Antique Sound Labs, and it's a transformer, which is supposed to go between output of power amp and headphones, and the headphones in that picture are HD600s.

The HD600s have an impedance of 300 Ohms, and that would lead me to the conclusion that the output available from the respective power amp would be even lower than with the K-1000s.

On the other hand, the HD600s' sensitivity is much higher than that of the K-1000s. This means that every mW that goes into the headphones results in much higher volume because of the cans' higher efficiency.

But then, isn't this just a question of being really careful with the volume control? Surely, hooking up HD600s to a 2 x 20W amp would not becessarily mean frying the headphones, or am I fundamentally wrong? And what about more powerful amps?

In other words, is there a technical necessity for transformers such as the Antique Sound Labs product? What do they do? Is that circuit just for safety and convenience? Or will hooking up "normal" (i.e. non-K-1000) headphones to power amps necessarily ruin your cans?

I would guess that the answer depends also on the impedance of the headphones, i.e. the operation would be much more risky with 16 or 32 Ohm cans than with 120 or 300 Ohms.

Thanks for your feedback.

 

[Dusty Chalk]

Some amps don't like driving an open connection. If the impedance of the headphones is too high, then it will be like driving an open connection. Hence, bad.

That's just one example. The short answer is, it depends on the amp.

Here's another: depending on the combination, you may be driving your headphones to audible volumes at the bottom end of the volume dial, at which it is least accurate.

 

[ManiacSmile]

In a way what you're thinking is called impedance matching and aside from having easier volume adjustment, there may be no audible difference - as Dusty Chalk said, it depends on the amps topology.

 

[Joe Lau]

It is major for converet you amplifiers to Headphone with safety power to avoid damage your headphone and your ears. It is difference from jusr series a resistors with headphone. It will not increase output impedance and not limited in current.