Using power amps for headphones

[Cbdb2]

I just bought a Wiim amp ultra and one of the main reasons many people say they wont buy one is no headphone out. Ive been in recording studios where they use this kind of adapter to power a dozen headphones from a large amp (ive seen 400watt Brystons used). Here is an easy cheap DIY solution. With a few dollars and a soldering iron you can make an adapter that hooks up to the speaker outputs of any amp. So it saves you buying a headphone amp. You can go straight into HPs with no loss in fidelity except more noise but you risk damaging the HPs and your ears so not recomended.

From Elliot Sound products: https://sound-au.com/project100.htm

Make sure to head the warnings

 

[wwenze]

1) Can't do that with bridged amp like Wiim amp ultra - Which is ironic because it is the warning that is stated in the webpage
2) Speaker amps have higher noise than headphone amps
3) Not recommended to do that with class D amp like Wiim amp ultra due to RF noise

 

[Cbdb2]

1) Did not know the Wiim is a bridged amp. Thanks, thats good to know, supprised I have not seen that bit of info anywhere.
2)The S/N will be the same as the amps, your reducing the noise as much as the signal.
3)How does RF noise at -60? db matter when HP FR dosnt go past 20something khz?

 

[Curupira]

While it's possible and used to be done when high power headphone amplifiers weren't so commonplace (or were expensive), it is not recommended on the majority of cheap power amplifiers, as most of them are Class D amplifiers made to be used with low impedance loads (4 - 8 ohm speakers), not a headphone's >32 ohm impedance. Even with the recommended loads, Class D amplifiers have significant distortion on the higher frequencies, as per below.

This load dependence gets worse when you go to 8ohm and beyond, eventually skewing the FR of the headphone up top. While the Wiim Ultra is not the worst offender at this (its pretty flat for 4ohms to at least 20khz), there are some that will tilt the FR a lot.

Given that most headphones today are pretty efficient and that dedicated amplifiers are cheaper than ever, I see little sense in investing in this solution.

 

[DonH56]

In the past a lot of headphone outputs were tapped off the speaker outputs, not always even padded down. The effective SNR using a power amp is probably much lower than using a headphone amp or low-power amp since the power level is so low. You could use a standard H-pad attenuator (with the output resistors just wires) with a bridged amp, and use power resistors in the attenuator to keep the impedance low enough to keep the amp stable if that is an issue. That is what I did in the past when I did not have (or built) a headphone amplifier (typically an op-amp with a power op-amp output buffer). Even single-ended, non-bridged amps would sometimes have the negative lead floating or grounded by a low-value resistor for various reasons, so I always used an H instead of T circuit.

 

[egellings]

1) Can't do that with bridged amp like Wiim amp ultra - Which is ironic because it is the warning that is stated in the webpage
2) Speaker amps have higher noise than headphone amps
3) Not recommended to do that with class D amp like Wiim amp ultra due to RF noise

Another problem is the power available; make a mistake with the volume control or input source connection and pop go the headphones and the eardrums.

 

[wwenze]

Even with a H-pad, the best case SINAD you can get with speaker amps is like 80-100dB since that is the value you get from a TPA3255 with speakers. And that's with the H-pad dissipating 5W of heat per channel. SINAD is even worse without the H-pad.

3)How does RF noise at -60? db matter when HP FR dosnt go past 20something khz?

It's not audible, but the FCC will want to pay you a visit since the attenuation of the RF switching noise by the output filter depends on the load impedance, and it radiates out from the cable.

Switching noise residue does not depend on volume control btw since it depends on the voltage of the power supply, switching frequency and how you switch. Something to think about for people who buy and use extremely overly powerful class D amps.