[71 dB]

So, I expect for someone to correct what I am going to say here, because it is at the edge of my understanding. That is to say, my reach is exceeding my grasp. But it’s a start.

Here are some measurements for the DT 770 250 ohms.

https://reference-audio-analyzer.pro/en/report/hp/beyerdynamic-dt-770-pro-250.php#gsc.tab=0

Scroll a ways down and you will see that the impedance curve is very flat from high to low frequencies.

The impedance curve looks very flat, because the weird choice of logarithmic impedance axis going from 0.25 Ω to 7.9 kΩ! The measured minimum and maximum impedances between 40 Hz and 15 kHz are listed as about 234 Ω and 302 Ω. Now, for a open over the ears headphone this isn't massive variation of impedance, but it isn't "very flat" either. If we want the frequency response error due loed impedance variation with frequency to be 0.5 dB or less, the maximum amp output impedance for this headphone can be:

𝜷 = 10^(0.5 dB/20 dB) ≈ 1.06

Rout ≤ ( Zmax * Zmin * (𝜷 -1) ) / (Zmax - 𝜷 * Zmin) = (302 * 234 * 0.06) / (302 - 1.06 * 234) ≈ 80 Ω.

It is my understanding that the sound of one otherwise suitable amp to another otherwise suitable suitable amp will
therefore be very similar, irrespective of impedance of the amp, because the impedance curve for the headphone is very flat.

The problem here is that the headphone outputs of typical speaker amps are wired from the speaker terminal, but there are serial resistors to limit the power to the headphones. Typically these serial resistors and in the ballpark of 220 to 470 Ω depending on how powerful amp we are talking about. So, connecting DT 770 250 ohms to a speaker amp headphone output is likely to cause frequency response errors larger than 0.5 dB, but no more than a few decibels. So, it is mostly a matter of taste, if it matters. Mid bass gets boosted and higher midrange/lower treble gets attenuated.

One solution is to make a headphone "extension cable" with 100 Ω resistors between the L/R channels and the ground. Together with 220 to 470 Ω "internal" output impedance this creates an effective output impedance of 69-82 Ω for the headphones.

So, I would venture to guess, a good higher-impedance receiver headphone amp would sound very much the same as a 0-impedance headphone amp with these particular headphones.

Not the case unless the impedance curve of the headphone is very flat (and not only on a weirdly chosen axis). Usually open over the head headphones aren't like that, but closed headphones often are.

By contrast, the HD 598 has a less even impedance curve, with the impedence getting highest in the vicinity of the mid-bass. Again, scroll down a ways for the impedance curve.

https://reference-audio-analyzer.pro/en/report/hp/sennheiser-hd-598.php#gsc.tab=0

So, with a higher impedence headphone out, perhaps like a 100 to 120 ohm receiver headphone out, I would expect (and I could very much be wrong about this), I would expect the HD 598s to have somewhat more bass in the area where the impedance peaks, maybe 80 to 100 hertz. As compared to a headphone amp with a near-zero impedance, where I would expect the impedance curve of the headphone not to affect the frequency response.

I use HD 598, and it is one of the most demanding headphone models in regards of output impedance. The 0.5 dB limit for it is only about 5 Ω! So, 10 Ω output impedance causes about 1 dB bass boost. My DIY headphone adapters have output impedances of 1 Ω and 2.2 Ω, but I also tend to use 10 Ω serial resistors with the headphone to intentionally create the 1 dB bass boost. This also makes the sound a bit less controlled and "relaxed."

Now, I prepare to stand corrected. For those in the know, is this sort of correct?

You were on the right track for sure, but I wanted to make some refinements on what you said.

 

[71 dB]

That depends on the headphones. My Yamaha AVR puts out fine output for my purposes. But I have headphones with low impedance and high sensitivity.

The quarter inch jack on receivers are designed for headphones. They should work with all but the most temperamental cans.

Manufacturers don't spend much money on these jacks. Power is not a problem. High output impedance (cheap hack to use the speaker output to drive headphones) of then is. With taylored "extention cable" with suitable resistor solution one can improve the performance of these speaker amp headphone outputs for a given headphone model.

 

[PurpleAngel]

Hi Everyone,

I'm asking this question here because it seems like the right place to dispense with BS and get objective answers. I just want some clarification.

I have a Sony STR DH-190 receiver. I also have a Schiit Magni 2 headphone amp. My main headphones with this setup are Beyerdynamic DT770 Pros, 250ohm version.

I have the Magni plugged into the back of the receiver, but I'm tired of the extra cables and the extra steps, etc. Some folks say the built-in receiver jack is garbage, others say it sounds fine. I *BELIEVE* the Magni does sound better, but I also know that I'm susceptible to bias and I could be full of crap. I have been before, but I've changed a lot of my views on things like DAC quality, bitrates, etc, based on what I learned in this forum.

So objectively, is one of those two options superior? Or is it all marketing or whatever? Do differences in design and engineering really result in different sound?

The Sony STR190 receiver is a $200 unit, so it's going to use the speaker amplifier(s)to also drive the headphone jack, so you going to get a high output impedance (Ohm).
High output impedance causes damping control issues, like a bloated (louder, less detailed) bass (and other sound issues).
Even thou the DT770 is 250-Ohms, it still not enough to compensate for the Sony headphone jacks high output impedance (like maybe 100-Ohms or 150-Ohms or 200-Ohms, etc)
Where as the Schiit Magni 2 output impedance is around 1-Ohm, which is just fine for damping control, with 250-Ohm headphones.

So the Sony has the power the drive 250-Ohm headphones, but it just does so in a more crude way.

 

[71 dB]

Where as the Schiit Magni 2 output impedance is around 1-Ohm, which is just fine for damping control, with 250-Ohm headphones.

"Just fine" is an understatement. 1 Ω output impedance is good for ANY headphone let alone 250 Ω cans. As I calculated above, for the model in question 80 Ω is low enough output impedance and anything below 20 Ω is excellent.

So the Sony has the power the drive 250-Ohm headphones, but it just does so in a more crude way.

Exactly.

 

[gregorio]

So, connecting DT 770 250 ohms to a speaker amp headphone output is likely to cause frequency response errors larger than 0.5 dB, but no more than a few decibels.

I stand corrected, I should have looked at the figures properly!

G

 

[PurpleAngel]

Well, sound wise I think the Sony receiver sounds a little treblier than the Schiit but I could be imagining it. One didn’t sound crazy better, so I feel better about that.

With my DT770s (250ohm), I had the volume at 30 (out of 75) and it was good. With the Schiit, I had it on the high setting and I still needed to crank the knob to around 60%. So I’m guessing the Sony receiver is actually a better match.

However I tried my HD598 (60ohm) and it was a whole other story. The Sony sounded awful and the Schiit sounded great. Huge noticeable difference to me.

So in short, am I correct in saying that I shouldn’t care one bit about how the amplifier is made as long as it matches my headphones well?

For 50-Ohm headphones like the Sennheiser HD598 and good damping control, you would want a headphone jack (head amp) with an output impedance of around 5-Ohms (or less).

 

[71 dB]

For 50-Ohm headphones like the Sennheiser HD598 and good damping control, you would want a headphone jack (head amp) with an output impedance of around 5-Ohms (or less).

All correct, but lets add that for other types of headphones with adequate mechanical damping there is no need for additional electronic damping and the output impedance can be very high (as long and the amp has enough voltage to drive the headphone at reasonable levels).

 

[PurpleAngel]

All correct, but lets add that for other types of headphones with adequate mechanical damping there is no need for additional electronic damping and the output impedance can be very high (as long and the amp has enough voltage to drive the headphone at reasonable levels).

Which other type of headphones?

 

[71 dB]

Which other type of headphones?

Closed for instance or IEM. However, adequate overall damping doesn't guarantee frequency response error below 0.5 dB, which requires that Zmax is only 6 % on less bigger than Zmin.