Yamaha A-S700 Headphone out: What does this mean?

[L5730]

Hi all,
Apologies if this thread should go under the noob section or under some other. Seeing as it's an amp and the socket is for headphones, I chucked it in here.

The manual shows this. I know, lots of useful info there!

No sure what they are saying, the headphone amp impedance is 470 ohms ?!?
Seems an awfully cryptic way of giving stats.

I have some Takstar Pro 82s on order, they'll work of course.

 

[sergeauckland]

I take that to mean the headphone output provides 470mV from a source impedance of 470 ohms. What voltage you get into the headphones then depends on the headphones' own impedance. It also suggests that they have a separate headphone amplifier, not just a resistor on the main loudspeaker outputs, but of course that could be wrong...marketing departments generally write the specs, not the engineers.

S.

 

[Fluffy]

marketing departments generally write the specs, not the engineers.

That's the sad part about these kind of receivers. In the few times I tried to look up the specs of a headphone out in an AV receiver (and integrated that are meant mostly for stereo like this one), I haven't found really useful information. I think the headphone outputs on those receivers are mostly an afterthought, probably engineered to be "good enough" to people who occasionally plug in headphones when their family is sleeping or something.

 

[L5730]

It wouldn't surprise me to find out that the headphone out is exactly that, a whacked on utility rather than a nicely crafted and thought out part of the design.
We've a Yamaha CD player from the mid 90s and that has it's own headphone output. The similar tier amplifier at the time also had a headphone output. The CD-S700 (same family/era as this amp) does not have a headphone output at all, and the USB input is not the most intelligently designed or thought out (not even LPCM WAV support, no playlist support).

Ah from an AudioKarma post:

I had inquired about the design, and Yamaha provided an informative response. The 700 uses a feed directly from the power amp, while the 1000 uses a chip (read op-amp, I gather). Thus, the 700 uses the "classic" approach employed on many fine pieces of vintage equipment--a feed from the power amp with power resistors to lower the power for the headamp.

https://audiokarma.org/forums/index.php?threads/yamaha-a-s700-or-the-onkyo-a-9050.505593/

So yes, the typical tap the power amp and shove a resistor on it approach that is employed most of the time.
It'll work, but there are better options for powering headphones.

 

[sergeauckland]

One issue I have with that spec and the idea that it's just a 470 ohm resistor, that it quotes a voltage output. If it's just a resistor, then with a high impedance load, the voltage will be whatever the amplifier's maximum voltage is. In the case of the AS-700, it gives some 32v out at full power so that's what would be at the headphone output with a high impedance load. With a 470 ohm in series and a 32 ohm load, the maximum voltage will be around 2v. With a 75 ohm load, it'll be 4.4v, and with a 600 ohm load around 18v. The spec, therefore is pretty much meaningless, if the headphone output is derived from the 'speaker outputs with just a series resistor.

S.

 

[pozz]

The headphone out is exactly that: an afterthought. See @trl's review, teardown and measurements here: https://www.audiosciencereview.com/...ts-about-the-internals-few-measurements.9459/