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I've been looking at getting some cans for my living room (mostly gaming/movies, some music) and I'm pretty sold on the K712s or K702 Annies. I'd like to use them with my Yamaha RX-V371 receiver, as I've read Silent Cinema is actually pretty good. The problem is my receiver's headphone amp has an output impedance of 470 ohms, and the AKGs are around 60 ohms. I know a lot of people are double amping their MixAmps and was thinking I could probably do the same with my receiver and an Objective2.
 
Will there be any problems using my V371's headphone output as the source for an O2? The manual says it's rated 100 mV/470 Ohms.
Also, is it okay to leave the O2's gain/volume set relatively high so I can still use my receiver's remote to adjust the volume? I'm lazy and don't want to have to get up

 

[PurpleAngel]

I believe the Yamaha RX-V371 manual is saying it provides headphones with 100mV of power at 470-Ohms.
So if you plugged in headphones rated at 470-Ohms, the Yamaha would provide the headphones with 100mV of power.
I would think your Yamaha's headphone output impedance would not be any higher then 100-Ohms.
And I would guess(?) it's under 100-Ohms.
 
I plug my 50-Ohm HD558s into my Yamaha RX-V671 receiver and they sound fairly good.
Where as your 62-Ohm K712s should deal better with high impedance headphone jacks then my HD558s
So I'm thinking you will not need to buy a separate headphone amplifier.

 

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You could be right. Here's what it says in the specs section of my manual:

 - Headphone Jack Rated Ouput/Impedance
AV5, etc. (1 kHz, 50 mV, 8 ohm).................................................100 mV/470 ohm

 
I guess I'm a little confused on which is the load impedance and which is the output impedance. If you look at the other specs, like the power ratings for the speaker outputs, it appears that the load impedance is on the left and the output impedance would be on the right. 8 ohm would be shockingly low too, since I'm pretty sure this unit just uses resistors on one of the main amp circuits to power the headphones, which usually results in a very high output impedance.
 
Here's a link to the manual if anybody is willing to help me try to decipher this; it's on page 69: http://download.yamaha.com/api/asset/file/?language=en&site=usa.yamaha.com&asset_id=46217

 

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Just took a peek at the V671 manual.

 - Headphone Jack Rated Ouput/Impedance AV5, etc. (1 kHz, 50 mV, 8 ohm).................................................100 mV/560 ohm

 
I think the numbers on the right are the output impedance. It would make sense that the V671 would have a higher output impedance, since it's a more powerful amp that needs more resistance to bring the headphone output down to the same level. That being said, if you're enjoying your 50 ohm HD558s with 560 ohm output impedance, then maybe hooking the 60 ohm AKGs up to 470 ohm output might actually sound pretty good.
 
Really appreciate the input, PurpleAngel. Maybe I should hold off on buying the amp at first to see how they sound directly powered by the Yamaha.
 
I'm still curious about my two original questions in case I decide to get the O2, though.

 

[PurpleAngel]

  Just took a peek at the V671 manual.
 
I think the numbers on the right are the output impedance. It would make sense that the V671 would have a higher output impedance, since it's a more powerful amp that needs more resistance to bring the headphone output down to the same level. That being said, if you're enjoying your 50 ohm HD558s with 560 ohm output impedance, then maybe hooking the 60 ohm AKGs up to 470 ohm output might actually sound pretty good.
 
Really appreciate the input, PurpleAngel. Maybe I should hold off on buying the amp at first to see how they sound directly powered by the Yamaha.
 
I'm still curious about my two original questions in case I decide to get the O2, though.

 
I'm sure my RX-V671 does not have a high output impedance, it just outputs more voltage for driving headphones.
So it's feeding around 100mV of power to my 600-Ohm headphones (DT880 & DT990).
I'm sure with lower impedance headphones it provides well more then 100mV.
 
But yea, try plugging the AKGs directly into the Yamaha, see if you like it.

 

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Welp, I just placed an order for some Annies off Amazon I'm excited. I guess I'll just wait and order the O2 if they sound too muddy or congested with the V371, assuming nobody chimes in on any issues double amping.
 
Based on my research, it sounds like double amping is generally fine so long as neither of the amps are particularly noisy or distorted. I'm mostly worried about my second question, since it sounds like most people recommend turning the first amp (the Yamaha in this case) up to 3/4 volume or so and leaving it there. The reasoning seems to be the second amp amplifies the noise from the first amp, so you want the best signal noise ratio you can get out of the first amp, which is usually at higher output levels. Does anybody have any experience with this? Is the difference really that noticeable if I leave the second amp turned up and adjust the volume with the first amp?

 

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I just looked at the Yamaha A3030 manual. The A3030's rating says 150 mV/100 ohms and it actually specifies that 100 ohms is the output impedance. They also use 8 ohms as the standard load impedance for just about all of the other ratings. Now I'm fairly certain that 470 ohms is my output impedance and 8 ohms is most likely the load impedance used for the power rating.
 
But I also got the AKGs today, and you were right; they don't sound noticeably bad straight off the receiver. Knowing how pathetic my damping factor is, though, I can't help but wonder how they'd sound with a decent headphone amp.

 

[PurpleAngel]

  I just looked at the Yamaha A3030 manual. The A3030's rating says 150 mV/100 ohms and it actually specifies that 100 ohms is the output impedance. They also use 8 ohms as the standard load impedance for just about all of the other ratings. Now I'm fairly certain that 470 ohms is my output impedance and 8 ohms is most likely the load impedance used for the power rating.
 
But I also got the AKGs today, and you were right, they don't sound noticeably bad straight off the receiver. Knowing how bad my damping factor is, though, I can't help but wonder how they'd sound with a proper amp.

 
A low impedance headphone amplifier might(?) improve the detail in the audio.
But maybe hold off on buying on buying a headphone amplifier and see if the AKG improve after 50 hours of use.

 

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I just realized I forgot to update this thread in case anybody else is interested in my findings.
 
I did end up purchasing an O2 to experiment with. When double amping, the difference is marginal at best. It might even just be placebo effect, since I'd expect the O2 to sound better with the lower output impedance. I haven't tried a blind A/B test. But it seems like the whole frequency range gets maybe slightly more controlled and the imaging might be a tiny bit sharper. I also noticed that I get roughly the same amount of usable power from either plugging straight into the receiver or double amping with the O2. I can go louder when using the O2, but if I go much louder than just plugging straight into the receiver, the noise floor starts to creep up pretty significantly. The receiver gets plenty loud for me anyway, so it's not a problem.
 
A while back, I tried contracting Yamaha for help deciphering the spec for my receiver. I got a couple ambiguously worded responses and when I started asking for clarification I stopped hearing back. I didn't get the impression the customer support rep really knew what he was talking about. So I'm still not sure whether the receiver's output impedance really is 470 ohms or if that's actually the load impedance for their power rating, but the Annies do sound great plugged straight into the Yamaha nonetheless.

 

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Out of curiosity, I did a quick test comparing my Apple Earpods connected to the receiver vs the receiver + O2, and I found the difference is much more significant especially at higher volumes. The Yamaha easily loses control over the bass resulting in a very muddy, somewhat distorted sound at times. While the Earpods still sound very thin with the O2, the bass no longer distorts the sound.
 
Perhaps the lower impedance of the Earpods (~40 ohms vs the ~65 ohm AKGs) might explain the difference. Might be interesting to experiment with my M50s next, since they have even lower impedance. I've been keeping them at work lately, so I don't know when I'll get around to it.