Sennheiser HD 800 Redux

[Dusty Chalk]

And the HE60 is?

[catscratch]

Ok, maybe "affordable" was not the right word. How about "significantly less likely to make you homeless or divorced compared to the HE90?"

Edited July 30, 2012 by catscratch

[spritzer]

The HE60's are also better... More neutral and with a more honest soundstage. They just love powerful amps and work perfectly on Stax Pro bias outputs (with an extra ballast resistor inside the plug). They also weigh nothing so very, very comfy.

[swt61]

The HD800 - Beta22 combo was also a poor match IMO. Very recessed mids with that combo.

[Tari]

Higher output impedance on the amp actually increases the bass and low mid response. There's some graphs around of 0 vs 120 vs 680, I'll try to dredge them up.

I would not be surprised if Sennheiser's new amp actually hewed to the 120 IEC spec (as Donald North claims ze germans do) as that would accentuate the bass and lower mids, which seems to be what many listeners prefer these days.

[spritzer]

There is certainly something to the IEC standard in all of this but I've never gotten the Sennheiser engineers to reveal anything in my discussions with them. Still, this is easy enough to test with adapters so some cheap TRS plugs are on my shopping list...

Funny story, does anybody know why the new Sennheiser amp has a window on top? To save crazy people like me time ripping it apart... This is what the head of Sennheiser R&D said at the recent distributors meeting but I'm still going to get one and rip it apart...

[nikongod]

High output impedance FTMFW.

If 5.3Kohms is right for STAX, why cant 120 ohms be right for Sennheiser?

[Tari]

I figured the window was just a design choice, although an odd one for a solid state device (why have a window unless it's to see the perty toobs) like the AMR DP-777 or, in the headphone world, the LF. I guess even for solid state its nice to have a window, if just to dispel the notion that amps are boxes of magic.

[The Monkey]

Higher output impedance on the amp actually increases the bass and low mid response.

If correct, can someone explain to me why this is so?

[recstar24]

If correct, can someone explain to me why this is so?

Reduces the damping factor. What is being argued is that it may be possible something like the hd800 is meant to be driven by a higher output than your typical close to zero. The German standard is 120 ohms output, and in my experience makes a lot of the beyers like the 600 ohm dt880 a different beast. I never experienced that with the senn hd600 or 650 and my ears always preferred a lower output impedance.

[Knuckledragger]

For many years I drove a pair of HD-650s with a Headamp GLite, which has ~0 output impedance, IIRC. The combination sounded fantastic to my tin ears.

[The Monkey]

Is output impedance something that is usually disclosed in the specs? And if not, how does one measure it?

[recstar24]

Is output impedance something that is usually disclosed in the specs? And if not, how does one measure it?

Yeah man it's a pretty standard and normal thing that is clearly advertised. It's one of the easier and more objective things to measure hence why it's almost always included, as well as having a pretty direct influence on sound for many cans.

[johnwmclean]

The HD800 - Beta22 combo was also a poor match IMO. Very recessed mids with that combo.

Agreed. The combo is not optimum.

[The Monkey]

So for instance, here are the specs for the Luxman P1-u. What am I looking at for output impedance?

EDIT: Sorry, that didn't paste in the way I'd hoped. Here's the linky.

Continuous power output 2W+2W (8Ω)/1W+1W (16Ω) / 500mW+500mW (32Ω) /

27mW+27mW (600Ω) Input sensitivity/

input impedance Unbalanced 1.0 V/26 kΩ,

balanced 1.0 V/67 kΩ Total harmonic distortion rate 0.0025% (1kHz)

0.02% (20Hz–20kHz) Digital output 1 coaxial line,

1 optical line (TOS-LINK) S/N ratio 115dB Power consumption 19W (Electrical Appliance and Material Safety Law) ,

9W (under no signal) Outside dimensions 400 (W) x 82 (H) x 408 (D) mm

(terminals and knobs included) Weight 8.3Kg

[recstar24]

Ok. That example it isn't particular listed

However, you can tell it is very low and probably near zero based on a few things. One, it's solid state. Two, look at the output numbers, notice how they decrease as the load impedance increases. That means there is maximum power transfer efficiency when driving lower impedances, which we can conclude the amp at maximum has an 8 ohm output impedance but in reality is probably close to zero.

[Tari]

Its a solid state amp - I'd be surprised it it's more than 1 ohm.

Edit - beat to it.

Edited July 30, 2012 by Tari

[mypasswordis]

Output impedance and impedance matching is a lot more complicated than that. Decreasing output impedance usually increases the bass, but it may also increase other higher frequencies and make the frequency response very uneven, depending on both the impedance of the amp and of the headphone (they both vary with frequency). Damping factor is a measure of how well the headphone load is electrically damped by the amp, as opposed to mechanically damped through physical construction of the drivers and surrounding parts. Drastically decreasing damping will be especially apparent at the natural frequency of the driver, which is usually somewhere in the bass. Would be interesting to make some CSD plots at different output impedances.

170kohms/5.3k is still 32+ damping factor, and it's mainly a reactive load anyway. Of course, you could try going in the opposite direction and make a transconductance amplifier like the F1 except with much higher output impedance for headphones. Also the HD800 is a mediocre headphone IMO, the K1000 is much better if you want a dynamic.

[Tyll Hertsens]

Solid state amps can have current limiting (short circuit protection) and feedback resistors that raise the output impedance to 2-8 ohms fairly regularly ... I think.

The 120 Ohm European number exists, but it's for a bullshit reason: Back before "real" headphone amps, receivers used to provide a headphone jack by taking the power amp output and putting it through a resistor to the headphone jack. For that and other reasons, headphone makers HAD to assume they weren't going to get any damping from the amplifier and had to do it for themselves acoustically. DOn't know the exact reason, but 120 Ohms was the number choosen for the "average headphone jack" output impedance.

Dinny, you can measure output impedance by:

1) Set an output reference voltage without any load. (Say, 1 Vrms)

2) Put a resistor as a load.

3)Read new voltage.

4)Calculate output impedance.

For example, if you put on a 1 ohm resistor and the voltage drops in half, then the output impedance is also 1 ohm.

[RudeWolf]

Yeah, only the really crappy solid state designs have output impedance on the high side. My local electronics guys have a few interesting ideas about building an amp with switchable outputs- one super clean solid state with suoerb damping factor, other with higher Z_out and a third with a simple tube output for even order harmonics.

P.S. I recently took a look at some Russian DIY designs and I must say that these guys are pretty damn advanced. Especially the DAC's.

[spritzer]

I'm sure Tyll is right about the origins of that standard. Knowing the Germans they might still be using it though... Does anybody know the spec of the Beyer A1 amp? I couldn't find the schematic either...

170kohms/5.3k is still 32+ damping factor, and it's mainly a reactive load anyway. Of course, you could try going in the opposite direction and make a transconductance amplifier like the F1 except with much higher output impedance for headphones. Also the HD800 is a mediocre headphone IMO, the K1000 is much better if you want a dynamic.

I'm with Justin on this. Those resistors (5.1K actually) are there for short circuit protection should the stator become grounded or touch the housing. This is a problem with the metal case headphones and the previous solution was to wire 10M resistors from the stators to the housing.

Edited July 31, 2012 by spritzer

[The Monkey]

I'm sure Tyll is right about the origins of that standard. Knowing the Germans they might still be using it though... Does anybody know the spec of the Beyer A1 amp? I couldn't find the schematic either...

All I remember is the look of utter confusion on the Beyer rep's face when Colin asked that question at an NYC meet.

[Tari]

The A1 has a 100 ohms output impedance.

[spritzer]

The plot thickens...

All I remember is the look of utter confusion on the Beyer rep's face when Colin asked that question at an NYC meet.

We tend to have that effect on people. Here the Senn reps contact me first and then tell the other Sennheiser distributors stories about "this crazy guy". They really liked the story of me bringing a gigantic 20+kg amp (ESX) to power the HE60's for a comparison against the HD800.

[Tari]

These sales reps are usually chosen for their charisma and the fact that they don't shun sunlight like the engineers. You can tell the Beyer engineers from the rest because they wear surgical blue gloves everywhere they go.

Edited July 31, 2012 by Tari