Topic: HD800 and IEC Standard of 120ohm Output Impedance (Read 7336 times)

Marvey · « **on:** January 11, 2012, 10:05:59 PM »

Much has been said (and it seems forgotten) on HF about the HD800 and output impedance in regards to the 120ohm IEC spec. I only bring this up because of the Donald North 2A3 amp and vintage Sansui Receiver Anax and I heard with the HD800 (which I believe had a ~~120~~ 8 ohm and 680 ohm output impedance.) The HD800 sounded very lush and awesome out of these amps instead of what's typically associated with it (thin, bright, etc.) The HD800 out of the Sansui just sounded flat out bassy.

I'm not going to speak for Donald, but I do recall him mentioning his views on certain headphones (particularly of German manufacture) that seem to sound better with an output impedance of 120ohm. In some ways, this kind of makes sense. I believe IEC is a European standard (USA is ANSI), and I can totally see from a cultural point of view the European engineers designing around this spec.

The measurement below is with a 170ohm resistor and without from a Melos SHA1 (transistor output stage - so output impedance of the amp should be low.) I didn't have the right resistor of proper wattage, so I paralleled a bunch to get a value somewhat close to the target of 120 ohms.

Of course we who can do that math already know this would happen given the shape of the HD800 impedance graph, but I figured a measurement to confirm the math (and subjective impressions) wouldn't hurt. Finally it's important to note that these FR changes would not occur with headphones with flat impedance graphs (LCD2, etc.)

Marvey · « **Reply #1 on:** January 11, 2012, 10:20:03 PM »

Here are the impulse responses (output is inverted.) Effectively the same.

RexAeterna · « **Reply #2 on:** January 12, 2012, 07:51:19 AM »

Anax...he's the guy if i remember has the sansui 5000x receiver? i think i remember telling him why it worked so well with low impedance phones as well, or i'm thinking of another guy maybe. great receiver though. lots of power even for speakers. still one of my favorite right next to my Yamaha R-9.

anyways, great results. i would assume output impedance wasn't really much an issue with most headphones since most of them are mechanically dampened well. i forgot a test while ago i tried to test speakers if they're mechanically well dampened. i think something do with hooking bare wire to the speaker terminals and that will give it 0ohm resistance and can press on the cone to check the resistive force. not sure. good results though.

Questhate · « **Reply #3 on:** January 12, 2012, 09:58:38 PM »

The black line is 120ohms vs. orange at 0ohms?

Marvey · « **Reply #4 on:** January 12, 2012, 11:50:47 PM »

Yup. 170ohms.

Questhate · « **Reply #5 on:** January 13, 2012, 12:21:31 AM »

Hmm... interesting.

It's funny that 0 ohms has been touted as the "holy grail" of amp specs lately, specifically from folks who've read one or two blog posts from a certain electrical engineer and now act as if they're all engineers themselves. I'm all for adding objectivity into the discussion, but some of those guys are the biggest snobs -- especially ones that run an LCD-2 out of their soundcard and then roll their eyes at anyone who *thinks* they notice a difference out of an amp. (sorry for the rant).

These measurements seem to back up that certain headphones may have been tuned such that 0 ohms may not be the most ideal.

On another note, anyone ever tried the Bottlehead Smack? I was looking at it the other day, considering for a future project maybe. It has balanced output and switchable output impedance.

RexAeterna · « **Reply #6 on:** January 13, 2012, 06:13:16 AM »

headphones are not like phonelines. impedance matching is not a must. besides impedance varies with frequency on most if all dynamic drivers since it's very hard to make a voice coil perfectly stay at it's nominal impedance when the voice coil heats up and adds resistance. i tested headphones on close to 0ohm output and up to 680ohm output impedances. not much difference i noticed to be honest, but will admit i notice bit more clarity but that's probably from higher voltages being fed off the speaker outputs. who knows. can be in my head all you know. my one receiver(Sansui 5000x) has a 680ohm output impedance cause it has pair of 680ohm@1/2w resistors in place between the headphone out section and power amp section. did i notice flabby low-end or other claims people made if pairing a headphone with high output impedance? nope, not at all, and i tried multiple impedance headphones ranging from 4ohms to 600ohms off the same output. all came out sounding amazing with great clarity out the headphone out.

n3rdling · « **Reply #7 on:** January 13, 2012, 07:14:20 AM »

Cool stuff

My understanding is that the SHA1 actually has a pretty high output imp for a SS amp. I think around 8 Ohm. Maybe check on something like a Dynalo or B22 and then add the resistor to that since those are essentially 0 Ohm amps.

As for the 120 Ohm European spec, I know that was the standard in the past but is it still used today? Sennheiser used the BCL to demo the HD800 upon release, you'd think they would use something with the 120 Ohm spec if that's what the HD800 was designed to be driven by.

Hi

Marvey · « **Reply #8 on:** January 13, 2012, 07:20:33 AM »

Oh crap. You are 100% correct. No wonder the SHA-1 sounded good with the HD800!

I should use a paralleled desktop CMOY with a JRC4556 then. Should well less than 1/2 ohm. Probably a tenth of that.

As far as the IEC standard. I really don't know. Donald North has stated on record that he felt certain Beyers needed that 120ohm Z. Then again, didn't Sennheiser use the Benchmark at CES when the HD800 was introduced. What is interesting is that many of the amps which have been said to work well with the HD800 have very high Z: Bottlehead Crack, DNA Sonett, etc. Some other amps which I felt worked well were the BA and DNA Stratus with moderately high Z at 16 and 8 ohms respectively. Anax mentioned the Burson worked well too with the HD800. The Burson output Z is 5 ohms. Still moderately high.

Marvey · « **Reply #9 on:** January 13, 2012, 08:01:19 AM »

Here we go. Out of a desktop paralleled CMOY. Output Z should be near 0. With 170ohm and 680ohm resistors in series. The 680 ohms is the simulate the Sansui. And yes, the Sansui receiver does sound like that! Crazy bass.

Author Topic: HD800 and IEC Standard of 120ohm Output Impedance (Read 7336 times)

Marvey

HD800 and IEC Standard of 120ohm Output Impedance

Marvey

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RexAeterna

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Questhate

Re: HD800 and IEC Standard of 120ohm Output Impedance

Marvey

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Questhate

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RexAeterna

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n3rdling

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Marvey

Re: HD800 and IEC Standard of 120ohm Output Impedance

Marvey

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Author Topic: HD800 and IEC Standard of 120ohm Output Impedance (Read 7336 times)