Mainline & K812 - what impedance?

[Mike Ross]

I believe the K812 is 36Ohm. Would best performance be achieved with low impedance or high?

[fullheadofnothing]

Low

[Mike Ross]

Thanks! Did some reading up on impedance match between amps/headphones, the 1/8 rule, etc. If low impedance is 16 Ohm, the 36 Ohm of the 812 is less than optimum with the 1/8 rule.

A couple of questions from the savvy ones;

* I imagine this rule is true; is it audibly true with an efficient headphone like the 812?
* If it is, would it be straightforward to adjust the low impedance down ~4 Ohms. Even possible? If so, I'd greatly appreciate directions.

Thanks in advance!

Mike

[fullheadofnothing]

A 4Ω output would require changing the output transformers.

What audible problems are you having that lead you to believe your impedance is not low enough?

[Paul Birkeland]

Thanks! Did some reading up on impedance match between amps/headphones, the 1/8 rule, etc. If low impedance is 16 Ohm, the 36 Ohm of the 812 is less than optimum with the 1/8 rule.

A couple of questions from the savvy ones;

* I imagine this rule is true; is it audibly true with an efficient headphone like the 812?
* If it is, would it be straightforward to adjust the low impedance down ~4 Ohms. Even possible? If so, I'd greatly appreciate directions.

Hello Mike,

This has already been factored into the design of the amplifier.  The 16 Ohm tap has been appropriately designed to drive headphones down to 16 Ohms.

-PB

[Mike Ross]

Thanks guys. As to audible problems - no problems per se, just wanting to understand impedance matching, and specifically whether Mainline is a good/great match with the 812's.

Put into context, I'm trying to decide if I'll keep the 812's, and since the chain has much to do with how any headphone performs, I'm trying to calibrate what I'm hearing, or maybe expect to hear.

[Paul Joppa]

Technically, the output impedance  of an SET amp (including the Mainline) is a fraction of the design load impedance - on the 16 ohm setting the actual output impedance is closer to 5 ohms.

[Doc B.]

Yes, they will perform as expected on the low impedance switch setting. If 812s are your thang then I think you will find the combo quite nice.

[dubiousmike]

Interesting thread!  I had no idea the low impedance setting on the mainline was effectively in the single digits.  I previously assumed that part of the reason Senn hd800's sound so good with the mainline was that they were getting a very slight bass boost due to output impedance.  (The guys at changstar have an interesting thread on this with some comparative measurements: http://www.changstar.com/index.php?topic=90.0 )

That said, I have tended to gravitate towards the low ohm setting in my setup - but thought that the switch was toggling between 32 and 64 ohms (based on the description here - http://bottlehead.com/which-amp-should-i-buy-for-my-headphones/ ).  Curiously, what is the effective output impedance on the high setting if the low is actually around 5 ohms?  I also find it interesting that Senn designed its own hp amps with a 40 ohm output notwithstanding the craze on certain sites about trying to minimize output impedance.   But given my general preference for the low setting, it sounds like none of this is really coming into play in terms of my profound enjoyment of my mainline, hd800 combo.  Thanks again for producing such a wonderful kit and for the ongoing education I get to enjoy through this site!

[Mike Ross]

Thanks for chiming in all. Good stuff. As to the K812 with Mainline; I think the Mainline is doing a wonderful job of driving them. With the actual output impedance being close to 5, it's pretty close to optimum formula wise. The 812's are an interesting animal. I was fortunate to have the HE-560 in the house (using a different fully balanced chain), and on quick comparison I requested an RMA for the 812's. Work got in the way of getting them out the door, and that afforded more time to listen to them. Now, I'm probably going to hang on to them. I think it took me awhile to get used to the combination of Mainline sound with their spatial presentation.

Listening now to Steely Dan 'Two Against Nature' right now, and I'm very much enjoying the sound.