[megabigeye]

Actually, I believe the Crack's output impedance is closer to 120Ω, as measured by Tyll at InnerFidelity. I regard the 8:1 damping factor to be a rule of thumb rather than law.

 

[megabigeye]

Eh. Double post. Stupid phone. Stupid internet. Stupid, impatient self.

 

[DavidA]

Your statments raises some questions. What is the 75 ohms doing? 75 ohms is 25% of 300 ohms, and general rule of thumb is less than of equal to 12.5% of total ohmage.

Another question is what specifically is synergy? It is a vague term that doesn't explain.

What is actually going on?

Does my 2 ohm output impedance solid-state sound worse or more proper?

As explained to me by some with more knowledge than I, dynamic drivers don't have a flat impedance like planar drivers so how a amp "see" it as the impedance of the driver varies with frequency is what "synergy" is being talked about IIRC. And I've been told that there is also a possibility of over damping a driver and like @megabigeye noted the 1/8 ratio is a rule of thumb and not a hard and fast rule. Another thing about "synergy" is over the years I've found that some pairings of amp and headphone just seem to work better than others, the effect of an amps output impedance can have quite an effect on the sound, to me there is no good or bad most of the time, just differences/preferences and I've found that I have a lot more to learn in this crazy hobby and having a SO that understands this and even shares the passion for good/great audio is as good as it gets. I hope another can chime in on what "synergy" is since I know my explanation is only my thoughts and other may have a much better way of saying/explaining it.

Actually, I believe the Crack's output impedance is closer to 120Ω, as measured by Tyll at InnerFidelity. I regard the 8:1 damping factor to be a rule of thumb rather than law.

The BH Crack's output impedance is dependent on the power/output tube used, and IIRC the stock 6080 is rated around 120ohms. My choice of power tubes are TS5998 or WE421A which are known for having lower output impedance of 70-75ohm I'm told by those on the BH Crack thread and there are some tubes that have even higher output impedance than 120ohms so this could be why some say the BH Crack is really good while others say its just okay. WARNING: tube rolling is a very deep rabbit hole but is quite fun. I think the cost of the tubes I have makes the cost of the BH Crack kit the cheap part of the investment by a 4 to 1 margin by my estimates. One nice point is that my Ember uses the same tubes as my BH Crack for drivers and can also share tubes with my Lyr2

 

[Pharmaboy]

Please indulge the electrically/electronically impaired for a moment...this 1 to 8 ratio: does it suggest that optimum impedance match is an amp w/an output impedance 1/8th the impedance of the headphone?

Interestingly enough, I can't find an output impedance spec for my Woo WA3 (the only OTL/higher output impedance amp I have).

 

[megabigeye]

Please indulge the electrically/electronically impaired for a moment...this 1 to 8 ratio: does it suggest that optimum impedance match is an amp w/an output impedance 1/8th the impedance of the headphone?

Yes.

 

[jasonb]

After all these years, I still can't decide if I like my HD650 more, or my Q701 (with a bass boost) more. I plan to continue to own both, but I can't decide which I like better.

 

[megabigeye]

After all these years, I still can't decide if I like my HD650 more, or my Q701 (with a bass boost) more. I plan to continue to own both, but I can't decide which I like better.

Similarly, my mom can't decide if she loves me most because I was the first boy, or if she loves her grandson the most because he's the youngest boy. (<-- because there's no really ironic looking smiley)

 

[koover]

I saw love them both equally and they’ll sound that much better to you.

 

[Deftone]

After all these years, I still can't decide if I like my HD650 more, or my Q701 (with a bass boost) more. I plan to continue to own both, but I can't decide which I like better.

Run them both at the same time and put one HD650 earcup on left ear and Q701 on right ear.

 

[jasonb]

Run them both at the same time and put one HD650 earcup on left ear and Q701 on right ear.

Good plan

 

[megabigeye]

I say listen to the Q701. Take it out for dinner and a movie. Buy it a fancy bottle of wine. Tell it what a great time you're having. Keep talking to it about how romantic you find the HD 650.

Spend some time with the HD 650. Take it for a walk by the river. Do something off the cuff and whimsical. Maybe get a little too drunk and go dancing. Keep mentioning your cute neon friend from Austria.

Introduce the Q701 and HD 650. Just all three of you can hang together. See if maybe they'd be into... you know... maybe one of them on the right ear, the other one on the left ear. Maybe you could even, you know, if they're into it, they could listen to each other and you could, you know, listen to them listening to each other.

I'm sure Tucker Max has a story about this exact scenario.

 

[megabigeye]

I feel like my DT 1990 and HD 650 probably just gave each other a rather long and uncomfortable look from across the room.

 

[gefski]

Please indulge the electrically/electronically impaired for a moment...this 1 to 8 ratio: does it suggest that optimum impedance match is an amp w/an output impedance 1/8th the impedance of the headphone?

Interestingly enough, I can't find an output impedance spec for my Woo WA3 (the only OTL/higher output impedance amp I have).

Right, but they provide a very useful look at power output into various impedances. I was surprised to see that Woo states "OK" for 30 to 600 ohms. Also looks like 300 is a sweet spot. My WA6+ puts out more power into all impedances, but I would now like to scare up a WA3 among Seattle head-fiers for some quality listening. Wouldn't be surprised if the WA3 was more "pure".

Have done similar listening at the Bottlehead Spring meet with Crack and S.E.X.

 

[castleofargh]

Please indulge the electrically/electronically impaired for a moment...this 1 to 8 ratio: does it suggest that optimum impedance match is an amp w/an output impedance 1/8th the impedance of the headphone?

Interestingly enough, I can't find an output impedance spec for my Woo WA3 (the only OTL/higher output impedance amp I have).

the "at least" 1/8 rule of thumb is like a crossroad where various ideas can coexist pretty well:
1) simply getting an efficient system. ideally you'd want the amp with as close to zero ohm as possible to achieve https://en.wikipedia.org/wiki/Impedance_bridging

2) limiting frequency response variations. when the lowest impedance of a headphone is already 8 times or more that of the amplifier, you get a stability within about 1dB in the response compared to another amp with a different impedance but also at least 1/8th of the headphone's impedance. obviously when I'm talking about 1dB or less, I'm assuming that the amps are identical in response into such load. this only helps limiting the FR impact due to impedance.
here with the hd650, a high impedance amps will boost around 100hz a little compared to a low impedance amp. not really a big deal here thanks to the lowest impedance of the phone already being quite high. for multidriver IEMs, it can become very important and ruin the signature of an IEM(or make it subjectively better if we're super lucky).
2a) same idea when there are protective caps at the output of the amp. the caps will roll off the low end, and the smaller the impedance ratio(amp/headphone), the smaller the roll off. so getting a headphone at least 8 times the impedance of the amp will mitigate the roll off if protective caps are present at the output.

3) electrical damping. the movement of the driver is determined by mechanical damping(how stiff is the membrane, how heavy is the coil...). there is also how easily the air can flow when moved by the driver and how much air is being moved. and of course one hell of an important parameter is the electrical signal itself making the coil move ^_^.
http://hyperphysics.phy-astr.gsu.edu/hbase/oscda2.html in that link you can see the oscillating behavior for underdamped, critically damped, and overdamped conditions. you don't have to care about why or how,, just know that better electrical damping results in better control of the diaphragm. as I said, it's only one damping parameter for how the driver will move. but it still makes sense to avoid a massively underdamped behavior. unless you happen to like how it sounds. all those concepts are more or less important when it comes to fidelity of the signal reaching our ears, but they don't give the recipe for euphony or personal taste.

4) irrelevant for the HD650. looking at the amp this time, not all designs will be happy when a low impedance headphone is used. in an indirect way, sticking with the "at least 1/8th" rule, might on occasion help us stay within nominal use of the amp.



the 1/8th rule of thumb tends to increase our chances for stability and correct use of the gears. so it's a good rule as soon as we're not too sure about the gears we're using. of course audiophiles who constantly seek change might decide to take this the other way around. and to never follow the idea of impedance bridging for the opportunity to perhaps get bigger changes. ^_^

 

[Deftone]

I have no idea what the output impedance is CMA400i but i do know it sounds pehenomenal with HD650, its growing on me like mold.