There’s always better above, but if it sounds good to you that’s a good place to be lol
Does look very nice
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Do we know what the output impedance of the amp is?
It would be nice to know, but honestly I’ve found for planar stuff it’s typically less important to know than some dynamics
Output power RMS: sinus 1KHz @ 250Ohm – 550mW per channel
I’ve read that some newer OTL amps are designed to be suitable for low-impedance and planar headphones, by using specific capacitors.
The issue at the center of all this is “maximum” power transfer.
When the load and power source, ie the amp have a prefect match the maximum amount of power will be available to the load, ie the headphone.
There is no loss of power due to mis-matching.
Then depending on the sensitivity of the load, this speaks to the loudness that the load can obtain in the case of a headphone.
This in an AC circuit varies with frequency…and most of the specs are at the nice “midpoint” of 1 Khz.
So the variance in music is indeed much more than that. Music though at frequencies other than 1 Khz are at these other frequencies for short periods of times…so its often a moot point. Music is not a single 1 Khz test tone…
Any possible damage would most likely be in the amp side…depending on how the amp is designed. The damage with really BIG impedance mis-matched amp to load is usually in the heat that the components of the amp can experience. The only way to hurt the headphone is to exceed its voltage/current handling capacity…well yeah if you drop them on the floor! lol.
The OTL amps like a BH Crack is designed to work with loads of 120 ohms or Greater. Why because of this matching for power transfer if the load needs it to say reproduce a low bass note with some clarity etc…
Many amps attemp to get around this with multiple gain settings via switches or jumpers. Some like the PassLabs HPA-1 are designed to handle a wide load…
Very interesting topic for sure.
Alex
NOTE: SWR
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The only way to hurt the headphone is to exceed its voltage/current handling capacity
Is there a chance that the amplifier can deliver more voltage or more current to a headphone that could damage it if the listening level was in the normal 70 to 80 db range? As in, could a current drive or tube amplifier damage a headphone by delivering power in a way that was not meant for it or would it come down to the Watts being sent to the headphone, which would still be in a normal range?
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Great question.
The power source (amp) is designed to deliver a finite amount of power. The design and parts choices should support the design safely.
The amp is usually “fuzed” or protected from drawing too much power from the grid. (In case of a circuit or part malfunction or a unexpected load (in this case headphone) issue…ie a short?
The amp should only deliver what the load needs to perform its function. All things being equal with no faults your safe.
Amps like a tube amp with high voltages can have a part failure (ie grid resistor shorting) etc that for a finite time-frame would draw a potentially large amount of current…until the failing device “opens up” or the fuse blows etc…this might cause a loud “pop” (I have experienced this!) and this large pop might move the driver to one physical limit and damage the driver.
Depending where the “failure” occurs is key here. And it could damage the load depending on the failure.
The good news is under most operating conditions these failures seems to be rare. Having a well designed power supply, with its design protections, voltage regulations etc…coupling modes etc…
Some recent failures or damage to a headphone were related to
the amp putting out a large DC component and this drove a driver into its mechanical limits and caused damage.
Good practice IMO is to make sure your volume control is turned down plugging and unplugging headphones…unplug your headphones before turning off and not plugging in headphones until the amp is turned on with the volume control is all the way down. Common sense goes a long way here.
As usual YMMV.
Alex
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There’s also some risk in that too depending on the amp, some tube amps can be pretty fussy without having a load on them when turned on. It’s probably fine most of the time, but I’d double check if it’s specifically mentioned to not plug or unplug when on in the amps manual. But it’s probably not an issue, this is a much bigger problem with speaker amps than headphone amps (because of power output and transformer design?)
(or ask the manufacturer, for example woo suggests headphones be connected at all times when on at least for the wa33, but not some of their other amps).
Out of curiosity, would a transformer coupled amp be immune or less likely to having this happen? Assuming that it would given how you can remove DC offset with an isolation transformer for power, so I’d assume having a transformer on the output of the amp would end up doing the same
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There are so many things to consider here.
Transformers are AC devices.
Step up or step down.
Caps pass AC ( music) and block DC.
Caps shunt unwanted AC from a circuit.
Most amps that ARE direct coupled in the output (and in the interstages) are the ones prone to having issues with popping etc due to no signal in and a dc offset etc…all depends on the design and implementation.
So understanding transformer action, simply two winding that are not electrically connected so only the induction from the AC connected to the primary winding’s gets induced in the secondary winding’s etc…so they wont pass a 0 hz DC signal ( voltage level’s)…so yes its a “safer” route possibly.
If the amp “needs” a load attached, there is a reason. But if not and the amp fails its not a concern for the load…still a BIG ouch! But the question was can the amp damage the headphone. In this case no…but agree you need to understand the design of the amp.
Amps that are DC coupled should have a fast turn off function to detect DC and shut the amp down before damage.
Another thing to be concerned with is tubes are tubes and they will fail. The failure can be catastrophic…physical elements inside a tube can fail, and parts of the failed parts can touch and short other parts and then its a real issue…for the amp and the load.
Welcome to the wonderful world of vacuum tubes!
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someone needs to summon @MazeFrame and hope an transformer argument starts!
Optimus Prime! no, Megatron! no, Optimus! no, Megatron! 
No transformer arguments here…transformers are one of those physical things that work thru the physics magnetism, currents flowing in a wire, expanding and collapsing…its been so well defined its really old hat…
If you want a debate it would be how to make a transformer, what materials for what purpose, the type and size of the wire for the windings, the physical build etc…thats very much debatable…What the core material should be hysteresis etc…
Have at at…I am not interested in this at all…
Its “magic!”
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I wasn’t serious… the Optimus / Megatron shiuld have given that away. 
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Yeah I know…just me being the anal old guy!!
All is good here!!..
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Same.
- Transformers only pass AC along
- Capacitors only couple AC along
There could be a circuit involving an auto-transformer that could be fussy about having a low impedance on its output.
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The magic with transformers and this “passing” AC along is one of the basic mis-understood points of electrical theory…
Hard for many to understand the concept of rising and collapsing fields of energy inducing a current in another set of windings…with know real hard electrical connection…
“its magic”…magic of physics…and sooo sooo important…so basic yet so important.
:>)
Funny aspect of transformers is how they, due to conductors in proximity, can have a significant capacitive problem.
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As you guys are discussing transformers, could you please help with a question I’ve had bubbling for a while?
As OTL amps don’t have an output transformer to lower impedance - but other tube amps do have this component - are there stand-alone output transformers available, that you could add in the signal chain (between amp and headphones) that would achieve the same result?
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This is a great idea tbh.
While that would be totally possible, I am not aware of such a product.