What causes this (amp related)? - Page 3  

Quote:

Originally Posted by xnor 

I've never seen a diaphragm crinkle like that under normal operation.

 

Shike wrote "I'm hitting 150-250mv DC offset".

 

The best way to measure this would be with a digital scope on a suitably slow sweep speed so you can catch the peak value of the transient. But this is not what's normally called DC offset. DC offset is typically present all the time. This is power down transient and is likely caused by the DC operating point of the Asgard becoming unstable as the power supply voltage falls. With such a beefy power supply you need big power supply caps which can store a lot of charge. Typical headphone amps can use much smaller capacitors so such transients are typically much less significant.

Is anyone else having a problem like this, with either the Asgard or Lyr?

Are other headphones being affected? Would this potentially damage a planar magnetic driver, like the LCD-2?

I've got no scientific insight about it. I'm just worried, I was eyeing the Asgard and Lyr for my next amp 

Shike, if you haven't yet you should post this video in the Amp subforum too. If the issue is widespread and as dangerous as nwavguy suggests, word needs spreading. This subforum isn't very popular.

Before letting this thing blow up, I suggest we first find out:

1. is there a freak manufacturing defect in this particular Asgard?

2. is there a freak manufacturing defect in this particular K701?

In my experience with tube amps, it is normal practice to always unplug the headphones before powering the amp on or off. I've seen the unloaded DC go higher than 9V while it is warming up or powering down. Never knew that solid state had something similar.

Quote:

Originally Posted by revolink24 

I highly doubt that the level of DC offset we're dealing with here will damage any headphones that are made, well, correctly. Dynamic drivers are far from as fragile as many people think. Has anyone actually measured the transient voltage?

Yes, several have measured it including the manufacturer and the original poster.

Schiit Audio says:

 "Our measurements show a 100-150mV transient into a 32 ohm load. This is 0.0007W of transient--or 7/10000 of a watt."  That's 0.7mW

Most, if not all headphones have their relative sensitivity rated based upon an input of 1mW which is 30% higher than the measured turn off transient.  No properly designed headphone would be affected by any number of such transients.

@kwarth I strongly don't agree with the manufacture on the measurement. As I said, this has nothing to do with excessive power in mW.

@Shike, Head Injury and Yoga Flame: It's worth confirming this isn't a freak problem, but Jason from Schiit has already said it's normal. And single ended amps are pretty simple. If there was something wrong with the amp it's rather unlikely it would affect both channels and still sound OK while playing.

This should be easy enough for another Asgard owner with similar headphones (they don't have to be AKGs) to confirm--at least if they're willing to risk damage to their headphones by turning it off with the headphones plugged in.

There's an interesting irony here. There are some amps, including the AMB Mini3, that can allegedly be damaged by unplugging the headphones with the amp powered on. But with the Asgard things are reversed. You're supposed to unplug the headphones with the amp on. Obviously neither situation is ideal if getting it wrong can cause damage. And it's a lot of wear and tear on the headphone jack unless you just leave the amp on 24/7.

Sooner or later, it's likely you'll get it wrong, the power will go out, or whatever. And it might just take once to damage your headphones.

An interesting idea would be to direct one or more headphone manufactures to this thread (or at least the video) and get their input on potential damage to the headphone drivers.

Quote:

Originally Posted by nwavguy 

Sooner or later, it's likely you'll get it wrong, the power will go out, or whatever. And it might just take once to damage your headphones.

This.  Or are we required to get a UPS for our headamps?

Quote:

Originally Posted by revolink24 

nwavguy, you're welcome to trash the Asgard all you want as you seem to feel obliged to do with anything you measure if you have actually seen and measured it for yourself. I do not understand, however, how you are determining this transient to be dangerous just from a Youtube video of someone else's K701s. It's an unfair assessment of an amplifier that has not had any problems reported on here for many months now. It's like sentencing without a trial.

I'm not trying to trash anything just offer an engineer's perspective on a question many are obviously concerned about. I've praised far more products than I've "trashed". When you see what's happening in the video, I think it's fair to be concerned about the health of the headphones. I didn't start this thread, and I'm not the first person to be concerned.

An engineer from AKG would be the best resource but that might be easier said than done with AKG now being owned by giant Harman which I'm sure has layers of defenses against anyone distracting their engineers--especially when this issue isn't related to any fault in the headphones. Harman also likely has policies that prohibit employees from representing the company in forums like this one. But hopefully at least one headphone manufacture can offer a suitably informed opinion.

Just blindly taking Schiit's word this isn't a problem seems foolish to me when expensive headphones are potentially at stake. I think those spending money on expensive headphones and amps should value independent information rather than try to marginalize it or accuse the person of having some hidden agenda. It should be obvious Jason at Schiit is the one with the biggest agenda and the largest bias regarding this issue, followed by those who own Schiit amps. There's not much in this for me except being attacked by the Schiit fan club.

It's certainly possible the transient is harmless to most headphones and the AKGs are somehow unusually sensitive. But, regardless, it's something to take seriously. 

Quote:

Originally Posted by Shike 

It did the same to my K601, so it's either the amp I received is bad, the Varimotion driver is highly sensitive to DC transients, or there's a potential for design flaw.  We won't know until the Asgard I'm returning is tested, K6/7XX series are tested on others, etc.  We also don't know whether it is or isn't damaging yet, something we need headphone manufactures to weigh in on.

 

I'll say it again people, cart and horse - only one belongs before the other.

 

EDIT:

 

It's also worth mentioning I didn't hear the crinkling with my Grado SR-60 or AT ATH-AD700, only the K601 and K702.

I own the K701 and the K501 and they both have been working great with both the Asgard and the Lyr.
 

Quote:

Originally Posted by nwavguy 

 

I'm not trying to trash anything just offer an engineer's perspective on a question many are obviously concerned about. I've praised far more products than I've "trashed". When you see what's happening in the video, I think it's fair to be concerned about the health of the headphones. I didn't start this thread, and I'm not the first person to be concerned.

 

An engineer from AKG would be the best resource but that might be easier said than done with AKG now being owned by giant Harman which I'm sure has layers of defenses against anyone distracting their engineers--especially when this issue isn't related to any fault in the headphones. Harman also likely has policies that prohibit employees from representing the company in forums like this one. But hopefully at least one headphone manufacture can offer a suitably informed opinion.

 

Just blindly taking Schiit's word this isn't a problem seems foolish to me when expensive headphones are potentially at stake. I think those spending money on expensive headphones and amps should value independent information rather than try to marginalize it or accuse the person of having some hidden agenda. It should be obvious Jason at Schiit is the one with the biggest agenda and the largest bias regarding this issue, followed by those who own Schiit amps. There's not much in this for me except being attacked by the Schiit fan club.

 

It's certainly possible the transient is harmless to most headphones and the AKGs are somehow unusually sensitive. But, regardless, it's something to take seriously. 

The AKGs are NOT overly sensitive.  Look at their published sensitivity specs.  This is not rocket science.
 

Quote:

Originally Posted by kwkarth 

The AKGs are NOT overly sensitive.  Look at their published sensitivity specs.  This is not rocket science.

He didn't mean that sort of sensitivity. He meant that the driver design might be more susceptible to the issue.

There was no need to be so hostile.

Quote:

Originally Posted by kwkarth 

The AKGs are NOT overly sensitive.  Look at their published sensitivity specs.  This is not rocket science.

You're talking about a different kind of sensitivity.  That's not rocket science...

So do your 701s crinkle up on your Asgard like like Shike's pair does on his?