[Shike]

Hey guys,
 
I got a new Asgard amp.  I found something odd when I shut off the power, the dome on my K702 pulls in to where the surround crumples a bit.  I contacted Jason and he noted this is normal operation.  I was wondering: what causes this?  Any thoughts?  Here's a video:
 

 

[upstateguy]

Wow, that's weird.
 
Does it do it if you pull the plug out of the jack while the amp is on?
 
Do any of your other headphones do that? Does any other amp do that?
 
Is it making a sound when it does that?  Maybe it's an off thump.

 

[Shike]

Let's see:
 
1) Nope, only when they're plugged in and the amp is turned off.  Fun trivia, I can unplug them, shut the amp off, plug them in and it will happen to a lesser degree.  Something to do with the caps maybe?
 
2) Only my AKG K601 and K702 that I can tell.  Their dome shape seems to make them oddly susceptible.
 
3) A sucking noise then a mild "pop" when they return to shape -- not like any turn-off thump I'm used to, but I never had a headphone amp do that honestly.
 
 
What's bothering me is it's really crumpling the K702 diaphragm -- with their multi-layer design I'm not sure this crinkling is particularly good for them :|

 

[deadlylover]

I don't know a thing about dynamic amps, and I don't know how the Asgard works.
 
Could it be a DC offset as the amp is powered off? Since it's off, the servo won't be able to compensate in it's dieing breath. Just a completely wild guess.

 

[Shike]

Quote:

I don't know a thing about dynamic amps, and I don't know how the Asgard works.
 
Could it be a DC offset as the amp is powered off? Since it's off, the servo won't be able to compensate in it's dieing breath. Just a completely wild guess.

 
Good guess, when I turn the amp on and off with a 33 ohm dummy load I'm hitting 150-250mv DC offset.  Now I need to figure out if it's by design, my amp, or if my dummy load made the test faulty.

 

[maverickronin]

Apparently the Lyr does something similar as well.  There have been a few reports of it blowing ED8s and D7000s on turn-on or turn-off.

 

[deadlylover]

How much DC offset is your source packing? A few hundred mV is quite a lot.

 

[Shike]

A whopping zero, I'm using an ipod which is cap coupled obviously.  It's not a thump like the Lyr (at least I don't think so).  I contacted Jason letting him know how much DC offset was found turning on/off with load (it's dismal after these events) and he said that it's normal.

 

[upstateguy]

Quote:

Let's see:
 
1) Nope, only when they're plugged in and the amp is turned off.  Fun trivia, I can unplug them, shut the amp off, plug them in and it will happen to a lesser degree.  Something to do with the caps maybe?
 
2) Only my AKG K601 and K702 that I can tell.  Their dome shape seems to make them oddly susceptible.
 
3) A sucking noise then a mild "pop" when they return to shape -- not like any turn-off thump I'm used to, but I never had a headphone amp do that honestly.
 
 
What's bothering me is it's really crumpling the K702 diaphragm -- with their multi-layer design I'm not sure this crinkling is particularly good for them :|

 
I agree.  Probably doesn't matter why it's happening.  I guess the thing to do is to pull the headphone plug out before turning the amp off just to be on the safe side???
 
RE: the trivia
 
when the amp is off, if you plug it in a second time, is there enough juice left in the caps for it to happen a second time?
 
 

 

[Shike]

Quote:

 
RE: the trivia
 
when the amp is off, if you plug it in a second time, is there enough juice left in the caps for it to happen a second time?

If I turn it off, the crinkling happens and music continues for three seconds before diminishing.  If I let them crinkle, unplug, re-plug nothing happens.  If I unplug before turning off, turn off, then plug in depending on how long I wait I get anything from crinkling to minor pull in (driver retains shape).
 

 

[xnor]

I don't think the short DC offset will blow up the drivers but the deformation of the diaphragm is not good.
 
Can't you just unplug, turn the amp off and later turn it on again before pluggin the headphones in again?
 
It indeed looks like caps are slowly discharging after you turn it off and the amp slams into one power supply rail or what deadlylover wrote above.
The power switch should be placed after the PSU caps...

 

[Shike]

Quote:

I don't think the short DC offset will blow up the drivers but the deformation of the diaphragm is not good.
 
Can't you just unplug, turn the amp off and later turn it on again before pluggin the headphones in again?

I should be able to do that.  Actually, I'll probably make an adapter with a switch so I don't even have to unplug the headphones -- just toggle them connected or not.

 

[upstateguy]

Quote:

I should be able to do that.  Actually, I'll probably make an adapter with a switch so I don't even have to unplug the headphones -- just toggle them connected or not.

Will that degrade the sound??
 

 

[jcx]

it might be possible to find a switch worse than the TRS jack/plug conncetion you already listen through - but its real easy to get get much better switch contacts

 

[Yoga Flame]

 
Quote:

I should be able to do that.  Actually, I'll probably make an adapter with a switch so I don't even have to unplug the headphones -- just toggle them connected or not.

Or you could even make an adapter that senses DC offset and toggles it automatically.
http://www.amb.org/audio/epsilon12/