[wualta]

Even an owner of orthos can't tell from the outside if a strange new kopfhoerer is ortho or not. If he's certain it is, he must've had it apart and can tell us what he found inside (PMB, KMH, whatever). PMB did supply slidey-type volume controls (handy if you're connected to speaker terminals, perhaps), but I've never seen an ortho with tone controls. We await developments and eventualities.
 
The SFIs are, what, 38mm? He might not have measured carefully, who knows. If he did, they're not the SFIs we know.  I hope he answers that guy who asked where he got them from.

 

[vid]

Quote:

 
Hey VID do you have another amp with terminals you could also try ( carefully ) to see if it repeats the issue again?  I forgot what the Hok's max input is rated at. Imma gowun look

 
Nope, just one amp. Since I don't use speakers, the speaker outs on this amp have been untested until this, so it's possible there's something wrong with them. The headphone out (which runs off the speaker amp) works fine, or at least seems to.
 
I'll stick the multimeter probes into various places on Monday and see what comes up.

 

[nick n]

Latest project is complete.
 
Take two 32 ohm SFI's khbaur was generous enough to sell me a while ago, one vintage minty classy looking ( IMHO ) Grundig 211-A from ~1968/9,  stir in one pile of coffee and a night of modding.
Gradually add Newplast and rest of ingredients. Bring temper and frustrations to a boil and then lower heat and cool off,
Enjoy.
 Serves one generously.
 
Here we have it. This is a very interesting donor can. It's earcups use absolutely no screws yet seal up very tight. They are made from a sturdy yet pliable rubbery plastic. All you need to do is twist out the seam along the baffle and the baffles pop right out.
 Other than the tiny extra bass hole I drilled in the cups this is completely reversible. A very surprising Grundig driver if it was to go below 30 hz I would have kept it stock no question. Onthe hunt for one of their other model for a keeper. The particular one is rather ugly but should be fantastic if I can find a mint one.
 
Different damping scheme used here. Time will tell but nice so far. Very unclosed sounding. Super detailed so far, treble is up but non-fatiguing, a very slight drop to that will be perfect. I bet this is due to some slight compression against the rear cupspace around the foam disc edges. A quick fix.
Stock 1/8 nicely hidden and moulded bass ports below the cable entry but I made two new ones also I think maybe the same size.
 I took a ring of the thin 1/8 inch Creatology adhesive foam and stuck it to the driver rear, leaving the center opening so i could fill that area with a disc of the Arctic Bamboo felty fabric ( half cotton half bamboo fibres ).  I find this stuff adds a great sense of depth to things YMMV ( like an superultra gauze with built in semi-damping ). The drivers were missing their stock dust guard fabrics so i replaced them prior to doing all this.
 
In order to still dampen this SFI up a bit beyond that Arctic bamboo disc, I topped this layer off with a disc of Acousti 3 layer foam that only has the adhesive on the outer edges to match up to the red Creatology foam and let the sound go through the middle.
 It sort of could be seen as a sealed chambered damping stack. Sort of.
 
Secured drivers to baffles which came from another donor can. Cut and filed them down to shape.I used red ( right ) and blue ( left ) Newplast to secure those. Each baffle side after weighed out @ 55.1 grams. Extra space inside around the driver filled with an acoustic filler. Cup rears covered in Creatology adhesive foam.
 
Added 2 strips of Akasa topped with some actual foam on the headband for comfort.
Will whip up a leather thing sometime later.
 

 

 
Donor baffle below is shown with outer ear side up. Driver protrudes a few mm higher than the baffle level, not much. You can find similar easy to mod baffles like this in many Koss cans.

 

 
 

 
I thought I had learned my lesson about drilling holes from outside inwards from screwing up the first Alder pair way back. I guess not.
After fixing these and opening them back up  I saw the drill bit tip had swirled up almost all the acoustic filler essentially making it useless so that's all replaced . Also rounded off the outer edges of Acousti foam damping pads. A bit of acoustic filler directly behind the driver now also in the very rear.
 Taped off the baffle/cup seam just to be sure.
 
This is the way they should sound now. Very good sense of depth/dimensionality. Good bass. No treble fatigue.
 
DAMPING UPDATE
 
Determined bass levels could be brought up a touch, so in I went again to make this a version of the "double-stack" Acoustifoam damping like I have in the Dead Rebel mod. Previous damping kept intact but added a second 3 layer tapered cap to the top.
 
Also
-Reduced the acoustic filler down to half
-Opened up the extra bass port to 7/32 in.  in addition to the preexisting stock one that is1/8 inch.
 
Picture below shows new top damping pad ( secured with it's intact outer ring of adhesive, center is clear of adhesive backing like the one below it.)
Not shown is the acoustic filler that gets added. That's tohp sekrit

I can discern every single nuance in the music however subtle. Beautiful. Sensitivity is dropped down though, guess i need to look into a newer portable amp that puts out 200mw plus. E5 isn't cutting it now even after the 76mw of the Cowon

 

[vid]

Measured the DC offset on the SU-300 using the instructions in the AK thread. Left channel gave -3.2 mV and the right one -9.5 mV (200m setting on the multimeter); so that doesn't seem to be a problem.
 
The DC resistance on the HOK was about 50 for both channels (HP-50S was about 130).
 
Also checked for continuity between the left and right ground connectors on the amp, and there was.
 
Who knows, then.

 

[wualta]

Yeah, I got nothin'. Voice coil heating you can feel just shouldn't be happening.

 

[dBel84]

maybe the load is making the amp oscillate? did the amp get really hot too ? ..dB

 

[vid]

I didn't realize to test if the amp was heating up as well. There's a pair of Senn Unipolars somewhere in the world coming towards me - I'll see what happens when I plug in the box for those.

 

[GREQ]

I know this is reviving an old topic, but I recently acquired a nice Yamaha HP-3. 
It sounded great straight out of my PA2V2, but it was fairly 'dark' so I scoured the thread for the damping mods to level out the bass.
 
I didn't have any felt lying around so I just cut out 2 circular pads of denim from some old jeans and placed them on top of the original damping foam. This set up got rid of most of the bass which I didn't like, so I cut out circles from each making them 'denim donuts'. 
Now they sound absolutely incredible. Everything sounds a little bit distant to my ears (which are mostly used to the direct sound dynamic headphones), but it's a fairly flat response with excellent deep bass extension and practically no fatigue or significant peaking at any frequency.  
 
Just thought I should share my budget mod. 
 
I think I'm getting addicted to orthodynamics.

 

[wualta]

Quote:

I didn't realize to test if the amp was heating up as well. There's a pair of Senn Unipolars somewhere in the world coming towards me - I'll see what happens when I plug in the box for those.

If a 50 ohm resistive load is driving an amp into oscillation, you know something's very wrong with that amp. I hope that's not the problem-- if it is, connecting the Unipolar transformer box is likely to cause worse problems. But do double check your wiring and monitor the temperature over the heat sink as you listen. Sending ultrasonic frequencies at high power through an ortho-- anything, really-- will pop it for sure, but like I said, it seems improbable. Still...
 
Quote:

Originally Posted by GREQ /img/forum/go_quote.gif 
 
I cut out circles from each making them 'denim donuts'. Now they sound absolutely incredible. Everything sounds a little bit distant to my ears (which are mostly used to the direct sound dynamic headphones), but it's a fairly flat response with excellent deep bass extension and practically no fatigue or significant peaking at any frequency.  

Thanks for telling the denim story. That's how this whole thang got started-- using household materials at ~zero cost to correct a perceived flaw, then finding the improvement much greater than expected.

 

[vid]

Quote:

If a 50 ohm resistive load is driving an amp into oscillation, you know something's very wrong with that amp. I hope that's not the problem-- if it is, connecting the Unipolar transformer box is likely to cause worse problems. But do double check your wiring and monitor the temperature over the heat sink as you listen. Sending ultrasonic frequencies at high power through an ortho-- anything, really-- will pop it for sure, but like I said, it seems improbable. Still...

 
Thanks for the fair warning and palpitations. Any idea if the transformer box on its own acts as a proper load - i.e. should I first try and play music with only the box and not the phones connected? In case of meltings.
 
The HOKs didn't exactly overheat, but they did feel increasingly warm to the touch especially at the center bulge. This was during about five to ten-ish minutes of having them connected and playing sound.

 

[wualta]

Sure, try sending audio into the transformer box alone first. If the amp doesn't shut itself down, try connecting the phones, bring up the volume slowly and listen for distortion and intermittent sound. 
 
As for loads, anything with coils in it will be more reactive than a load that's virtually pure resistance. Amps do vary widely in their ability to handle reactive loads-- there's the famous example of someone using a highly-regarded Toshiba microcomponent amp to drive his ATH-8 transformer box and sending the poor amp into conniptions.
 
The Unipolar has quite a reputation-- I hope yours arrives in good working condition.

 

[vid]

Quote:

The Unipolar has quite a reputation-- I hope yours arrives in good working condition.

 
My thoughts as well.

 

[nick n]

is it the 2000 or 2002 model?

 

[vid]

It's the 2000.

 

[kalbee]

Well, looks like I was able to fit the SFI's into a shell without destroying anything... by simply adding pieces of cork as spacers.
Awesome. Too bad these headphones don't isolate very well to act as my main portables =/