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Stax SR-40 / SRD-4 Not Sounding Great...

mmcc

mmcc

Well-Known Member
Hi All - I just bought a pair of Stax SR-40, and the corresponding SRD-4 transformer. They are not sounding great - I have to crank my receiver's volume to levels that would destroy most speakers to get much sound, and there isn't much bass. I'm pretty sure I have them connected correctly.

I'm starting to regret my purchase :)

Since both ears suck roughly equivalently, I'm hoping the problem is with the transformer box. When I crack it open, are there any common problems I should be looking for?
 
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IIRC the self polarizing electret diaphragm in the SR-40's will lose some of it's charge over time. This could be why you're experiencing problems.
 
JoeESP9 said:
IIRC the self polarizing electret diaphragm in the SR-40's will lose some of it's charge over time. This could be why you're experiencing problems.
Click to expand...

So I've seen that suggested in a number of threads, and I've seen it refuted in a number of threads. I hope that isn't the case :)

I found this blog posting where someone opened up both the headset and the transformer box... there are a couple of thermistors in there cleverly disguised as capacitors, and I'm hoping one of those has gone bad. https://nick3137.wordpress.com/2012/12/16/stax-sr-40-electret-headphones/

I also have no idea how to determine if a thermistor is bad.
 
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Playing them for quite a while MAY help. I had a pair recently, they seemed to be in good working order. The sound was very detailed and transparent but on the light and bright side. They were never bass monsters and certainly will not improve with age. With a bit of EQ they did sound quite nice. I had no problems getting good levels.
 
I don't know squat about Stax headphones or their circuitry but a thermistor is a device whose resistance changes with temperature. You could put an ohmmeter on them (with power off of course) and see if they read the same (assuming they are the same component) at room temp. Warming or cooling should change the resistance. If these are a current protection device, the resistance may go up with temperature, i.e. as they heat up from excessive current they automatically limit the current.

If the resistance is already pretty high, that could explain the low volume. You could bypass them and see if that makes a big difference, but do so very carefully.
 
toxcrusadr said:
You could bypass them and see if that makes a big difference, but do so very carefully.
Click to expand...

I like the way you think my friend, but that seems rather risky.

I found this posting: http://thestereoclub.blogspot.com/2009/01/capacitor-codes.html

The thermistor in the SRD-4 has the same code . The blog posting suggests that it gets more resistive as it gets hotter.

In a follow-up post he reports success in replacing the thermistor - I'd be nervous that the replacement has the same temp/resistance curve as the original, but whatevs:
http://thestereoclub.blogspot.com/2009/02/success.html
 
So I opened up the box, and none of the components were obviously bad. It seemed like they sounded fine when I started using them, but then degraded. So, I pulled the thermistors and I'm gonna replace them. I'll report back in when I get the parts in the mail.
 
If you have the codes from those you could look up the specs at least, and see if the cold resistance is what it's supposed to be. If not, you should be able to find replacements or an equivalent.
 
My pair work real well with 5 to 10 watt peaks. Though it take 50 watts to start taking you to rock and roll levels.
 
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