[evil-zen]

Recently I bought a Stax Sr-x Mk3 normal bias. Later on i found the left side is softer than the right. What could be the cause of it? I opened it up and the wires are really thin and fragile.

Could it be the wires? Will changing a cable help? Or is it the membrane or the electrodes?

 

[hembergler]

Are you sure it's the Stax themselves? Sometimes when you get in the habit of thinking that one side is louder than the other the placebo effect kicks in, and actually it's playing normally.

If you reverse the channels or headphones themselves and they still sound imbalanced, then it's headphones. If not, then it's just in your head.

 

[kevin gilmore]

Not so fast.

It could be the headphones, but unless they are really damaged, it is
probably not so. What is the drive box or amplifier. Since its low bias
it has to be one of the old tube amps, or the transformer boxes.
Many people drove too much power into the transformer boxes damaging
the input protection resistor. If its the tube amp, it could definitely be
a bad tube.

 

[John Buchanan]

I remember this happening to an SRX Mk3 I had. The mylar diaphragm is covered at its periphery by a pressure fit conductive foil circle. I presume this allows the bias voltage better access to the whole of the diaphragm. Unfortunately, the sharpish electrode that impinges on the foil could possibly oxidize at the point of contact. OTOH, there is also a possibility that the foil was on the non-electrode side of the diaphragm, and the contact point with the electrode has oxidized. The latter was the problem with mine and after an expensive repair (matched transducers remember - thus both replaced), I pulled apart the old drivers, put the foil on the correct side and away it went.
Warning - only try this if you are feeling fearless.

 

[evil-zen]

I actually tried putting on the headphones without looking at the orientation (i flip them randomly) and got it right 8 out of 8 times I think. So i guess it is not a placebo.

I use the current SRM 313 with both normal and pro bias. Since I have a 303 headphones as well, i tried plugging in them into the normal bias and they sound fine. So it is not the amp either.

Thanks John Buchanan though I do not really understand what you meant. I'll open it up again once I have time and put the pictures here for more assistance. Where did you get the repair or matched transducers?

 

[evil-zen]

I think I know what foil you are talking about. Is it the tiny flat silvery wire from the + and - to underneath the electrodes? This is the furthest I went. How do you get access to the mylar diaphragm? The 4 tiny screws at the side are removed but I have no idea how to get any deeper without using some brute force.

Thanks in advance!

 

[John Buchanan]

I'm sorry - the above is all I remember after about 25-30 years - one of those 3 wires is attached to pointy electrode that touches the foil circle surrounding the diaphragm. Think of the system as a sandwich - pieces of bread = signal electrodes, filling = biased diaphragm. The bias is applied via wire -> pointy electrode -> foil circle surrounding diaphragm. The sandwich needs to be opened to see what I mean. If I were you, at that point, I would be saying I don't want to do this on the memory of an old guy from 25 years ago. I had nothing to lose - the old transducers were returned to me and I thought I would have a look inside them. I really can't remember how I got inside them!
The foil covers the whole of the periphery of the diaphragm, not just part.

 

[evil-zen]

Weirdly after plugging them in for nearly 24 hours now, the problem is gone... The first time I detected it happening I had it plugged in for many hours too. I'll see how it goes the next few days. Sounding damn great again.