Any advice as to how I can get a vintage SRA 12S to work properly. One channel is fine but the other is out. Do you know of anyone who repairs this kind of thing? Thanks.
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Energizer help. I'm getting in to Stax from the bottom up. I have a pair of SR-A Lambda's (that need some work) and a pair of SRX-Mk3. The sound of the SRX paired with an SRD6sb has really taken me by surprise....I'm a pretty happy camper right now. But I can't leave my stereo on all the time or my batteries will drain so I needed a way to keep the headphones charged.
I picked up an older SRD-5 on ebay...not in great shape but I figured I could keep all my headphones charged and set off to the side until I'm ready to listen to them.
I did hook up the 5 to my system and there was a bit of hum..ground loop maybe? But as long as I'm only using it to bias....
My question is how do I measure the bias output so that I can make sure the thing is working properly? I also don't want to get killed measuring what I hope will be 230v.
Thanks for your help.
Edited by triodesteve - 5/17/14 at 10:30am
if the volume of the music is comparable to your SRD-6SB with the SRD-5, its bias should be fine. Although I'm not really sure why you would want to keep your phones biased when you don't listen - if everything works ok, biasing the phones with the with a self-bias energizers takes a few seconds...
"Although I'm not really sure why you would want to keep your phones biased when you don't listen - if everything works ok, biasing the phones with the with a self-bias energizers takes a few seconds..."
I've read that especially with older models, keeping them biased is the best option. Did I misunderstand?
Thanks for your help.
Hm, I think I read keeping them biased all the time as a workaround for marginal speakers which take a long time to get up to equal volume but if yours work ok after a short time from your SRD-6SB, switching off your system should be fine.
and now a nice little repair story and a testament of STAX build quality - or rather the lack of...
I have a pair of lambda pros which I got off german ebay along with an SRD-7 mk2 some time ago. Unfortunately they had quite a bit of channel imbalance - it could still be fixed with some balance adjustment but the right earspeaker was significantly too low and also slightly distorted and I had very rare cases of no sound at all after hours of listening which took some time powered off to fix.
Not too bad, they were very cheap... that's what I thought..
Today I decided to have a look into the SRD-7 mk2... and this is what I found:
So obviously STAX decided to solder the zener diodes ZL01-ZL04 from the schematics found here
directly to the pro bias jack 8-O
But it gets better... closer inspection showed that the contact for the pro bias (grey wire on bottom) was almost touching a piece of wire standing over from one of the right channel contacts and did actually make contact with some light tapping (or possibly by the unit getting warmer after some hours). I corrected this with wire cutters and some careful bending.
After reassembly the channel imbalance was still there but then I applied what had helped temporarily before - slight tapping of the right system made me dash for the balance pot to set it to neutral. Unplugging the phones and uncharging the bias (breath on your fingers to slightly moisten and touch contacts of the phone plug - no worry, doesn't hurt) and replugging showed the channel balance was still good...
So I guess the channel imbalance was caused by one of the right side leads occasionally shorting to the pro bias and partially fusing the diaphragm to one of the stators. Tapping the affected speaker managed to get the diaphragm free and with the short circuit removed it hopefully won't get stuck again...
- If your energizer is acting funny, having a closer look on the jack contacts might be a good idea... BUT REMEMBER TO UNPLUG IT FIRST - LINE VOLTAGE IN THERE CAN KILL YOU!
- If your stax speakers show channel imbalance slight tapping of the low system might help... if the diaphragm is just stuck and not perforated.
Edited by jring - 5/19/14 at 1:06pm
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It doesn't make any sense to add a socket for the Koss. First off it's one model with a unique connector, one which is also impossible to source without ripping it from an E/90 amp. It's also very easy to make an adapter to Stax for them and they are electrically compatible. To make the amp compatible with pretty much everything under the sun it is fitted with a variable bias supply which can be set between 0-1000V and easily lifted to 1400V simply by floating it on top of the main B+ rail. It's fitted with a 2000V rated 4M7 ballast resistor but that is socketed so easily swapped out for any value.
The only headphone I'd ever consider adding a special connector for is the HE90, which I did. It's so fragile and electrically different from anything else that it needs special consideration.