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Stax Tube Driver for Headphone: Why should I rebias it?

post #1 of 6
Thread Starter 

Hello,

I am a newby here, so sorry for any inconvinience....and due to the fact I am from Germany, I do my very best in talking english.

 

 

A few weeks ago, I upgraded my old Stax SRD7 MKII and now I own a Stax SRM-006T.

 

It was and still is really amazing how much nicer my Lambda Pro sounds now...just brilliant, it makes me smile.....

 

 

I read a lot about this Tube amp up to now and found out, that some owners readjusted it after they replaced the tubes.

 

Others wrote, that all those tube are going to drift over life time.

 

I also found a good explanation how adjustment should be done...and because I am an electrical engineer (with no experience in tubes but in semiconductors only), I have a good chance in making it correctly.....

 

 

But why should I do it?

 

Are there any indications when those amps should be readjusted (in case tubes are not to be replaced)?

 

Do you assume sound would be nicer or life time would be longer after readjustment?

 

 

 

Thanks for helping me.

 

 

heizermaik

post #2 of 6

Adjusting the tubes does not matter a whole lot in terms of extra lifetime unless the bias is way out of spec.  What the biasing really does is to maintain the proper balanced between the + and - sides of each channel and  remove any DC offset which will cause diminished output from the transducers. 

 

The power supply in all Stax amps is non regulated so the adjustment will drift just because of that plus the age of the tubes.  It certainly won't hurt to measure the amp and see how much it is out of spec, anything less than 10VDC is nothing to worry about. 

post #3 of 6
Thread Starter 

Hello and thanks for explanation.

 

I measured the DC offset and balance as well, both channels drifted to values of about 31 Volts which seems too much to me.

 

So I made the settings new on my Stax SRM-006T and finally values were about 0.5 Volts.

 

Back to my Arcam CD player, sound was as nice as before....maybe it sound funny, but I really believe it is a little more brilliant now.

 

I still own a Stax SRM-1T which was maintained with new tubes and settings about 6 month ago (and which I would like to sell now) and the 006T as its substitute.

 

I always had the feeling that the older SMR-1T sounded a little bit smoother in directl comparison to the SRM-006T before I readjusted Offset and balance.

 

After readjustment, I am not able to hear any differences....this is how it should be.

 

So I would suggest to any Stax Tube Amp owner to check those settings from while to while (without knowing what period of checks would make sense up to now) and have them be readjusted in neccessary. If you would never check, I think, those amps drift away very slowly....and a little bit of their superb sound drifts away also.

 

There is one Stax dealer in the net, who thinks a readjustment every 10 years should be performed.

 

Readjustment is explained quite well in this forum, it takes about 30 minutes and it is not so difficult....

 

Because settings will change only when touching the potis with a screwdriver, it seems very likely that a check or readjustment would be needed after the amp was transported by post, UPS or anyone like this....

 

 

post #4 of 6

A good hint for me to do it on my SRM-T1, too. I think it wasn't readjusted over the whole lifetime of the amp yet.

When the readjustment is done, I will report.

post #5 of 6

I should do this also for my SRM-T1S.  Can someone post the link to the procedure (e.g. pinouts, which pot does what)?  Since I'm taking it to the local NY meet in a couple of weeks, this is good timing.

Thanks

 

answered my own question:

 

http://www.head-fi.org/t/415385/tube-change-biasing-a-stax-006t-ii/15#post_5540679

 

http://www.head-fi.org/t/179285/best-tube-for-the-stax-srm-t1/30#post_2143859

 

http://www.head-fi.org/t/324155/biasing-stax-srm-t1#post_4194869


Edited by cat6man - 10/28/11 at 1:35pm
post #6 of 6

Thank you!

Will be printed as PDF and stored on my HD in the folder for technical manuals within the category "to be done". smily_headphones1.gif

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