[pavment]

I wanted to get an idea if their Stratos is very cool on both sides. My stratos is hot on the left side. I noticed some hum which was alleviated when I switched the outlet plug. Should I be worried? Why only 1 channel?

[nickd]

likely a bias current setting. Most SS amps use little potentiometers in the bias circut that you adjust with a micro screw driver. The procedure for testing and adjustment is not usually difficult but should be performed by someone proper tools and circut knowledge. They somtimes vibrate out of their factory setting during long trips on the delivery truck.

I would consult the factory service dept.

[pavment]

I can probably try to adjust the pot. Have all the tools and DMM. Anyone have any Voltage values or instructions?

[smata67]

Bias doesn't drift so much under normal circumstances that one side would be noticeably hotter than the other, you probably have a problem that goes beyond a simple adjustment.  Time to talk to the K man.  A 60 Hz hum could be a sign of filter capacitor failure.  These are the big ones in the center of the board or out on the sides.  If you have an older green board and have kept it on 24/7 it may be time for a recap.

[pavment]

That's a possibility. I would like to try adjusting the bias before taking further steps. It's a green board and it's not used as often as 24/7. I had gone through some issues with the fuse, the hum is also gone with a dedicated power outlet.  At a certain it was not used for a long period of time.
I wonder if recapping would cost more than getting a new board altogether.

[srb]

I wonder if recapping would cost more than getting a new board altogether.

From a recent post by Klaus:  (http://www.audiocircle.com/index.php?topic=117928.msg1241019#msg1241019)
"What I do tell customers and recommend is a re-capping of every 7-10 years, which, obviously, can vary wildly as far as hours played are concerned....yet, I'll do this pretty much close at cost, starting at $ 50 with a free complete tune-up included !!!!!"

If you have a version with additional outboard caps obviously it would be more expensive, and 2-way shipping isn't cheap, but it's got to be a whole lot less expensive than replacing entire boards.

Steve

[pavment]

Shipping the unit back and forth is ~$190. I also don't have the box. But since it was not used 24/7 over the years, I assume a year before recapping would be warranted. I have opened the unit up and looked into the board during the fuse debugging. So has anyone shipped their boards only back for recap?

[smata67]

Shipping a Stratos is a big deal.  It is a monster, as you know.  If you feel comfortable pulling a board out of it, why not just ask Klaus for a tested board and swap it out?  Do you have a good quality soldering iron, such as a Hakko or Weller station?  If not, ship the whole thing in, you are not up to the task.  No matter, Klaus has proven himself to be a straight up guy, perhaps you need to talk to him about what you have and what can be done. 

[pavment]

Thanks for the advice everyone and smata67. I talk to Herr Klaus further. I have techs in my office who can desolder and solder back the connections so I can ask for a test board.

[pavment]

Klaus sent me a detailed biasing instruction set. Will have to roll up my sleeves and give it a go sometime next week.

[pavment]

Managed to bias the unit last night. Instructions were a bit difficult to follow, as it was a pastiche of emails and instructions in one body of message. Talking to a preoccupied Klaus helped clarify and let me experiment. The internal bias was very high at ~30mV. I adjusted it to ~19mV.

After the bias and offset adjustment, here are the changes:
1. Not hot to the touch anymore. However it is still warm on one side. This may be expected since there are 2 boards with one channel above another.
2. Reduction in brightness. This is a welcome change for me. I had some sibilance issues with a many recordings. This is not a big issue anymore as I like warmer sound.

Thanks to Klaus for his help.

[Detuned]

For those of us who are comfortable and capable of carrying out such a procedure, can the bias and offset setting procedure be posted here? The ability to confirm that our amps are at their best would be much appreciated.

[pavment]

I would like to post it but not without Klaus' permission.

[Detuned]

Klaus, would it be acceptable if the bias procedure was made accessible?

[Oystein]

I also got the adjustment procedure from Klaus almost 3 years ago.
It was in raw text and based on a mono amplifier as Klaus explained but it did the trick for my stereo version.

For my own convenience I made a more readable document with drawing for future reference (stereo version).
I already sent it to other Odyssey owners here earlier so if anybody is interested in a copy send me a message with your email address.

[klaus@odyssey]

Well,  some small things did change,  and while I have no problem to send over instructions,  I do want to talk with everyone in person first,  for obvious reasons.......
And the short answer is yes,  biasing is that important,  and relatively easy to do....

[Oystein]

@ Klaus,

What is your experience with thermal drift?

My example: I set my bias etc. having the amplifier open without any limitations of free airflow.
Closed the lid an put my amp back in my rack with only few cm free space above the amp so obviously it will get al little warmer during normal operation.
Is there some drift to be expected when the unit gets a little warmer ? The middle of the top lid is quite warm ( I expect almost 50 C ) so I expect the bias increased during the heat buildup.

Here are some pictures: http://my.hifi.nl/index.php?user=16089

Of course i could connect some measuring wires and run them trough the top plate holes so I can measure bias outside the unit but it is a bit cumbersome finding ideal bias this way.

[pavment]

As I stated in my last post, my bias was ~30mV. Reducing the bias reduced the temp very well. I suspect you will have the same result. Additionally bias will change some sonic characteristic as it did to a reasonable extent on my setup.

[JoseL]

I also got the adjustment procedure from Klaus almost 3 years ago.
It was in raw text and based on a mono amplifier as Klaus explained but it did the trick for my stereo version.

For my own convenience I made a more readable document with drawing for future reference (stereo version).
I already sent it to other Odyssey owners here earlier so if anybody is interested in a copy send me a message with your email address.

I just sent you a message. Thanks in advance.