2A3 Build

[Alonzo]

Will be rebuilding the C4S board this weekend, messed up something while changing 431's and one channel of LED's blew.  It was an awesome pop, but didn't blow the fuse.  So somewhere I have a problem that caused too high a voltage maybe.  Going to the ON Semiconductor 431's and will post the board voltages and the output voltages.

 

[Alonzo]

An update in the search.
Both Stereomours now have STMicro TL431ACZ's and both still have a hiss that is apparent with no source playing and in the quiet passages or single instrument music from about 5 feet from the speakers.  Each amp measures less than 0.020V.  It can be adjusted to 0.000 for about half a turn of the hum pot (10 turn pots) then jumps back up to 0.020.
Next steps;
Made up some shorting plugs so will test/measure with them later.
Tube roll the 12AT7's
Swap out the 431's in the Smash for STMicro's
purchase some extra boards so all can be changed at once
Try the TL431AILPG in pre and amps

 

[mcandmar]

Just had a read of my own thread to remind myself, http://bottlehead.com/smf/index.php?topic=5316.msg76160#msg76160 in my application i found the On Semi TL431AILPG was the quietest of the lot (tried half a dozen), but ultimately none of them were quiet enough.  Keep us updated as i'm curious to know where you get with this...

 

[Alonzo]

Yep, will do.  Trying the On Semi's next but my boards are crappy now from all the desoldering and installs.  Sent Eileen an email to see if I can buy a few more.  In the mean time I can tube roll. 
With all this, the amps do sound wonderful.  It's just that nag that now that I know it's there I have to at least try to fix

 

[Alonzo]

Is the shunt regulator/active load printed circuit board for the Stereomour available to purchase?  Haven't heard a response from Eileen via email, thought I'd post the question and call tomorrow.  Is the 4.4 version for the SEX the same or does it have extra traces?

 

[fullheadofnothing]

Eileen is out of the office. Send another e-mail later in the week after she has had a chance to go through her correspondence.

That is the correct board.

 

[Alonzo]

Ok thanks!

 

[Alonzo]

Just to finish this out.  Currently all the TL431's in my system have been changed out.  Received new SmashUp boards today and put them in with ON Semiconductor 431's.  While assembling I ran both amps into my horns to test, only a very low hiss could be heard at about the 1" range from the speaker, with no music, drowned out with music playing.  Finished the SmashUp and the hiss is back but not equal, left side is louder, and really obvious in the tweeters (duh).  Threshold moved about a foot out from the speakers, with no music and with music you can hear it during quiet passages.
So it seems the Smash is amplifying the background hash I have.  I'm about done with chasing it in the pre and amps, I'm going to work with maybe adapting one of my Fix's to filter it next, maybe pad down the tweeters more.

 

[Alonzo]

Finally fixed!!!!  Replaced the Smash w/Smash-Up with a passive preamp.  No haze, no hash, no hiss.  Loving Mike's B7 Mexico series input transformers.
The ugly wiring job shown...