Threshold SA-2 front end updates? - diyAudio
Go Back   Home > Forums > Amplifiers > Pass Labs

Pass Labs This forum is dedicated to Pass Labs discussion.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 10th May 2011, 10:39 AM   #1
Surfy is offline Surfy  Belgium
diyAudio Member
 
Join Date: May 2011
Default Threshold SA-2 front end updates?

Hello DIY'ers,

I am the new and proud (but 3000 euro lighter) owner of a pair of SA-2's with optical bias
After reading the thread by BrianEno I noticed that Mr Pass stated there was a more perfect front end designed, but "management" at the time did not go with it...
Would it be possible to modify the front end of these optical bias version SA-2's to that / a more perfect version?
The seller also owned a pair of SA-11M thresholds which, according to him sounded better on voices; he also stated they were specificly designed for the german market...
My amplifiers seem to work fine (they are almost spot on as far as heatsink temperature is concerned), an sound great except indeed for the highs, which could be a bit sweeter, would this be because of the front end used?
One amplifier does give a bigger "thud" on the woofer when switching on and off, the second only when switching on. I read here Mr Pass recommends replacing electrolytic capacitors. Could I start with just those small ones in the front end, anyone recommendations for specific good sounding brands?
As the amplifiers are working fine (except for the thud, and a little treble harshness) I would not like to take unnecessary risks, I am not an engineer, just a hifi enthousiast with some solduring skills and a multimeter but I am willing to try with some help of you guys!
  Reply With Quote
Old 11th May 2011, 07:37 AM   #2
Surfy is offline Surfy  Belgium
diyAudio Member
 
Join Date: May 2011
This should be the same front end board as in the SA-1 optical bias version... Nobody any ideas or suggestions for upgrades, or experience with these front end boards?
thanks in advance!
  Reply With Quote
Old 11th May 2011, 08:27 AM   #3
Zen Mod is offline Zen Mod  Serbia
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
Papa isn't all the time on board

give him some time for answer
__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa... by Mighty ZM
  Reply With Quote
Old 23rd May 2011, 09:31 PM   #4
Surfy is offline Surfy  Belgium
diyAudio Member
 
Join Date: May 2011
I noticed an SA/2e for sale recently, there was a sticker on it, it was upgraded to the e series. Can anyone, or maybe Mr Pass, please tell me what to do to upgrade my SA2 too? It would be interesting to know if it is just some components I have to change (and by what I have to replace them with) or if it is a totally different front end board alltogether.
Thanks in advance for help!
  Reply With Quote
Old 23rd May 2011, 10:12 PM   #5
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
Attached are the last sets of front end schematics. FE89 saw production,
FE90 represents some improvements to that. As to how you alter your
existing circuits to implement this is a DIY project.

Attached Images
File Type: jpg FE89.jpg (96.3 KB, 408 views)
File Type: jpg FE90.jpg (91.7 KB, 407 views)
  Reply With Quote
Old 24th May 2011, 07:28 AM   #6
Surfy is offline Surfy  Belgium
diyAudio Member
 
Join Date: May 2011
Dear mr Pass, thank you for the fast reply and schemes!Would you happen to have this scheme also for my production line which uses the front end board with single ended input only and optical bias, I suppose 1987 production run? thank you!
  Reply With Quote
Old 24th May 2011, 10:58 AM   #7
diyAudio Member
 
Join Date: Jul 2007
I would leave it as it is.
You have already the last SA/2 Series 'optical bias'.
The only thing you could consider is an update of the electrolytics.
I would not tamper with a 'Nelson Pass' Original.

The DC problem that you have is probably a failed transistor you have to isolate.
I had one in my SA/1's and I discoverd it because it had a much higher biasvoltage then the other ones. I replaced the faulty one, don't worry for matching because that's not necessary with all the parallel devices and the emmitterresistors that will balance the load.
You need some tools of cause like a Variac, DMM, dummyload and preferably a Scope.
These guys here can help you out I'm for sure.

You said you bought it for 3000 Euro's and that's a lot of money for a not working set of SA/2's
The seller should refund you the money if you did not already knew before that they had problems.
I sold mine for only a thousand more and they were perfect, had all the electrolytics updated and were SA/1's.
The seller should solve your problem for that amount you payed!
  Reply With Quote
Old 29th July 2011, 11:17 PM   #8
diyAudio Member
 
Join Date: Aug 2007
Send a message via AIM to SL10User Send a message via MSN to SL10User Send a message via Yahoo to SL10User
Default unknown frontend

Hello all,

recently got a S/500. It had DC offset 3 V in one channel and distortions at higher levels.

Found defective device 2N5566. Have ordered replacement already, hope it will work...



I noticed that these both previously posted schematics (Thanks, Nelson!) doesn't match with the PCB in my S/500. A matching schematic would have been very helpful. So I had to find the defective device by swapping with the good channel...

Does anybody (Nelson?) have knowledge of this specific version? Seems to be an early version (or stripped down)?

Here is a picture:

Thanks
Attached Images
File Type: jpg opticalbiasfrontend.jpg (153.7 KB, 297 views)
  Reply With Quote
Old 29th July 2011, 11:54 PM   #9
diyAudio Member
 
Join Date: Aug 2007
Send a message via AIM to SL10User Send a message via MSN to SL10User Send a message via Yahoo to SL10User
Second picture.

There is a # on the board - 540305b.
Attached Images
File Type: jpg FrontendBack.jpg (345.8 KB, 290 views)
  Reply With Quote
Old 30th July 2011, 05:07 PM   #10
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
Well, there's this:
Attached Images
File Type: jpg threshold stasis sch 84.jpg (62.9 KB, 282 views)
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Threshold SA 1 reinhard Pass Labs 12 13th September 2013 09:25 AM
Threshold SA/2 SA/3 Soderburg site? johnsciolino Pass Labs 3 14th January 2012 06:31 AM
Threshold SA/4e vs SA/1 RobertS61 Pass Labs 62 17th July 2011 01:31 PM
Threshold SA/ and SA/e series monoblocks gigi.vassallo Pass Labs 0 6th January 2010 07:07 PM
Threshold SA/4e and SA/2 Mywing Pass Labs 8 4th January 2010 10:45 PM


New To Site? Need Help?

All times are GMT. The time now is 07:44 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2