sima amplifier questions - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 16th November 2009, 10:47 PM   #1
diyAudio Member
 
Join Date: Sep 2009
Default sima amplifier questions

I have an amplifier made in the early 80's by Sima Audio of Montreal, Canada. The model number is AB200 and appears to be 100W/ch into 8 ohms.

I rescued it from a local rock'n'roll band (who thought it was a tube amp!) just for the enclosure and power supply, but after looking at the amplifier sections it seems worthy of refurbishment.

It has been around the block a few times but as far as I can tell it has never needed repair (until I started tinkering with it, sigh).

I have reversed engineered the schematic from the pcb (hopefully attached) and I have some questions which I will follow up with.
Attached Images
File Type: png sima.png (24.0 KB, 130 views)
  Reply With Quote
Old 17th November 2009, 12:03 AM   #2
diyAudio Member
 
Join Date: Nov 2008
Location: Brazil
What are questions?
  Reply With Quote
Old 17th November 2009, 12:50 AM   #3
diyAudio Member
 
Join Date: Sep 2009
1. While playing with the bias adjustment, I went too far and 2N6553-Q6 died (shorted). Is this an inherent limitation of this bias design circuit, or was it just an old (underspec'ed perhaps?) component operating on the edge?

2. I think 29113/114 would be a suitable replacement TO3 for the 15003/004, but what about replacing the 2N6553/6556 drivers with MJE15030/31? The bias circuit also uses the 6553/6556, what is a suitable replacement for these? I anticpate mods to handle the different pinouts on newer devices of course.

3. Why does the high side driver Q6 have a base resistor R9 but the low side Q7 does not? (I am just starting to read Self and Slone books about the theory of operation...)
  Reply With Quote
Old 17th November 2009, 01:49 AM   #4
diyAudio Member
 
Miles Prower's Avatar
 
Join Date: May 2005
Location: USA
Blog Entries: 6
Quote:
Originally Posted by lmartine3 View Post
1. While playing with the bias adjustment, I went too far and 2N6553-Q6 died (shorted). Is this an inherent limitation of this bias design circuit, or was it just an old (underspec'ed perhaps?) component operating on the edge?
Since it's operating into just 47R of emitter resistance, there isn't much in the way of current limiting. Should have had either more emitter resistance or a transistor with a higher Pc rating.

Quote:
3. Why does the high side driver Q6 have a base resistor R9 but the low side Q7 does not? (I am just starting to read Self and Slone books about the theory of operation...)
Looks like a quick 'n' dirty fix for oscillation. Putting a base stopper there fixed the problem, and so they didn't bother to add one to the other side.
__________________
There are no foxes in atheistholes
www.dolphin-hsl.com
  Reply With Quote
Old 17th November 2009, 01:05 PM   #5
diyAudio Member
 
Join Date: Sep 2009
Quote:
Originally Posted by Miles Prower View Post
Since it's operating into just 47R of emitter resistance, there isn't much in the way of current limiting. Should have had either more emitter resistance or a transistor with a higher Pc rating.



Looks like a quick 'n' dirty fix for oscillation. Putting a base stopper there fixed the problem, and so they didn't bother to add one to the other side.
Hmm, thanks for the info.

Just adding a pic of the internals, check out the heat sinks.
Attached Images
File Type: jpg DSC_0089.jpg (99.5 KB, 97 views)
  Reply With Quote
Old 17th November 2009, 05:59 PM   #6
diyAudio Member
 
Laszlo Ferencz's Avatar
 
Join Date: Jul 2009
Location: Budapest
Nice find!

I'm interested what are the spec's of the power transformer and PSU caps (these huge blue ones)?
  Reply With Quote
Old 17th November 2009, 10:37 PM   #7
diyAudio Member
 
Join Date: Sep 2009
Quote:
Originally Posted by Laszlo Ferencz View Post
Nice find!

I'm interested what are the spec's of the power transformer and PSU caps (these huge blue ones)?
The transformer has a nameplate rating of 371VA (exactly!) at 75Vct. The caps are I think 10000 uF at 63V (85V surge). No ripple current rating though.

With no load, the rails are at +-56V, clipping at 30.5Vrms.

With only one channel driven with a sine wave, it clips at 30.1Vrms into 8 ohms (52V rails) and 29.5Vrms into 4 ohms (49V rails).

The 8 ohm load showed 220W input on the primary and 405W with the 4 ohm load, basically only 50% efficient end to end.
  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
I need the Sima W-3050 or W-2002 schematic gaetan8888 Solid State 12 19th March 2014 03:26 AM
amplifier questions Professor smith Pass Labs 14 14th November 2008 02:32 PM
Questions about how to decrease the PASS A-40 amplifier into a class AB amplifier. novtango Pass Labs 2 21st October 2002 01:50 AM


New To Site? Need Help?

All times are GMT. The time now is 10:56 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