img pa-amp issue - 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 9th August 2009, 01:57 PM   #1
gruni is offline gruni  Germany
diyAudio Member
 
Join Date: Feb 2008
Default img pa-amp issue

hello everybody!
i have a img stage line sta-160 pa amplifier. it works perfectly but when i opened it i realized that there are the two 100mA fuses of the 56v rails blown. what could the rail have been for?
perhaps anybody has a schematic for the amp?

thank you
  Reply With Quote
Old 9th August 2009, 06:17 PM   #2
diyAudio Member
 
megajocke's Avatar
 
Join Date: Jan 2003
You can find the schematic here:
http://www.abeltronics.co.uk/diagrams.php?z=stageline

Those fuses are for the higher front-end voltage. If blown the front-end is still powered through D11 and D33, so the amplifier will work but with lower output power as the rail loss will be higher. I'd guess they just became tired and blew because of the inrush current of the 1000F 25V capacitors filtering this rail.
  Reply With Quote
Old 9th August 2009, 06:42 PM   #3
gruni is offline gruni  Germany
diyAudio Member
 
Join Date: Feb 2008
hi megajoke!

thank you very much for the answer and the schematic!
i hope it will help me fixing the bit of hissing on the left channel.
  Reply With Quote
Old 9th August 2009, 06:46 PM   #4
AndrewT is online now AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
the hissing could be a symptom of another fault.
That same fault may be why the fuse/s blew (another symptom).
__________________
regards Andrew T.
  Reply With Quote
Old 9th August 2009, 06:57 PM   #5
gruni is offline gruni  Germany
diyAudio Member
 
Join Date: Feb 2008
what could it be? something in the 55v-part?
i think it cant be any bad damage, because the channel works perfectly except for he hissing
  Reply With Quote
Old 9th August 2009, 07:12 PM   #6
diyAudio Member
 
megajocke's Avatar
 
Join Date: Jan 2003
If anything, the filter caps, decoupling caps or rectifier. There isn't much else that can go wrong if the amplifiers are still working. I suggest you check those. If one of the decoupling capacitors or the bridge rectifier did short it would take out the front-end supply fuses and then the main power supply, backfeeding through the diodes, would probably destroy the shorted part leaving the amplifier in a still working condition.

The hissing might be another, non-related, fault. Is it dependent on level contol setting?
  Reply With Quote
Old 9th August 2009, 07:20 PM   #7
gruni is offline gruni  Germany
diyAudio Member
 
Join Date: Feb 2008
yes, a bit. if i set the left volume to 0, there is no hissing at all. but after about 9 o'clock the hissing doesnt increase... so i don't think its the preamplifier

edit: tomorrow i'll take the amp apart so i can measure for any short-circuits.

i realized another thing: in the schematic there are two output transistor pairs per channel. but my amp only has two transistors for each channel? are there different versions or so of the amp?
  Reply With Quote
Old 9th August 2009, 07:36 PM   #8
diyAudio Member
 
megajocke's Avatar
 
Join Date: Jan 2003
The board is probably shared with a higher power model. I didn't notice at first, but the schematic says "N.F." (not fitted) besides one pair of outputs so it's not supposed to have two pairs.
  Reply With Quote
Old 11th August 2009, 05:18 PM   #9
gruni is offline gruni  Germany
diyAudio Member
 
Join Date: Feb 2008
the hissing was produced by the preamp. just swapped the two connectors for left/right coming from the preamp, and the hissing was on the other channel. replaced the opamp in the preamp, now the amp is dead quiet i will disassmble it completely to look for short-circuits and then order new 100ma fuses, as i dont have such ones lying around.
  Reply With Quote
Old 11th August 2009, 05:22 PM   #10
AndrewT is online now AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
are the fuses T100mA or F100mA?
__________________
regards Andrew T.
  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
Hum issue e_fortier Class D 6 3rd March 2009 03:42 AM
Issue with cdrom and Dac in a Box toolkit Digital Source 0 31st October 2007 10:05 AM
Help With TLB / Amp Issue Forster Multi-Way 0 2nd May 2007 08:51 PM
Amp and Sub issue AudioMistake Car Audio 1 26th June 2005 09:59 PM


New To Site? Need Help?

All times are GMT. The time now is 11:37 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