Disaster NEED HELP PLS! - 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 18th September 2005, 06:25 PM   #1
leander is offline leander  Malta
diyAudio Member
 
Join Date: Aug 2005
Unhappy Disaster NEED HELP PLS!

Disaster

Hi people, I am in urgent need of help before going mad!
This is the amp Iíve just made and it took me a whole week to do it and managed to make it working perfectly.
( http://www.ampslab.com/c300.htm )
I wasnít so lucky the second time I hooked it up because as pumping up some music, the center tap wire (ground of amp) went loose and the thing just freaked out!
I switched of immediately and rehooked the ground properly, however only a loud buzzing sound was heard! A disaster!
Checked out the components, no components were carbonized.
Checked out two power transistors any hfe resulted to be fine (aprox150)
As a start Iím thinking of replacing all small power bjt transistors.
Iím not an expert in troubleshooting, PLS what is your opinion about the problem


Here below is a schematic of the amp with grounds illustrated with red boxes
Attached Images
File Type: jpg c300_schemahires.jpg (64.7 KB, 360 views)
  Reply With Quote
Old 18th September 2005, 07:19 PM   #2
diyAudio Member
 
Jan Dupont's Avatar
 
Join Date: Apr 2003
Location: Copenhagen, Denmark
Send a message via MSN to Jan Dupont
Check the Vbe (Voltage between base and emitter) on all transistors like this:

Connect the input to gnd.
Do not connect any load.
Watch out for components that get hot.

Power up the amp, and meassure the Vbe's.
They should ALL meassure app. 0.6 Volt +/-50mV

Good luck
__________________
Free Schematic and Service Manual downloads www.audio-circuit.dk, Company: www.dupont-audio.com, Joint venture: www.DupontMantra.com
  Reply With Quote
Old 18th September 2005, 07:47 PM   #3
dtrif is offline dtrif  Greece
diyAudio Member
 
Join Date: Apr 2005
Location: Athens, Greece
Default Keep in mind that a transistor that measures a normal hfe,

may be damaged (it has happened to me). Your desicion to replace small transistors is quite reasonable, as they are more commonly damaged in such situations. In a situation like this, where I couldn't find a solution, I simulated the whole thing, found voltages in different places in the simulator, and compared them with real life. Wrong voltages existed around a small signal transistor (previously measured with a normal hfe). When I replaced it everything was ok.
I am not a repairer professionally, so this approach may be wrong. It's just what I did. Anyone else with more experience please contribute. It may be even a passive component (capacitor perhaps), which would be very unfortunate, because I thing it will be much more difficult to find it.
__________________
Dimitris
  Reply With Quote
Old 18th September 2005, 08:26 PM   #4
jaycee is offline jaycee  United Kingdom
diyAudio Member
 
Join Date: Apr 2004
Location: Norwich, UK
Check Q5, Q6, Q8. Also check your filter capacitors arent damaged.
  Reply With Quote
Old 18th September 2005, 09:48 PM   #5
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
Did you check that your supply voltages are normal? Fuses?

Jan Didden
__________________
If you don't change your beliefs, your life will be like this forever. Is that good news? - W. S. Maugham
Check out Linear Audio!
  Reply With Quote
Old 18th September 2005, 10:55 PM   #6
diyAudio Member
 
Ultima Thule's Avatar
 
Join Date: Jan 2004
Location: Koskenkorva Land
Hi leander,

just of curiosity to your amplifier, I may be a bit tired to think clearly as it's 2 a clock in the night here, but what is the idea behind the VAS formation around Q 9 and Q 10?

Cheers Michael
__________________
"If transistors are blueberries and FETs are strawberries, then tubes must be.. pears"
Michael 29th January 2010
  Reply With Quote
Old 18th September 2005, 11:05 PM   #7
Tim__x is offline Tim__x  Canada
diyAudio Member
 
Join Date: Jun 2004
Location: Edmonton area, Alberta
At first glance, Q9 appears to speed up turn-off of Q10. Though perhaps there is more to it than that.
  Reply With Quote
Old 18th September 2005, 11:26 PM   #8
diyAudio Member
 
darkfenriz's Avatar
 
Join Date: Jun 2004
Location: Warsaw
With mirrored LTP and EF buffer at clipping Q10 needs such limiting. Otherwise would saturate very deeply and potential on its base would be close to zener voltage of D1. I'm not sure if I'm right but it definitely looks to do nothing in 'linear' range.
  Reply With Quote
Old 18th September 2005, 11:40 PM   #9
jaycee is offline jaycee  United Kingdom
diyAudio Member
 
Join Date: Apr 2004
Location: Norwich, UK
Q8 and Q10 form an EF VAS. Q9 is a safety cutoff, when the VI limiter activates it can result in Q10 being saturated. Q9 detects this and cuts the base current.

Leach explains this for his own amplifer here
  Reply With Quote
Old 19th September 2005, 06:23 AM   #10
diyAudio Member
 
Join Date: Dec 2004
Location: Berlin
Quote:
Originally posted by jaycee
Q8 and Q10 form an EF VAS. Q9 is a safety cutoff, when the VI limiter activates it can result in Q10 being saturated. Q9 detects this and cuts the base current.

Leach explains this for his own amplifer here
Yes and no :collector of Q9 must go to base of Q8, R18 should be zero!
  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
[DIY] HEXFET AMP total disaster? egberttheone Solid State 73 6th June 2013 12:30 PM
Ebay Tube amp buy disaster itsmejto Tubes / Valves 55 20th June 2008 08:34 AM
Zanden tda1541a NOS review disaster! ash_dac Digital Source 0 21st February 2007 03:37 PM
Near Disaster! Bikeman Everything Else 1 4th September 2003 05:18 AM


New To Site? Need Help?

All times are GMT. The time now is 02:48 PM.


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