Here's a challenge.... - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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
Thread Tools Search this Thread
Old 6th November 2011, 11:03 PM   #1
diyAudio Member
Join Date: Jun 2006
Location: South East Queensland
Default Here's a challenge....

So I am looking at a high power Mosfet amp...400W plus and there is a couple of burnt tracks. From the output to the speaker connector is frazzled...also there is a high power Triac from speaker output to ground and this has burnt tracks to the ground point. Its almost as if this was designed to short the output to ground given a signal on the gate! What design consideration is this? Anyone seen it before? Its like a self destruct system!
Yes I checked the circuit very carefully, can't believe my eyes. I do not have a circuit diagram so had to draw it out....doesn't make sense.
Anyone?.............( Output Mosfets seem to be OK! )
BTW this is the "Soundpower" amp I wrote about info.
  Reply With Quote
Old 6th November 2011, 11:17 PM   #2
sregor is offline sregor  United States
diyAudio Member
Join Date: Jan 2006
Location: massachusetts
search for "crow bar" circuits. I've seen them in a few consumer products (pioneer integrated amp) I believe they are more common in pro and PA products. The idea, I think, was that without a relay, the best way to protect the speakers in case of an amplifier malfunction was to make it blow the fuse. Also found in power supplies. (I think BGW used them). YMMV Good luck.

Last edited by sregor; 6th November 2011 at 11:20 PM.
  Reply With Quote
Old 6th November 2011, 11:30 PM   #3
diyAudio Member
Join Date: Jun 2006
Location: South East Queensland
Thanks Steve, yes I never took 'crowbar' very seriously.
When your speakers are worth hundreds of dollars, maybe that's a way of saving money....who'd a thunk?
I will rebuild it all and check it out. The fuses were all blown but the tracks were certainly fried too........must have been one hell of a party!
  Reply With Quote
Old 6th November 2011, 11:43 PM   #4
CBS240 is offline CBS240  United States
diyAudio Member
CBS240's Avatar
Join Date: Aug 2005
Location: K-town
Hence the phrase, "My amp blew up!!!". The crow bar was triggered by something, better check the sand in the output stage.
All the trouble I've ever been in started out as fun......
  Reply With Quote
Old 6th November 2011, 11:56 PM   #5
diyAudio Member
Join Date: Jun 2006
Location: South East Queensland
It runs 2SJ056/2SK176 Hitachi Mosfets, ten on each channel and they are pretty indestructable I think so should be OK. I will have a close look though... Thanks guys!
  Reply With Quote
Old 7th November 2011, 06:33 AM   #6
diyAudio Member
east electronics's Avatar
Join Date: Jan 2006
Location: Athens GREECE
crow bar protection based on the DC presence in the output .If excessive Dc is there means that the amplifier is toasted any way so shunt the output to round to prevent speaker damage ...

i would say that more fear exist that crowbar will be activated for no or obvious reason than real false activations ....people really afraid of this but doesn't actually happen that often

truth is that if false activated you are about to blow an amplifier with a minor problem ... for PA use logic is good enough

  Reply With Quote
Old 7th November 2011, 10:04 AM   #7
diyAudio Member
Join Date: Jun 2006
Location: South East Queensland
Hello Sakis,
I have read some of your threads here. Ijasuu (Yahsu) Sorry I don
  Reply With Quote
Old 7th November 2011, 10:10 AM   #8
diyAudio Member
Join Date: Jun 2006
Location: South East Queensland
Hmmmm Computer was doing maintenance!

I have read some of your threads here....Yasu? (dont know how to spell Greek words in English.)

Thanks, yes, I will check for offset before I put it back together. Need a big variac now.

Good luck with your economy, Greeks have been around along time...great history. Youll be OK. Cheers
  Reply With Quote
Old 7th November 2011, 10:39 AM   #9
AndrewT is online now AndrewT  Scotland
diyAudio Member
Join Date: Jul 2004
Location: Scottish Borders
Can you check that the correctly rated fuses have been fitted to the supply rails?
Can you also check that these fuses are fitted between the main smoothing capacitor bank and the amplifier output devices?

It would seem sensible to me to design the output stage and the smoothing and the fuses and the Crowbar such that activation of the crowbar to protect the load does not destroy the amplifier.

It also seems very tempting when the crowbar has previously triggered that the operator having lost speaker output and incurred the wrath of the audience, chose to fit bigger/wrong fuses to try to prevent a re-occurrence.

If this was the case, then Crowbar did not destroy the amplifier, the operator destroyed the amplifier !!!!
regards Andrew T.
Sent from my desktop computer using a keyboard
  Reply With Quote
Old 7th November 2011, 12:33 PM   #10
diyAudio Member
indianajo's Avatar
Join Date: Jan 2010
Location: Jeffersonville, Indiana USA
When testing your repairs, get everything working, test it thoroughly for AC & DC with load resistors on the speaker terminals (insensitive to DC) before putting the crowbar back. I had to replace both triacs, and one trigger diac. Output transistor faults tend to cause a lot of damage to the bias circuit. My $55 PV1.3k amp is putting out 65 VDC right now- another handful of blown diodes + who knows. The 1.3k burned circuit traces at the triacs, so I installed 25 A 32V AG3 fuses between the power supply and the O.T. subassembly. (1000 W @ 2 ohm = 22 amps). Another O.T. that passed the double diode test blew while debugging and took a circuit trace when the triac went off again. The fuses have drops on the wires but didn't melt. So the 1000W rating is a bit suspect, considering the traces melt before the fuses. Trying 20 amp fuses this time. Main breaker didn't go off this time, either, I got to the AC strip switch first.
As far as Andrew's recommended fuses between the transformer and capacitor bank, it would take a better soft start circuit than the 1.3k has to protect the fuses due to turn on surge. It surges so hard the trouble light goes dim when I turn it on. I think refrigerator motor start NTC thermistors are about $30, but they don't work at 95 VDC. The other trouble with thermistors is that when the band takes a break, they go cold and protect again at the first chord.
My most expensive amp was $60, I'm up to $600 a pair on the speakers now, used, so I like having a crowbar on an amp with the O.T.'s direct coupled to the speakers. As much trouble as this PV1.3k has been to repair, I'm selling it off if I can't figure out a better protection circuit - and then build 3 channels of single supply capacitor coupled amp which destroys itself when overheated, not the unpurchaseable soft suspension hammond speakers.
Dynakit ST70, ST120, PAS2,Hammond H182(2 ea),H112,A100,10-82TC,Peavey CS800S,1.3K, SP2-XT's, T-300 HF Proj's, Steinway console, Herald RA88a mixer, Wurlitzer 4500, 4300

Last edited by indianajo; 7th November 2011 at 12:46 PM.
  Reply With Quote


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
Here is a Challenge latala Solid State 41 12th May 2011 01:13 AM
Design Challenge #2 kgillies Subwoofers 3 12th June 2007 06:05 AM
A challenge for the brave! Kennmunk Subwoofers 3 4th January 2006 10:40 PM
a challenge --or I need help lawrence99 Car Audio 0 9th March 2005 04:44 AM
The challenge ! thylantyr Solid State 51 24th July 2003 08:41 PM

New To Site? Need Help?

All times are GMT. The time now is 09:31 AM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2