Dc protection with gainclone? - diyAudio
Go Back   Home > Forums > Amplifiers > Chip Amps

Chip Amps Amplifiers based on integrated circuits

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 2004, 02:24 PM   #1
edpgc is offline edpgc  United Kingdom
diyAudio Member
 
Join Date: Apr 2004
Location: Birmingham, UK
Default Dc protection with gainclone?

Hi I've got a LM4780 based amp and have implemented some relay driven DC protection for the speakers, however is it necessary? What failure modes are there for the LM4780 or similar that could cause it to output a DC dignal? How good is its built in protection?

If one of the rails potential was lost, even partially would it protect the speakers?

Im just wondering whether I should take it out or leave it there!?

Cheers

Ed
  Reply With Quote
Old 18th September 2004, 02:40 PM   #2
diyAudio Member
 
Peter Daniel's Avatar
 
Join Date: Jul 2002
Location: Toronto, Canada
Send a message via AIM to Peter Daniel
I'm not sure about 4780, but LM3875 has a protection against one rail being off.

When one rail fails, there is no DC on the output. You need to have a load present to observe it (high power resistor is fine for testing).

You might want to protect the input, from DC being passed from a previous stage, especially with minimized circuits when the amp hasn't unity gain at DC.

A simple coupling cap would do a job, and basically output protection circuit is not a neccessity.
__________________
www.audiosector.com
“Do something really well. See how much time it takes. It might be a product, a work of art, who knows? Then give it away cheaply, just because you feel that it should not cost so much, even if it took a lot of time and expensive materials to make it.” - JC
  Reply With Quote
Old 18th September 2004, 03:41 PM   #3
edpgc is offline edpgc  United Kingdom
diyAudio Member
 
Join Date: Apr 2004
Location: Birmingham, UK
Hmm, well that was a wate of a few hours using spice. lol So is there any scenario whereby output protection would be necessary? I suspect only the failure of the chip itself in some rather specific way.

Thanks
  Reply With Quote
Old 18th September 2004, 03:54 PM   #4
Banned
 
Join Date: Aug 2002
Location: New York, NY
Send a message via AIM to yldouright Send a message via Yahoo to yldouright
edpgc

As I understand it, the only failure danger with this chip is if it starts oscillating and even that is mitigated when you don't invert it but I'm not the authority on this chip here.
  Reply With Quote
Old 18th September 2004, 04:44 PM   #5
diyAudio Member
 
analog_sa's Avatar
 
Join Date: Aug 2002
Location: Sofia
Quote:
So is there any scenario whereby output protection would be necessary? I suspect only the failure of the chip itself in some rather specific way.
There is no doubt that a complete meltdown of the chip may result DC at output. It doesn't seem to happen often and most of us prefer to not have a relay along the signal line but if you want 100% protection a relay seems the only option
  Reply With Quote
Old 18th September 2004, 05:01 PM   #6
Banned
 
Join Date: Aug 2002
Location: New York, NY
Send a message via AIM to yldouright Send a message via Yahoo to yldouright
ananlog_sa

I think I read in another thread that you run a battery gainclone. If this is so, which circuit did you use? I'm planning on gutting an old Kenwood integrated to put in a gainclone, DAC and phono stage to run on 4 12V/7Ah SLA batteries and could definitely use your help and experience in this adventure if you have any.
  Reply With Quote
Old 18th September 2004, 05:44 PM   #7
diyAudio Member
 
analog_sa's Avatar
 
Join Date: Aug 2002
Location: Sofia
Quote:
run a battery gainclone
No. I only tried batteries briefly. PD is your guy.
  Reply With Quote
Old 18th September 2004, 07:31 PM   #8
diyAudio Member
 
moving_electron's Avatar
 
Join Date: Jan 2004
Location: Where the rain does fall but the trees grow tall
Quote:
Originally posted by analog_sa


There is no doubt that a complete meltdown of the chip may result DC at output. It doesn't seem to happen often and most of us prefer to not have a relay along the signal line but if you want 100% protection a relay seems the only option
Fuses are an alternative.

I use fast blow fuses in series with the speaker +, especially during amp testing. I use 3/4 - 1 amps worth of fuse for every 25W of speaker continuous RMS rating.

Saved me when I did a bonehead thing related to making a change in an amp. It was not a DC problem but would have been a "to much output" problem for my speakers. I was glad to have the protection.
  Reply With Quote
Old 18th September 2004, 07:48 PM   #9
usekgb is offline usekgb  United States
diyAudio Member
 
usekgb's Avatar
 
Join Date: Feb 2003
Location: Salt Lake City, UT, USA
I have seen quite a number of LM3886 chips fail, and pass 40 volts DC to the outputs, frying the compression driver the chip was powering. This happened to the first generation of the JBL EON G2 powered PA speakers. Basically, the chip got too hot, failed, and started passing DC. I believe this was happening because JBL was just trying to get too much power out of the 3886. In the next generation of amp boards, they switched to the TDA7293, and the problem was solved.

So, to make a long story short, these chips can fail and pass DC. But this will only occur in extreme circumstances.

Cheers,
Zach
__________________
Ahhhhhhhhh...............That's what that button does.
  Reply With Quote
Old 18th September 2004, 07:51 PM   #10
Nuuk is offline Nuuk  United Kingdom
diyAudio Member
 
Nuuk's Avatar
 
Join Date: Feb 2003
Location: Somerset, SW England
If you want to 'play safe' have a look at these .

As already stated, in theory it is not a good idea to have a relay in the speaker line but in practice, it hardly notices at all and the peace of mind it gives you may even help you enjoy the music more.
__________________
The truth need not be veiled, for it veils itself from the eyes of the ignorant.
  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
ESP P3a protection? roger-k Solid State 14 3rd November 2006 01:27 AM
speaker protection (OR) overload protection myanmar Solid State 7 13th July 2006 08:21 AM
protection Dj BASS AMP Solid State 7 26th March 2003 09:53 AM
PCB Protection DieterD Solid State 13 28th August 2002 12:02 PM


New To Site? Need Help?

All times are GMT. The time now is 03:09 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