Go Back   Home > Forums > Loudspeakers > Multi-Way

Multi-Way Conventional loudspeakers with crossovers

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 1st April 2004, 06:48 PM   #1
diyAudio Member
 
Join Date: Jan 2002
Location: Spfld, OR
Default Does having two amplifiers hooked into the same pair of speakers cause any problems?

Many times in the past I have had two diffferent amplifiiers hooked into the same pair of speakers so I could switch between them to see if I could hear any differences, and recently someone has absolutely insisted that I never did that because it would cause one of them to blow. I don't even think that would happen if they were both on at the same time, but I could be wrong... any input?
  Reply With Quote
Old 1st April 2004, 06:55 PM   #2
sreten is offline sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
I suggest verifying this with both on at the same time could be expensive.

With similar rated amplifiers as long as one is turned off then there is no real
danger, though cable loading and possible zobel correction will be unrealistic.
As well as reverse voltage diode practise differences in the amplifiers.

Its a practise of little merit for direct comparisons.

sreten.
  Reply With Quote
Old 1st April 2004, 06:58 PM   #3
Speakerholic
diyAudio Moderator
 
Cal Weldon's Avatar
 
Join Date: Jan 2004
Location: British Columbia
The possibility of send high level input back into the speaker outputs of an amplifier doesn't sound very productive. I agree this should be avoided.

Cal
  Reply With Quote
Old 1st April 2004, 07:03 PM   #4
diyAudio Member
 
jneutron's Avatar
 
Join Date: Jan 2004
Location: away
For a simple class b output, that would be rather dangerous.

With the supplies off, it is possible to reverse bias the emitter-base junctions, and forward the collector-base junction.

That would mean that somewhere in the 5 to 15 volt region, you would be able to put the e-b junctions into reverse avalanch breakdown, with very little to prevent destroying the output transistors..

Do not do it for any solid state amps..

John
  Reply With Quote
Old 1st April 2004, 07:18 PM   #5
sreten is offline sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
Quote:
Originally posted by jneutron
With the supplies off, it is possible to reverse bias the emitter-base junctions, and forward the collector-base junction.

That would mean that somewhere in the 5 to 15 volt region, you would be able to put the e-b junctions into reverse avalanch breakdown, with very little to prevent destroying the output transistors..
John
Can't see this happening myself, sreten.
  Reply With Quote
Old 1st April 2004, 07:32 PM   #6
diyAudio Member
 
jneutron's Avatar
 
Join Date: Jan 2004
Location: away
Quote:
Originally posted by sreten


Can't see this happening myself, sreten.
Hmmm...

Pop up a schematic of a simple B output stage, emitter out..

Short across the supply capacitors, to represent the off condition.

Put 20 volts positive on the output line.

You are taking the NPN emitter above the supply voltage present on the collector.

C-B junction will be forward biased, E-B junction reversed.

Typical E-B reverse breakdowns are 5 to 15 volts..

If good current is drawn at 15 volts, the base dissipation will fry the unit.

Cheers, John
  Reply With Quote
Old 1st April 2004, 08:01 PM   #7
sreten is offline sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
Hi John,

don't really want to argue about this as we both agree its not a good idea.

Seems to me quite complicated if you include the drivers (which supply base
current so we are talking 10V to 30V for both junctions) and the driver base
resistance will limit current, which is usually ridiculousy high.

sreten.
  Reply With Quote
Old 1st April 2004, 08:12 PM   #8
diyAudio Member
 
jneutron's Avatar
 
Join Date: Jan 2004
Location: away
Quote:
Originally posted by sreten
Hi John,

don't really want to argue about this as we both agree its not a good idea.

Seems to me quite complicated if you include the drivers (which supply base
current so we are talking 10V to 30V for both junctions) and the driver base
resistance will limit current, which is usually ridiculousy high.

sreten.
We appear to disagree on a point...we are not arguing. We are having a nice discussion...

I have been talking about when an amplifier is off..you have obviously been talking about the amplifier being on...a funny discontinuity of understanding...

On, I agree with you completely..

Off is what I have been talking about...where the output devices are subjected to reversed voltages..

Cheers, John
  Reply With Quote
Old 1st April 2004, 08:37 PM   #9
sreten is offline sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
No I'm talking off.

The output pairs bases are not connected to the voltage rail,
they are typically driven by the emitters of the driver pair.

This is for the most common emitter follower pair, CFP is different....

sreten.
  Reply With Quote
Old 1st April 2004, 08:46 PM   #10
Svante is offline Svante  Sweden
diyAudio Member
 
Svante's Avatar
 
Join Date: Feb 2004
Location: Stockholm
At the risk of making a fool of myself:
isn't the back direction of the typical B-E "diode" somewhat like a poor zener, at about 5 volts? Given this and the diode between B-E, there seems to be a great risk of damage if the supply is grounded and say 20 volts is applied to the output of the amplifier.
For sure, I'd recommend him to have a (non-shorting) switch or relay to flip between the amplifiers.
__________________
Simulate loudspeakers: Basta!
Simulate the baffle step: The Edge
  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
Aleph-X: problems when hooked up xcel Pass Labs 3 26th April 2009 12:22 PM
speakers hooked in series kendt Multi-Way 11 13th April 2009 09:53 AM
I'm hooked on large coax, now to build a pair. johnsonad Multi-Way 52 13th February 2009 12:16 AM


New To Site? Need Help?

All times are GMT. The time now is 03:33 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