Post by thread:[EE]: Unloaded outputs on audio amps.. will they b

On rec.audio.car there is a recent discussion on whether or not unused speaker outputs on amplifiers should be loaded or not. so I figure there are far more knowledgeable people on this list when it comes to the actual how's and whys then on the car stereo newsgroup so I come to ya'll looking of answers :) Someone suggested that if left unloaded the output transistors could oscillate and burn themselves out it not protected (i.e. thermal disabling or some other method) I talked to my father and he explained the theory behind this and I believe it basically follows along the same thread of the grounding of unused PIC pins... hence my idea to post it here. someone also asked if the outputs on the headunit itself would also be prone to this or is it all a bunch of urban ledgend type stuff. I guess I'm looking for yes, no or a maybe and sometype of description that I can relay back to the interested people. Thanks, Damon Hopkins -- /-=-=-=-=-=-=-=-=-=-=-=-=-\ | http://www.openpic.com | | New OpenSource Pic site | \-=-=-=-=-=-=-=-==-=-==-=-/ -- http://www.piclist.com hint: To leave the PICList spam_OUTpiclist-unsubscribe-requestTakeThisOuTmitvma.mit.edu>

Damon Hopkins wrote: >On rec.audio.car there is a recent discussion on whether or not unused >speaker outputs on amplifiers should be loaded or not. >so I figure there are far more knowledgeable people on this list when it >comes to the actual how's and whys then on the car stereo newsgroup so I >come to ya'll looking of answers :) > > Someone suggested that if left unloaded the output > transistors could >oscillate and burn themselves out it not protected (i.e. thermal >disabling or some other method) >I talked to my father and he explained the theory behind this and I >believe it basically follows along the same thread of the grounding of >unused PIC pins... hence my idea to post it here. >someone also asked if the outputs on the headunit itself would also be >prone to this or is it all a bunch of urban ledgend type stuff. > > I guess I'm looking for yes, no or a maybe and sometype of > description >that I can relay back to the interested people. I can't see any good reason for it in modern amplifier designs. The amplifier output stage should not rely on the speaker loading to determine its stability. I'd say it might be a left-over from the old days of valve (tube) amplifiers which were unstable if the output transformer was left unloaded. I remember sparks flying (internal to the amp) a long time ago when I accidently turned my old Sansui HiFi (valve) amplifier way up with the speakers not connected. As you say, what happens to the speaker outputs of a car audio head unit that is only feeding a bigger external amplifier via the line level outputs? (Hint: nothing !) As you've probably guessed, a lot of car audio people are badly informed. :-) Regards... -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-requestKILLspam@spam@mitvma.mit.edu>

Leave them floating, no need to load them. Unloaded power amps are stable. Shoot any engineer that designs an audio power amp that is unstable into no load! -Bob At 10:07 PM 8/17/2000 -0400, you wrote: >On rec.audio.car there is a recent discussion on whether or not unused >speaker outputs on amplifiers should be loaded or not. >so I figure there are far more knowledgeable people on this list when it >comes to the actual how's and whys then on the car stereo newsgroup so I >come to ya'll looking of answers :) > > Someone suggested that if left unloaded the output transistors could >oscillate and burn themselves out it not protected (i.e. thermal >disabling or some other method) -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestKILLspammitvma.mit.edu>

I remember that some of the early transistor amps with transformer output had a similar problem - unloaded outputs could generate enough volts to cause insulation breakdown in the transformer or high dissipation in the output transistors. Shouldn't be a problem these days I would hope! Richard P David Duffy <piclist@AUDIOVISUALDEVIC To: .....PICLISTKILLspam.....MITVMA.MIT.EDU ES.COM.AU> cc: Sent by: pic Subject: Re: [EE]: Unloaded outputs on audio amps.. will they burn out? microcontroller discussion list <EraseMEPICLISTspam_OUTTakeThisOuTMITVMA.MIT.EDU> 18/08/00 14:21 Please respond to pic microcontroller discussion list Damon Hopkins wrote: {Quote hidden}>On rec.audio.car there is a recent discussion on whether or not unused >speaker outputs on amplifiers should be loaded or not. >so I figure there are far more knowledgeable people on this list when it >comes to the actual how's and whys then on the car stereo newsgroup so I >come to ya'll looking of answers :) > > Someone suggested that if left unloaded the output > transistors could >oscillate and burn themselves out it not protected (i.e. thermal >disabling or some other method) >I talked to my father and he explained the theory behind this and I >believe it basically follows along the same thread of the grounding of >unused PIC pins... hence my idea to post it here. >someone also asked if the outputs on the headunit itself would also be >prone to this or is it all a bunch of urban ledgend type stuff. > > I guess I'm looking for yes, no or a maybe and sometype of > description >that I can relay back to the interested people. I can't see any good reason for it in modern amplifier designs. The amplifier output stage should not rely on the speaker loading to determine its stability. I'd say it might be a left-over from the old days of valve (tube) amplifiers which were unstable if the output transformer was left unloaded. I remember sparks flying (internal to the amp) a long time ago when I accidently turned my old Sansui HiFi (valve) amplifier way up with the speakers not connected. As you say, what happens to the speaker outputs of a car audio head unit that is only feeding a bigger external amplifier via the line level outputs? (Hint: nothing !) As you've probably guessed, a lot of car audio people are badly informed. :-) Regards... -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestspam_OUTmitvma.mit.edu -- http://www.piclist.com hint: To leave the PICList @spam@piclist-unsubscribe-requestKILLspammitvma.mit.edu>

It depends... well that's a pretty generic answer. - Unused outputs of valve amplifiers need to be terminated with the correct load due to the fact that 99.9% of them have an output transformer configured as a current transformer. With no load the voltage on the output tends to 'infinity', only limited by real-life things like magnetic saturation, huge sparks and so on... - Car audio amps are made to drive into very low impedance loads, often as low as 2 ohms. Like all consumer goods component cost is very important. With even a 'classic' design (dc-dc and linear amp) a designer may decide to make the (not totally unreasonable) assumption that all outputs are always connected. This might lead to a design which is not stable with no load connected, leading to (usually) high frequency oscillations of the output stage and destruction of that stage. - Car audio amps are also a good place to find innovative amplification technology, such as 'pure' class c amplifiers; i.e. the whole amp is in fact a cleverly controlled switch mode power supply. Some SMPS are unstable with no load, usually they don't oscillate in a destructive manner, and those that are vulnerable to an unloaded output are usually step-up converters with no (or a very small) internal output capacitor... not a likely design for an amplifier. Thankfully you can pretty easy check if an amp is stable with no load by looking at the output with no load on an oscilloscope. Remember that both outputs on a car amp are floating, and that the scope probe _is_ actually putting a small capacitive load on the output, which if you are really unlucky will be enough to damp out the horrific oscillation that is occurring the rest of the time. or: stick the amp on a bench hooked up to a car battery with a load (speaker) connected, running at a reasonably quiet volume. Let it run for 'a while'. put your hand over the amp and try and get a feel for how hot it is. Now try the same thing without the speaker connected. If it's cooler then you don't need a load. If it is a lot hotter then you probably do. Well I couldn't let this fascinating debate actually be _resolved_ now, could I ? Regards, Simon -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]: PIC only [EE]: engineering [OT]: off topic [AD]: advertisements

Ultimately it comes down to how the manufacturer designed the unit. While it would be better and not much more costly to design a unit which is not prone to this, it is reasonable for a designer to assume that if you aren't connecting speakers then there is no point in even powering the amp. So, in short, RTM! (Read the Manual) If having an unconnected speaker is going to destroy the amp, then you can bet your money they have a note in the manual saying, "Never run the amp without speakers or a suitable load resister attached." Otherwise they have a customer service nightmare. But, I imagine, even in amps that may oscillate to infinity they probably install some sort of protection which keeps it just barely within spec. You may find that your amp consumes as much power as though a speaker were connected. -Adam Damon Hopkins wrote: {Quote hidden}> > On rec.audio.car there is a recent discussion on whether or not unused > speaker outputs on amplifiers should be loaded or not. > so I figure there are far more knowledgeable people on this list when it > comes to the actual how's and whys then on the car stereo newsgroup so I > come to ya'll looking of answers :) > > Someone suggested that if left unloaded the output transistors could > oscillate and burn themselves out it not protected (i.e. thermal > disabling or some other method) > I talked to my father and he explained the theory behind this and I > believe it basically follows along the same thread of the grounding of > unused PIC pins... hence my idea to post it here. > someone also asked if the outputs on the headunit itself would also be > prone to this or is it all a bunch of urban ledgend type stuff. > > I guess I'm looking for yes, no or a maybe and sometype of description > that I can relay back to the interested people. > > Thanks, > > Damon Hopkins > > -- > /-=-=-=-=-=-=-=-=-=-=-=-=-\ > | http://www.openpic.com | > | New OpenSource Pic site | > \-=-=-=-=-=-=-=-==-=-==-=-/ > > -- > http://www.piclist.com hint: To leave the PICList > KILLspampiclist-unsubscribe-requestKILLspammitvma.mit.edu -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]: PIC only [EE]: engineering [OT]: off topic [AD]: advertisements

For only $79.95, I'll sell you my precision output terminator. This keeps reflected energy from the unterminated outputs from coming back through the supply, and causing distortion on the other channels. If you prefer, the Ultra-Terminator is available, at $129.95, for higher end systems, where exact matching is important. There is an adjustment you can trim to exactly match your system, and remove that confused soundstage that results from reflected energy distortion. The standard model is adequate for automotive systems, since the tiny bit of remaining distortion after termination is inaudible in the automotive environment. You will need one per unused channel. (did I miss my calling, or what? :) -- Where's dave? http://www.findu.com/cgi-bin/find.cgi?kc6ete-9 -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]: PIC only [EE]: engineering [OT]: off topic [AD]: advertisements

Love It <G G G> Keith -----Original Message----- From: David VanHorn [SMTP:RemoveMEdvanhornTakeThisOuTCEDAR.NET] Sent: Friday, August 18, 2000 1:50 PM To: spamBeGonePICLISTspamBeGoneMITVMA.MIT.EDU Subject: Re: [EE]: Unloaded outputs on audio amps.. will they burn out? For only $79.95, I'll sell you my precision output terminator. This keeps reflected energy from the unterminated outputs from coming back through the supply, and causing distortion on the other channels. If you prefer, the Ultra-Terminator is available, at $129.95, for higher end systems, where exact matching is important. There is an adjustment you can trim to exactly match your system, and remove that confused soundstage that results from reflected energy distortion. The standard model is adequate for automotive systems, since the tiny bit of remaining distortion after termination is inaudible in the automotive environment. You will need one per unused channel. (did I miss my calling, or what? :) -- Where's dave? http://www.findu.com/cgi-bin/find.cgi?kc6ete-9 -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]: PIC only [EE]: engineering [OT]: off topic [AD]: advertisements -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]: PIC only [EE]: engineering [OT]: off topic [AD]: advertisements

rotflol! ----- Original Message ----- From: David VanHorn <TakeThisOuTdvanhornEraseMEspam_OUTCEDAR.NET> To: <RemoveMEPICLISTTakeThisOuTMITVMA.MIT.EDU> Sent: Friday, August 18, 2000 1:50 PM Subject: Re: [EE]: Unloaded outputs on audio amps.. will they burn out? > For only $79.95, I'll sell you my precision output terminator. > > This keeps reflected energy from the unterminated outputs from coming back > through the supply, and causing distortion on the other channels. If you > prefer, the Ultra-Terminator is available, at $129.95, for higher end > systems, where exact matching is important. There is an adjustment you can > trim to exactly match your system, and remove that confused soundstage that {Quote hidden}> results from reflected energy distortion. The standard model is adequate > for automotive systems, since the tiny bit of remaining distortion after > termination is inaudible in the automotive environment. > > You will need one per unused channel. > > (did I miss my calling, or what? :) > -- > Where's dave? http://www.findu.com/cgi-bin/find.cgi?kc6ete-9 > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]: PIC only [EE]: engineering [OT]: off topic [AD]: advertisements -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]: PIC only [EE]: engineering [OT]: off topic [AD]: advertisements

I'll Take 5.1 of them for my new surround system. Stuart ----- Original Message ----- From: David VanHorn <dvanhornEraseME.....CEDAR.NET> To: <EraseMEPICLISTMITVMA.MIT.EDU> Sent: Saturday, August 19, 2000 3:50 AM Subject: Re: [EE]: Unloaded outputs on audio amps.. will they burn out? > For only $79.95, I'll sell you my precision output terminator. > > This keeps reflected energy from the unterminated outputs from coming back > through the supply, and causing distortion on the other channels. If you > prefer, the Ultra-Terminator is available, at $129.95, for higher end > systems, where exact matching is important. There is an adjustment you can > trim to exactly match your system, and remove that confused soundstage that {Quote hidden}> results from reflected energy distortion. The standard model is adequate > for automotive systems, since the tiny bit of remaining distortion after > termination is inaudible in the automotive environment. > > You will need one per unused channel. > > (did I miss my calling, or what? :) > -- > Where's dave? http://www.findu.com/cgi-bin/find.cgi?kc6ete-9 > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]: PIC only [EE]: engineering [OT]: off topic [AD]: advertisements > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics