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Old 20th September 2007, 08:10 AM   #11
Shaun is offline Shaun  South Africa
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I did not mean to imply that it was your idea to use it. I merely quoted your post because I was agreeing with you in principle.
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Old 20th September 2007, 08:20 AM   #12
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Quote:
Originally posted by Shaun
I did not mean to imply that it was your idea to use it. I merely quoted your post because I was agreeing with you in principle.

In my answer to Jarthel , I was trying to emphasize that there are no audible difference in the two options, so no interest in changing the relay for the ground wire.

But of course , the classic arrangement is safer for the reasons you pointed .

At the end of the day we agree .

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Old 20th September 2007, 08:35 AM   #13
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Hi jarthel, greetings fellow Aussie. I am sympathetic to the idea of trying to get the relay out of the signal path (and the earth also) so my thoughts (which I've put up some time ago on another thread) are these. Use all the conventional dectection circuitry and relay BUT instead of having the relay in series with the speaker have the relay across the amp' output terminals i.e. in parrallel with the speaker but in the "normally open position". In normal safe conditions the relay is open circuit (and not degrading the signal) But in the event of it detecting DC the relay will close and short the output to earth there by protecting the speaker. Now a few common sense things need to be done. All leads must be able to sustain the current or you are back to square one and tragedy. When I posted this previously someone subsequently said that this arrangement is in use in one or two commercial amp's so it looks like it is a viable option. Short of an expensive arrangement that closes down a regulated power supply this seems to meet the needs of protection and signal integrity.
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Old 20th September 2007, 10:26 AM   #14
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Quote:
Originally posted by Jonathan Bright
Use all the conventional dectection circuitry and relay BUT instead of having the relay in series with the speaker have the relay across the amp' output terminals i.e. in parrallel with the speaker but in the "normally open position". In normal safe conditions the relay is open circuit (and not degrading the signal) But in the event of it detecting DC the relay will close and short the output to earth there by protecting the speaker. Now a few common sense things need to be done. All leads must be able to sustain the current or you are back to square one and tragedy.

So, in the event of a short in the speaker cables or a very difficult load when the amp deliverers to much current , protection come in and the relay close shorting even more the output , then output transistors BANG... ... and the story end...
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Old 20th September 2007, 10:49 AM   #15
djQUAN is offline djQUAN  Philippines
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Quote:
Originally posted by Tube_Dude



So, in the event of a short in the speaker cables or a very difficult load when the amp deliverers to much current , protection come in and the relay close shorting even more the output , then output transistors BANG... ... and the story end...

that's what I've been trying to say.
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Old 20th September 2007, 10:53 AM   #16
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Quote:
Originally posted by djQUAN



that's what I've been trying to say.



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Old 20th September 2007, 11:56 AM   #17
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Hi Tudedude......Jorge. I was only thinking of this as a speaker protector in the event of a output stage failure, ok? It assumes that the output stage is in "melt down" and the owner wants a protection circuit with the minimal ammount of signal degredation.
Also I have JLH Class A amps so current limiting is not such an issue in my case.
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Old 20th September 2007, 12:12 PM   #18
DonoMan is offline DonoMan  United States
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If you're trying to protect the speaker from DC, you use a capacitor in series. Period. If you want the capacitor to be full-range, it'll need to be quite large, though, so that the F3 is really low.

If you want to use a relay, how about just disconnecting the speakers instead of shorting them? Leave the output open or replace it with a dummy resistor (which may burn, but dummy resistors are cheap compared to speakers)
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Old 21st September 2007, 01:38 AM   #19
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Hi DonoMan this is just to bring you up to speed on the history of the debate that is occuring in audio circles about amp/speaker interfaces. You are right in what you say about capacitors and from a simple physics point of view quite correct. But it is generally agreed (but not by 100% of the audio world) that that we want to avoid possible degredation of sound by minimizing the number of components in the signal path. Hence the move since the early '70s to split rail amps with no caps. In the same way people saw the absence of transformers as one of the attractions of solid-state amps over valves.
Now, given that people generally like OCL (output capacitorless) amps the question of protection arises in the event of an output stage failure. This leads to relays that will disconnecct when DC is on the centre rail. But as time went on people became suspicious of relays. Perhaps they added to the distortion of the signal? As I understand it that is where this thread started.....Jartel wanted to get the relay out of the signal path....ok?

If you read this thread in the light of what I've just written it will make more sense. Now you can, at this point reply, that we are paranoid about this and if you did then you won't get any complaints from me......most of us are PARANOID....... Guilty as charged.

Hope this makes sense. The basic physics are on your side but the perfectionist will say that you're only scrathing the surface.....and that there are more demons lurking in the system.

Kind regards, Jonathan
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Old 21st September 2007, 03:26 AM   #20
Shaun is offline Shaun  South Africa
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Quote:
Originally posted by Jonathan Bright
As I understand it that is where this thread started.....Jartel wanted to get the relay out of the signal path....ok?

If you read this thread in the light of what I've just written it will make more sense.
If that is what jarthel meant, it is certainly not what he said....

@ jarthel: Perhaps you should step in here and not leave it to the likes of PARANOID/Jonathan to define what this thread is about!!??
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