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Old 18th September 2007, 12:56 PM   #1
jarthel is offline jarthel  Australia
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Default a thought on speaker protection using relays

I've seen designs where the signal passes through the relay.

why not use ground on the relay contacts? something like this: http://img464.imageshack.us/my.php?i...itled1sv4.png.

I saw a design by an Italian guy in the chipamp section. I'm just wondering that maybe using ground on the relay contacts is not applicable to every design?

the left/right output wires are connected directly to the binding posts.

thanks for the replies
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Old 18th September 2007, 01:47 PM   #2
OzMikeH is offline OzMikeH  Australia
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Your link doesn't work.

Amplifier will probably go BANG. On deeper thought the speaker protection is really for after things go BANG anyway... With a fast blow fuse before the relay it should work.
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Old 18th September 2007, 02:28 PM   #3
djQUAN is offline djQUAN  Philippines
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the problem with doing it that way is that if your protection circuit malfunctions or false triggers, it takes the amp with it to amplifier heaven.
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Old 18th September 2007, 06:09 PM   #4
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Quote:
Originally posted by OzMikeH
Your link doesn't work.

The forum software accidentally made the full stop part of the URL

The following should work:

http://img464.imageshack.us/my.php?i...titled1sv4.png
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Old 18th September 2007, 08:41 PM   #5
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Default Re: a thought on speaker protection using relays

Quote:
Originally posted by jarthel
I've seen designs where the signal passes through the relay.

why not use ground on the relay contacts? something like this: http://img464.imageshack.us/my.php?i...itled1sv4.png.

I saw a design by an Italian guy in the chipamp section. I'm just wondering that maybe using ground on the relay contacts is not applicable to every design?

the left/right output wires are connected directly to the binding posts.

thanks for the replies
Hi jarthel

It will make no audible difference.

In a output stage feeding a speaker , the current left the output stage , pass trough the positive speaker wire , traverse the speaker and return to ground , by the negative return speaker wire.

In a serial circuit like this , it makes no difference that the relay interrupts the sending or the receiving way, because the current in the circuit will always be the same...

Regards
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Old 19th September 2007, 05:18 AM   #6
jarthel is offline jarthel  Australia
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Quote:
Originally posted by djQUAN
the problem with doing it that way is that if your protection circuit malfunctions or false triggers, it takes the amp with it to amplifier heaven.

care to enlighten me?

=====

thanks everyone for the reply
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Old 19th September 2007, 02:45 PM   #7
djQUAN is offline djQUAN  Philippines
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Quote:
Originally posted by jarthel



care to enlighten me?

=====

thanks everyone for the reply

when your protection circuit false triggers, it shorts the amplifier output to ground so that will certainly blow the output transistors.


also, muting circuit like those often incorporate turn on mute and instant mute at turn off to eliminate pops, whistles or other weird noises when the supply voltage is not yet stable. if your amp has a loud thump at turn on (some amps do this normally) and the relay is closed, the thump goes to a direct short which (hopefully) blows the supply fuse (or worse) the expensive power transistors.
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Old 20th September 2007, 02:59 AM   #8
jarthel is offline jarthel  Australia
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Quote:
Originally posted by djQUAN



when your protection circuit false triggers, it shorts the amplifier output to ground so that will certainly blow the output transistors.

I'm somewhat confused. how can this happen? the relay contacts doesn't use the amplifier output. so if triggers falsely, I would've thought the speaker's ground is connected to nothing?

thanks again
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Old 20th September 2007, 08:46 AM   #9
Shaun is offline Shaun  South Africa
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Default Re: Re: a thought on speaker protection using relays

Quote:
Originally posted by Tube_Dude
Hi jarthel

It will make no audible difference.

In a output stage feeding a speaker , the current left the output stage , pass trough the positive speaker wire , traverse the speaker and return to ground , by the negative return speaker wire.

In a serial circuit like this , it makes no difference that the relay interrupts the sending or the receiving way, because the current in the circuit will always be the same...

Regards
I agree that it will not make a sonic difference. It will actually work.

However, an important difference between this scheme and the conventional arrangement is that the latter completely disconnects the amplifier output. With your proposal, the amp output is not disconnected from the output terminal, so it is still possible to short the amp to chassis, which is often connected to 0V.

For this reason, I would not recommend using your idea.
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Old 20th September 2007, 09:02 AM   #10
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Default Re: Re: Re: a thought on speaker protection using relays

Quote:
Originally posted by Shaun


For this reason, I would not recommend using your idea.
My idea??

Have you read the first post?
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