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Old 1st August 2009, 08:49 PM   #1
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Default Amp Muting

There are two options I wish to examine to mute an amp at start-up to avoid pops etc getting to the loudspeaker.

1. Relay in series with speaker, close to pass signal.

2. Relay in parallel with speaker, short amp o/p to ground while starting up.

#2 avoids a relay in the signal path, but would you really like to have brief shorts on your amps at start-up?
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Old 1st August 2009, 09:31 PM   #2
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Shorting the output can prevent the amp from establishing its correct DC operating level: it will then still 'thump' when the relay opens and DC levels normalise. Plus, it can damage the amp.
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Old 1st August 2009, 09:31 PM   #3
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Default Re: Amp Muting

Quote:
Originally posted by richie00boy
There are two options I wish to examine to mute an amp at start-up to avoid pops etc getting to the loudspeaker.

1. Relay in series with speaker, close to pass signal.

2. Relay in parallel with speaker, short amp o/p to ground while starting up.

#2 avoids a relay in the signal path, but would you really like to have brief shorts on your amps at start-up?

I have always used a relay i nseries with the speaker and never had any sound problems.

I use a PIC microcontroller to delay the relay for 3 seconds.
I also use the PIC to monitor the audio out for a DC condition above 20 volts for 500mS and if this happens the PCI disconnects the speakers using the relay. This has saved me a fortune in speakers !


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Old 2nd August 2009, 01:21 PM   #4
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20 volts? I'd think that anything above 3V ought to signal an alarm...

Other than that, I agree. A properly selected and implemented relay is a very good thing.
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Old 2nd August 2009, 01:28 PM   #5
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Quote:
Originally posted by EchoWars
20 volts? I'd think that anything above 3V ought to signal an alarm...

Other than that, I agree. A properly selected and implemented relay is a very good thing.

Its a simple matter of changing the resistors to trigger at 3 volts instead of 20.
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Old 2nd August 2009, 04:23 PM   #6
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Hi,
look at a simultaneous mute on the input to remove drive voltage/current to the speaker. This will reduce the sparking erosion of the relay contacts, particularly when opening (power off shutdown).

You can also look at disabling the LTP and/or the VAS by cutting off their CCS currents.

If the output were to go into full DC offset, then consider a relay or FET crowbar across the speaker terminals as a last resort. This will blow the LV supply fuses if they are rated low enough.
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Old 21st August 2009, 11:57 PM   #7
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I am in the process of adding this module to my JLH amps.

If you don't like this ready made thing, which works quite nice, I had an idea for using a relay with three contacts. In rest the middle contact shorts the speaker, leaving a series resistor as load for the amp. Upon activation of the relay (by some RC induced delay) the middle contact would move from one contact to the next, leaving the series resistor in series with the LS. When the middle contact reaches the other contact it shorts the series resistor leaving just the speaker as load for your amp.

I did make a schematic of this once, but cannot find it (yet)
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