Greetings All, I would like to be able to mute my car stereo with just a push of a button. The volume control is the digital type where a button is pressed and the volume slowly rises or falls. If it was a knob type I'd just twist it fast to zero and then twist it back to the original setting. If the radio is turned off to mute it then it takes several seconds for the sound to return when the radio is turned back on. If a switch is used in the speaker wires will it harm the radio to have the speakers connected and disconnected when the radio is playing? If so, is there a way around this? Like maybe switching in a dummy load with a make then break switch? Any other suggestions? Thanks, Eric
Should not have any problem disconnecting the (analog) speaker wires because it decreases the load. Do not short them though. I did that to my home stereo and nothing bad happened.
Probably switching into a dummy load would be best. I know for guitar amps that its not a good idea to have no load on the amp when in use because the the amp is's impedence is matched with the speaker to give optimial power transfer. If you have no load then the amp will absorb all the power instead of the 1/2 of it going to the speaker. I'm not sure if the same thing goes on in a car stereo but surely can't hurt to use a dummy load. I doubt that using break before make or make before break matters to much... in each cause there will be an impedence mismatch and the amp will have to absorb the power(but make before break will take a little of the power away from the amp). I doubt it matters much though since in either case the time that the amp will be absorbing more power than it is rated for only durring the time of the switching. Although I suppose that it could destory the amp if its to much. (You probably need a special switch to do the break before make version though just so it doesn' wear out)
Maybe a better idea is to simply switch in a resistor on the volumn pot to simulate turning the volumn all the way down instantly. The way you don't have to worry about anything in the above. This is assuming ofcourse that increasing the resistance decreases the volumn. If its a digital pot then it could be switched and then you'll have to do more. Its also probably more intrusive as you might have to tear apart your stereo.
If your really into hacking it up you could use a small motor and gear system to turn the volumn for you. I bet though that since the volumn attenuation is "timed" that you probably can find a simple RC circuit that they use to decrease the volumn and modify it to decrease the time constant. If its all digital then it might be much harder than this.
Phil put the last piece in place. The times I have encountered this, the (relatively cheap and relatively easy-to-get) phenolic tube sockets burned up. Here's a description of what happens:
The amp I was using was actually solid state and it blew out the power amps... used tda7294 I think. I replaced them and its worked fine since. I actually ran the things quite a while without an speaker load before they blew.
It would seem to me that impedence matching is a universal law for audio? I'm not sure how solid state changes that fact? Is there a buffer that acts as the output transformer or something like that? (I think another reason for the output transformer is to remove the dc bias that might exist also. One could cap-couple the speakers I suppose but still doesn't resolve the issue of power transfer?)
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That\'s not true. For a solid state amplifier with no output
transformer, regardless of where the output voltage may lie,
connecting the load will only let whatever current its [the load\'s]
resistance will allow out of the amplifier\'s output.
Since the output stage of the amplifier is essentially a voltage
source, its output voltage won\'t change whether there\'s a load
connected to it or not, within the limits designed into the amp, of
course.
Put a 10 watt, maybe 20 ohm resistor in series with you speaker outputs and then connect your mute switch to short that resistor for normal play. That way you will still hear the sound, justat a much lower volume.. DPDT swith with 2 20ohm 10 wat resistors. JTT ..
Put a 10 watt, maybe 20 ohm resistor in series with you speaker outputs and then connect your mute switch to short that resistor for normal play. That way you will still hear the sound, justat a much lower volume.. DPDT swith with 2 20ohm 10 wat resistors. JTT ..
*-energy-in-this-magnetic-field-has-to-go-somewhere+Normally-it-would-be-dissipated-by-the-load+output-tubes-or+the-windings-of-*-transformer+high-flyback-voltage-generated+*-close-*-*-*+no-speaker-conne cted
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