"Thumpremover" for computer speakers - diyAudio
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Old 20th December 2008, 01:47 PM   #1
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Default "Thumpremover" for computer speakers

Hi

I have read about grounding the outputs on preamps and such (with a delay and relays) to avoid a thump in speakers at power on but how do I apply that on my soundsystem on my computer?

I got an amp (from old active speakers) connected to Line out on the soundcard and a couple of Zigmahornets hooked up to the amp.

Grounding the amps inputs doesnt feel right but maybe with a small resistor between signalpath and the relay (and the relay to ground)?

Well, any suggestions would be thankful.
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Old 20th December 2008, 03:10 PM   #2
cuibono is offline cuibono  United States
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I'm currently building this power supply for a large amp, and it has a 'soft start' relay on the AC input to the transformer. There are probably many designs for this, the link has a short section explaining the circuit. Another way is to use a relay to mute the output of the amp, which is also relatively easy.
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Old 20th December 2008, 04:31 PM   #3
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Thanks but I'm using a dc power adaptor to the amp so... And I have a "circuit" and a suitable relay ready so it would be convenient if I could use those.
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Old 20th December 2008, 06:59 PM   #4
Nuuk is offline Nuuk  United Kingdom
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Shorting the input of your amp is the same as shorting the output of a buffer/preamp so using something like this should work fine.
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Old 20th December 2008, 08:12 PM   #5
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Yeah, that's the one I was planning on using. Had to ask though, didn't want to burn my soundcard. So there's no need for a resistor between signalpath and relay?
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Old 20th December 2008, 08:25 PM   #6
Nuuk is offline Nuuk  United Kingdom
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I'm not sure if you need a resistor. With a buffer/preamp I just short the signal to ground with no ill effect.
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Old 21st December 2008, 12:54 PM   #7
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by MammaMumin
Yeah, that's the one I was planning on using. Had to ask though, didn't want to burn my soundcard. So there's no need for a resistor between signalpath and relay?
It depends on how robust the output stage is and whether they designed it to survive an output short.

I would play safe and measure the output impedance of the sound card. This will give a clue to whether a protection resistor has been included.
Simpler to add a 220r followed by the muting relay or FET.
But even 220r may be too low to offer sufficient loading. I would NOT increase this to 1k0. It will make the next stage and the interconnects difficult to drive.
But, if fitted at the receive end will have much less effect.
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Old 21st December 2008, 01:35 PM   #8
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Didn't play safe but ran in to some other trouble. Forgott that I had a split from the soundcard output. Signal goes to the amp and a switch (the switch gives me the option wether to use my headphones with the computer or my stereo).

And to make it even more funny I had reversed + and - (soldering at night, tired and sleepy) from the power adaptor. Blew the timercircuit but the amp and soundcard's ok. Anyways, the inputs where shorted but the signal level where really low, volyme down at the headphones. So to speak.

I guess the split messes things up. Maybee have to solve this another way.
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Old 26th December 2008, 09:46 PM   #9
Igla is offline Igla  Slovenia
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I have very simple solution;
just use switch between speakers and the amp - first power on the system and then power on the loudspeakers. I had this on one of my class A amps.
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Old 27th December 2008, 01:49 AM   #10
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I have thought of that but.. "learn old dogs to sit" you know. Probably forgett the second switch everytime. Anyways, I'm gonna build a small amp and there's a mute in the chip so... I'll see how that works out.
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