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Old 8th January 2011, 03:58 AM   #1
DQ828 is offline DQ828  Australia
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Default Stopping Speaker Destruction

I have been working on my Active Crossover DSP setup lately & have an issue that I would like to solve before I kill a speaker or two.

I am using MiniDSP as the crossover, this morning I accidently turned the DSP on while the amp was on & turned up high. The noise that came from the speakers was most unpleasant & dangerous.

The MiniDSP is powered by two phone charges, I was wondering if I installed a capacitor between the charger & the DSP would this help with the problem should I accidently do it again. If it will, what sort & size capacitor should I use?

David
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Old 8th January 2011, 04:06 AM   #2
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The pops are most likely emanating from the output stages of the miniDSP unfortunately. You either need to be careful, or use muting relays.
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Old 8th January 2011, 04:13 AM   #3
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The noise was probably "digital hash" as the miniDSP locked on to its signal. The way to make sure it doesn't get through is to make a mute circuit. I don't know if the MiniDSP has a resistor in series with the output so put a 100R in series with the output, and use something like Project 104 - Preamp/ crossover muting circuit to mute the output. It may take some tweaking to operate on lower voltages.

You'll probably like the sound of your miniDSP better with a proper linear power supply. If you use a transformer with a pair of 9V windings you can get 12V to operate the relay and mute circuit and then regulate that down to the 5V the MiniDSP needs, with separate supplies for each channel.
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Old 8th January 2011, 04:54 AM   #4
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Quote:
Originally Posted by fb View Post
The pops are most likely emanating from the output stages of the miniDSP unfortunately. You either need to be careful, or use muting relays.

The pop sounded more like a very loud CRACK. Interestingly, the receiver turned itself off when it happened.
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Old 8th January 2011, 04:55 AM   #5
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Thanks for the input guy's.

David
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Old 8th January 2011, 05:59 AM   #6
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Use a Polyswitch on the speakers while your figuring things out to protect them until your ready. Cheap, fits in line on the + speaker wire, come in 6 values.
http://www.jaycar.com.au/images_uploaded/polyswit.pdf

Jaycar Electronics - Search results poly switch

Cheers George
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Old 8th January 2011, 06:16 AM   #7
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It looks like a polyswitch won't protect from overexcursion, which is the main danger to speakers (especially tweeters) with an amplified pop/crack.
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Old 8th January 2011, 09:37 AM   #8
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Basically the CRACK came from (I think) the arch & surge that was created in the power point switch when I turned it on.

I have a Kingrex T amp, that causes a loud crack if I turn it on at the amp, but only a small crack if I turn it on at its power supply, which is full of capacitors. I was thinking the capacitor would absorb some of the surge, but I guess I would need a far amount of capacitance to do a good job.

David
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Old 8th January 2011, 10:47 AM   #9
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It's not the PSU, it's inherent in the miniDSP boards (and many other pieces of audio gear - RME FF400 and Sandisk Sansa Clip are misbehaving devices I own).

Read this for more on the miniDSP: MiniDSP - When minidsp close there is a ?kntoup? noise . - MiniDSP
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Old 8th January 2011, 01:50 PM   #10
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A crack may be switch arcing or a different psu startup behavior than your T amp. You could spend a lot of time tracking it down, but since the MiniDSP boards are known to have startup/shutdown issues, mute relays are the solution that will do you the most good.

Of courser at less than a watt, it wouldn't hurt to leave it on all the time.

Last edited by BobEllis; 8th January 2011 at 02:07 PM.
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