8x8 turn-off thump - Page 3 - diyAudio
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Old 18th June 2013, 06:20 PM   #21
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I think all the DIY solutions are great but I feel MiniDSP should be proactive fixing this problem. This is unacceptable. My 2x8 fried my Usher 9950 tweets when we had a power failure. Shut down of the unit needs to be clean. Trying to use the product in a car/12v setup or a portable setup with this shutdown problem makes the board unusable.

Brad

PS
Tauro, I don't think a SSR on the speaker output or any audio signal is a good idea. Most SSRs have a zero cross/ breakover voltage null of about 1v or so. I think the signal will be deformed because of the internal circuitry of the SSR. Be interesting to run a side by side or put the signal on a scope.

Figure 8a. ON-Mode Waveforms
http://www.omega.com/temperature/Z/pdf/z124-127.pdf

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Old 18th June 2013, 07:00 PM   #22
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Hi,
That it is the wrong SSR. You can not use triac for audio. Attached it is a schematic for the one I am using in my board.
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File Type: doc Speaker solid state relay_0.doc (79.0 KB, 12 views)
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Old 19th June 2013, 05:01 PM   #23
Davey is offline Davey  United States
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Brad,

I think you have to be pro-active here. Yes, the miniDSP transients on turn on/off are not insignificant, but your existing board can't easily be retrofitted so some sort of external setup would be good.

However, I don't think it's wise to be connecting fragile tweeters directly to power amps...especially when the power amps don't mute the speaker outputs immediately on power failure. This could be a problem regardless of what type of source you have upstream of your power amp.

Maybe a different power amp that is more friendly to drivers? Maybe a capacitor between power amp and tweeter? Maybe some other solution as well?

Best to look at all possible areas for a protection solution vice blaming miniDSP exclusively.

Cheers,

Dave.
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Old 19th June 2013, 06:38 PM   #24
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Dave, I do not think any equipment placed before the amps should ever output a spike on power down so loud the kids come running to check to see if all is OK. Would you be OK with a loud spike when you turn off your blueray, preamp, TV, Sat box or xbox and your amp is still on? This spike on power down problem is solely the MiniDSP. The spike was present with an Emotive amp and an Adcom amp. This board is designed to be hooked directly to the amp used as a xover. What would be the point in doing an active xover if I have to put blocking , relays anc circuit protection in the line to hide the defect in the mini DSP?If the POP was small I don’t think it is a problem but this output from the DSP is full power or more. I will try and remember to turn the amp off and be using a blocking cap until I get this solved.
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Old 19th June 2013, 06:41 PM   #25
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Hi,
Yes, I am working on it. Few members have some concerned about disconnect the speaker output in case of a power failure. Since I am looking at the zero crossing to turn OFF/ON the amplifier, I can monitor the AC zero crossing pulses and as soon I see missing the zero crossing pulses I will disconnect the speaker output and also locked the switch preventing the power amplifier turn On when the AC power it is restore. This is in development right now. I think it is a good idea. Right now the problem is how to handle the micro when the AC goes off. I can use a large capacitor or a battery for backup to allow the micro to operate without the AC power.
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Old 20th June 2013, 02:03 PM   #26
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tauro, I have been using an IO module here at work to bring signals into PLCs. It is an AC 90-280v input, optical isolation, DC 4-28v switched output 100ma. Switch time is 20ms. Close to 1 sine wave of a 60hz signal, 16ms, or your circuit 8ms. The unit could monitor the AC line for power fail. When AC goes down the other side could turn remote on->off, or switch relays etc. All for $25USD

DIN Rail Mounted Mini Input/Output Modules ? IO Series

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Old 20th June 2013, 03:00 PM   #27
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Hi,
Practically it is the same thing I am doing in my board. The only thing it is that I am using the MOC3023 to trigger the triac to turn ON/OFF the amplifier.

Attached it is a schematic showing all the circuits I used to control the different options in the amplifier. You can custom your board by selecting which one you want to use.
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Old 20th June 2013, 03:17 PM   #28
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Hi,
Ops the file was too big. I missed the attachment. Let me try it again.
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File Type: gif amplifier micro control gif.gif (51.4 KB, 21 views)
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