8x8 turn-off thump - Page 2 - diyAudio
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Old 9th March 2013, 01:33 AM   #11
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Hi,
Here it is a suggestion on how to prevent the speaker output "thump" when the power it is turn off by using the Basic micro NANO 8. Attached it is a schematic how to do it. I will try to explain how it is works but I am not a technical writer. I Know that when you speak about using a micro that it is the end of the discussion but it is not big science programming the NANO 8 using basic instructions.

Here it is description how it work.

The purpose of the micro it is to read the zero crossing pulses every time that the AC cross the base line as shown in the schematic. It will produce a pulse that the micro will read and will keep monitoring it until one of the pulse failed. If one of the pulse failed means that there it is a problem with the AC power and the micro will immediately open the output relay preventing the "thump" in the speaker. Also at the powered up can be programmable to delay the close of the output relay to allow the settling of the PS voltages. It is a simple circuit and can be done easily using common components. The micro NANO 8 cost only 2.99 and the all project will run under $ 30 dollars.

If interesting I will write the program to show how easy it. I call the NANO8 the programmable LM555 with 4 individually programmable outputs and only cost $2.99.
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File Type: jpg zero crossing speaker protection.jpg (129.1 KB, 130 views)
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Old 9th March 2013, 03:02 AM   #12
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Quote:
Originally Posted by thomasjefferson View Post
Maybe it's important to note that the transient is only severe when the AC power cord is unplugged from the power supply
Hmm.... the thump for me is also very severe when disconnecting the DC plug form the miniDSP. (Haven't tried disconnecting from the AC side)

I'm using the power adapter supplied with the MiniDSP 8x8 "in a box" (4x10 HD)
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Old 9th March 2013, 03:14 AM   #13
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Originally Posted by tauro0221 View Post
Here it is a suggestion
Thanks! I understand the concept... but not quite clear on how to wire it up from your diagram.

What do people think about the increasing supply capacitor solution?... This seems a more desirable solution than having relays between amps and speakers.
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Old 13th March 2013, 03:23 PM   #14
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Tauro, that's a good suggestion, if you do write a program for Nano to control relays I'd be interested in experimenting with it. It needs to control 8 speaker outputs. For those of us who are not electrical engineers it would help to have more of a layman's description of how this gets wired in the system.
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Old 13th March 2013, 05:47 PM   #15
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Hi,
Right now I am working in a project that control the speaker outputs using solid state relays by monitoring the current going to the speakers. If for any reason the current reach the trip setting it will open the relays immediately and enable the mute. If the output it is shorted the relays will be open protecting the speakers from burning up and the amplifier transistors outputs. I am sensing the speakers current going to ground. Attached it is picture of my controller. Also slowly ramp up/down the AC at zero crossing when the amplifier it is turn ON/OFF. This is to prevent the inrush current from the transformer. Finally also it monitor the temperature of the heat sink and will shutdown the amplifier if the temperature reach the trip setting. Attache it is the a picture of the controller.

PM what you want and I will look into and may come up with a circuit design using the micro.
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Old 13th March 2013, 05:50 PM   #16
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Hi,
This picture showed all the options in the control board.
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Old 13th March 2013, 06:02 PM   #17
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Hi,
Last here it is another picture of the all system including the traic, the temerature sensor and the display. This will control/mounted in a LM3886 amplifier.
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Old 15th March 2013, 09:10 PM   #18
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Tauro, this is nice work, although a bit more effort to assemble than I'm looking to do. Just came across this speaker protector board, which looks simple enough. It includes relays to interrupt speaker outputs when mains power is cut, and a few seconds of delay timer on power up. An 8 channel system would need four of these boards.
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Old 15th March 2013, 09:21 PM   #19
frank1 is offline frank1  United Kingdom
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Quote:
Originally Posted by tauro0221 View Post
Hi,
Right now I am working in a project that control the speaker outputs using solid state relays
What are the solid state relays please?
Frank
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Old 15th March 2013, 09:59 PM   #20
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Hi,
thomasjefferson No, you do not need 4 board. The NANO still have 12 output so you can add more but you have to made a board specifically for your need.

frank1 For the SSR I am using two mosfet enable by an Avago optical coupler.
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