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Old 2nd August 2005, 06:16 AM   #1
cowanrg is offline cowanrg  United States
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Default thoughts on MOX power supply

so im almost ready to start my next project, the mox active crossover.

all the discrete opamps are built and ready to go, and i ordered the parts for the actual crossover. i already have a case, so last step is a power supply (well, except for months of frustration of testing and mistakes).

i already have a battery power supply that was built for another project that never happened. it will supply about +-13v and last about 1.5 days straight. i was going to use that, but a thought occurred... if this unit is battery powered, wont it have to turn on and off to operate (it will need to charge SOMETIME). and if thats the case, will the mox have a popping/clicking sound that will come through the speakers? i keep my amps on all the time, and if the mox comes on and off, will it pop through the speakers? i would rather aviod this.

so the other alternative is to just leave it on all the time (which is cool with me), but i cant use batteries then...

and IF i go that route, i was thinking about this xformer from parts express:

http://www.partsexpress.com/pe/showd...number=129-082

will i need to regulate the power supply, or can i just use a basic unregulated power supply with decent filtering? i found a few really cheap ($5) regulator kits that will give me 1.5-30v output if i need a regulated supply.

so, those are my questions... ultimately, if i can use batteries and not worry about noise coming through the speakers, that would be best. i have programmable 12v trigger outs from my processor so i can just toss a relay on the charger and have it turn on and off with the processor.
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Old 2nd August 2005, 11:31 AM   #2
moamps is offline moamps  Croatia
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Default Re: thoughts on MOX power supply

Quote:
Originally posted by cowanrg
....if this unit is battery powered, wont it have to turn on and off to operate (it will need to charge SOMETIME). and if thats the case, will the mox have a popping/clicking sound that will come through the speakers? i keep my amps on all the time, and if the mox comes on and off, will it pop through the speakers? i would rather aviod this...
Hi,

Yes, the MOX will produce cliks/pops, which can be very dangerous for your amps/speakers. If you have processor charge control circuitry, it might be possible to use the control signal to switch on mute relays on the xover outputs when the batteries start charging.

Quote:
and IF i go that route, i was thinking about this xformer from parts express:
http://www.partsexpress.com/pe/showd...number=129-082
I'm not sure that the 14V CT transformer has two 14V or two 7V secondary outputs. You need the former.

Quote:
..will i need to regulate the power supply..
Yes. LM317/337 PS, for example, should do the job.

Regards,
Milan
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Old 2nd August 2005, 06:48 PM   #3
AndrewT is online now AndrewT  Scotland
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Hi,
317/337 are the minimum standard I would aim for.
But you may get away with this if instead you spend the money on avoiding electrolytics after the regulators and use plastic film caps all the way to the discrete opamps. At constant voltage (PSU rails to ground) remember that ceramic perform very well.
I am a believer in many small caps in parallel rather than one large hi quality (very expensive) cap.

A transistor or preferably fet muting circuit on the inputs to your amps which switch in to short the input to ground with a time delay would be effective protection from early stage shutdown/ startup
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Old 2nd August 2005, 07:51 PM   #4
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Talking Re: thoughts on MOX power supply

Quote:
Originally posted by cowanrg
so im almost ready to start my next project, the mox active crossover.

all the discrete opamps are built and ready to go, and i ordered the parts for the actual crossover. i already have a case, so last step is a power supply (well, except for months of frustration of testing and mistakes).

i already have a battery power supply that was built for another project that never happened. it will supply about +-13v and last about 1.5 days straight. i was going to use that, but a thought occurred... if this unit is battery powered, wont it have to turn on and off to operate (it will need to charge SOMETIME). and if thats the case, will the mox have a popping/clicking sound that will come through the speakers? i keep my amps on all the time, and if the mox comes on and off, will it pop through the speakers? i would rather aviod this.

so the other alternative is to just leave it on all the time (which is cool with me), but i cant use batteries then...


so, those are my questions... ultimately, if i can use batteries and not worry about noise coming through the speakers, that would be best. i have programmable 12v trigger outs from my processor so i can just toss a relay on the charger and have it turn on and off with the processor.

My take on this:
as I use in my latest DAC you can run the xover on batteries and keep it on all the time, just use a charger to keep batteries charged while not in use and use the 12V trigger to detach it when you switch the processor on (i.e a NC relay contact between charger and batteries, that are permanently* connected to the xover).
The trick is that the charger is always on and the battery works as a tamper when the charger is detached, so the supply of the xover is never lost and you shouldn't experience thumps.

If I hadn't already installed the super-regulators I would have probably done so in my MOX

Cheers

Andrea

* a switch is suggested to detach completely the battery in case you need to switch it off for some time
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Old 2nd August 2005, 09:15 PM   #5
cowanrg is offline cowanrg  United States
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well, if i used a regulated linear supply, i would just never ever turn it off. so i wouldnt bother with muting circuits, etc...

Andypairo,

i understand what you are saying, but im not 100% getting what you mean though. i have a charger, batteries, and some relays, etc...

do you have a diagram or could you explain further how this would work? can the batteries be charged AND be powering the preamp at the same time? im just not understanding how power would always be applied to the circuit. but since i have all the necessary items to do a battery supply, i would like to go that route.
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