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Old 15th April 2007, 04:46 PM   #1
skogs is offline skogs  Norway
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Default Power Supply for Preamplifier

Hi. i have a "zachry dsw-250" subwoofer plate amp, which dont have a rumble filter, which i need, badly:P
so, i just wondered if i could steal the power from the present preamp in the amp and use it for my active filter? or will this affect the sound or amp in any negativ way?

thx, Řyvind
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Old 15th April 2007, 05:51 PM   #2
skogs is offline skogs  Norway
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and one more thing: alternatly, and maybe preferably, i will make a new power supply, but how much VAC do you think a 6.order active subsonic filter will need? i will try to make this as cost-effective as possible.
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Old 15th April 2007, 10:46 PM   #3
AndrewT is offline AndrewT  Scotland
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Hi,
Quote:
how much VAC do you think
2*9Vac & 6VA would manage.
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Old 8th June 2007, 12:36 PM   #4
skogs is offline skogs  Norway
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Hi again.
would i need to build a dedicated preamp power supply like for example this: http://sound.westhost.com/project05.htm , or could i simply use a 2*15Vac transformer or something?

and if i have to make the power supply, would it do to use only a 4,5A trafo?

im going to use it on this project: http://sound.westhost.com/project99.htm
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Old 8th June 2007, 01:10 PM   #5
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You should try to build a better power supply.
You should use LM317/LM337 or a voltage reference and a transistor.
You should not connect two wires of the transformer together to the ground.

Better use a floating ground.
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Old 8th June 2007, 03:06 PM   #6
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by skogs
Hi again.
would i need to build a dedicated preamp power supply like for example this: http://sound.westhost.com/project05.htm , or could i simply use a 2*15Vac transformer or something?

and if i have to make the power supply, would it do to use only a 4,5A trafo?

im going to use it on this project: http://sound.westhost.com/project99.htm
Hi,
I don't know the power requirement of your proposed pre-amp but most will require substantially less than 100mA @ +-15Vdc.
That amounts to just 3VA plus losses in the regulators.
If you over-rate the supply transformer by a factor of ten you still arrive at just 30VA. There may be a small gain in performance by over-rating the transformer by a factor of fifty, but most in this Forum would disagree with that philosophy. The only way would be to try and prove it is better, buy 30VA and 150VA and see what difference there is.
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Old 9th June 2007, 03:18 PM   #7
skogs is offline skogs  Norway
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Hi again, thanks for the advices.
im quite a novice, a newbie in these things. Im also kind of poor at the moment, so i can only afford to buy the things i absolutely need.

but what do you mean by this over-rating? is it neccessary? or will it work to just use a 6A supply transformer?

Keruskerfuerst: what do mean with better power supply? could you give me an example or something? im on a reeeally tight budget. and im not capable of designing any of these things myself. i need schematics, i can make pcb layouts and such myself.

Thanks alot for the respons guys
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Old 9th June 2007, 03:29 PM   #8
AndrewT is offline AndrewT  Scotland
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Hi,
those projects need just 20mA to operate.
3VA meets this requirement. A transformer spec of 15-0,15-0 and 100mA will power this.

You can use a 4.5A transformer if that is all you have. The extra current capability will not damage your power supply and will not damage your filter project.
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Old 9th June 2007, 03:32 PM   #9
skogs is offline skogs  Norway
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Thank you very much Andrew
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Old 10th June 2007, 08:49 PM   #10
skogs is offline skogs  Norway
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Hi again, do you think i could use a +-12V power supply instead of +-15V? what would the difference be? would it work do you think?

its just an active 6. order subsonic filter.
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