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Old 31st May 2014, 09:53 AM   #1
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Default suitable power supply for dozen opamps?

Hi,

I've got a pair of active XO that i'll be assembling over the weekend, each one has 5 dual op-amps on board.

I will also be powering a hpf alongside the xo, from the same supply (230 in).

I bought a standard PCB mount transformer block (0.25VA/12v) but I was advised by the seller (of the xo kits) that this one would not be sufficient to power all 3 circuits.

I was recommended a 5VA transformer but I'm unsure of what voltage rating to look for.

Click the image to open in full size.
Any tips? remembering this is line level signals, just want as much as is needed, thanks!
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Last edited by giro1991; 31st May 2014 at 09:55 AM.
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Old 31st May 2014, 10:05 AM   #2
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Do you know how much current draws each xo?

I guess xo needs filtered and rectified 12VDC, right?
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Old 31st May 2014, 10:08 AM   #3
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Use a minimum 20VA transformer with 15 - 0 - 15 Volts secondary followed by LM7815 and LM7915 voltage regulator IC's to provide your DC supplies.
Info on the circuitry is within the datasheets, available from many sources on the net.

Line outputs can draw more current than expected especially if presented with lowish impedance loads

hope this assists
Mik
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Old 31st May 2014, 10:21 AM   #4
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What is the kit, in particular, does it have on board regulators ?

What are the opamps ?
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Old 31st May 2014, 10:22 AM   #5
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thanks mik,
merlin, I do not know how much current each draws no.

All I know from product page: single PCB needs a "dual dc power supply of 2 x 6V".

Seller said: "2 x 12V is a bit high. I would say if you are determined to run the crossovers at this voltage make sure the supply is well regulated and never exceeds this or you risk damaging the op-amps.." which seems in line with what mik says regarding regulating...

mooley, no, no regs on board: eBay ID: 111280863327
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Last edited by giro1991; 31st May 2014 at 10:33 AM.
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Old 31st May 2014, 10:33 AM   #6
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OK, those boards are shown as using OPA2134 FET opamps which draw around 10ma per device. So that's 150 milliamps quiescent so you need to add a safety margin and allow for dynamic conditions. So you are looking at around a -/+250 plus milliamp supply.

IMPORTANT. those boards can not accept AC from a transformer. They need a stable DC supply of -/+15 volts. If you connect a transformer the opamps and any electrolytics will be destroyed instantly.
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Old 31st May 2014, 10:38 AM   #7
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You need something like this together with a transformer,

Low Noise +/-15V Regulator Module, for Audio OPAMP. | eBay

There is a circuit diagram given and its easy and cheap to make something similar from separate components.
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Old 31st May 2014, 10:42 AM   #8
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though I was wanting to keep it on cheap side ... Thanksa anyway -
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Last edited by giro1991; 31st May 2014 at 10:44 AM.
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Old 31st May 2014, 10:46 AM   #9
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You're welcome. And if you are unsure then ask.

(All you really need parts wise is the transformer, a bridge rectifier, two reservoir caps and a 7812 and 7912 regulator chips. Total cost around 10-15. The regulators would need to be on a small heatsink)
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Old 31st May 2014, 10:56 AM   #10
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There was me thinking a transformer was all I needed to convert to DC to form a power supply!
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