Help with power supply

[Bonsaimaster]

I have purchased this VU meter but it did not come with a power supply. It has a mini XLR in the back. The Voltage Regulators are 7912 (312B). Should I get a wall wart supplying DC voltage or is AC needed?  How can I determine the amount of voltage and amps it needs. Don't want to blow up the unit. Any help is appreciated. I looked up the info on the board but no luck.

Thanks in advance

Bonsaimaster

 

[Andy Peters]

I have purchased this VU meter but it did not come with a power supply. It has a mini XLR in the back. The Voltage Regulators are 7912 (312B). Should I get a wall wart supplying DC voltage or is AC needed?  How can I determine the amount of voltage and amps it needs. Don't want to blow up the unit. Any help is appreciated. I looked up the info on the board but no luck.

Your picture shows both a 7812 positive regulator and a 7912 negative regulator. I don't see any rectifier diodes so perhaps the power input is a bipolar DC supply that is at least ± 15 V (to account for regulator drop-out voltage)? You need to show more.

 

[gswan]

Looks like a pretty bodged-up, poorly laid-out pair of 12V regulators (bipolar).
You need to include details of the VU meter circuit, as the picture does not tell the whole story.

 

[Bonsaimaster]

Here is a wide shot

 

[Bonsaimaster]

Meters

 

[Bonsaimaster]

whole board view

 

[gswan]

At a guess, J9 is an AC input which is half-wave rectified to + and - rails using the two diodes.  This supply looks like it is powering some kind of add-on illumination for the meters? If so then it can be replaced with a simple DC supply. Looks like just the +12V rail is being used.

The meters are connected directly across the signal without any kind of drivers. This is kind of bad as the rectifiers in the meter have a non-linear impedance and will add distortion to the signal.

Better to junk the guts and rebuild it with a decent meter driver and PSU.

 

[Andy Peters]

Here is a wide shot

OK, I see diodes D1 and D2, so it accepts an AC input (likely 12 VAC). It looks like the supply was meant for more than just the meter drive.

I'd do what gswan suggests.

 

[Bonsaimaster]

Thanks to everyone. I ordered a VU meter driver and power supply for the unit. Anyone want some VU parts??? Just kidding. Thanks again!