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power supply to separate box
#1
Hi;

I am contemplating putting preamps in a separate box from the power amp and power supply in a unit I am currently building. I was wondering if this is possible or safe? Are there any special types of connectors that would work really will for this? Anything I should consider for the wiring between the boxes? My concerns are about the plate voltages and heaters. The power supply is the PSU-25.

Thanks...
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#2
Hi Ticatfan

The assumption here is that the preamps are not stand-alone and will be powered from the PSU which is in a separate box?

In any case, you only need #22 wire for all connections and can use a number of different connector types. It depends a bit on how many of the supplies need to go to the preamp? In the worst case scenario, we assume plate, heater and aux, which is a total of seven including two grounds (plate, aux). If the PSU is supporting a power amp, then the grounds are tied together within that chassis and you can have the redundant ground or not through the cable.

If we assume the preamp signal output has to go to the supply chassis, then potentially two more wires, so a total of 9. The task is a lot simpler if signal is connected separately, in which case it can have a proper shielded cable.

There are many connectors that can handle the voltage and some types where you have to leave empty pins for voltage spacing. For example, a D-sub has a rating lower than needed for the plate voltage. If you place the Va connection second from the end of a row, then leave empty pins around it, you have the spacing of two pins to ground. other voltages can be grouped appropriately without spaces. There are some D-subs rated at 600V.

At the preamp end, you shuld decouple the incoming power and use the entry point as the star for the incoming power. This effectively isolates the preamp ground bus from the PA so there will not be any interaction. This is what is relied upon in mixers and multi-channel boxes where ground loops are unavoidable.
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#3
I have completed building the power supply. Decided to power it up and check out the voltages. Used the power limiting safety socket, rechecked after on bypass. I think it all checks out good except for the AUX supply. I get +12 and -20. Everything seems balanced till it comes out the voltage regulators. Should I replace the 7912 or does this indicate other possible problems. If I had a 7912 kicking around I would just replace it, but I don't. Thanks ....
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#4
Hi TiCatFan

If you used the protection diodes around the regulators, make sure the one across the 7912 is not backwards. otherwise, likely a missing connection for the adjust pin on that reg.
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