umbilical for BrianGT kit

[waltona]

Hi all,

I'm building Brian's 3875 kit with the power supply in a separate case to the amp boards. I'm using a tranny with dual secondaies and one rectifier board. My question is how many wires do I need in the umbilical connecting the 2 boxes? Can I combine the PG+ and PG- at the rectifier board and use one connecting wire?

At the moment I was thinking of using 1 wire for each of the following:

V+ (one wire from rectifier to amp box which is then split to each amp board)
V- (as above)
Earth (for chassis only)
PG (+ and - combined at rectifier board and split in the amp box)

I know this is a very smple question and YES I have searched the forums but I'm a bit confused and thought it was better to ask and be safe.

Thanks

BIG A

 

[homer09]

yes it is safe, if done properly to avoid hums. i suggest you follow carlos fm's way:

http://www.diyaudio.com/forums/showthread.php?postid=617246#post617246

 

[waltona]

Thanks for the reply.

Ok I'm sorted with V+, V-, PG+ and PG-.

Now about chassis ground...do I connect the mains earth to the power supply chassis, run a second wire in the umbilical to the amp chassis and not use the CHG on the PCBs?

 

[homer09]

sounds right, u'll know for sure when there's no hum.

 

[Nuuk]

Now about chassis ground.

Yes run the ground wire from the PSU chassis through the umbilical and connect it to the metal cahssis of the amp case. The connect CHG to the case via a cpa and resitor in parallel as shown in this design .

 

[Sherman]

Thanks for the reply.

Ok I'm sorted with V+, V-, PG+ and PG-.

Now about chassis ground...do I connect the mains earth to the power supply chassis...

If your umbilical is relatively short (say under a meter) then a five wire DIN plug works well. In the amp box use a panel mount DIN connector. Easy to disconnect and it can't be connected wrong.

Connect 1 wire each to V+, V-, PG+, PG- and earth or safety ground in the PS box.

In the amp box make the 4 power connections to the amp boards and connect the earth or safety ground pin to the chassis.

Just make sure to match the right pins to the right PS connection!

 

[carlosfm]

Connect 1 wire each to V+, V-, PG+, PG- and earth or safety ground in the PS box.

In the amp box make the 4 power connections to the amp boards and connect the earth or safety ground pin to the chassis.

That's the ticket for a ground loop.
Bigger or smaller, depending on the distance between the two channels.
But always a ground loop.

 

[waltona]

So what would you suggest Carlos?

 

[Sherman]

That's the ticket for a ground loop.
Bigger or smaller, depending on the distance between the two channels.
But always a ground loop.

Built four amps exactly this way with no groundloop issues whatsoever. Remember your individual boxes each must have a safety ground within the box. The two can then be connected in the umbilical with no problem and the whole thing is safer.

 

[waltona]

Thanks for everyones help on this one. I appreciate it.

 

[jeff mai]

Built four amps exactly this way with no groundloop issues whatsoever.

You have ground loops then. They just aren't causing a problem for you. Seriously - trace all the ground wires and draw a picture.

 

[scottw]

ummmmbilical

I'm also planning a separate PSU for my GC(to make more room for capacitors). This is a dual mono- two transformers, each with dual secondaries. Bridges in the PSU.

So for both channels this will be 8 leads for the power(voltages and their corresponding neutrals)-that's easy enough.

That leaves the grounding. Was planning to run a separate lead for just the amp chassis ground back to the PSU earth. Then for the power ground for the amps, should I run a single ground lead for both the amps or should each amp have its own power ground back to PSU earth?

Thanks,

scott