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Old 11th June 2016, 01:47 PM   #1
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Default PSU and amp in separate encolsures

Have anyone tried to build a PSU (transformer, rectifier, capacitors)
in a separate box, and have it connected to the amp by 1 meter cable?
Any issues with hum/grounding?
I would like to re-use one PSU (say +/64V) with multiple amps,
rather than building ($$) new PSU in every amp I'm testing in my
living room. Also, amp case can be thinner/smaller in this case.
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Old 11th June 2016, 02:11 PM   #2
xrk971 is online now xrk971  United States
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I want to do something similar when I make a box for my amps. Right now they all get tested in a sheet of plywood and the power supply transformer and PSU rectifier and caps are shared by putting various amps under test in and out. Seeing this - it would seem that a separate PSU box maybe adjacent to main amp and connected by large gauge wires with crimped eyelet connectors and screw terminal blocks makes sense. You have to make sure to use star ground topology to avoid ground loops. The longer run of 1m is probably not an issue with noise as you would be running high current low impedance DC lines.

I have been able to use a common center tap for both monoblock channels with separate rectifiers and caps but have heard that ground loop issues could arise in such a case. Dual transformers or transformers with dual center tap outputs would avoid ground loops to start with.

Here is my current setup that will be transferred to a case. Probably separate PSU case...
Click the image to open in full size.
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Old 11th June 2016, 06:19 PM   #3
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A non-issue I would say. Not much different from using a regular lab PSU, which is commonly used for hobby projects such as this. I used one when I built a Circlophone.
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Old 11th June 2016, 07:04 PM   #4
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understanding star grounding

There may be a later post, but this gives some idea on where this Thread was going.
Worth reading the whole Thread from post1.
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Old 11th June 2016, 08:00 PM   #5
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Quote:
Originally Posted by AndrewT View Post
understanding star grounding

There may be a later post, but this gives some idea on where this Thread was going.
Worth reading the whole Thread from post1.
Thanks Andrew.
"dual mono grounding" as mentioned in that thread - that's what I need (kind of).
Interesting thing: chassis ground wire is routed separately
from PSU 0V wire.
So 4 wires in total between PSU and amp (plus remote start, etc.. signals).
What can go wrong if there is only one 'ground' wire?
I know with AC mains it's different story, but with DC? These two are surely connected together in the PSU.
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Old 11th June 2016, 08:06 PM   #6
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Read the whole Thread and get a feeling for the Safety issues.
Then you can make up your mind on what you decide is necessary for home insurance and friends/children in the vicinity.
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Old 11th June 2016, 08:09 PM   #7
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I'm reading.

Quote:
Originally Posted by AndrewT View Post
Read the whole Thread and get a feeling for the Safety issues.
Then you can make up your mind on what you decide is necessary for home insurance and friends/children in the vicinity.
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Old 11th June 2016, 09:41 PM   #8
xrk971 is online now xrk971  United States
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So this is the recommended topology? What about when only one set of shared center tap transformer is used but two separate rectifiers and filter banks? Or is this diagram already accounting for that?

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Old 12th June 2016, 01:55 AM   #9
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Quote:
Originally Posted by minek123 View Post
Have anyone tried to build a PSU (transformer, rectifier, capacitors)
in a separate box, and have it connected to the amp by 1 meter cable?
Any issues with hum/grounding?
A classAB amplifier has half-wave rectified versions of the output current flowing on its supplies. It doesn't make sense to increase the loop area and impedance of the wiring those currents are flowing through.

I'd suggest series inductors between the boxes and having substantial capacitance local to the amp. In other words, configure your supply as CLC with the first C in the transformer box and the second one as close to the amp as you can manage.
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Old 12th June 2016, 02:04 AM   #10
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The long power leads have inductance and resistance and you might get some instability in the amp.
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