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Old 27th October 2005, 06:35 PM   #1
reins is offline reins  Germany
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Default Transporting DC over longer cable

Hi,

I thought to centralize some power supplies out of view. Is there any disadvantage, if I run a 2 m say micro cable between my supply and the preamp?

Thanks
stephanr
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Old 28th October 2005, 02:32 PM   #2
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Basically a power supply should be there, where tho power is needed. This has several reasons:

1. Power
If you need large currents the impedance of the cable will be a problem with dynamic effects.

2. Noise
You easily catch any radio transmissions and hum with a long cable.

So if you only want to supply a preamp there shouldn´t be current problems. For the noise problem I would recommend some filtering at the power input of the amp, combined with large caps as current buffer. And you should use a good quality shielded cable.

The remote power supply should also be ground-lifted to avoid ground-loop humming.
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Old 28th October 2005, 02:50 PM   #3
AndrewT is offline AndrewT  Scotland
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Hi,
interference pick up should not be a serious problem since you are working with low impedance source and input, particularly the source. I recommend the addition of substantial local decoupling at the preamp PCB as suggested by Cybergent.
I also suggest low value 10nF to 100nF decoupling at both ends of the cables (just in case some interference gets through, airborne and mains borne).

If you combine smoothing C at the transformer end with decoupling C at the preamp end you have created a CRC psu using the cable resistance as your R. Best of all worlds in my view. Just do some numbers on the relative values of R and C to ensure the RC time constant is adequately large.
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Old 28th October 2005, 04:59 PM   #4
reins is offline reins  Germany
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The filtering is a good idea. I had the buffer already in mind.

Thanks
stephan
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Old 28th October 2005, 05:02 PM   #5
Eva is offline Eva  Spain
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Do you want to power several pieces of equipment with the same PSU? This may generate serious ground loop issues if these pieces of equipment are interconnected with unbalanced signal lines.
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Old 28th October 2005, 08:03 PM   #6
reins is offline reins  Germany
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Quote:
Originally posted by Eva
Do you want to power several pieces of equipment with the same PSU? This may generate serious ground loop issues if these pieces of equipment are interconnected with unbalanced signal lines.
I'm not sure about that, but I will use balanced connections anyway.

stephan
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Old 28th October 2005, 08:14 PM   #7
Eva is offline Eva  Spain
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Note that in order to get a balanced transmission (and ground loop inmunity) at least one of the ends of the line must be electronically or transformer balanced. However, you may use independent PSU transformers to circumvent that (no loops), or even a single transformer with multiple secondaries (one or more for each piece of equipment).
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