Transporting DC over longer cable

reins · 27th October 2005, 05:35 PM

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

Cybergent · 28th October 2005, 01:32 PM

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.

AndrewT · 28th October 2005, 01:50 PM

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.

reins · 28th October 2005, 03:59 PM

The filtering is a good idea. I had the buffer already in mind.

Thanks
stephan

Eva · 28th October 2005, 04:02 PM

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.

reins · 28th October 2005, 07:03 PM

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

Eva · 28th October 2005, 07:14 PM

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).

27th October 2005, 05:35 PM	#1
reins diyAudio Member Join Date: Mar 2004 Location: Bayern	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

28th October 2005, 01:32 PM	#2
Cybergent diyAudio Member Join Date: Jan 2004 Location: Germany / Bavaria / Augsburg	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. __________________ Best Regards, Cybergent

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28th October 2005, 01:50 PM	#3
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	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.

28th October 2005, 03:59 PM	#4
reins diyAudio Member Join Date: Mar 2004 Location: Bayern	The filtering is a good idea. I had the buffer already in mind. Thanks stephan

28th October 2005, 04:02 PM	#5
Eva diyAudio Member Join Date: Oct 2003 Location: Near the sea	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.

28th October 2005, 07:14 PM	#7
Eva diyAudio Member Join Date: Oct 2003 Location: Near the sea	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).