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How long can a console PSU cable run? Audio Interfaces
Old 6th December 2018
  #1
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How long can a console PSU cable run?

Hello gearslutz,

I'm about to be the proud owner of an SSL 4000 E Series (24ch) in about a week or so.

I've started preparing my studio for the console and i was wandering, how long can the cable from PSU to Console run before you start having noise problems etc.. ?

What will become my "machine room" is not that close to where the console is going to go, and the psu is kinda noisy so..

Thank you
Old 7th December 2018
  #2
Lives for gear
I can't tell for sure without a schematic, but external power supplies on high end equipment (not just audio) often have a sensing lead... So if there's a voltage drop over a long cable, the supply can compensate.


YMMV.
Old 7th December 2018
  #3
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Richard Crowley's Avatar
 

Do you have the original power cable?
Or do you have the power cable connectors for the power end and the console end?
Do you have the manual for the power supply? for the console?
How far do you need to run the cable?

The main issue with long power cables is not noise.
The main problem is voltage droop through the cable.

As Jay Rose mentioned, some higher-end power supplies use separate "sense" wires.
They sense the voltage at the console end and boost the voltage out of the supply to compensate for droop in the cable.

Does your power supply have the provision for sense wires?

It is difficult to offer much more practical suggestions without details of your power supply and your distance.
Old 7th December 2018
  #4
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gyraf's Avatar
for reference, we ran our 4000 some 20-25m from PSU/Computer rack.

The many multicables for computer/analog interfacing were somewhat sensitive, the power supplies presented no problem.

Jakob E.
Old 8th December 2018
  #5
DC will drop from cable resistance just like it did for Edison. AC holds up much better. Sense lines can also generate errors as the sense from one end of a large console cannot compensate for the losses across the console's buss feeds. The other end can be off by a volt or so.
Old 8th December 2018
  #6
Gear Addict
 

Quote:
Originally Posted by Jim Williams View Post
DC will drop from cable resistance just like it did for Edison. AC holds up much better. Sense lines can also generate errors as the sense from one end of a large console cannot compensate for the losses across the console's buss feeds. The other end can be off by a volt or so.
AC has the same voltage loss as DC for the same current and wire resistance. The advantage of AC distribution over Edison-style DC power distribution is that it can easily be stepped up to a higher voltage (and lower current) with a transformer, and back down again when needed. The voltage drop is lower in absolute terms because there is less current, per Ohm's law, and the percentage voltage drop is even more lower because the nominal voltage is higher, and the power loss is likewise reduced (less voltage time less current). High voltage DC power has the same efficiency advantages and a few of its own, due to lower inductive losses, but is harder to convert up or down efficiently...and that was doubly true before high voltage, high power solid state electronics were developed.

If there are voltage drops within a console, the power supply can't reasonably be expected to do much about that whether it's three feet away or thirty feet away or three hundred feet away. Voltage sense lines do very well at making sure the proper voltage is seen at the (connection to the) load.
Old 8th December 2018
  #7
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DC will drop from cable resistance just like it did for Edison. AC holds up much better.

I was dating a theater major when I was in college. She told me her tech theater prof said "AC can go further than DC because it gets a boost every cycle."

She was very sweet and very pretty, so I bought her dinner and explained ohm's law and Westinghouse/Tesla's great contribution to distribution. She got it... and we kept dating.
Old 8th December 2018
  #8
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Hi
I don't remember the SSL Linear supplies having sensing and I can't be bothered to fetch the manual.
Depending how long the run in it may be wise to increase the CSA of the cable so you don't lose too much over the run. You might run into problems with the overvoltage crowbar but they can be adjusted but it is a 'fun' exercise.
I seem to remember that the main supplies are 3 'cores' of 4mm CSA wire.
It is worth cleaning the supply out before installing it, brush and vacuum cleaner.
Matt S
Old 9th December 2018
  #9
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JohnRoberts's Avatar
 

Quote:
Originally Posted by Jay Rose View Post
DC will drop from cable resistance just like it did for Edison. AC holds up much better.

I was dating a theater major when I was in college. She told me her tech theater prof said "AC can go further than DC because it gets a boost every cycle."

She was very sweet and very pretty, so I bought her dinner and explained ohm's law and Westinghouse/Tesla's great contribution to distribution. She got it... and we kept dating.
Giving Jim the benefit of the doubt (because he knows this stuff) I suspect he was referring to the mains power line cord (120V) vs the 20-40V DC cable... for the same power on both, lower voltage requires more current and higher IxR losses.

The answer to the OP is as long as it needs to be...

JR
Old 9th December 2018
  #10
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nosebleedaudio's Avatar
 

30 to 40 feet is not uncommon.. If I was to guess I would say 20' to 25' was the most common..
IF the voltage drop is more than expected, simple, you bump the supply up a volt or so to compensate...Done..
Old 9th December 2018
  #11
Here for the gear
My PSU is CF611E. I don't have the schematics yet.. i need it to run 40 feet and the power cable i'm getting is about 15 feet.
Old 10th December 2018
  #12
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JohnRoberts's Avatar
 

Quote:
Originally Posted by IliasPre View Post
My PSU is CF611E. I don't have the schematics yet.. i need it to run 40 feet and the power cable i'm getting is about 15 feet.
If worried about voltage drop due to IxR losses you can use heavier gauge wire... not rocket science, but actual science....

JR
Old 10th December 2018
  #13
Gear Maniac
 

I helped install an SSL 4000 G in 1998.

There were no sense lines for the PSUs. The PSUs were in a machine room, about 20 feet away from the console, but because the cables were pre-terminated with circular connectors, we didn't shorten them, just coiled up the excess in a cable trough. There was actually about 40 feet of cable supplied by SSL.

The commissioning tech adjusted each PSU to supply ±18V at the console when under load. Since one supply couldn't power the entire 40 channels reliably, I think we made the adjustment with 3 or 4 buckets and the master section running, and then the same load for the other supply. The resistance of the supply cables is the only mechanism for load sharing, so it was important that the PSUs put out the same voltage when under the same load. The actual voltage was not as important as the match between them.

With only one supply and 24 channels, your task is easier, although it's a bit of a trick to measure in one room, and then adjust in another. Consider some temporary "sense" lines (maybe on an XLR line) back to the PSU location to make the job easier.

I think if I had to extend the power cables myself, rather than messing around with re-pinning the circular connectors, I'd cut the cable, crimp on spade lugs, and add some suitably heavy wire between a pair of barrier terminal strips.

Whatever you do, you do not want the PSU and computer roaring away in the same room you're trying to mix in. They are VERY noisy.

Geoff
Old 10th December 2018
  #14
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Thank you all,

I will wait for the console to arrive first and try it out with my tech!
Old 10th December 2018
  #15
I once ran 50 foot power cable runs for a 40 input Soundcraft TS-24. I ended up having a tech sit at the console measuring the DC rails at both ends of the buss boards. I then adjusted the power supply trims to make up for the drop. There were two supplies used so it was double the work.
Old 10th December 2018
  #16
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Richard Crowley's Avatar
 

We have had power supplies with remote sensing for decades.
And multi-supply load-sharing also.
Why is the audio world so backwards?
Old 11th December 2018
  #17
"Standard SSL lengths were 5 meters, 10 meters, 15 meters. SSL made a couple longer than that that were custom, but the issue was voltage loss down the line. Longer runs on bigger consoles required dual cables to mitigate the voltage loss. I can think of one that SSL did custom that was 18 meters"

-Bruce Millett, TDD
Old 11th December 2018
  #18
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nosebleedaudio's Avatar
 

Quote:
Originally Posted by Matt Syson View Post
Hi
I don't remember the SSL Linear supplies having sensing and I can't be bothered to fetch the manual.
Matt S
Most supplys I have seen had the sensing points tied at the supply end...
So, maybe its NOT a great idea sometimes...
Old 12th December 2018
  #19
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Hi
Getting power of say 20 Amps from a supply to a desk at low impedance (at the distribution inside the desk) is quite a challenge as the supply is getting a bit beyond what 'usual' supplies can handle easily and using multiple smaller supplies creates problems with either having to split the load (separate the channel buckets) or combining them to feed them simultaneously. Add to this that it has to be made 'idiot proof' and you get to the point where no one can agree the 'best' way of doing it.
I had a go at running a desk at 200 feet of power cable 'for laughs' as an experiment. It just worked fine but highlighted a different issue in that the wiring INSIDE the supply box lost more than the 200 foot run (16mm squared cables).
Matt S
Old 12th December 2018
  #20
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nosebleedaudio's Avatar
 

Quote:
Originally Posted by Matt Syson View Post
Hi
Getting power of say 20 Amps from a supply to a desk at low impedance (at the distribution inside the desk) is quite a challenge as the supply is getting a bit beyond what 'usual' supplies can handle easily and using multiple smaller supplies creates problems with either having to split the load (separate the channel buckets) or combining them to feed them simultaneously. Add to this that it has to be made 'idiot proof' and you get to the point where no one can agree the 'best' way of doing it.
I had a go at running a desk at 200 feet of power cable 'for laughs' as an experiment. It just worked fine but highlighted a different issue in that the wiring INSIDE the supply box lost more than the 200 foot run (16mm squared cables).
Matt S
Considering the fact that MOST consoles modules have decoupling circuits that have a resistor is series with the +- rails, plus most have the same for most sub circuits on the same module...
Some consoles have a large decoupling pcb before it hits ANY modules..
So, I guess you see my point...
This is NOT a power amp...

One more point is even getting from channel one to channel 48 on a large console going thru PCB traces will NO doubt have a voltage drop...so people are worrying about something that they really can't eliminate..
Because decoupling is VERY effective in isolating channel to channel ect..

Last edited by nosebleedaudio; 12th December 2018 at 09:30 PM..
Old 13th December 2018
  #21
10 ohm fuse resistors typically drop the rails about 1/2 volt. For the precision crowd, adjust the trims on your supply so you get the desired voltage AFTER the 10 ohm fuse resistors. AMEK used 1N4002 rectifier diodes, those drop 3/4 a volt.
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