Calrec Z3018-3 PSU

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Calrec Z3018-3 PSU

Postby lukecore » Tue Mar 12, 2013 2:50 am

Hello people, I have joined this forum after finding lots of useful information but I thought it was time to ask a question. My question is not directly related to a Calrec console but the power supply.
I have a Soundtracs Megas which I have had for about 5 years but decided to decommission it in the first year after having nothing but troubles with the power supply.
The switch mode circuitry of the supply is strange and unreliable, and would constantly induce high pitched noise into the signal path.
Skip forward 3 or 4 years and after keeping an eye out for a linear power supply I finally came across a Calrec supply for the right price.
It has the required voltages and should work nicely but here's the catch.

The question.

The Soundtracs console uses mains earth as the 0volt reference for the supply.
The Calrec supply's 0volt reference is completely isolated from the earth of the unit (at least when it is switched off).
I can try to isolate all incoming earth points from the console itself but I can there being noise issues and I really don't want to blow up the supply or the console at this point of time.
Do you think there is a work around for this problem or should I just bite the bullet and build a custom supply for the console, perhaps using the components or at least the transformer from the Calrec supply?

Any help would be greatly appreciated.

Lucas in Melbourne, Australia.
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Re: Calrec Z3018-3 PSU

Postby GJC Designs » Tue Mar 12, 2013 5:02 pm

The reason for the Calrec supply having totally isolated earths is for the reduction (elimination) of earth loops by having a finely defined point where all earths connect together to form the system ground reference.

Bear with me...... first an explanation of the Calrec philosophy, then how to apply your ZN3018 to the Soundtracs.

The way it works is this:

A typical Calrec desk will have several PSUs that current-share.
Each PSU has a derived ground (Calrec call it "Centre Rail" or CR) that, as you have measured, is isolated from the PSU chassis.
The mains power protective earth is connected to the ZN3018 chassis. It also has its own wire in the 19-pin connector that feeds the Calrec desk.
There is another 0V net that comes from the PSU; this is the logic ground (with respect to logic +9V). It is isolated from CR and chassis.

In summary there are therefore three different 0V nets from the PSU:
Centre Rail which is 0V analogue, logic 0V and chassis ground (protective earth)

To achieve the best possible audio performance regarding low-level hum, all three 0V nets from the PSUs need to be connected together at one place. The same is true of the CR, chassis and 0V logic nets within the console.

The power distribution module in the back of each Calrec desk does this linking of 0V nets.
The console is the star-grounding point of the audio installation.

Moving on to Soundtracs:

Leave the ZN3018 as it is and take advantage of its designed-in features.
All grounds need to be connected together at some point, and the console is the ideal place (just as with Calrec consoles).

Hope this helps. Feel free to quiz me or Richard Lumb if you need further info.
GJC Designs
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Re: Calrec Z3018-3 PSU

Postby lukecore » Wed Mar 13, 2013 7:54 am

Thankyou for your quick reply, it makes sense when there is more than one supply for a star wiring configuration. I have got it working but I think there is a problem with the +17volt rail because the led on the meter bridge is dim, the headphone amp is nowhere near as powerful as my A&H consoles and when the gain is increased on a channel not much happens.... There is a slight increase in gain and then it falls away again as if it is being cancelled out. The noise is gone though, the eq's work brilliantly and with a bit of luck I will have the problem fixed in the morning. Once figured out I will post what I have done to make it work.

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