Trident series 65. Converting Mackie 8 bus PSU for use.
« on: March 18, 2021, 09:28:03 PM »
Any thoughts on beefing up the 48v supply for 32 channels?

The mackie supply says it can do 250mA of 48v. Seems like I would need more for the 32 chs?

1. Replace with a TL783? The datasheet on that can do "over 700mA."

2. Use the 12v supply? it says it can do 1.5A. Voltage doulbe or tripler? somehow?


squarewave

Re: Trident series 65. Converting Mackie 8 bus PSU for use.
« Reply #1 on: March 18, 2021, 10:18:06 PM »
Each channel could use up to 10mA of 48V maybe. For 32 channels you probably need more like 500mA. So it sounds like the Mackie supply might be a little short (although the fuse does say 1A). If it isn't enough, you can't just beef up some parts. If the transformer and filtering struggles, you could get some noise and in the worst case a drop in voltage(s). But you could just try it and see what happens.

The proper way to make a replacement console supply these days IMO is to stack some SMPS followed by capacitance multiplers and then a fat cap on each rail. Someone just did that here a few months ago and got good results.

Brian Roth

Re: Trident series 65. Converting Mackie 8 bus PSU for use.
« Reply #2 on: March 18, 2021, 10:52:26 PM »
Re. phantom powering:

ASSuming 48 VDC and 6k81 resistors, the worst case current consumption will be if pins 1, 2 and 3 of the mic input XLR were all shorted together due to a fault.  In that case, the two 6k81 resistors are in parallel (3405 Ohms).  With 48V across them, that calculates to just under 14.1 mA.

If you short 1/2/3 on all the mic inputs on a 32 channel desk, calculation says approx 291 mA will be drawn.

And if all mic input jacks are totally shorted, you have much larger problems!  <g>

Any mic/DI/whatever will draw less than that worst case.  Plus, how often does (most) anyone use that many (32) phantom powered devices at once?

My larger concern about using the Mackie PSU on the Trident would be how much current does the desk require for the audio and other rails?

Bri

PS as a phantom "sidebar".  The 6k8 resistors will each dissipate approx 0.34 Watts in the "dead short" failure condition I described above.  I've seen more than a few desks that used 0.25 W resistors and the resistors "browned" due to the heat after a prolonged failure at the mic input jack.
Brian Roth Technical Services
Salina Kansas, home of the best vinyl on the planet!

http://www.BrianRoth.com
recordingservicesandsupply.com/
www.qualityrecordpressings.com/
store.acousticsounds.com

Re: Trident series 65. Converting Mackie 8 bus PSU for use.
« Reply #3 on: March 18, 2021, 11:00:06 PM »
The mackie says it will do 3.5A on the +/-18v rails and 3A on the 5v rail.

The Trident PSU seems to be rated at 3A for these rails.
« Last Edit: March 18, 2021, 11:03:30 PM by mkiijam »

Brian Roth

Re: Trident series 65. Converting Mackie 8 bus PSU for use.
« Reply #4 on: March 18, 2021, 11:05:12 PM »
The mackie says it will do 3.5A on the +/-18v rails and 3A on the 5v rail.

The Trident PSU seems to be rated at 3A for these rails.

Well, in theory you might be OK then.

Bri
Brian Roth Technical Services
Salina Kansas, home of the best vinyl on the planet!

http://www.BrianRoth.com
recordingservicesandsupply.com/
www.qualityrecordpressings.com/
store.acousticsounds.com

Re: Trident series 65. Converting Mackie 8 bus PSU for use.
« Reply #5 on: April 01, 2021, 01:56:18 PM »
Okay, I've got the big new cable made and am going to add a breakout "sub-panel" inside the Trident. This got me thinking if there would be any benefit to making a PCB and adding local power caps etc?


 

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