Reversing components to get -48V instead of +48V

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bxt403
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Joined: Fri May 14, 2010 7:53 am

Reversing components to get -48V instead of +48V

Post by bxt403 »

I've successfully used the JLM AC/DC, and Trex2 to rack some Studer modules into 3 separate enclosures.

For one two of them I used a Trex2 with TIP127s installed and reversed capacitors to get a secondary -ve supply from the main negative rail supply (while I kept the +48V components installed on the AC/DC kit but have it adjusted to minimum with nothing connected as I don't need phantom power).

I now have a small Studer mixer (with 6 input modules and 2 for the master output) that needs a new power supply. Unlike my other builds: I'd rather install an LM337 (instead of LM317 for +48V) onto an AC/DC, as the mixer doesn't need phantom power but does require -8V for the limiter section of the two output modules.

My other options are daisy-chaining a modified Trex from the -ve rail of an AC/DC kit or getting a Powerstation (with 1 +ve and 2 -ve rails will be used while the second +ve and +48V rail would be populated but unused). The main issue is that I want to minimize the components installed and avoid using a modified Trex.

I'm uncertain how much current the -8V rail needs but the mixer (when I checked with a power-meter before I decided to re-calibrate everything) used around 18W.

My biggest concerns are:
-if I can get away with getting a Powerstation and leaving the components for the sections that won't be used (+48V and the second +V rail) unpopulated

-if I can reverse the polarity of specific components and install an LM337 instead of a LM317 in the +48 section of the AC/DC kit and maybe even increase the current for 48V

As the mixer uses less than 20W- I'm certain most of the power is needed for +/-15V but am not sure exactly how much current the -8V rail needs to be.

Any help is greatly appreciated.

:)

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Joe Malone
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Re: Reversing components to get -48V instead of +48V

Post by Joe Malone »

bxt403 wrote:I've successfully used the JLM AC/DC, and Trex2 to rack some Studer modules into 3 separate enclosures.

For one two of them I used a Trex2 with TIP127s installed and reversed capacitors to get a secondary -ve supply from the main negative rail supply (while I kept the +48V components installed on the AC/DC kit but have it adjusted to minimum with nothing connected as I don't need phantom power).

I now have a small Studer mixer (with 6 input modules and 2 for the master output) that needs a new power supply. Unlike my other builds: I'd rather install an LM337 (instead of LM317 for +48V) onto an AC/DC, as the mixer doesn't need phantom power but does require -8V for the limiter section of the two output modules.

My other options are daisy-chaining a modified Trex (which is what I'm trying to avoid) from the -ve rail of an AC/DC kit or getting a Powerstation (with 1 +ve and 2 -ve rails will be used while the second +ve and +48V rail would be populated but unused).

I'm uncertain how much the -8V rail needs but the mixer (when I checked with a power-meter before I decided to re-calibrate everything) used around 18W.

My biggest concerns are:
-if I can get away with getting a Powerstation and leaving the components for the sections that won't be used (+48V and the second +V rail) unpopulated --if I can reverse the polarity of specific components and install an LM337 instead of a LM317 in the +48 section of the AC/DC kit and maybe even increase the current.

As the mixer uses less than 20W- I'm certain most of the power is needed for +/-15V but am not sure exactly how much current the -8V rail needs to be.

Any help is greatly appreciated.

:)
The title says -48v but in the text you say -8vdc?

If -8vdc Best to use a powerstation and it is fine to not use or not fit the rails you don't need. So you can have +/-15v & -8vdc on a 2 x 18vdc power transformer.

The LM337 and LM317 pinouts are not the same so reversing can work but is a mess due to the pinout problem and reversing the 48v section is even worse.

If you need -48vdc can you send me the schematic of the desk so I can have a look at what is it doing with the 48v :-)
Joe :-)
JLM Audio
Capturing Audio without Injury

bxt403
Posts: 3
Joined: Fri May 14, 2010 7:53 am

Re: Reversing components to get -48V instead of +48V

Post by bxt403 »

Joe Malone wrote:
bxt403 wrote:I've successfully used the JLM AC/DC, and Trex2 to rack some Studer modules into 3 separate enclosures.

For one two of them I used a Trex2 with TIP127s installed and reversed capacitors to get a secondary -ve supply from the main negative rail supply (while I kept the +48V components installed on the AC/DC kit but have it adjusted to minimum with nothing connected as I don't need phantom power).

I now have a small Studer mixer (with 6 input modules and 2 for the master output) that needs a new power supply. Unlike my other builds: I'd rather install an LM337 (instead of LM317 for +48V) onto an AC/DC, as the mixer doesn't need phantom power but does require -8V for the limiter section of the two output modules.

My other options are daisy-chaining a modified Trex (which is what I'm trying to avoid) from the -ve rail of an AC/DC kit or getting a Powerstation (with 1 +ve and 2 -ve rails will be used while the second +ve and +48V rail would be populated but unused).

I'm uncertain how much the -8V rail needs but the mixer (when I checked with a power-meter before I decided to re-calibrate everything) used around 18W.

My biggest concerns are:
-if I can get away with getting a Powerstation and leaving the components for the sections that won't be used (+48V and the second +V rail) unpopulated --if I can reverse the polarity of specific components and install an LM337 instead of a LM317 in the +48 section of the AC/DC kit and maybe even increase the current.

As the mixer uses less than 20W- I'm certain most of the power is needed for +/-15V but am not sure exactly how much current the -8V rail needs to be.

Any help is greatly appreciated.

:)
The title says -48v but in the text you say -8vdc?

If -8vdc Best to use a powerstation and it is fine to not use or not fit the rails you don't need. So you can have +/-15v & -8vdc on a 2 x 18vdc power transformer.

The LM337 and LM317 pinouts are not the same so reversing can work but is a mess due to the pinout problem and reversing the 48v section is even worse.

If you need -48vdc can you send me the schematic of the desk so I can have a look at what is it doing with the 48v :-)
Since the 48V rail is adjustable (to lower voltages) on all the JLM power kits: I figured I might as well ask the generalized question first (since I used the 48 rail from an AC/DC with a Trex2 to supply 5 VDC for logic and 3VDC for LED on one of the modules). I figured I could do something similar with an adjustable -48 Volt rail (in that I can just adjust it to -8VDC since I only need one extra voltage outside of the main +/- DC rails).

In any case: it seems like the process to get a -48VDC rail from the phantom power rail on a Powerstation or AC/DC kit is more complicated than getting a -ve supply from a Trex.

A partially populated Powerstation kit is probably the best option, as I won't be under powering anything.

Thanks.

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Joe Malone
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Re: Reversing components to get -48V instead of +48V

Post by Joe Malone »

Yes part built powerstation will make it easy.

Whenever using the 48v rail for low voltage don't fit any jumper to doubler/tripler and short out C1 & C2 so turn the rail back into a normal power rail to set for low volts.

Always run a series resistor on leds and use a higher voltage rail. If no resistor and the rail voltage varies slightly or the led goes short it will not end well.
Joe :-)
JLM Audio
Capturing Audio without Injury

bxt403
Posts: 3
Joined: Fri May 14, 2010 7:53 am

Re: Reversing components to get -48V instead of +48V

Post by bxt403 »

I double-checked and remembered the builds uses a Powerstation (the AC/DC was for another module). I was using the 48V rail to supply +ve to the Trex2 but switched the one of the V+ supplies instead.

I must've been under powering everything connected to the Trex2 since the LEDs were dimmer (albeit the logic circuits and CPU on the module were still functioning).

In any case: at least I know the mixer will have ample power (as it only needs around 20 Watts for everything). I look forward to getting another Powerstation, as the 980 module (which has also uses a microcontoller/CPU) is working perfectly.

Thanks.

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