Console Power Supply Question

I'm new to the forum (long time lurker), so let me know if this is the wrong section to post this in.

I recently bought a Sony MXP-2900 console (let's be honest, I bought a project not a console) without the power supply. I'd like to avoid spending a ridiculous amount on it if possible. It requires +/- 18V @5A, as well as +5V and +48v. The later two I have handled, but the +/-18v is a little more problematic.

I haven't been successful in finding any 18V power one linear supplies- just 15V and 24V versions. I already have a pair of F24-12 power supplies, or I could buy a pair of HD15-6A power supplies on eBay, but I'm wondering if anyone here knows whether either of these models can be adjusted to output 18V.  I'm a little worried about doing that with the F24, as that would be an additional 30 watts of dissipation from the pass transistors- seems like a lot.

Thanks for the suggestions!

HD15-6 is based on IC 723 IIRC, and has trimmers on the PCB for output voltage and max. current adjustment. So, most probably the output voltage can be raised for 3 volts easily, but there is a question would be voltage on smoothing capacitor high enough for correct regulation at maximum current. It should be tested.
The best solution IMO would be using Soundcraft CPS275 here, at ebay.com is auction for USD400 (negotiable), so if you are in USA, the shipping costs wouldn't be so high. 

Are the connecting ends your concern? There's older broadcast desk PSU's out there with your voltage requirements.


missing 5v, but the 12v might be tweakable:

https://www.ebay.com/itm/Wheatstone-Audioarts-PS-20A-Broadcast-Console-Power-Supply-18V-24V-12V-PS20A/231386827709

Forgot to mention there's DC to DC converters that can possibly let you run everything from one PSU.
Not sure how accurate or clean buck converters are, but they are cheap!
https://www.ebay.com/itm/DC-DC-15A-Buck-Adjustable-4-32V-12V-to-1-2-32V-5V-Converter-Step-Down-Module-DT/152675836256

Also note, the difference between a +-15v and +-18v supply headroom wise is about 2db..... 

H713 said:

I recently bought a Sony MXP-2900 console (let's be honest, I bought a project not a console) without the power supply. I'd like to avoid spending a ridiculous amount on it if possible. It requires +/- 18V @5A

I haven't been successful in finding any 18V power one linear supplies- just 15V and 24V versions. I already have a pair of F24-12 power supplies, or I could buy a pair of HD15-6A power supplies on eBay, but I'm wondering if anyone here knows whether either of these models can be adjusted to output 18V. 

Click to expand...

the + output of a Power-One mode HCC 15-3-A can be adjusted up to 16.6 VDC.
Into an 8 ohm load, maintains line regulation down to 97 VAC.

By adjustment of the voltage divider resistors associated with the 723, +18 VDC can be obtained.
Line regulation will suffer but should be adequate.

Even with the reduced dissipation of the series pass transistors at a higher output voltage,
the 6 ampere rating seems marginal.
Those open frame supplies get HOT when operated near their max ratings:
rudimentary heat sink, no thermal grease, poor  emissivity of the bare aluminum.

Quoting from Power-One data sheet
drawing no. 51281  rev .L
"Temperature Rating:
0 degrees C to 50 degrees C full-rated, derated linearly to 40% at 70 degrees C.
12 CFM forced air cooling required to meet IEC 380/950 above 80% of total rated output power."

I would de-rate an open frame supply by at least 75%, perhaps more.
or employ forced air cooling.

Thanks,

Earlier today I read a thread over on Gearslutz that suggested that the F24-12 can be trimmed down to 18V with a simple mod, and that doing so is reasonably common. While this would cause it to run hotter, I'd be well below the current rating by about 50%, and I'd run forced air cooling anyways. Given that I have them in stock, the only thing that really sucks is the fact that they're not .25 inches shorter so as to fit in the 3u chassis I have laying around.

How about building this PSU but with LM7818 instead of LM7812?

The author says it's able to deliver 30A, what do you guys think?

http://electronics-diy.com/12v-power-supply.php

I someone don't think that the failure mode, or a shorted rail with that design would end very well....... 

iampoor1 said:

I someone don't think that the failure mode, or a shorted rail with that design would end very well....... 

Click to expand...

Adding protection diodes doesn't seem a problem. simple and easy

Whoops said:

Adding protection diodes doesn't seem a problem. simple and easy

Click to expand...

On a regulator of that magnitude, you need more than protection diodes!

If you want to roll your own supply, Douglas self has a great schematic for a +-17v 6amp supply in "Small signal audio design" using lt1038 regulators I believe.

I absolutely could roll my own supply. There are options- LT1038, LM317 with a pass transistor, LM317K, 10 others I'm not thinking of, and quite honestly I probably could design one discrete if I really wanted- it's not rocket science. The fact of the matter is, however, I don't want to spend two months designing and testing a power supply- I bought this desk because I want to redesign the channel strips, not because I want to bumble around with the power supply forever.

If I can use the F24-12A power supplies I have right now, I'm going to, unless someone has a reason why I shouldn't (or a better idea). At the moment, if all else fails I can go with one of those Wheatstone power supplies someone mentioned above... for some reason none of those showed up on my searches.

The Wheatstone power supply has a 1 Amp mains fuse. Look at the photo.
They call it the model 20A, But you'll never get 20A out of that box.

Whoops said:

The author says it's able to deliver 30A, what do you guys think?
http://electronics-diy.com/12v-power-supply.php

Click to expand...

The calculation in the article is incorrect, IMO.  And 24Vac at secondary for 12V regulated at the output looks too high. 

rlaury said:

The Wheatstone power supply has a 1 Amp mains fuse. Look at the photo.
They call it the model 20A, But you'll never get 20A out of that box.

Click to expand...

It's 1 Amp Slow Blow  on the transformer primary , 110V.
It's not on the secondaries

If your happy with it.

Whoops said:

It's 1 Amp Slow Blow  on the transformer primary , 110V.

Click to expand...

It is 110VA at primary side max.
Console needs +/-18V/5A or 180W plus power for 5V and 48V  continuous ...
So, Wheatstone Audioarts PS-20A is obviously inadequate.

It's a 3 terminal type supply. No pass transistors.

Good catch on the Wheatstone PSU,  though there are indeed other (larger) Wheatstone power supplies on eBay for similar prices.

That said, I found the datasheet for the LM723 and was able to reverse-engineer the Power One F24-12 enough to trim it down to 18 volts (Changed R17 from a 3k to a 2k), giving it an adjustment range from 16 to 24 volts instead of the 20 to 28 volts that was originally an option. Even though my current draw (~5A) technically wouldn't mandate forced-air cooling, given the additional 30 watts dissipated by the pass transistors from trimming it down to 18V, I'm probably going to put some fans in the chassis to keep them cool.

I was a little shocked by the fact that they didn't use any thermal compound on the pass transistors- just a dry mica washer. Is there a particular reason for this? It seems extremely odd.

H713 said:

Even though my current draw (~5A) technically wouldn't mandate forced-air cooling, given the additional 30 watts dissipated by the pass transistors from trimming it down to 18V, I'm probably going to put some fans in the chassis to keep them cool.

Click to expand...

another option to bypass the drama of cooling fans:
a bucking transformer on the primary, relatively small and inexpensive.
am sure you can do the math.

H713 said:

I was a little shocked by the fact that they didn't use any thermal compound on the pass transistors- just a dry mica washer. Is there a particular reason for this? It seems extremely odd.

Click to expand...

been using Power-One linears  and equivalent for longer than I want to admit,
you are the first person to  note that peculiar omission.  can we say "cheap"?