soundcraft series 800B power supply build

hey guys,

I'm trying to figure out what the current draw requirement is from the power supply for my 24 channel soundcraft 800B. I need to build a PSU and I plan to overdesign the current handling a hair, but I don't want to go too crazy.. just enough to work well and play it safe while not burning up the wallet.  Any idea what current handling I should design for per rail?

I can't find an 800B schematic, but the 1600 is considered to be very similar ( according to rumors* ) and here is the schemo for it's power supply.

+/-17VDC I know the schemo for the 1600 says +/-18 but the manual for the 800B says +/-17 which is the only voltage difference I've seen. Plus, it would probaby run well even with the 2V difference.
+/-7VDC
+24VDC
+48VDC

Thanks regardless,

can this whole desk be running off of low enough current to only need 317's and 337's and 338's?  ???

Ah the 338 is a 5A regulator.. good to know such exists without external pass transistors.
Then the negative op amp supply rail must be designed to handle close to that?

I could buy condor, power one, or interational supplies but building and designing stuff is cheaper and more fun.

ha! the T-03 vs T0-220 package for a LM338 is a $54 difference! $2 vs $56. Either one would need a heat sink.  The negative side is the pain in the butt part.. the rest seems fairly low current.  I wish there was a negative compliment for the 338..

buildafriend said:

can this whole desk be running off of low enough current to only need 317's and 337's and 338's? 

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It uses discrete regulators with 2955/3055 power transistors for +/-17V. The current limit is about 6 amps.

You can use the 338 as a negative reg too.  You just build 2 completely isolated supplies, on for positive, one for negative & stack one on top of the other.  So your zero V is where the pos of one is connected to the neg of the other.  This is how AMEK did the PSU for the Einstein.  If youneed more current then if you can find some LT1083 they are rated for 7.5A. 

However the more voltage that any of these regulators are burning up, the less their current capability,c heck out the graphs in their data sheets.

Since it has *two* 2N3055 each rail, it is unlikely any IC regulator will cover the load without 3 or 4 slaved together. At this point it may be simplest to use a cheap 1A reg and several TO220 transistor boosters.

Supplies this size are prone to expensive faults. I know DIY, but a bought solution is sometimes wiser.

I'll use cheap adjustable regulators and 2 pass transistors per rail for the op amp supply. positive section will be a clone of the negative section simply flipped as done with the Amek supply. I'm aware the negative section probably draws a bit less. I appreciate the symmetry.

I'm searching for the cheapest heat sinks and cheapest 20V 5A or higher transformers. I wonder if there are any old pieces of industrial equipment with transformers like this that I can find and use... Heat sinks too..

18VAC 4.44A per rail.. they are usually a few volts up anyway. I'll probably get 20VAC in reality. Then x1.41 should be enough to prevent any voltage dropout

http://www.mouser.com/Search/ProductDetail.aspx?R=VPT36-4440virtualkey55310000virtualkey553-VPT36-4440

now, heat sinks heat sinks...

PRR said:

Supplies this size are prone to expensive faults. I know DIY, but a bought solution is sometimes wiser.

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Having done some repairs to a high current console supply in the last year I would agree, it's not something I would wish to DIY.

I'm not too worried 

The faults here are usually just the pass transistors or regulators in my experience. If the toriod go's bad it gets hot and melts the plastic around it or it does nothing. If you're really concerned add a crowbar or current sense transistor and resistor. I have repaired a lot of power supplies and also built many. Thermal management is my biggest concern.

I really did want to build a solution from scratch but I'm too short on time, therefore I'm taking the previous advice and ordering some pre made solutions that will be stuffed into a PSU chassis.

The LT1083 kits on eBay seem pretty hard to beat for the price. There is a kit that has the LT1083 mounted so that it can be bolted directly to a large heat sink with it's associated PCB. The cap values are only 25VDC which is a little low IMO and they look like Cornell Dubilier but I think they''ll be okay. They may need to be upgraded..

buildafriend said:

I can't find an 800B schematic, but the 1600 is considered to be very similar ( according to rumors* )

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Indeed, they were; the 800B was the live one, the 1600 the studio one. Originally, the input channels were the same, only the outputs were different. Later there were variants that made them somewhat dissimilar, but still had a lot in common.

buildafriend said:

Any idea what current handling I should design for per rail?

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Each channel and output would draw about 40mA on the +/-17V rails and about 10mA on the +24V rail. The master module would draw about 100mA on the +/-17V rails and about 40mA on the +24V rail.
Now, the 24V rail is used for the meter lighting, which uses incandescent bulbs; IIRC each pair of meters draws 40mA. These bulbs are such a PITN to replace, I would recommend replacing them with LED's. It's somewhat tedious but it's worth it.

The CPS450 will work fine on an 800b I think the original was a 300, but they were essentially the same. I have the schematic for it

http://www.drivehq.com/file/df.aspx/shareID3748302/fileID516159973/516159973.pdf


or you could buy one,

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F122375237572

I'm positive CPS450 was not suitable for the larger frames (32+), so a sturdier CPS750 (650?) was introduced.

Yes that's correct for the 6000 above 24 8 bus and 800b/1600 above 32 channels. There were some desks release that could run each half of the desk with a separate cps450.

Bet I just saw a depressing sight of a series 5 going for £1000. I bought one of them new for the best part of £47,000 in 2004!! Wow! Large non A list consoles are going for nothing at the moment, some really quality mixers too, I can't believe they'll stay that low now large mixers are coming back into vogue

Thanks everyone for your input 

I'm back on the hunt for big heat sinks while I wait for these Chinese LT1083 kits to come in. I ordered 6 of them, two are the ones pictured and the others are also Chinese 1083 kits but they come with heatsinks. They won't be here until April  : but that leaves me time to hunt down the part numbers for the twist lock connector, the right cabling, and a few toroids. The twist lock connector part number might be hard to find..

And thanks for the input on the meter bulbs Abbey. I recently realized how much I disliked bulbs compared to LED's when I replaced a meter bulb with a cheapie LED I had sitting around and the associated regulator ran much cooler to the touch. I might not have thought to do this to my who desk if you had not mentioned it. And your current draw information was very helpful!

All the best,

buildafriend said:

I'm back on the hunt for big heat sinks while I wait for these Chinese LT1083 kits to come in. I ordered 6 of them, two are the ones pictured and the others are also Chinese 1083 kits but they come with heatsinks. They won't be here until April  : but that leaves me time to hunt down the part numbers for the twist lock connector, the right cabling, and a few toroids. The twist lock connector part number might be hard to find..

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Make sure to test those kits under load before hooking up the console. I also wouldnt use the capacitors or regulators they come with...seen too many counterfeits. Make sure the heatsinks are adequate for your application too. Big high current power supplys are not trivial to build.

Another solution is to use Power one modules, IIRC you can get the +15v modules up to 16.5v or so. I have 4 of the 15v 8amp modules, and a rack case that fits them and has standoffs mounted if you really want to try building something easy.  ;D

iampoor1 said:

Another solution is to use Power one modules, IIRC you can get the +15v modules up to 16.5v or so. I have 4 of the 15v 8amp modules, and a rack case that fits them and has standoffs mounted if you really want to try building something easy.  ;D

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+1. SMPS now are reliable, silent, cool and cheap. And I'm lazy ...

iampoor1 said:

Make sure to test those kits under load before hooking up the console. I also wouldnt use the capacitors or regulators they come with...seen too many counterfeits. Make sure the heatsinks are adequate for your application too. Big high current power supplys are not trivial to build.

Another solution is to use Power one modules, IIRC you can get the +15v modules up to 16.5v or so. I have 4 of the 15v 8amp modules, and a rack case that fits them and has standoffs mounted if you really want to try building something easy.  ;D

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Oh I'm well aware of those manufacturers!  They are too expensive though! I got this desk for $200 untested and had it shipped from South Carolina to Baltimore for $100 through an app called uShip which is like an Uber for shipping. It looked like it had been sitting for a long time so I cleaned it up and looked over all the modules, nothing looks burnt or broken.  These 1083 kits are only $15+$15 for the ones pictured and $11x4 for the smaller ones and I have a box of assorted toroids that a local factory threw out.  I'll test the regulators under load that's good advice  Ohm's law.. what a thing. 

lets see how many degrees C/W these heat sinks need to be. Whats the specific heat of aluminum? How many watts we talking?