Should I turn it on?

altruistica

altruistica

Member
Hi Guys,
Long time since I posted as this last year has been a busy year with family commitments.

Anyhow between all of that, I've replaced my computer (now has 64Gb RAM and potential for 192Gb). Why so much? I've wanted to get back into Cubase and mocking up orchestral stuff so needed the massive sample memory for libraries (got Kontakt Ultimate and Symphonic Series Library).
This all interfaces to a Soundtracs Solo MIDI analogue desk via 3 x Behringer ADA8200 units and an RME Hammerfall 9652 PCI card. That lot comes up on the Solo's 'LINE' inputs and can be fed to the Fostex G24S via the direct outs or the buss outs. The G24S can be returned to the desk via the 'TAPE RETURNS' and can be put on the large faders via 'MIX' which swops INPUTS and TAPE RETURNS. The Solo is the 32 channel version but in a tiny 1.2m footprint. I've also connected the MACKIE ULTRAMIX to the consoles inserts so I have fader automation (VCA). The automation means I can perfect a mix using the PC's digital tracks and then turn the tape machine on for a final pass, saving wear and tear on the G24S.

I've only had the console for about a month and I wanted to run it for a bit and see what problems it had. They were minor until last night, when the PSU deciding to dump the -17V rail. As I'm in the UK, Tim Jones at Studio Systems is the Soundtracs guru. I'd contacted him before buying the desk so he knew I had it. He said the Soundtracs Solo power supplies (Soundtracs 'Source' ) were a nightmare and an accident waiting to happen because of their hybrid construction. He sells new PSUs under the name 'Blue Dog' for £250 which may well be the way to go. Apparently, because the construction is so much more efficient these days, the PSU would pay for itself in three years in the savings on electricity alone. It also makes the mix buss quieter.

Anyhow, as I still had a Soundcraft CPS275 PSU left over from my ventures with a Soundcraft Ghost, after checking the specs I wondered if I could re-purpose it to be used with the Solo desk. I checked the manuals....the CPS275 has +17V, -17V, +5V (not needed), GRD and +48V rails. It provides up to 5.25A on the +17 /-17V rails, o.3A on the +48V. Checking the Soundtracs PSU, it can deliver 4A on +/-17 V rails and 0.25A on the 48V rail.

So I stripped the output looms from both PSUs. The connect via spade connectors so that was easy. I had to transfer the Soundtracs' loom to the Soundcraft's as the HIROSE connectors are different, one 8 pin and one 10 pin.

So here's my question. I've turned the CPS275 on and checked the rails. +17V (+17.668V), -17V (-17.667V), +48V (+48.3V).

The voltages are on the right pins etc.........should I turn the PSU or I have not taken something into consideration (cause I don't know it) which I should have. I've emailed but I think he may now be on holiday.

So should I flick the switch?

Thanks,
Al
 
That's a question I've asked myself many times recently. Building a new power supply for a Cheetah MS6, and with the mixing desk too.
For what it's worth, the Blue Dog supplies are nice. I have one on my GL2400. The snag is that there are several models of GL2400, and two types of power connector. Tim only knew about the 40-channel connector, so I ended up making an adaptor. In my case, it worked.

The GL2400 can get away with 15v (+ and -). The 10v line is for the lamp which I don't use, and I don't need phantom power either. The Blue Dog is indeed very quiet, the snake-oil claims of it making the desk quieter are in fact true. If you think about it, a mixing desk has maybe 10 op-amps per channel, plus the ones for the output buses. Each of those is running off the main power bus, so if that is noisy you'll get a small amount of noise injected in every one of 240 or more op-amps, and it will add up. The Blue Dog actually contains several independent power supplies, which I assume he's somehow modified from stock. In mine there's one for +16, one for -16 and one for +48. Each PSU has a trimmer so that you can adjust the voltage, which he suggested I do since the GL2400-24 is allegedly expecting 15v.

Anyway. If I were in your position, I would weigh up the risk of damaging the desk. Can you afford to get a new one if this goes bad? If you can, or you're happy to take the risk, I would then make sure that you've got the +
and - connectors the right way round.
The most critical thing in this case is to be 100% certain that the 48v line is NOT going to get anywhere it shouldn't, because that's liable to pop the logic and probably most of the op-amps. It might be repairable in that instance, but you'll be replacing a hell of a lot of chips.
In fact, I would leave the 48v line disconnected initially, and maybe attach it later if you're not using external preamps.

For my money you're risking less damage if you're only testing with the low-voltage lines. e.g. if you end up with +17v and no -17v, it'll probably work but distort everything. (EDIT: Apparently this is wrong - an unbalanced supply may toast the op-amps). The one thing I'm not completely sure about is what will happen if you reverse the + and -, or + and ground. That could get a bit ugly, depending on whether there are any protection diodes after the PSU.

TL;DR - if this desk is most precious and you can't risk damaging it, get the Blue Dog. If you're feeling adventurous, switch on, but leave the +48v line disconnected until you're sure the rest of it works.
 
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Thanks for the replies. The waiting is killing me....

Good to know JP that the Blue Dog stuff is working out for you. I am sure the voltages are correct, since all I've really done is remove the Hirose connector that was on the Soundtracs PSU and put it on the Soundcraft PSU. The spade connectors are clearly marked so I haven't had to solder anything, just plug the spades in. Even the colour of wires was the same (orange = +48V, blue = -17V, brown = +17V, green = GRD).

It's whether there are other factors that come into play. I may have been a little worried if the amperages of the rails had been the other way round (ie. if the Soundtracs PSU had larger onesr than the Soundcraft's). As it is, if I've understood this correctly, the Soundcraft's PSU will have some spare capacity to cope with peaks.....but as I said, I'm a novice when it comes to electronics.
 
altruistica said:
Thanks for the replies. The waiting is killing me....

Good to know JP that the Blue Dog stuff is working out for you. I am sure the voltages are correct, since all I've really done is remove the Hirose connector that was on the Soundtracs PSU and put it on the Soundcraft PSU. The spade connectors are clearly marked so I haven't had to solder anything, just plug the spades in. Even the colour of wires was the same (orange = +48V, blue = -17V, brown = +17V, green = GRD).

It's whether there are other factors that come into play. I may have been a little worried if the amperages of the rails had been the other way round (ie. if the Soundtracs PSU had larger onesr than the Soundcraft's). As it is, if I've understood this correctly, the Soundcraft's PSU will have some spare capacity to cope with peaks.....but as I said, I'm a novice when it comes to electronics.
Click to expand...

That does look like it ought to work, yes.
 
From what you say it looks like it should work. On a modular mixer I'd probably remove all the modules from the mixer before applying power so that you can measure voltages on the backplane and check everything is OK. I'm not sure if there is any way of doing something similar with your mixer by removing an internal connector Once all the voltages measure OK you should be able to replace the connector.
 
Thanks Guys....it's takem me a few years to get round to settling on this setup and finding a Solo Midi in good cosmetic condition. The footprint is brilliant, the only thing the mixer lacks is a HPF, but I can live with that.....so I'm going to resist the urge to turn it on......for now. The funny thing is, the people I do know who are into electronics all have blown things up at one time or another...it seems par for the course in trying to get your head round things that you haven't tried before.
 
I know nothing of the equipment in question but it makes abundant sense to power the mixer in as "bare bones" state as possible and then check for voltages in the right places and polarity. I would also cobble a couple of 500mA fuses in the 17V lines for test purposes. One VERY important point. I bet that mixer uses a bucketful of NE5532S? The chip must always have BOTH supplies connected, if one dies, so do the chips!

Douglas Self, top man at Soundcraft warns of this and shows a simple circuit to achieve "mutual shutdown". The circuit in Small Signal Amplifiers, assumes the use of 317 type adjustable regulators (yours might us them with current booster bipolars) but you can use a relay across the whole 34V to achieve the same thing.

Dave.
 
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