Putting 2xDMP2 guts into a rack enclosure

[antichef]

OK - I have two M-Audio DMP2 microphone preamp units, but only one wall wart (I wasn't paying attention when I bought the second one, and they #\@F! gave me a 5volt instead of a 9 volt - anyway...). I haven't used them yet, really - I had planned to install them on a rack tray and put them in my rack. Now I can't find the rack tray, and only having one wall wart is bugging me (and you'd be surprised how hard it is to find a 9volt AC to AC 1000 miliamp (1 amp?) wall wart). Given that, and the fact that the 48v phantom button is on the *back* of the units (which would be totally inaccessible when they're racked on the tray) and that they don't quite put out the whole 48v, anyway, I was thinking: wouldn't it be nice to pull the guts out of these and build them into a nice 4 channel rack unit with a reworked 48v phantom circuit for each channel and all the buttons and switches and stuff where I want them? (sure it would ). I started looking around for rack enclosures, and found myself in a cold, unfriendly world.

Then I remembered that I also got one of these Art "Powerbase 4x4" rackmount power strips:

http://www.artproaudio.com/products....84&cat=7&id=54

as a bonus when I bought my Digital MPA, and it's just sitting there, too. I was thinking, assuming everything fits (which it may not), why not use that to house the DMP2 guts? I guess I'd have to build a new power supply inside (but perhaps I have a head start because of what's already there) also and rework the phantom circuits, of course.

Is this crazy thinking?

[mshilarious]

If all it wants for power is 9VAC, then all you need is a fuse (the one on the ART box will be too big) and a transformer.

What's the phantom spec now? I don't know if I'd mess with that, if it's close the large majority of mics will be happy, until you get up to the stuff that takes more than 7mA. There are a few of those out there, but if you don't have 'em, I wouldn't bother with it. Just leave the phantom switches on. If you have ribbon mics though, well I guess you have an issue there, you do NOT want to hot-patch a ribbon mic while phantom is on.

[dgatwood]

Originally Posted by mshilarious

What's the phantom spec now? I don't know if I'd mess with that, if it's close the large majority of mics will be happy, until you get up to the stuff that takes more than 7mA. There are a few of those out there, but if you don't have 'em, I wouldn't bother with it. Just leave the phantom switches on. If you have ribbon mics though, well I guess you have an issue there, you do NOT want to hot-patch a ribbon mic while phantom is on.

The most obvious improvement for the phantom in the DMP2 (particularly if you own ribbon mics) would be adding per-channel phantom power switches instead of having to apply phantom to both inputs at once.... I'm always amazed at how many devices take an all-or-nothing approach. That's one of the things I like most about my 8Pre interfaces: I can bring up phantom on only the channels with condensers and not on the ribbon channels....

[antichef]

Yeah - per-channel phantom power would be good, and I also would like them to be pegged at 48v instead of having a slight sag under load as they do.

But I can wait on that part. Since I've got 2 DMP2s, I'd be turning it on and off for two out of four channels at a time.

As for the power supply, for two units, do I need a transformer with two 9 volt taps? or two transformers? [winces as knowledge gap becomes evident]

[sweetbeats]

I just fire off the questions with my eyes and mouth wide open completely oblivious that I could hide the knowledge canyon...A little drool comes out with the mouth open that way too.

[mshilarious]

Originally Posted by antichef

Yeah - per-channel phantom power would be good, and I also would like them to be pegged at 48v instead of having a slight sag under load as they do.

But I can wait on that part. Since I've got 2 DMP2s, I'd be turning it on and off for two out of four channels at a time.

As for the power supply, for two units, do I need a transformer with two 9 volt taps? or two transformers? [winces as knowledge gap becomes evident]

You need one transformer with a 9V secondary that can drive at least 2A. Something like Digikey #TE62061-ND. That has a dual secondary, which you could wire in parallel, or use a separate winding for each unit. It shouldn't make a lot of difference. Make sure you have a good common ground for the chassis and the wall safety ground.

[evm1024]

I was thinking about this project of yours. You could get an enclosure, drill the front panel for meters and knobs. Pull the DMP2 out of their cases and mouunt them inthe enclosure. Then you could but a JLM 3 voltage adjustable power supply kit and a nice toroid transformer. Gut the PS on your DMP2 and use the +- rails from the JML and the +48 from the JLM to power your DMP2. Plus you could put the phantom switched on the front panel.

Eeek to many projects!

[antichef]

Here are a couple of pics:


(that might win the prize for "emptiest commercially available rack unit")

(here I just set the two open DMP2s on top of the PB4:


It's almost too good of a fit, because the circuit boards of the DMP2s would take up just about all the floor space in the rack unit (definitely from side-to-side -- I'd have to re-work the existing circuit breaker and power switch to make room), but I'm still thinking about it.