DBX 900 frame with 2x312 pres...
« on: December 23, 2007, 11:32:37 PM »
So awhile back I picked up a DBX 900 frame because I thought it would be a cool platform to work with.  Friday I finally did my first project with it.

2 312 style pres on a single 900 card.

The 900 PS gives me +-15V regulated and +- 24V unregulated.

I don't have a front panel for it yet so everything is just hangin' off the board which isn't too bad as I'm still hunting down some issues.

So the pres fired up first go.  I just plugged a 57 in and did some speech tests and life was good.  I had the gain pots wired backwards but that was an easy fix.  I thought I could get away with using the +-24V as 48V potential for phantom power but that doesn't seem to work so well.  All the power rails share the same common reference point.

So no worries...I'll just cheat and use the +24V rail as my phantom.  I test it out with a AT 4033 and life is good.  Clean, no noise, nice clean sound.  However when I go to test it with a Shure Beta 98 I get all sorts of hum and buzz when the phantom is on.  I don't get it with the 4033 or a KM184...Just the Beta 98.

Any ideas?

I've considered just doing a "house" phantom supply that way I wouldn't have to keep reinventing the wheel with every time I needed phantom.

I've also thought about rebuilding the supply in the 900 and customizing it for preamps since that's what I'm building right now.  But I'm not too sure I like the idea of bastardizing the 900 frame as I would like to get a 903 comp or two.  (also thinking of getting a couple of Pico comps. :grin:)

Or is there a way that I can turn 24V into 48V without a ton of parts?

Thanks,

James


Sleeper

DBX 900 frame with 2x312 pres...
« Reply #1 on: December 27, 2007, 04:12:34 PM »
You have options there,  there are plenty of extra connection terminals on the rear of the unit so you could inject the 48volt at those points.
why don't you make a little phantom supply to fit in the slot closest to the power supply.  
I'm sure you could pick up your AC voltage off the front panel switch.  a little flatpack transformer or a small toroid and an LM317 regulator circuit.
shoot the power out through the spare terminals and add some jumpers to the spare terminals on you preamp modules.

There are doubler circuits around too, you would need to tap in to the transformer...  look at the ssltech powersupply in the meta.

Kelly

DBX 900 frame with 2x312 pres...
« Reply #2 on: December 27, 2007, 04:54:19 PM »
Thanks Kelly,

I thought about that...My original plan was to put 2 312 style pres per card.  With that being the case I use up all of the terminals on the back.  Upon closer examination I noticed that a couple of mics had some hum in them so I did a little clean up of the +24v rail and most everything I have is content with it as phantom except for the Beta 98's.  My Neumanns, AT's and even my Bo 1975 DI are all quite happy using the +24v rail.

I actually stumbled onto a +48V supply here at work that looks identical to the JLM 48V 380ma ps.  So I'm gonna see if that makes things better.

Overall I'm really happy with the sound of these things.  The pres are DEAD quiet (unless I'm using the Beta 98s) and sound stellar!  I ran my bass last night through the Bo 1975 DI and into the 312 and heard all that I've been missing from my sound.  I'm looking forward to fab'ing the front panel and moving on to more of these.

James

DBX 900 frame with 2x312 pres...
« Reply #3 on: December 27, 2007, 08:54:54 PM »
Phantom was indeed the issue.

Cisco uses +48V for their WAPs and IP phones and I found a spare power injector at work.  It makes a nice clean +48V @ 380ma (just like the JLM supply) and you can find these on ebay for about $15 shipped.

I wired that in and tried the Beta 98's again and they're quiet as a mouse.  It's pretty crazy how quiet all this is.  I'm used to having hiss on just about everything.  I never realized how much my A&H board sucked.  :(

Looking around, I've got a panel from an old mixer that has 16 XLRFs, 16 switches, and matched 6.8k resistors already wired up.  I just need to fit that to a rack panel and wire it to the inputs on the back of the DBX 900 frame.

Sweet!  :)

James

Sleeper

DBX 900 frame with 2x312 pres...
« Reply #4 on: December 28, 2007, 01:22:31 AM »
hey James, glad you got it sorted out.
This gave me a good idea for my 900 rack though...
for some reason I hadn't thought of putting the api pre's I'm about to build in the 900.
Cheers.
Kelly

DBX 900 frame with 2x312 pres...
« Reply #5 on: December 28, 2007, 08:49:39 AM »
Hey Kelly,

I picked up a 900 frame back in November for like $100.  Since I suck at metal work I figured building into the 900 frame would be an easy way to get into some gear.  I haven't fully worked out the details of the actual front panel...But...

www.onlinemetals.com has 1.5" aluminum angle that's 1/8" thick.  not only that...But they'll cut it to length for you.  8 pieces of 1.5" x 1.5" x 5.25" 1/8" thick angle will run you about $25.  The cuts are a bit pricey, 4' of the stuff is only $10.  If I can get access to a band saw I might tackle it myself.

My plan was to cut down one of those 1.5" sides to 1/4" ID and drill/tap a couple of holes to mount my boards to it.

Since my phantom is going to be external, the only controls on the front panel are gain and pad.  Now I'm wondering if I should put in DI's or maybe a polarity flip.  I wasn't planning on polarity inversion since that's a simple mouse click in the DAW.  It might be handy to have though.

Currently I'm padding down the output with a U-pad using a 200r between a pair of 1k as those were the values I had available.  I might change out the switch and put in a rotary to give me 2-3 different pad amounts.  I'm still tinkering.

James

Re: DBX 900 frame with 2x312 pres...
« Reply #6 on: August 25, 2008, 11:33:13 AM »
Quote from: "TheJames"


Any ideas?

I've considered just doing a "house" phantom supply that way I wouldn't have to keep reinventing the wheel with every time I needed phantom.

I've also thought about rebuilding the supply in the 900 and customizing it for preamps since that's what I'm building right now.  But I'm not too sure I like the idea of bastardizing the 900 frame as I would like to get a 903 comp or two.  (also thinking of getting a couple of Pico comps. :grin:)

Or is there a way that I can turn 24V into 48V without a ton of parts?

Thanks,

James


My DBX 900 came without a powersupply (I didn't pay careful attention to the listing on ebay).  I ended up installing a JLM powerstation in there with a transformer.  I think my powersupply is far beefer than the original plus I have a 48v power rail.  You could use either the D or C contacts to route phantom power in there from an external powersupply.  Something like JLMs 48volt power supply might do the job nice.  You could couple that with one of Joe's Go Between and have a real nice 312 setup.

CC


 

Related Topics

  Subject / Started by Replies Last post
12 Replies
6818 Views
Last post May 28, 2007, 08:45:14 PM
by leigh
4 Replies
3861 Views
Last post September 04, 2009, 03:47:12 PM
by Sleeper
5 Replies
2838 Views
Last post September 16, 2010, 11:50:47 PM
by ewlewl
5 Replies
3478 Views
Last post May 09, 2011, 05:24:40 PM
by moamps