ADM 2783 help for a beginner

I got the adm 2783 and 1540 combo off ebay and have been trying to wire it, but since it is my first mic pre wiring project, i have run into a lot of problems and probably wasted some money too.

I know the schematics aren't handy (i'll try to scan them for you dave), but hopefully my question can be answered without them.

I have run both logic power (24V) and audio power to the units, and the eq will turn on (the light will come on), but the mic pre will not. For obvious reasons, i feel like it has to do with a pin marked "EXT ON CNTL", but i have tried applying voltage and tried grounding it (with it switched to on), but nothing lights up and no signal is passed.

Has anyone heard of this EXT ON CNTL (i assume its a common automation thing) or know what to do with it?

thanks guys, sorry for the long winded post.

ok, so i am posting an update and fix to my own post because someone asked me if i figured it out and i thought it might be useful for future searchers. . .

the main thing that fixed the problem was connecting the External On Control (pin *22) to ground. Another thing to look out for is that the big green connector is facing the correct way (when i recieved mine, it was upside down on the microphone preamp).

Here is my wiring so far:

WIRING FOR ADM 2783 mic pre and 1540 equalizer module

2783

1 to EQ 2 [pre PGM amp In Hi --- PGM LO Out]
2 --- Ground [Transformer Shield -- Star Ground]
3 --- Ground [Transformer Ground -- Star Ground]
4 --- output TIP [Direct Output HI -- Jack TIP]
*4 --- output RING [Direct Output Lo --- Jack Ring]
17 --- EQ 10 [Logic Power Input --- Logic Power Input pin on EQ]
19 --- Ground [Logic Ground to Star Ground]
21 --- EQ14 [ - Audio Pwr --- Negative Audio Pwr on EQ]
*22 --- Ground [External On Control --- Star Ground]
*24 --- Ground [Audio Pwr Gnd --- Star Gnd]
26 --- EQ 13 [ + Audio Pwr --- + Audio Pwr On EQ]
27 --- EQ *17 [ Preamp Out Hi --- PGM In Hi On EQ]
30 --- Ground [ Shield --- Star Gnd]
31 --- Input TIP [Line Amp In Hi --- Jack Tip]
*31 --- Input RING [Line Amp in Lo --- Jack Ring]
34 --- Ground [Shield --- Star Ground]
36 --- Microphone XLR pin 2 [Mic Preamp In Hi --- XLR Pin 2]
*36 --- Microphone XLR Pin3 [Mic Preamp In Lo --- XLR Pin 3]

1540

1 is connected to 3 by a 5700 ohm Resistor
2 - 1 on Pre
*3 - Ground
9- Ground
10 - Logic Pwr and 17 on Pre
12 - Ground and Shield on audio power cable (i used a microphone cable)
13 - 26 on pre
*13 - Positive lead on audio Power cable
14 - 21 on pre
14 - negative lead on audio power cable
15 - Ground
*17 - 27 on Pre

At this stage the setup works and sounds pretty good with very low level signals. Unfortunately it distorts at any moderate levels, i am not sure the cause of this, but i am going to try to setup a pad. . . There is a line amp pad input, but it does not come standard, so i am going to have to make one. . .

Did you ever get the units to work properly? I am having the EXACT same problems with the same units!

alright, so it's been what, two years? and the thing still doesn't f**king work. in that time i've refurbished an entire console (not adm). what a mess.
anyway, giganova, here's my update. there is a VCA built onto an additional pc board on my 2783. i took it out and jumpered where it says "vca bypass jumper" on the layout bluprint. then i put a 1k resistor from pin 1 to pin 7. i think that should be a bigger resistor, but i really don't know. . . the eq is fried, but the input module is still kicking and is still really really way to hot. . .

i tried posting on and emailing Orphan audio. com, but there doesn't seem to be anybody home.

what a mess. . .

I looked around on my hard drive for a 2783 schemo but can't seem to find it. I do have a 1540 diagram, however.

Bri

hey brian, thanks for replying, i've got the schematic and layout for both, but no scanner. I think giganova has pdf's of both.

I tried stripping everything down to the bare minimum and to just get the LINE IN to PRE OUT to work, but the output signal is still really hot and the module is clipping without much input.

When i look at the schematic the signal seems to be going like this:

LINE IN === T1 ==== ADM 202 opamp ==== LF356 ==== NE5534 ==== PRE OUT

All the rails read 20V.
Pins 1 and 8 on the NE5534 read around 16V, which seems weird, but i wouldn't know. Pin 5 reads around 0.6V.

-chris

I should also mention that the overload LED circuit takes it's input after the NE5534 and before PRE OUT. And the LED is confirming what i'm hearing, etc. . .

Maybe take your schemo(s) to kinko's for some scans? I'm almost certain I have that preamp circuit here, but damned if I can find it.

Bri

did anybody ever find a readable 1540 eq schematic?

i'm happy to chip in on scanning fees if somebody here has a hard copy they don't mind sharing..

I finally found the 2783 PDF which also has the 1540 info. I have *no* idea where I found this, and the scanning is a bit odd (page rotations all over the map), but they seem pretty legible:

http://www.brianroth.com/library/adm2783&1540schematics.pdf

Bri

Hi guys!
Old thread but I'm hoping you're still with us.

Did you fix the clipping issues? I'm finishing up an old racking job, REALY old, and I'm getting the same clippings as you guys.
/
Emil