ADM Modules

[MediaWorksOKC]

Hello gents,

Any thoughts as to what these ADM cards might be for? I know a schematic is probably out of the question.

They are marked "DA-160, 163 or 168", the last digit is obscured, can't be sure. No info to be found out there as far as I can tell.

The card edge says +/-20v.

There is a single UTC/TRW 0-8 as an input. The signal goes into the O-8 then to a can 5534 then to each channel through a heatsinked LM318 into a pair of output transistors through a bipolar cap into the output transformer.

I'm naturally interested in repurposing the mysterious-maker black-can output transformers which are apparently 1:2's (per Brian Roth). Any further info about these would be helpful and appreciated.

One board is very similar to the others with the exception that the output transformers are about 25% taller than the rest of the boards.

Regards,

Chris

 

[rackmonkey]

Look like distribution amps to me.

 

[Brian Roth]

Yep, ADM sold a line of audio distribution amps.  I found a catalog sheet, but no schemos.

Bri

 

[rackmonkey]

Good find, Brian. I suspect those UTC O-8s are wired “backwards”, which would give you 600:15k impedance step up. The output transformers look suspiciously like Hammond 850 series.

A good line level distribution amp can be useful in the studio. So you could consider restoring them (or at least maybe one or two cards).

If you’re trying to repurpose them, since  these would be line level in, you should be able to put mic input transformers in front of each amplifier and use them as preamps. Any good 150/200/250 to 10k or 15k nominal impedance transformers would be good candidates (that is, 1:5, 1:7 or 1:8; Cinemag, Edcor, OEP, Jensen and Lundahl have off-the-shelf models that would work). The brochure Brian uploaded says that “the outputs...have individual front access level adjustments”. The wording makes me think those were probably attenuators/pots on the output, which you could experiment with to provide level control.

 

[Brian Roth]

I've always wondered who made the ADM "flat pack" output transformers which are found in a wide variety of their modules.  I looked up the info for the Hammond 850 units mentioned, but the ADM's are not those;  the ADM's are PCB mounted vs flying leads.

Most of the ADM's I've seen had a black epoxy fill in the metal can, but I ran across a few with a slightly less opaque epoxy, and saw a toroid construction buried inside.

Bri

 

[rackmonkey]

I saw that Hammond discontinued the header versions of their potted audios due to the high cost of the headers. Now only seem to offer the flying lead type. But for years, they had circular pin arrangement headers. Were the ADM's like the one in the picture? It shows the 900 series (which is also about the right size/shape of the ADMs) not the 850 series. Not all of the headers had the little hooks, but had pins instead. But they had the same header. I'm just curious myself what those outputs might be.

 

[Brian Roth]

The ADMs had thick-ish solid wires coming through the epoxy on the bottom of the metal can.  The lead spacing was pretty wide....towards the edges of the can.

I have some misc. ADM modules with those flatpacks sitting somewhere in a box.  I'll look around to find them.  Perhaps CJ could do a teardown!!  <g>

Bri

 

[rackmonkey]

Definitely not Hammonds then. A CJ autopsy is always fun.

 

[alexc]

Beautifully built cards  imho 

Nice score!

 

[Winston OBoogie]

... I suspect those UTC O-8s are wired “backwards”, which would give you 600:15k impedance step up.

Probably not.  The UTC will be presenting a bridging input impedance of nominal 15K to the line being distributed. The idea being not to load down the line
This is then stepped down to a low secondary impedance so that it can, in turn, be bridged by the 6 gain/driver stages which feed the output transformers. 
No loading losses involved, no needlessly high input impedance required on the 6 amps, everyone happy