The Autogram AC-8 is well on its way to being up and running.


My intent is to situate the AC-8 as master summing console in the studio, freeing up the other desks for branch/sub-mixes or abuse, depending on unit and project. This was a weak attempt at trying to induce some sort of saturation, I don't think I got anywhere near the headroom threshold. The Program/Audition outputs offer support of two independent stereo pairs.


Here's the input/output connectivity block. The good people at Autogram have uploaded user manuals for this era of gear here: http://autogram.net/manuals/ this goes a very long way in clearing up what is what. Pictured is channel 3A input (red wire) and Program output.


I've pulled all the active stages per channel out (slotting those into the AC-6) and populated all the stereo channels with 1:1 600 ohm interstage transformers. I believe this means that the functional block above is the only active electronics each channel passes through.


Schematic for the MXA-1 mix summing stage is above and the LA-1 line amplifier stage is below.


These stages share PCB artwork, clearly there are only minor differences between the two. Since I have the luxury of having a complete quartet of spares (sitting in the AC-6) I'm thinking about rebuilding these stages, upgrading components where I can and eliminating redundant or unnecessary parts (the caps on input/output for example). As it stands now though, the desk is super quiet and full sounding and justifies the 38 by 20 inch footprint it consumes.

This past week has been one obstacle after another on the electronics front. Old vehicles, learning software and a mass of other trifling happenings has pushed me off the map for a bit. Though, on a somewhat superstitious mumbo-jumbo front an illustration has been drawn regarding the delay of gratification cultivating a proportionally larger boon for the field which had so recently been repressed.

I went hunting for a home stereo preamp yesterday, armed with a budget figure based on a locally advertised unit carrying more modern features than I need but at roughly 10% of the mid 1990s MSRP. Then I happened on a couple of broadcast mixing consoles, an Autogram AC-8 and a Wheatstone A-32, which more or less derailed my hunt for a preamp, having consumed, to the dollar my established budget.


I'm running through the AC-8 in this installation as I am somewhat familiar with this beast, already having it's smaller sibling the AC-6. Typical broadcast console interface, a mixer refined to the barest of features, routing switches and volume controls.


One of my favorite things about old radio mixers is the ease of access they afford the technician. These were often designed with 100% up time and field repairs in mind, the Autogram/Rockwell stuff exemplifies this by confining the various stages into cans that can plugged and unplugged in seconds while another channel is active.


From the upper left of the picture on the base chassis: input terminal blocks; output stages left and right program, mono and left and right audition; amplifier and power supply board and output terminal blocks. The front panel modules are two MPA-1 microphone preamps, one for each input channel which is set to mono via the configuration switch next to the empty sockets, followed by five stereo channels of MT-1 socketed interstage audio transformers and a pair of IA-1 variable gain op-amp modules.


With the exception of the microphone preamp and op-amp modules, all the routing and level controls are passive. Two pair of balanced input wires terminate to an input selection switch which feeds the module, a stepped attenuator and an output routing switch.


Large, low loss connectors to impede the 600 ohm line as minimally as possible.


Here's a gutshot of the MPA-1 microphone preamp module from the AC-6 I took 6 years ago. Input transformer at bottom feeding the active circuitry.


Here's the innards of an MT-1 module, a Triad A-67J.

More fixing stuff and less showcasing on the horizon, once I climb through that Wheatstone unit..

Another week with minimal actual work on the electronics front. Sadly, this seems to be the norm. So, in the meantime here's some gutshot of a Langevin AM301 discrete solid state mixer. As it stands, I have a stupid amount of mixers in my to-fix pile. This one is no exception.


As you can see in this pic, channel cards G & H are different from the rest. They've been modified for more gain at some point in this units history. My to-do list on this involves reproducing that mod on the rest of the cards, a recap and some front panel slider replacement. I've hunted for some faceplate photos of this unit, but nothing I've found meets my quality control, so I'll just have to post some exterior shots next time.

For the moment , here's a component side shot of a standard card, my apologies on the poor depth of field and flash washout in this photo, it is the best of the current bunch:


And a shot of the trace plane: