Monday, December 27, 2010

The past week and a half or so has been steeped in speculation and other mainly mental endeavours; so I'm digging up another long-standing project as opposed to some actual current progress shots, which is what I'd really prefer to populate these pages with. Elementary CAD screenshots and reinforced joint solutions are seem more boring than quips about blown woofers and asbestos bearing wire insulation, so without further ado I guess now is as good a time to unearth the RCA BC3C project as any.

I've plundered my binauralaboratories (out of date) write-up on these units for this shot taken in ~2001.

I'll upload some honest gutshot eventually. The mixer is essentially three pre-amplified microphone inputs, a transformer coupled input and a handful of low Z line level inputs feeding a two summed outputs, one tailored to line level feeds, the other bearing a PP 6V6 amplifier to drive in house monitoring systems.

I cut this card free a while back in order to scan the traces and facilitate tracing the signal path and recreating the schematic. This was right before I found a copy of the service manual, saving a lot of work.

I seem to have been suffering from focus related issues when I took this shot, but I'm sure the sense of a somewhat sparse printed circuit board is conveyed. Barring the modification of a printer to lay out diagrams and text, this is the level of construction I will be working with in the future.

This particular pre-amplifier module is in the summing recovery section that drives either the program output or monitor amplifier. The microphone level preamp card is similar, though it carries a few additional components to facilitate quiet switching. The first actual work on this will entail a power supply rebuild (squared, since there are two of these). Cost of a bunch of multisection can caps has been something of an impediment, but I can certainly dig into the rectifier and replace the selenium.


msnbcritic said...

I''m working on a BC-3c too, very interesting! Is there any chance you could share your scans of the preamp board traces? I want to add 2 more.


crochambeau said...

Hi msnbcritic, apologies on the delay! I can't find my scans, but seem to recall having a layout in the printed manual. I'll dig and see if I can find a scan of that, or worst case - I think I have a loose card and can simply scan that. Good luck with it!