Edit:
Ed, do you mean that the pinouts on ALL of the Cinemag's are compatible? My problem is I can't figure out which one might do the trick. The "CMLI-4x150D" appears to be able to do the stepdown, but I can't find a PC mount version, the "CMLI-600/600C" (doesn't appear to do the step down) maybe a "CMMI-2CPC" wired backwards? Any ideas here? I am going to contact cinemag and see if they can enlighten me.
bb
Ed, Thanks so much. I actually was just perusing that material (but for my addled brain it wasn't 10 minutes, it was all day, and included a lot of research on the OEP, Cinemag, HAIRBALL and MNATS sites)
I understand that you created the C-3837-1 on hairball? The C-3837-1 on hairball seems to have a 500:200 impedance ratio, but it says it is a reproduction of the 0-12. Is it usable both ways? Do you know what input level it can handle at 30HZ (or any frequency for that matter) within some THD range?
The original 0-12 UTC was 200:500, but I don't know how it was used in the 1176. I did find a schematic on the MNATS site that shows the C-3837-1 wired with the step down RATIO. and shows how to wire the attenuator, but I cannot find the same information in the schematic for the F76, which omits any attenuator.
Assuming that I have this right the the possible part numbers are:
Transformer part numbers APPARENTLY usable with the F76 (I have not tried these, but since it took all day to figure it out, this might help someone trying to do this project).
A262A2E or A262A2C (C is with Mu metal can) from OEP
C-3837-1 or CM-3837-1 from Anderson Altran Hairball
Cinemag transformer (says it is usable, but I have not found a part number (they don't appear to have a low impedance PCB mount 1:2 ratio transformer)
I did find a note in the build thread that says if I do use an attenuator I need to drill out the backplate, but I don't yet see where it goes. The space is so tight in this module that I cannot imagine where I would add one of those nice big hairball T attenuators, but gosh it's an option, and i want to do it.
The specs for all of these transformers sometimes give pin numbers but not the pin orientation on the can.
I can't find specs on anything but the UTC. The OEP looks REALLY easy to overload (I found a reference to 1mw at 30HZ with less than 1% THD and 100mw at 300HZ), so maybe I will just do the C-3837-1 and hope the specs are up the O-12, which was easy to overload too it seems but not as bad as the OEP.
In the materials is possible to look at the PCB in my hand, and compare it with the PCB layout in each subdirectory, and there are some text comments in those directories.
It appears that Igor has 2 IC amps - On PCB's included
One for input, which is just a chip on a 2520 board.
One for output and the output has a current boost stage of BC140 BC139. Sort of like the JLM one but biased differently.
There is an "Input Amp" of his own design.
There is a clone of the original AMP circuits for input and output, and there are comments elsewhere in the board suggesting that he thinks the other choices are better than the original from a sound point of view.
I did not find an Attenuator card, there is a directory to change from grayhill to potentiometer on the attack and release controls.
I think I will do more research on the Cinemag site, maybe I can find a transformer there, they spec the max input levels, and I want this to be "forgiving" when I chain it in.