Pro Audio Design Forum

Looking more closely, I think you're right, and someone moved all the wiring on all of mine to the 200 ohm taps, very very cleanly. The 500 terminals look untouched at a glance, but not so under closer scrutiny. So, less weird than I thought.

The 200 taps all appear stock, with no evidence of 600 connection. Strange. I think I'd rather lose or change the secondary load resistor and see what happens, especially if introducing a 20 dB U pad on the input. The trend continues; all I have to do is hand draw a schematic, and the real one appea...

590 ohms for the 200 ohm tap; correct? Or is my math wrong? Every unit I've seen is hooked up for 200 ohms. Anyway, I covered it all earlier in the thread.

Also with old carbon; the amount of change after soldering. You can hand pick a value, but you can't count on it after heating.

Oh yeah, certainly. The critical values are all 1% types, and measure dead on. What did they used to use for 1% back then?

UTC A-24 and API 2520. I meant to mention this is the only RCA broadcast preamp I've encountered which has less than a bridging input Z, and I've pretty much had or seen them all. These things start in 1969, and run until at least 1974, meant for custom TV consoles specifically. They kept selling th...

I usually assume they knew exactly what they were doing, but the original gain method now gives me pause, as does the fixed 590 ohms presented to the mic.

Have a look.

This sucker is already old style 'spread out all over the place' layout, so improvements are pretty easy.

It's tantalum beads in this case, rather than can type electrolytic. Only problem I could imagine was potential build up of a bias at the cap, if it was above ground, and whether or not that might have a bit of micro-leakage that might still thump the gain switch. As I drew it in the alternate plan,...

next dumb question. The C in series with RG, almost always seen on the ground side. Is that placement important? If placed on top of the R, or even between two R's, do we have a biased condition that causes problems? Leakage enough to still cause DC gain? I could keep this rework more simple if I co...