Shure SR 107 documents question...

[iomegaman]

So I posted the tech documents in the appropriate thread but both I and OneRoomStudio have some questions about the documentation:

OneRoom asked:

"That output transformer is strange. The block diagram shows that the “line output” tap is -2dB (so something close to a 1:1 or 1.25:1 turns ratio), but it says the “mic output” is -52dB!

-52dB is a huge ratio…something like 400:1. If we assume that the primary impedance is around 10K (it really shouldn’t be any higher if it has a something near a 1:1 tap for line out), the output impedance of the mic winding would be something like 0.0625ohms. That can’t be right, can it?"

I measured the actual transformers and posted this:

Ok just measure the Transformer here's the actual data:
Primary (blue/red on schematic) = 66.4 Ohms
Secondary (white/green on schematic) = 66.4 Ohms
Secondary (brown/yellow) = .4 Ohms

For the "Mic line" output feature (brown/yellow):
Using .078 to determine turns a=ratio that makes it a 12.884 :1 step down for the mic...

If you read the manual it has a setting to run it out kind of like an inline EQ for consoles that use a "Link" jack it outputs a really low mic level there.



To which he replied:

Huh. 12.884:1 is only around -22dB, not -52dB. I wonder why they marked it that way.









and I followed with this:




Primary= 27 Ohms
Secondary = @ 600 ohms...I double checked its wired that way...
Green/yellow to XLR= 27 Ohms....black and white to amplifier board = 597 Ohms...1:4.7 step up...

Possible error in the schematic data?

Is it just an error or did we miss something?