Shure discret preamp with EQ.
Shure SR107 Discrete EQ
- Thread starter iomegaman
- Start date
Help Support GroupDIY Audio Forum:
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?
-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 just picked up one I'll measure it.
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.
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.
Huh. 12.884:1 is only around -22dB, not -52dB. I wonder why they marked it that way.
I have no idea the input transformer is:
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?
Walrus
Well-known member
From schematic, level pre transformer is 0.21 Volts. Mic output Post transformer says 0.6 mV.
That calculates as -50.88 dB.
That calculates as -50.88 dB.
That's what I'm questioning. A 0.21V to 0.6mV drop would require a transformer with a turns ratio of 350:1
@iomegaman said he measured it at ~13:1
That's a big discrepancy.
Also, @abbey road d enfer (or other admin) - I shouldn't have commented on this in the first place (I didn't realize I was in the Technical Docs section), sorry. Is it possible to move this conversation elsewhere?
Have you measured the DC resistence or the AC Impedance??…..How did you do these measurements?
opacheco
saulpickett
Member
level people. -52dB is the input level..... its like those old wierd yamaha boards. you set the input -60dB. and you think Okay this is great for line level. and then you turn it on and have a heart attack as all your speakers frenzy alarm. Japanese man say "Look you signal is -60dB you set knob to -60dB." as in, that is the MAXIMUM GAIN SETTING when you have it set to -60dB, because your INPUT SIGNAL is -60dB.... american man says "Look your signal is 20Db now you set it to -60dB and it is -40dB, because you are Subtracting Sixty Decibels from the original input.
Same wier'd ish with the british consoles. Like how do you know what a send or a return is if its british. Like there's something about... you have a device, you are Sending From the Device, or Returning To the device. but some of these british things are all reversed where the sends are the recieves and the recieves are the sends or something like that that makes no sense.
Same wier'd ish with the british consoles. Like how do you know what a send or a return is if its british. Like there's something about... you have a device, you are Sending From the Device, or Returning To the device. but some of these british things are all reversed where the sends are the recieves and the recieves are the sends or something like that that makes no sense.
