miketeachesclass
Active member
- Joined
- Aug 4, 2006
- Messages
- 29
So I've been searching for a couple days for a discussion about the 1176 circuit. I'm building one (on MNATS rev. J boards), and I figure if I'm going to invest this amount of time and effort, it's foolish to not learn more about how these circuits work. Since I couldn't find anything on this topic, I thought I'd start one myself. I've attached an image for your perusal in the discussion. I suppose this is a bit self serving, but it's really difficult to find practical discussion on circuit design and function. I've read several books, but nothing really seems to prepare you for circuit analysis.
Basically, I'm trying to go through one section at a time and figure out what's going on. I'll start with the input section; Please let me know if I'm on the right track.
So I've labeled the 100pf caps as RFI filters, as I believe they will shunt high frequency information to earth.
Following are the 6k8 EL's that should pass AC and block any superimposed DC, right? I believe the value is larger so it lowers the corner frequency of the HPF to the bottom of the audio spectrum.
Then we've got input caps. 10k on each leg. (+/- of the input) those resistors couple with the feedback resistors on each half of the IC to make a unity gain inverting amplifier.
I've labeled what I assume is the correct current flow through each half of the IC. Blue for the + leg of the input and Yellow for the - leg. I've also labeled polarity with respect to the incoming signal. (I'm assuming a balanced input will be symmetrical for the purposes of CMRR). I'll start with the + leg.
The + signal hits pin 6 (inverting input) of the IC, simply gets flipped over, because the IC is providing unity gain. At that point, I'm not sure of the function of R1-B (10k). The + input (now having been inverted; though the common mode will be opposite polarity with respect to the - input) now combines with the - input. The common mode cancels because of the polarity difference, but the input signal combines, both negative with respect to the desired input. The combined signal hits pin 2 and gets its polarity reversed at the exit of the IC, so now it's right way round again and can be passed through the input pot to the rest of the circuit. (Via C33; again a 6k8 EL).
I understand that R1-A and C32 in parallel are creating some kind of HPF, though I'm still not sure how that works. I also think that C30 in parallel with R4 is somehow necessary because of the relationship with R1-A and C32. Though I'm not sure exactly how that works, either.
Obviously, R3 and R4 are creating a voltage divider to provide +15 volts to the IC. It's also worth noting that pin 8 (vcc) is connected to the 30 volt rail on the PCB, though it's not noted in the schematic.
So, does it look like I'm on the right track here, or did I totally botch this?
Any comments would be sincerely appreciated.
Thanks!
Mike
Basically, I'm trying to go through one section at a time and figure out what's going on. I'll start with the input section; Please let me know if I'm on the right track.
So I've labeled the 100pf caps as RFI filters, as I believe they will shunt high frequency information to earth.
Following are the 6k8 EL's that should pass AC and block any superimposed DC, right? I believe the value is larger so it lowers the corner frequency of the HPF to the bottom of the audio spectrum.
Then we've got input caps. 10k on each leg. (+/- of the input) those resistors couple with the feedback resistors on each half of the IC to make a unity gain inverting amplifier.
I've labeled what I assume is the correct current flow through each half of the IC. Blue for the + leg of the input and Yellow for the - leg. I've also labeled polarity with respect to the incoming signal. (I'm assuming a balanced input will be symmetrical for the purposes of CMRR). I'll start with the + leg.
The + signal hits pin 6 (inverting input) of the IC, simply gets flipped over, because the IC is providing unity gain. At that point, I'm not sure of the function of R1-B (10k). The + input (now having been inverted; though the common mode will be opposite polarity with respect to the - input) now combines with the - input. The common mode cancels because of the polarity difference, but the input signal combines, both negative with respect to the desired input. The combined signal hits pin 2 and gets its polarity reversed at the exit of the IC, so now it's right way round again and can be passed through the input pot to the rest of the circuit. (Via C33; again a 6k8 EL).
I understand that R1-A and C32 in parallel are creating some kind of HPF, though I'm still not sure how that works. I also think that C30 in parallel with R4 is somehow necessary because of the relationship with R1-A and C32. Though I'm not sure exactly how that works, either.
Obviously, R3 and R4 are creating a voltage divider to provide +15 volts to the IC. It's also worth noting that pin 8 (vcc) is connected to the 30 volt rail on the PCB, though it's not noted in the schematic.
So, does it look like I'm on the right track here, or did I totally botch this?
Any comments would be sincerely appreciated.
Thanks!
Mike