House gnd = earth gnd = external gnd = chassis. This is what is used by a plug with a ground prong. "0V" = power supply 0V reference line (+15/0/-15). I made the power supply with the circuit isolated to prevent the possibility of AC induced in the chassis by the transformers getting into the power supply output. However, the chassis can be connected to 0V as necessary. I looked this up once online and found that it didn't really matter if they were connected because it usually made little difference in the operation. I believed it because I tried my circuit both ways and saw little difference (at the time I was only seeing something like a 3V difference between 0V and the chassis. I haven't yet traced down the source of the 14V I'm seeing now.)
I understand how the fets work and the diff amp. It's ICs like op amps and the in-amp which come premade with complicated circuitry inside and seemingly extra connections than I don't know where to connect. I'll admit though that I don't know all the details. For example, I noticed that when a fet was used in an audio amplifier, it was run in the linear region and I thought this was to avoid distortion. I thought there was more amplification if it was pushed harder, and because I'm not worried about distortion, I aimed for the saturation region.
I didn't know any of the stuff you described up to and including my Rds values. I was simply using Ohm's law on the fet.
How do you decide the tail current to use? Is this tail current = standing current? I've seen examples of calculations for audio amps and they would go for about 5 mA use by the fet. I've also been told that fets get quieter as Ids goes up and I have had good results last year in the 10-12mA range. I was also told to keep Vds "low, but not too low." I've found a few formulas online for Vd and Rd but they give very different values and I never knew which to use. At least one was for an audio amp, which this isn't, so I tended to discount that one.
It didn't seem like the gate and drain connections were reversed in the simulation. It would draw the fet symbol so you could see which was which and it also reacted by stopping immediately if the gate got reverse biased. I do find it entirely plausable that the math could have been done with the values swapped, thus resulting in an opposite sign on the results. I can't change this. It's an online site and I can only draw a circuit. If nothing is grossly wrong, it'll operate and do all the calculations for me (which I like, because I don't know how to do many of them). You can see this at: http://www.falstad.com/circuit/e-index.html
It's possible to make changes to the circuits shown, or blank the screen and draw a circuit from scratch.
As for my own preferences, being a chemist, I learned that current is electrons that leave atoms and it runs from neg to pos. In electronics class they said the opposite, but I know for a fact it's the electrons that move, not the positively charged wire ions they leave behind. It would be nice if everyone used the same standard nomenclature.
The noise and spikes are not due to any of my present pots. I have tapped them and get no reaction. I strongly feel they are some kind of artifact of either the meter or the software when faced with a data point they can't measure for some reason. This is a Radio Shack meter that came with data collection and graphing software called MeterView. It's got a few quirks, but it's all I have for visualizing my data. I've looked for a forum for owners of this software so I could ask about the spikes, but there isn't any. Radio Shack does not provide any support either.
I would get a cheap scope if I could find one. For the little bit I would use it, spending several hundred dollars for even a low end scope would be mostly a waste of money and just add one more thing to my menagerie of stuff I rarely use. I have many hobbies and I shift from one to another depending on what's interesting at the time so all the stuff I accumulate for each just sits in storage until I come back to it.
So, I keep trying to go as far as I can with this circuit. Which, BTW, is the first I ever designed (with lots of help from anything similar I could find online as a guide.)
What do you think about connecting the antenna and ground to the in-amp inputs? I don't know how it's sensitivity compares to the diff amp alone, and there would be problems with bias return resistors and noise and oscillation in the long antenna line that won't have a chance to be eliminated by a prior circuit, but it may be an option.
I understand how the fets work and the diff amp. It's ICs like op amps and the in-amp which come premade with complicated circuitry inside and seemingly extra connections than I don't know where to connect. I'll admit though that I don't know all the details. For example, I noticed that when a fet was used in an audio amplifier, it was run in the linear region and I thought this was to avoid distortion. I thought there was more amplification if it was pushed harder, and because I'm not worried about distortion, I aimed for the saturation region.
I didn't know any of the stuff you described up to and including my Rds values. I was simply using Ohm's law on the fet.
How do you decide the tail current to use? Is this tail current = standing current? I've seen examples of calculations for audio amps and they would go for about 5 mA use by the fet. I've also been told that fets get quieter as Ids goes up and I have had good results last year in the 10-12mA range. I was also told to keep Vds "low, but not too low." I've found a few formulas online for Vd and Rd but they give very different values and I never knew which to use. At least one was for an audio amp, which this isn't, so I tended to discount that one.
It didn't seem like the gate and drain connections were reversed in the simulation. It would draw the fet symbol so you could see which was which and it also reacted by stopping immediately if the gate got reverse biased. I do find it entirely plausable that the math could have been done with the values swapped, thus resulting in an opposite sign on the results. I can't change this. It's an online site and I can only draw a circuit. If nothing is grossly wrong, it'll operate and do all the calculations for me (which I like, because I don't know how to do many of them). You can see this at: http://www.falstad.com/circuit/e-index.html
It's possible to make changes to the circuits shown, or blank the screen and draw a circuit from scratch.
As for my own preferences, being a chemist, I learned that current is electrons that leave atoms and it runs from neg to pos. In electronics class they said the opposite, but I know for a fact it's the electrons that move, not the positively charged wire ions they leave behind. It would be nice if everyone used the same standard nomenclature.
The noise and spikes are not due to any of my present pots. I have tapped them and get no reaction. I strongly feel they are some kind of artifact of either the meter or the software when faced with a data point they can't measure for some reason. This is a Radio Shack meter that came with data collection and graphing software called MeterView. It's got a few quirks, but it's all I have for visualizing my data. I've looked for a forum for owners of this software so I could ask about the spikes, but there isn't any. Radio Shack does not provide any support either.
I would get a cheap scope if I could find one. For the little bit I would use it, spending several hundred dollars for even a low end scope would be mostly a waste of money and just add one more thing to my menagerie of stuff I rarely use. I have many hobbies and I shift from one to another depending on what's interesting at the time so all the stuff I accumulate for each just sits in storage until I come back to it.
So, I keep trying to go as far as I can with this circuit. Which, BTW, is the first I ever designed (with lots of help from anything similar I could find online as a guide.)
What do you think about connecting the antenna and ground to the in-amp inputs? I don't know how it's sensitivity compares to the diff amp alone, and there would be problems with bias return resistors and noise and oscillation in the long antenna line that won't have a chance to be eliminated by a prior circuit, but it may be an option.