John, that plot you said was "old" used 10G Ohms, it's there for anyone to see. KT/C noise predates us by decades.
Scott, the 2619 schematic IN FRONT OF ME, says 200M ohm. dated 68/69
I modified them in '73, Now WHEN was YOUR noise plot taken?
I modified them in '73, Now WHEN was YOUR noise plot taken?
I think Scott's graph showed clearly that the electronics noise is already way below the mic capsule noise, so it's pretty pointless to try to get lower noise electronics.
jan didden
Scott,
Just a quick reminder why cheap transformers are cheap. In a well designed audio transformer the windings may not be wound one layer on top of another as in a power transformer but may be interleaved to balanced L & C.
The cheapie's laminations of course will be thicker, but they also will typically only be an iron oxide finish which has higher resistivity than steel or iron but is not really an insulator. (I have no idea which version of iron oxide is used there are many.)
The secondary often has about 10% more turns than the straight ratio squared would indicate to make up for internal losses.
But they do work as a more than adequate transformer for many applications.
The op amps I see most in circuitry are the 558 or 072, so it is the same with transformers and probably buggy whips.
Oh I got it wrong I meant short range sensors!
As to running out of part numbers, these days Google tells me a 709 is an RS232 converter.
ES
Jan, the electronics TODAY are quiet enough. They were NOT when I first started to use them. AND this is ONLY for the 1" mike. The 1/2" has MUCH more need for quality electronics.
You want Esoteric and no one mentions the MX-16
"guaranteed to have a noise level <1.5nV @ 1KHz, 20°C. This JFET has excellent transconductance (gm) and input capacitance (Cgs) (gm=28mS, Cgs=4pF, 20°C)."
"Free of generation recombination noise"
gotta luv a device with a spec like
Transconductance (gm) 40mS Vds=4V, Id=5mA,-100°C
esoterrorist
"guaranteed to have a noise level <1.5nV @ 1KHz, 20°C. This JFET has excellent transconductance (gm) and input capacitance (Cgs) (gm=28mS, Cgs=4pF, 20°C)."
"Free of generation recombination noise"
gotta luv a device with a spec like
Transconductance (gm) 40mS Vds=4V, Id=5mA,-100°C
esoterrorist
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For the scientific applications it is designed for with 4pF at ZERO Vgs and 1nV, the Toshiba FET's are not even close. Also with 400fA at -10V Vgd and specs at cryo temperatures 100% tested it's pretty obvious this is for scientific instruments.
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But the source does not seem to be a manufacturer so who makes them? Or is it just selection?
The gm/Cgs figure of merit is process dependent so no selection possible. It is still possible they have a very low yield to all those tests. Maybe SY knows if BYU had a small classroom fab, MIT did. I could see that, baked up in small batches with grad students testing them. You sell a few pieces a month for $$$ each.
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I did find a Moxtek filled job posting for a job requiring semiconductor fab experience. Although their claim to fame is a polarizer, it may be they actually do make their own FETs! Some if there were a legitimate quantity buyer of custom FET's out there they might want to follow up!
I also came across one of the founders tried working at another start up and is now looking for work!
Ok, two seperate transformers. The primaries are in parallel and the secondaries are in series. A transformer that is it´s own common mode coil ?
scott wurcer said:
I don't know about BYU but the U of U does - go Utes! In class I fabricated my own Si wafer with MOSFETs on it. They worked good! 🙂
My teacher with grad students were testing GaAs devices for some companies. They had low yield. I guess GaAs devices were a dead end? I never hear about them.
BYU probably does fabrication too, but I wouldn't know.
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