john curl said:
And low noise opamps. And feedback. And 36dB headroom. And 0.005% distortions (like it matters
And 0.12nV/rtHz with BF961 and gate SMD inductors.BTW, I would love to measure your thingie today. It may be a little higher than 0.4nV/rtHz.
I (or many other here) would beat your BT left handed, unfortunately there's nothing to beat but silver wire, solid aluminum cases and subjective fluff.
Syn08, you might be an engineer, but are you really a low noise designer? If you are, you should understand that my input stage is composed of 4 devices that are twice the surface area as your devices, MADE BY THE SAME MANUFACTURER. You use 8 devices (I think) but smaller area. Our only difference is the effective source resistance. If I change the value of 2 resistors, I get your noise level. Please remember, you tended to exaggerate your noise level and I called you on it. It is true that I had some problem with the Vendetta owned by Stereophile. It is most probably the LF411 op amp, (I used AD711's once they were introduced a few years later). I have replaced a lot of LF411 IC's as they tend to be or get very noisy. I do it automatically with every repair or upgrade. However, the LF 411 spec sheet won't show the problem. This is why I changed to AD711's, and now OPA134's.
Joshua, I would instantly switch over to IC's, IF I could make them sound and even measure as good as discrete devices. Scott's paralleled 961's is a good solution for AC coupled instrumentation, as it would be very low effective capacitance, given the number of paralleled parts, because it avoids P channel devices. For precision ultra low frequency designs, and even DC coupling, we use Toshiba 2SK389, pre sorted for Idss and DC offset. Then pairs of 2SK389's are paralleled together, even multiple pairs would work, to subtract offset. Less than 100uV of DC offset is possible.
OK, let us get back to basics: First, you have to find low 1/f noise, bipolar transistors, or jfets with good transconductance, or Gm.
Many Japanese manufacturers supplied such devices from 1978 on, but most have dropped out, and even Toshiba (the last good manufacturer of jfets) is giving up.
The main thing with jfets is the effective voltage noise--equivalent resistance, which is .7/Gm (at working current) and any series source or gate resistance.
If you want to keep your noise down, forget the gate resistance, and minimize the source resistance, run as high current as possible, and parallel jfets, if necessary. This is all there is to it. I knew that much in 1966. Now, how do we make ELEGANT input circuits that have other qualities, such as inherent balance, and DC optimization, without losing the noise characteristics?
Many Japanese manufacturers supplied such devices from 1978 on, but most have dropped out, and even Toshiba (the last good manufacturer of jfets) is giving up.
The main thing with jfets is the effective voltage noise--equivalent resistance, which is .7/Gm (at working current) and any series source or gate resistance.
If you want to keep your noise down, forget the gate resistance, and minimize the source resistance, run as high current as possible, and parallel jfets, if necessary. This is all there is to it. I knew that much in 1966. Now, how do we make ELEGANT input circuits that have other qualities, such as inherent balance, and DC optimization, without losing the noise characteristics?
anatech said:
Many people posting here have been really testy, and rude especially toward JC. And then everyone just expects him to roll over.
Syn 08, no one is going to prove anything in this thread. The best anyone can do is offer there point of view on the engineering and subjective matters. I mean John trusts his ears. And given how our hearing works what do measurements really tell you. Not that measurements don't matter, but measurements alone don't prove anything.
No, I don't trust MY ears, necessarily, I trust other peoples' ears.
As far as power supplies, I make the best one that I know how to make. It runs rings around almost anything that many here have even considered. That is WHY it takes a separate box. It is almost stuffed full! Yet, batteries would, most likely, still be better. Why?
As far as power supplies, I make the best one that I know how to make. It runs rings around almost anything that many here have even considered. That is WHY it takes a separate box. It is almost stuffed full! Yet, batteries would, most likely, still be better. Why?
scott wurcer said:
exactly ...
http://www.google.com/search?hl=en&...s=en-us&newwindow=1&q=Porsche+914&btnG=Search
1044242
john curl said:
Neither is true a 10dB improvement over .4 nV is not trivial, Doug Self never published a .132nV preamp. The only one I have seen uses transformer feedback or maybe just a step up transformer. I suspect a complimentary input at this noise level with Toshiba FET's would have a pathological input capacitance.
tomtt said:
http://www.britishv8.org/Other/BruceBarrett.htm
http://www.johnscars.com/xj/xjv8.html
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