John Curl's Blowtorch preamplifier part II

[RNMarsh]

Originally Posted by jan.didden

@ RM: Wel if I stay with the total current through the device below the stated dissipation, than that's taken care of I guess.
Like a 5k pot in mid position, with 7 mA entering at each end terminal, and the wiper sinking the total. Dissipation is just 250mW, but the wiper current is 14mA. That OK you figure?

jan

If this is just for dc use, I would use a w.w. pot or ceramic type. How each mfr rates their parts would determine the life of the part. I would not run these liitle guys too close to their rating though. Contact (wiper) construction varies... Spectrol (now Vishey owned) uses a dual contact, gold plated for long life and stable contact resistance. They are cheap enough. NTE sells them under thier name/number. -RM

[scott wurcer]

Originally Posted by simon7000

Scott,

You made me look! It is 1/2 of a dual opamp!

Would you care to elaborate about how PSSR is measured for data sheet use? I.E. one side at a time etc.

Depends, it usually says under the conditions. Most I think say +PSRR and -PSRR on seperate graphs which are as stated.

[Esperado]

Scott, you did not answer my question: Why the hell the - input is the upper one on the Data sheet ICs schematics (and LT spice)?

[scott wurcer]

Originally Posted by Esperado

Scott, you did not answer my question: Why the hell the - input is the upper one on the Data sheet ICs schematics (and LT spice)?

That's probably the way it came out the first time, the rest is history.

[Esperado]

Too, i would like to know if the number of transistors in an IC OPA has a great impact on its manufacturing price.
(thanks for the previous answer)

[Triodethom]

Originally Posted by SY

Yes, that's how one gets ESL. Have you lost the context so fast?



Yes, lost in the noise left over from the Big Bang. But I wasn't the one claiming that this 3k/6k/whatever-new-one-you-come-up-with is significant, that was your claim. I just showed, using your logic but with uncooked books, that it's not even vaguely significant.

Nasa states that the backround noise is 10-6/(hz)raised to 1/2 . { ref. http://jila1.nickersonm.com/papers/E...Thesis_d12.pdf } What equipment was used that can measure above about .2hz aprox. the noise floor at -200db . some old tests showed that a few could hear below a noise floor by 10db when the floor was about -60db . How then is you are able to measure 80db below noise floor that must be one very very impressive grounding system used. This fantastic grounding (earthing) system must be share with all of us .

[jcx]

99%+ of monolithic op amps will have PSSR to one supply be lower, it will follow the open loop gain gain curve - the rail the internal Ccomp is connected to

since the PSRR is asymmetric, the better rail often orders better at most frequencies, the worse rail rejection dominates the common mode power supply rejection

input CMRR will usually be higher than the worse rail PSRR too

many datasheets don't show this right - use a test circuit limited by the op amp's own open loop gain - pointed out by Pease


"hearing below the noise floor" is often due to misunderstanding/misstating the details of frequency dependence of both "noise" and our hearing in "critical bands" of few hundred Hz to few kHz BW - human hearing doesn't use very long integration time times, and masking applies all the way down to the noise floor

[1audio]

Originally Posted by RNMarsh

If this is just for dc use, I would use a w.w. pot or ceramic type. How each mfr rates their parts would determine the life of the part. I would not run these liitle guys too close to their rating though. Contact (wiper) construction varies... Spectrol (now Vishey owned) uses a dual contact, gold plated for long life and stable contact resistance. They are cheap enough. NTE sells them under thier name/number. -RM

'

Jan:
14 mA will burn the contact points on anything but a larger wirewound. You will also get some instability from that. If you are using it as an offset trim (a guess) parallel some resistors to take most of the current and use the pot to make an offset tweak.
The best multiturn trimmer for that would be the Vishay bulk foil trimmer Vishay - Resistors, Variable - Trimmers - Bulk Metal® Foil Be prepared for sticker shock. They do work well for this. Datasheet: http://www.vishaypg.com/docs/63056/12801285.pdf (seems hard to find on the Vishay website).

[scott wurcer]

Originally Posted by Triodethom

Nasa states that the backround noise is 10-6/(hz)raised to 1/2 . { ref. http://jila1.nickersonm.com/papers/E...Thesis_d12.pdf } What equipment was used that can measure above about .2hz aprox. the noise floor at -200db . some old tests showed that a few could hear below a noise floor by 10db when the floor was about -60db . How then is you are able to measure 80db below noise floor that must be one very very impressive grounding system used. This fantastic grounding (earthing) system must be share with all of us .

This was 1/f noise at 10^-4 Hz of IC voltage references not exactly apples to apples.

[simon7000]

Originally Posted by scott wurcer

Depends, it usually says under the conditions. Most I think say +PSRR and -PSRR on seperate graphs which are as stated.

Scott,

I want to get a bit into that you start with a clean DC supply, add isolation so you can inject a test signal into one terminal or the other.

JCX

You are correct one supply side is more critical than the other. The secondary issue is what happens when you draw in the "Stray" capacitors and then connect this circuit to another with it's own power supply.

George,

You asked about other effects. Did you know that from the same manufacturer, the same series of capacitors, even the same values will have different resonant frequencies for axial vs. radial?


Anybody care to explain why?


ESP

When you draft in ink, most folks start the vertical lines from the left and draw them in, then wait till they dry before starting at the top and placing the horizontal lines. (Resistors are usually done with a template by themselves!) So the + sign is easier to draw the closer it is to the bottom of the drafting! (Try bending over a drafting table for 8 hours, you'll get a feel for it.)

Now for architectural drawings the horizontal and vertical lines never close! They just come close enough to appear closed. If they are closed they then look thicker at the corners and the architects didn't like that!