Jellybean suggestions

Low noise, high impedance, junk-box jelly-bean screams TL072 family to me. But I know nothing about that probe amp and the kind of bandwidth, dc offset, noise and other constraints involved.

piglet

You can buy better, quieter FET-input op amps, but they are better because the FETs are bigger, and they do cost more.

--
Bill Sloman, Sydney

The opa134 is my jellybean FET oapmp. (But I'm a big spender. :^)

To the OP (bringer of doom) I don't know that TEK plug in. What sort of currents, BW, noise, and input capacitance are we talking about.

George H.

It's not actually a plug-in; just a stand alone amp that connects between the probe and the scope. I can't answer your questions at this stage (other than BW which would ideally be up to 350Mhz so an opa134 is unsuitable). I'll be carrying out some tests next weekend, then hopefully I'll be able to specify the other parameters. I was kind of hoping someone here would have a rough idea off the top of their head what the likely figures would be for an approximation.

For a cheap jellybean amp, you'll probably have to make some tradeoffs.

There's the CA3140 BiMOS amp available for around 70 cents at Tayda. Higher input impedance (~2 TOhms IIRC), lower offset than the TL072. Not as good noise performance, but it gets better at frequencies above 10kHz.

The TL072 is around 35 cents. Lower input impedance, worse offset, better noise performance below 10kHz.

I have been using the AD706 for a power supply regulator where we had big

1/f noise problems. It has pretty low bandwidth, and not sure how well it would do with a high impedance input. But, the noise is REALLY LOW! Using another fairly quiet amp, we observed big jumps in the signal basline every couple minutes. The AD706 is tested with GUARANTEED noise down to .001 Hz, so we tried it, and it solved the problem.

Jon

But what makes you think you need a high-impedance amplifier for that? Current probes are usually terminated into a *low* impedance. The P6016 expects 50 Ohms.

I think you want a CFA along the lines of a THS3001, AD810 or something like that. No real need to go to 350MHz, because the probe won't do that anyway.

But why do you need an amplifier at all? What are you trying to do?

Jeroen Belleman

350Mhz op-amps are out of jellybean league in my world :)

piglet

I take your point, my dear Piglet. If I have to order one, at least it will save me sorting through hundreds of chips in my junkbox, I guess, looking on the bright side.

Oh! That's not what I've been given to understand; puts a completely different complexion on the matter.

I want to create something functionally identical to the device I linked to in the first post on the subject; no more, no less. I could simply buy one of course; they're not expensive, but I'd learn nothing that way, which is no good to me.

op

yep,

-Lasse

Roughly 100 Hz to 10 MHz, 15A max.

Manual here:

The probe is a low impedance device and is normally used with a termination. A low noise voltage opamp would be more appropriate.

--
Grizzly H.

Wow! I was blind but now I see! That's enormously helpful (thanks too to Lasse). As a boat-anchor collector that archive may have some other very useful stuff on it for me, too.

Note: your scope has an amplifier already.

The part you're referencing doesn't have DC capability.

If you're interested in small signals, this may have no importance.

The manuals are free. Read them before flying off in all directions.

RL

On Sun, 14 Feb 2016 16:32:54 -0500, legg wrote: [...] I had absolutely zero information on the probe until a couple of hours ago. Having had the valuable sight of the bandwidth graphs it is clear that an amplifier may not be necessary for my needs at all, but even if it is, I now have all the info needed to proceed without further assistance from anyone here. Accordingly, the thread may be treated as "solved" - thanks, all.

Here is the manual:

Here is the schematic:

The original circuit only has four transistors, and one of those is in the power supply.

There are three 2N1517 and one 2N1381.