MPP preamp is vastly improvable

[godigit1]

Ok. After reading the post, it becomes clearer now. Interesting.

Dealing with transients in the uS range is a bit daunting.
That's where all those electrical characteristics you see on those op amp datasheets really come to the fore.

Yes sir,

I've been looking at data sheets and the 081 has input clipping diodes built in this adds to the noise level also I was running the third amp on the same supply as the 4562.

I've separated the + and - 5 and added separate filter caps for the third amp. Also have decided that the max 410 was a better choice for a couple reasons, Bandwidth and noise level, also the 081 is recommended to not have over a 5k feedback resistor, you can go more but not without compensation.

I made the changes and added the 410 here is the 3 stage amp with the 410 and the filter caps.




You guys can see its slightly under damped ( I like it that way)but looks allot better.

[6666]

Which 081 are you looking at, just checked the TI data sheets for TL081 and TLC081, cannot see any clipping diodes on inputs

[godigit1]

Which 081 are you looking at, just checked the TI data sheets for TL081 and TLC081, cannot see any clipping diodes on inputs

Your right,
Sorry I was looking at 4 data sheets at the same time the opa37 Is the one I mixed it up with. Should have double checked my self this morning.

Also when I checked the 410 this morning Don't know how this happened but it all worked I damped the coil and the Mpp was working. everything looked so good I took a picture and did my last post.
I just had time to check the 081 and it did not work. then I realized the jumper was missing.
somehow the 410 is able to pick up the signal between the jumper pins and work so I think I was really looking at the 4562 being buffered by the 410.
When I plugged the jumper in the 081 worked as normal.

Performance with the filter caps and the separate +and -5 helped with the sensitivity and stability .
That being said it went back to 6us , couple more things to try then I think its on to the next one.

[6666]

I was looking at 4 data sheets at the same time the opa37

All good

[godigit1]

Just looking at page 24 of the tlc081 I'm not good with spice but in the macro model is that clipping diodes in the upper right hand corner of the model?
It would be nice if each datasheet had a chip layout included .
Spice layout is confusing to me still!

[6666]

From the TI site, the psice model for tlc08xxxxx

[godigit1]

From the TI site, the psice model for tlc08xxxxx

Hi 6666,
I never could get this file to open! I have Spice on My computer.
Appreciate the help.

If your still looking into this three amp set up I think I finally got it and the 081 is far superior to the 412 with this set up, the 412 is just as fast but did not like the diode much.
I tried a couple things cap on the feedback resistor , adding input resistor between amp 2 and three but Bat 85 seems to be it.

I'm still learning but it looks like first sample at 3.7 us "'ish" .
The threshold problem is gone solid as ever 1/4 by 1/4 beer can side distance doubled, gold samples all better.

Here is scope shot Channel 1 yellow 4562 two stage.
Blue channel 2 081 with the diode.



I have some room to play with the gain Ill see how that works out.
Thanks again

[6666]

Hi , I can open it with 7zip, I see 3 files .mod, .sch, .slb
have you got 7zip ?


how can I get the files to you unzipped

[6666]

first sample at 3.7 us "'ish"

close enough

Major roof leaks today, big storm last night tons of rain
if you get the chance could you scribble down your circuit, thanks.

[6666]

This page seems to explain how to do it
the video is still active, https://www.youtube.com/watch?v=ajcY...utu.be&t=7m12s


https://electronics.stackexchange.co...-ltspice-model

[godigit1]

Thanks for the links Ill download the 7.zip and give it a try.
Just changing projects at work so Its been hectic.

Sorry about the roof leaks you never know tell you get a big storm. Glad you guys are getting some good rain though.

Here is the Schematic I built to.
The first two stages are the MPP preamp .
I'm not sure why Telano had switched polarity on amp 2 but I built to the Mpp Schematic on the first two stages.
The filter caps at C6 and C3 should have been 6.8 uf tants but the 10 uh electrolytic were closest thing I had.



I haven't had time to test it much more but did try a 4562 as the third amp, Ill get some shots tomorrow of the 412 and the 4562 tomorrow.

Be Well

[6666]

Thanks for the info, do you have a LF356 to try for #3 op amp

[godigit1]

I found a couple LF 356's in my stuff, they are old and I got them at a estate sale so I tested both to see if one was better than the other.
But both acted the same so I think they are alright. The wave form is a little funny and sensitivity went down.
Iv'e been doing a quick target test with a 1.2 gram nugget a 1/4 by 1/4 can side and a nickel .

Here is the 4562-356 paired.



I tested some other pairs as well to see what would happen.
The 4562 as a lead amp is the fastest but the 412- 410 combo is interesting.
If the turn off wasn't so slow it would be great, Maybe a diode on the 412 ?
As is its performance is right up there with the 4562-081 combo.




Here is the 082- 081 combo




4562 -1/2, 4562 pair



On each amp I'm getting a spike at turn off with the 4562 pair its moved into first sample area.
Its before or right at where I can first sample at this point so I'm not seeing any effects I can tell.

The last combo is the 4562- 410 pair.



I don't know if we can find a way to pull down the 410 -412 amps faster or if its a product of their design but the turn off seems like a trade off for less saturation time.

Is their any gain to a trade off in this way ?

[dbanner]

How about a resistor between input pin and ground, say 1meg.

[godigit1]

How about a resistor between input pin and ground, say 1meg.

Hi dbanner,

Sorry for the late response and thanks for the suggestion.

I have had to put in seat time on a course for my job,.(10 more hours)
I don't know how much further I can take this version I'm sure the circuit can be refined.
I need to break it back down and start from the first amp again I made some changes that may not have been needed.

Ill try the pull down resistor as you suggested, Thinking the second amp maybe.
Its weird the 412 does not show the almost 2 us delay at turn off when in the normal double amp configuration.
if I can get rid of that its a pretty good combo, maybe below 4 Us and no saturation in the final output.

Ill be back at it soon and will get more info my diagnostic skills are lacking so any help is appreciated.

Be well