MPP preamp is vastly improvable

[Teleno]

Back to the original question, how about the current indicated through the one ohm resistor?
What is happening there?

It's D8 in series with D5 when the output of U4 goes negative.
D8 was an attempt to conserve slew rate in U4. It's not necessary with the amplifiers chosen, actually it slows them down a bit. Removal of this diode solves the problem. See the updated circuit.

You can also keep D8 and remove D5 which is actually not needed. D8 helps with slower opamps.

[6666]

godigit1 are you still working on this ?

[goldfinger1]

Yes, Just purchasing an 8 channel scope to allow me to complete this.

[godigit1]

godigit1 are you still working on this ?

Sorry for the inactivity.
Yes,
Im still working on this but have back tracked to try to make a faster coil.
One project leads to another. Im now setting up to experiment with making some custom litz.
Ive made the forward and reverse gearbox for the twister and just made my 80rpm to 2 reducer gears for the draw.

Have you been able to work on it and what version ?
Thanks
P,S that board I designed has a error maybe more than one but the J113s Are wired wrong.

[6666]

Hi godigit1, I have also gone off on a few different tangents while waiting for parts etc, but trying to steer back here, "What version" is a good question as the thread needs carefull reading, but still interested in project.

[godigit1]

Also the last two posts in the GB add on board thread. There is the auto zero version.

[6666]

Just ordered some parts for when I get over this damn virus, anybody still working on this project ?

[nonkapo]

Well i have almost completed my E-version after which i'm planning to see whether the swap will work. But before that i have a stupid question. Will BF256B work here instead of BF245C? I've compared them and see only a bit of difference in the ON characteristics, but as on the board is printed exactly BF245C i have some doubt?!?!?

[nonkapo]

I miss to correct my own question within the edit time.I mix up the FET's with the TGSL . Here the swap is for j113. Looking at the stage schematics it is very similar to the one of Baracuda, where i successfully implement BG256B so i gues i can use them here too. Am i right or wrong?

[dbanner]

Right. It is used just as fast switch, so any general purpose device should be fine. TUP TUN DUG DUS, and I would add FUN, which stands for FET Universal N channel(suitable for these projects). There is a list of appropriate FET devices for geotech projects somewhere on the forum.

[godigit1]

Just ordered some parts for when I get over this damn virus, anybody still working on this project ?

Hi 6666
I finally was able to make a little progress with this at least the first design on post #3.
I did not do the integrator changes at least not yet.

I built both a MPP rev e preamp as a stand alone and the three amp design for comparison.
Using the Mpp layout I added the third amp and used Teleno's recommendations for amps.

Testing the stock Mpp Pre amp with the 5532 time to 0v is about 3.5us and there is a little overshoot.
Swapping to 412 is not much better and the amp looks overcompensated.
The 4562 is far superior at 2us to 0.

Stock Mpp Preamp







Three stage preamp First two stages only Mock MPP







For some reason on my amp build the overshoot on the 5532 is worse. Other than that its a bit cleaner than the stock Mpp Preamp.

Here is the three amp set up.
I'm just including the 4562 in the tests from here on out as there is no reason to move forward with the other two.





I tested a TL071 and TLC081 as the third amp and as you can see the 081 is a winner.

Teleno's third amp design is also a winner. Its still capable of 2 Us recovery time and should by cleaner as far as noise I would think, Plus the increase in bandwidth.

Seems the preamp is plenty fast at this point.
Any help and or thoughts in cleaning it up and or more testing anyone wants to see done I would appreciate the input.

6666
What version did you gear up for and have you had a chance to play yet?

Thanks Again Teleno

[bklein]

Is the preamp test saturation/clipping recovery or small signal gain with no clipping?

[6666]

Hi Godigit1, wow you have been busy, and you have done the testing I was planning to do, when I got the flu and 3 colds last year my projects got put on hold, lately I have been working on 5 volt micro controlled PI circuits just for fun, my tlc081 arrived but I think my 4562's are fake, but it looks like your testing has proved the preamp a winner, thanks.

[moodz]

..the autoswitch works fine ... just make sure you dont feed it straight into an opamp with clamping diodes across the inputs
... or they will draw current and the switch wont work ... the blocking MOSFET relies on high source resistance a clamp diode will stuff it up.

[6666]

Thats interesting the TLC081 does not seem to have clipping diodes so that should work yes ?