MPP preamp is vastly improvable

[Teleno]

Thanks Teleno,
I will fix the legend on the board Thanks for catching that . Good thing there the same pinout.

Good thing too because you can swap them and see what works best.

[goldfinger1]

Please give values for 'C' and 'D' potentiometers

many Thanks

[Teleno]

Please give values for 'C' and 'D' potentiometers

many Thanks

C and D are not potentiometers, they're timing signals of the MPP Rev. D. Look up the schematic, replace the preamplifeir/integrator section shown in post #3 with my modifications.

[godigit1]

Hi Teleno,

Parts will be in tomorrow.
I was looking at my board and comparing to the rev e schematic and on the +and - inputs for the 5532 there are caps and resistors C4 R24 C5 R 11.
Should I delet them and tie directly to both rails? Thats what I did on my Pwb already.
The sample integrator is direct on the current MPP'S.
Im wondering If I should keep these caps or replace with a metal film maybe?

Thanks

[Teleno]

Hi Teleno,

Parts will be in tomorrow.
I was looking at my board and comparing to the rev e schematic and on the +and - inputs for the 5532 there are caps and resistors C4 R24 C5 R 11.
Should I delet them and tie directly to both rails? Thats what I did on my Pwb already.
The sample integrator is direct on the current MPP'S.
Im wondering If I should keep these caps or replace with a metal film maybe?

Thanks

I would just keep the caps, replace only if problems encountered.

[godigit1]

I have the circut up and running and its a definate improvement but wave forms are a bit different so Im not sure if its totally right yet.
Suprise is Thhe 5532 is doing the best.
Ive tested A 410, 4562 and the 5532.
Started with a MPP beach Just built to the sample integrator.
Im using a Digger John 6x9 folded mono coil to test with and its not the fastest.

ATTACH]45667[/ATTACH]
The first three photos are of the stock Mpp Pre amp .
Each was damped the best I think I can.
The rest of the shots are of the improved pre amp just after U2. Currently I dont have C6 inserted. Ordered the wrong cap.
The Square wave is after the added pre amp. Is this Correct?
You can see a definate time improvement especially with the 5532. It seemed the cleanest as well.
I dont have too much time now but will get better coil stats and readings later.
Thanks

[Teleno]

I have the circut up and running and its a definate improvement but wave forms are a bit different so Im not sure if its totally right yet.
Suprise is Thhe 5532 is doing the best.
Ive tested A 410, 4562 and the 5532.
Started with a MPP beach Just built to the sample integrator.
Im using a Digger John 6x9 folded mono coil to test with and its not the fastest.

[ATTACH]45664[/ATTACH][ATTACH]45665[/ATTACH][ATTACH]45666[/ATTACH]ATTACH]45667[/ATTACH][ATTACH]45668[/ATTACH][ATTACH]45669[/ATTACH][ATTACH]45670[/ATTACH]
The first three photos are of the stock Mpp Pre amp .
Each was damped the best I think I can.
The rest of the shots are of the improved pre amp just after U2. Currently I dont have C6 inserted. Ordered the wrong cap.

You can see a definate time improvement especially with the 5532. It seemed the cleanest as well.
I dont have too much time now but will get better coil stats and readings later.
Thanks

Thank you so much for proving my concept!

Regarding your measurements, I think you should take the peak of the blue waveform (Tx transient) as the time reference. You're using the left edge of the Rx signal, whis is affected by the slew rate of the op-amp. The left edge of the LM5532 starts later that the other, faster op amps.

In the mod, the time from the Tx peak to -1V relative to the baseline is 11us for both the LM5532 and the LM4562. This is an improvement of 5us over the MPP, which has 16us delay for the LM5523).

In any case, the coil seems slow and that's why all op-amps fare similary. I also see ripple in all the Rx waveforms, it would seem the coil is underdamped. You should have adjusted damping by varying R4, leaving R1 untouched at 1K.

The Square wave is after the added pre amp. Is this Correct?

To which node does the square wave correspond?

[godigit1]

Hi Teleno,
Thank you for the design.
This has been a helpful learning experiance for me. .

I should redo the before tests so things are apples and apples. In the stock tests I had the Pulse rate up around 1000 pps .
When I switched to your new amp I had a bad spike at turn off of the fet. I had it running too hot. so I backed it back to Mpp beach pulse rate at 125pps.

The square wave shot is of tp 3 on the new amp board.
I will get the rest of the integrator and Mpp board completed and a faster coil and see how it works.
Especially curious about moving the Ef sample Integration pulse and how it will effect the ground balance circut ive been trying to get right as well.
Thanks you again.

[Teleno]

When I switched to your new amp I had a bad spike at turn off of the fet. I had it running too hot. so I backed it back to Mpp beach pulse rate at 125pps.

The shouldn't have happened, the preamp doesn't affect the MOSFET circuit.

The TP3 signal looks weird, as if the coil were drawing too much current and causing the the battery voltage to drop. It looks like the Tx circuit is draining the electrolythic capacitor C7.
How does it compare to the TP3 signal of the original MPP?

[godigit1]

On the mosfet I had it adjusted wrong I was seeing it at the pre amp. The pre amp was not the problem there I was just explaining why I switched PPM rates. Sorry for the confushion on that .

The Tp 3 on the original Mpp is the before shots above.



I only have the Green section powered up and connected. So the 5us improvement is just coming from the new virtual ground so I think thats good.
On the Mpp board I just unplged the 5532 and pluged inputs in there .
The coil wire I switched to the new amp.
Part on the original circut is still running to give +and _ 5.
I dont know yet if thats causing anything yet.
I will get a finished Mpp on the bench too so I can further compare waveforms at the integrator amps.
Thanks

[Teleno]

can you share any data on the coil? inductance, self-resonating frequency, value of the damping resistor (R4) ...

The speed improvement of my design is more noticeable at lower inductances of 300uH or less, where the previous preamp was too slow.

Keep in mind that the MPP timing circuit will probably have to be modified as well to allow for earlier sampling (U7a in the schematic).

I've designed a version that uses a CFA op-amp (current feeedback) for improved slew rate. It allows you to amplify the signal to up to 3V without loss of bandwith. It uses less components for a gain of 800x (58 dB) and a BW of 1MHz.

[godigit1]

Hi Teleno,
I have been moving my test set u to a better location I hope.
I think I was having problems with metals being too close to the coil. Got to thinking about my test enviroment and 4 feet below my coil was two water heaters on the next story down.

The coil Ive been using is a .285 mh and 2.1ohm resistance shielded folded 8 mono 6x9. Originally razor back coils but now miner John has the name and he also makes the jimmy sierra folded 8. I am still working on a set up to measure the resonance , MAybe the nemo graph circut. Or just using another PI to ping it. I only have a audio signal generator and it has 600 ohms on the output. so It wants to damp the signals. Tried induction coupleing but no sucess there yet with it either.

Right now the fet is getting pretty hot with the new amp.
I think Im going to put everything on to a rev d board. I have two so I can compare signals as I try the different amps.

Your current feedback amp looks interesting Do you have a sim for it to check out?

Im also going to build a litz coil maybe a DD plainar coil Or just double layer Mono.
I need something that will sample down to at least 5 us nice and clean would be nice.
So Here I go another project HE HE.
Thanks agian for your designs hope I can make one happen.

[Teleno]

Hi Teleno,
I have been moving my test set u to a better location I hope.
I think I was having problems with metals being too close to the coil. Got to thinking about my test enviroment and 4 feet below my coil was two water heaters on the next story down.

The coil Ive been using is a .285 mh and 2.1ohm resistance shielded folded 8 mono 6x9. Originally razor back coils but now miner John has the name and he also makes the jimmy sierra folded 8. I am still working on a set up to measure the resonance , MAybe the nemo graph circut. Or just using another PI to ping it. I only have a audio signal generator and it has 600 ohms on the output. so It wants to damp the signals. Tried induction coupleing but no sucess there yet with it either.

Right now the fet is getting pretty hot with the new amp.
I think Im going to put everything on to a rev d board. I have two so I can compare signals as I try the different amps.

Your current feedback amp looks interesting Do you have a sim for it to check out?

Im also going to build a litz coil maybe a DD plainar coil Or just double layer Mono.
I need something that will sample down to at least 5 us nice and clean would be nice.
So Here I go another project HE HE.
Thanks agian for your designs hope I can make one happen.

You posted this schematic as the one you're working on: https://www.geotech1.com/forums/atta...9&d=1552570244

but the mod for the MPP is this one: http://www.geotech1.com/forums/attac...7&d=1549539823

U2b should be non-inverting for the MPP.

[godigit1]

I did actually catch that on my pwb Th e schematic I built to is in post 23.
I copied the wrong post, I was trying to show what nodes I was testing. So I think my Pwb is good.
One thing different is the caps at + and - 5 on the MPP they are not assumed in spice sim so Im wondering if I shoudnt just power directly of the rails?

[Teleno]

One thing different is the caps at + and - 5 on the MPP they are not assumed in spice sim so Im wondering if I shoudnt just power directly of the rails?

Use the caps by all means, ICs always need to be bypassed.