LF357 substitute

[Maurizio2]

This appears to be it ->
https://simplemetaldetector.com/puls...?cn-reloaded=1
It called the Minipuls-3. Note the spelling.

Not to be confused with the Pulse Technology Minipulse, or Geotech's Minipulse Plus.

Yes, that's it.

[algan]

Hi,
I was looking at the OPA637 (very expensive), but it has the same problem as the LT1122, so it's not suitable for the Delta Pulse.
But in other cases, it can replace the LF357 just as well as the LT1122.

Then I moved on to the OPA992, but its specifications are similar to the TLE2071, except for the package.

Finally, I looked at the AD8033, which, with a +-12V supply, has an input voltage range of −12.0 to +9.0V.

Sorry but for Delta Pulse lovers it is better to look for a "New Old Stock" LF357 or fall back on the TLE2071.

Colleague, these substitutes probably won't work, if it says it works once and doesn't work the second time, you need to be sure that we're not spending money on expensive integrals and that they are 100% like the original LF357 with delta pulse 2 or polonaise pi 1 Bulgarian lev, which is probably like 1 euro with a 28-centimeter antenna, the fake integrals detect from 16-18 cm, the original ones detect from 27-30 cm, that's all and then with larger antennas and frames the desired result is obtained.

[Maurizio2]

Colleague, these substitutes probably won't work, if it says it works once and doesn't work the second time, you need to be sure that we're not spending money on expensive integrals and that they are 100% like the original LF357 with delta pulse 2 or polonaise pi 1 Bulgarian lev, which is probably like 1 euro with a 28-centimeter antenna, the fake integrals detect from 16-18 cm, the original ones detect from 27-30 cm, that's all and then with larger antennas and frames the desired result is obtained.

Hi!
I have found the polonaise schematic.
It has the + input connected at +12V with a resistor.
Therefore all ICs listed can not be used for your application.

I listed the integrated circuits to make it clear what I was looking for.

I don't agree with using fake chips. So I think it's better to use an original TLE2071.

[algan]

TLE2071 is rail to rail is not suitable for this, I have tried more expensive ones than TLE2071 rail to rail does not work and colleagues should not be fooled by a rail to rail integral to replace the LF357.

[GeoMax]

Hi guys,

I don't quite understand why you don't simply use an NE5534 IC in your designs and/or add a trim circuit for the zero offset when needed. I use this NE5534 frequently, and it works perfectly in many designs. Eric Foster also used it in his later designs, and his detectors are exceptionally deep and good. There's no voltage issue with it either. The NE5534 can handle a +/-3 to +/-20 volt supply.
Perhaps the problem in the DP design is that the trim circuit for the LF357 is missing, even though other ICs or fake ICs require it. Actually, the original LF357 doesn't really need a trim circuit either, so it's not included. Over 20 years ago, the author named "Pulsi" from www.pulsdetektor.de once said that he had tested over 50 different LF357 ICs from various sources, and none of them required a trim circuit. Nevertheless, I always include this trim circuit for the zero offset in my designs, whether I need it or not, but it's there in the layout if needed. Also you should keep always in mind to check the original datasheet of the used IC-chip for the trim/null offset circuit. For example the null offset circuit for the LF357 and NE5534 are slightly different.

[Maurizio2]

TLE2071 is rail to rail is not suitable for this, I have tried more expensive ones than TLE2071 rail to rail does not work and colleagues should not be fooled by a rail to rail integral to replace the LF357.

I can't do that right now, but as soon as I can, I'll build a delta pulse.
I'll do the necessary tests and then we'll talk again.
In any case, I'm not here to fool my colleagues, but simply to help find an alternative to the LF357.

[algan]

In pulse star 2 the original lf357 with lf411 is also needed, it works but it is not like the original and when testing the rail to rail integral, it works but also does not work in depth and NE5534 is not suitable for those projects that are with lf357, it works but also very small depth and the output is at zero, so I am looking at projects that work with NE5534 and I have not done delta pulse 2 for years, it will also work with fake lf357 from China and lf356 from the Texas company, but with the original lf357 the depth is drastic.

[GeoMax]

In pulse star 2 the original lf357 with lf411 is also needed, it works but it is not like the original and when testing the rail to rail integral, it works but also does not work in depth and 5534 is not suitable for those projects that are with lf357, it works but also very small depth and the output is at zero, so I am looking at projects that work with 5534 and I have not done delta pulse 2 for years, it will also work with fake lf357 from China and lf356 from the Texas company, but with the original lf357 the depth is drastic.

Hello Algan,

I doubt that the DP works better with an LF357 than with an NE5534. When using an NE5534, there must be another problem that wasn't taken into account in the circuit. Looking at the DP circuit with the LF357, the input gain is only 120 times. This might be okay with the LF357, since the gain is subsequently varied with the gain potentiometer. The gain in other front-end detector circuits with an NE5534 is usually around 500 to 1000 times. Perhaps this is the problem here.

[algan]

Hi GeoMax, if you want, correct the Delta Pulse 2 schematic and post it. Someone will surely try if your proposed variant works well and if it will work the same as with the original or if it works deeper and better with NE5534 it will be great

[Carl-NC]

I use this NE5534 frequently, and it works perfectly in many designs.

The problem with the DP design is the preamp is operated with inputs all the way to +12v. So you need an opamp with true rail-to-rail inputs, or at least +rail inputs. This makes a sub difficult: you need an opamp with 24V supply, +rail inputs, 10MHz GBW, and a high slew rate to overcome a 24v saturation swing. On paper it looks like the TLE2071 will work so I don't know what the problem is with it.

You can also address the issue by changing the circuit to avoid needing a +rail opamp. Offset the coil like this:



Or offset the opamp inputs like this:



These are off the top of my head and may need some more thinking applied.

[GeoMax]

Hello Carl,

Your comments got me thinking, and I took another look at the DP's circuit diagram and the circuit board I made more than 20 years ago. As I understand it, it's a 12V circuit. The "-12V" is the negative terminal of the battery. I successfully built the DP, and the battery I used to power the detector was a 12V NiCad battery.

Here are some pictures of the PCB design I created back then on my kitchen table at home. I kept it for reference. I gave away all the other boards at the time. I designed the PCB using Protel99SE. It was one of the top EDA programs available at the time. The schematic I used to create the PCB was this one below.

[Carl-NC]

You are correct, and that makes finding a direct replacement a little easier.

[Nightryder]

You can buy used ones from https://www.utsource.net/