felezjoo PI(the best pulse induction metal detector that I made until now)

[inglucho]

in Colombia... what can i suggest you... try to find OLDEST american trash electronics boards, seek TL081. it was used in very old TV sets and EGA VGA SVGA monitors.
you can use LF356 too.

Hello Kr315, thank you for your response. I have a question: Does the TL081, with a bandwidth of 4 MHz, perform the same in this metal detector as the LF357, which has a bandwidth of 20 MHz?

Has anyone used these suggested replacements with equal or better performance in the metal detector?

[inglucho]

Hi
I asked an AI which one I could use as a replacement (LF357), and this is what it replied:



The LF357 is a high-speed JFET operational amplifier that, due to its age, is no longer in production. To replace it, it is important to find an operational amplifier with similar or improved characteristics in terms of bandwidth, slew rate, input bias current, and input noise.

Some modern options that could replace the LF357 are:

1. **OPA627** (Texas Instruments)
2. **AD8065** (Analog Devices)
3. **LT1357** (Analog Devices)

### Comparison:

#### LF357:
- **Supply Voltage**: ±5V to ±18V
- **Unity-Gain Bandwidth**: 20 MHz
- **Slew Rate**: 50 V/µs
- **Input Bias Current**: 50 pA (typical)
- **Input Noise**: 10 nV/√Hz

#### OPA627:
- **Supply Voltage**: ±4.5V to ±18V
- **Unity-Gain Bandwidth**: 16 MHz
- **Slew Rate**: 55 V/µs
- **Input Bias Current**: 10 pA (typical)
- **Input Noise**: 4.5 nV/√Hz

#### AD8065:
- **Supply Voltage**: ±5V to ±12V
- **Unity-Gain Bandwidth**: 145 MHz
- **Slew Rate**: 180 V/µs
- **Input Bias Current**: 0.6 pA (typical)
- **Input Noise**: 7 nV/√Hz

#### LT1357:
- **Supply Voltage**: ±5V to ±15V
- **Unity-Gain Bandwidth**: 250 MHz
- **Slew Rate**: 600 V/µs
- **Input Bias Current**: 2.5 nA (typical)
- **Input Noise**: 3.2 nV/√Hz

### Analysis:

- **OPA627**: This amplifier is an excellent choice for applications requiring high precision and low noise. Although its bandwidth is lower than the LF357, its slew rate and input noise are better.

- **AD8065**: It has a much higher bandwidth and a significantly higher slew rate. It also has a very low input bias current, making it suitable for high-speed and precision applications.

- **LT1357**: This is a very high-speed operational amplifier with much higher bandwidth and slew rate compared to the LF357. It has very low input noise, but its input bias current is higher.

### Conclusion:

The choice of replacement will depend on the specific application and the most critical characteristics for its operation. If bandwidth and slew rate are crucial, the **LT1357** or the **AD8065** would be excellent choices. If a combination of low noise and precision is needed, the **OPA627** would be a suitable option.

"
---


What do you think, with your much greater knowledge? Has anyone implemented one of these changes?

[kt315]

Hello Kr315, thank you for your response. I have a question: Does the TL081, with a bandwidth of 4 MHz, perform the same in this metal detector as the LF357, which has a bandwidth of 20 MHz?

Has anyone used these suggested replacements with equal or better performance in the metal detector?

if you can not find LF357 and LF356 in your county... what you can find then? bandwith? if you are not able to seek LF357, then no deal to bandwidth.
replacements
OPA627, OPA637, AD744, AD845, AD877,
OP42, LT1122, TLE2071, TLE2081,
soviet: KR574UD1, KR574UD3, K140UD23

[inglucho]

if you can not find LF357 and LF356 in your county... what you can find then? bandwith? if you are not able to seek LF357, then no deal to bandwidth.
replacements
OPA627, OPA637, AD744, AD845, AD877,
OP42, LT1122, TLE2071, TLE2081,
soviet: KR574UD1, KR574UD3, K140UD23

Thank you very much for taking the time to answer my questions. Here in Colombia, I was able to find the LF356, but I am unsure if its performance is inferior to the LF357 and what the differences are.

[hodhod]

lf357-lf257-lf157

[Aliavazpour]

Any Help for this please.

Hi my friend
Dear, to work with a metal detector, you must follow the method of working with conventional and new pulsed metal detectors, when using a 30 cm loop, you must keep the balance and distance within 10 cm of the ground. It is not reasonable to explore the sensitivity above 12, but with the ground above 5 because the sole 5 balances quickly and it is not good that it balances automatically every few seconds, only to test the disaster 15 then the ground turns on. Download and translate the guide from Fellzjo Forum, everything is there

[adem52]

Hello, I am using this, it works very well, the price is also affordable, I could not find lf357 in the market.

LM318
Small Signal Bandwidth . . . 15 MHz Typ
Slew Rate . . . 50 * 70 V/µs Min
Bias Current . . . 250 nA Max
Supply Voltage Range . . . ±5 V to ±20 V

[Emersonpaz]

LF357J I used them on the felezjoo and they worked very well old stock, they are made of sandwich type ceramic. from this link: https://a.aliexpress.com/_mLxlaRA

[Tanu]

[QUOTE=Emersonpaz;n426744]LF357J I used them on the felezjoo and they worked very well old stock, they are made of sandwich type ceramic. from this link: https://a.aliexpress.com/_mLxlaRA[/QUOI
i want to know felezjoo ground balance.
how about is it stable in real ground

[Nightryder]

This is a quote from the author: "OPA637 is another part that could be used. It is expensive. CA3130 could be used too and is tested. But its result is not as good as LF357.You can use LM318 but you MUST reduce offset of its output about 1 volt! Propably with 2 series 1N4148 on output."


I personally purchased LF157N DIP8 from https://www.utsource.net/ Used but not counterfeit. I also bought from the link Emersonpaz provided and they worked just fine. I cannot emphasize enough on judging ABC numbers only outdoors while being far away from any metal object especially what could be inside walls around you or in the ground.

[useus]

Looking at the various videos of the felezjoo I noticed that the sound of the buzzer changes tone and volume, which my felezjoo doesn't do, not even by changing the sound in the settings. I use a small active buzzer. I also tried with a normal buzzer but the result doesn't change. What could it be?

[Nightryder]

Looking at the various videos of the felezjoo I noticed that the sound of the buzzer changes tone and volume, which my felezjoo doesn't do, not even by changing the sound in the settings. I use a small active buzzer. I also tried with a normal buzzer but the result doesn't change. What could it be?

Try it with some earphones if you don't have a speaker and see if the issue from the buzzer or not. I recently noticed there were two schematics of Felezjoo. They differ in the location of C7. One of them has C7 associated with the audio circuit which I do not think it's the right one.

I run mine with a small 8 ohms speaker, however the audio npn transistor (T3) kept getting really hot to the point where it's not functional anymore and had to be replaced twice. As a last resort, I changed the audio voltage from (+12 v) to (+5v) and now it seems to be okay.

[useus]

Try it with some earphones if you don't have a speaker and see if the issue from the buzzer or not. I recently noticed there were two schematics of Felezjoo. They differ in the location of C7. One of them has C7 associated with the audio circuit which I do not think it's the right one.

I run mine with a small 8 ohms speaker, however the audio npn transistor (T3) kept getting really hot to the point where it's not functional anymore and had to be replaced twice. As a last resort, I changed the audio voltage from (+12 v) to (+5v) and now it seems to be okay.

Solved with little 8 ohm 0.2w speaker

[Tanu]

Looking at the various videos of the felezjoo I noticed that the sound of the buzzer changes tone and volume, which my felezjoo doesn't do, not even by changing the sound in the settings. I use a small active buzzer. I also tried with a normal buzzer but the result doesn't change. What could it be?

I mentioned this problem in the previous post. I did not get an answer. Can you post the speaker photo?

[useus]

I mentioned this problem in the previous post. I did not get an answer. Can you post the speaker photo?

It's a 2cm diameter speaker

Use the values I mentioned and you find it