PI Audio

[Teleno]

Sorry for my questions.
I can find JFET 2N3819 in my city. Do you think it's a good replacement for JFET PMBF4393?
Thank you

I would say you can basically use any N-JFET as long as its parameter "Gate-source cut-off voltage V(p)GS" is 2V above -Vcc. In this case above -3V (-5V + 2V). Otherwise the OpAmp output may not go low enough to turn it off completely when needed.
However, this parameter varies a lot between JFETs of the same type. Some manufacturers group then by ranges, otherwise you need to buy a few and manually measure them to select the good ones.

[h9361]

Then it will be best to use Dom?s through hole version, mine is surface mount
BTW, the original circuit is Mickstv design, not mine, I just did some mods to suit what I wanted.

cheers

Dear Mdtoday.
I want to use TL072 instead of your amp because it's low noise. Please see attached, do you think lm386 part is correct (especially emitter and collector of Q1).
Thank you.

[h9361]

I would say you can basically use any N-JFET as long as its parameter "Gate-source cut-off voltage V(p)GS" is 2V above -Vcc. In this case above -3V (-5V + 2V). Otherwise the OpAmp output may not go low enough to turn it off completely when needed.
However, this parameter varies a lot between JFETs of the same type. Some manufacturers group then by ranges, otherwise you need to buy a few and manually measure them to select the good ones.

Thanks for your information.

[dbanner]

Dear Mdtoday.
I want to use TL072 instead of your amp because it's low noise. Please see attached, do you think lm386 part is correct (especially emitter and collector of Q1).
Thank you.
[ATTACH]55068[/ATTACH]

The common I think is referenced to battery positive, so yes, it seems correct. The ground shown in the schematic for the lm386 is battery negative.
Use any general purpose nfet.

[h9361]

The common I think is referenced to battery positive, so yes, it seems correct. The ground shown in the schematic for the lm386 is battery negative.
Use any general purpose nfet.

Thanks dear dbanner,
I have a question about calculating frequency of CD4046 in the AUDIO schematic.
First see the CD4046 setup, it has not used R2. Now, see the link, it's online CD4046 calculator. The calculator does not calculate frequency without R2!

[h9361]

The common I think is referenced to battery positive, so yes, it seems correct. The ground shown in the schematic for the lm386 is battery negative.
Use any general purpose nfet.

Dear dbanner
Please see attached, it's designed by Mr. Dom44. Please see its LM386, i think both emitter of Q1 and ground of LM386 is connected to battery negative, it it true?

[surfdetector]

Thanks dear dbanner,
I have a question about calculating frequency of CD4046 in the AUDIO schematic.
First see the CD4046 setup, it has not used R2. Now, see the link, it's online CD4046 calculator. The calculator does not calculate frequency without R2!

Just add R2 into the circuit. All that you are doing with the addition of R2 is ensuring that your minimum end of the frequency range is not zero.

[Mdtoday]

Sorry for my questions.
I can find JFET 2N3819 in my city. Do you think it's a good replacement for JFET PMBF4393?
Thank you

no need to be sorry, all good.
2n3819 will be fine. Just be mindful of the different pin outs available with T092

cheers

[h9361]

Just add R2 into the circuit. All that you are doing with the addition of R2 is ensuring that your minimum end of the frequency range is not zero.

Thanks for your tip.
Do you have any idea about adding LM386?

[h9361]

no need to be sorry, all good.
2n3819 will be fine. Just be mindful of the different pin outs available with T092

cheers

Thank you dear Mdtoday. About your schematic, we can add a uF capacitor before Pin 9. In this case, we have a nice delay than target and we can easily detect small change in sound (soft sould) like GPX audio.
Please see the video, time 5:00. He adds a 10Uf in pin 9, then we have a delay in audio.

[Mdtoday]

Thanks for your tip.
Do you have any idea about adding LM386?

AC couple the input to the LM386
Dom44’s board layout doesn’t look correct, emitter of the BC557 should not be tied to GND.
its late, maybe I’m seeing things

cheers

[h9361]

AC couple the input to the LM386
Dom44’s board layout doesn’t look correct, emitter of the BC557 should not be tied to GND.
its late, maybe I’m seeing things

cheers

So, it's better to be connected to -5V, true?

[Mdtoday]

Thank you dear Mdtoday. About your schematic, we can add a uF capacitor before Pin 9. In this case, we have a nice delay than target and we can easily detect small change in sound (soft sould) like GPX audio.
Please see the video, time 5:00. He adds a 10Uf in pin 9, then we have a delay in audio.

No, that is not a very good idea!
You need fast response not slow.
The Mickstv circuit produces variable frequency, variable amplitude and for gold prospecting is ideal.
Response is clean and crisp.
Best thing to do is build on breadboard and experiment

[h9361]

No, that is not a very good idea!
You need fast response not slow.
The Mickstv circuit produces variable frequency, variable amplitude and for gold prospecting is ideal.
Response is clean and crisp.
Best thing to do is build on breadboard and experiment

Do you remember audio Frequency of CD4046 in your schematic?

[Mdtoday]

So, it's better to be connected to -5V, true?
[ATTACH]55072[/ATTACH]

Yes

Build as per the schematic and notes in first post of this thread and it will work.
I’m off for some shut eye

cheers