Problems with the circuit

Thursday August 19th 2021

Hi and thanks in advance to all for your time, knowledge and help.

I found this circuit, it´s a variable signal generator that goes from 5KHz to 25KHz. The fuse is a 2 Amperes and the voltage 12VDC. The L1 must be wind with 24 gauge and is only 50 turns, the E cores where must be wind is a Hitachi 30.48 Inductor which does not appear in internet and for that reason the dimensions and material of which is made is unknown..

I built the circuit according to the diagram and as I could not find the specifications of L1
I end up making my own inductor with the help of software, one called Calculo de Bobinas and also miniRing Core Calculator.

The inductor I made is:
Air core one layer
Core diameter 70mm no space between turns.
29 gauge wire
116 turns
8 Ohms of resistance

I made it that way so the current is in the range of the fuse (2 Amps). 12vDC/8 Ohms =1.5 Amps.

The circuit never sounded, it did not work until I made the modification that appears in the second diagram.
This one is the original diagram.



This is the modification.
With this modification the piezo tweeter produced sound but the volumen is really low not the powerfull sound that I expected, (of course this in the audible range).

There are some things, some connections that I suspect are not correct but I am not an expert even though I see no reason to join the pin 3 with pin 8 of the 555 timers.

Should the connection of Q1(a PNP transistor) to pin 5 of IC2 be in the lower part of the transistor which is the collector?

This diagram shows what I think is not correct.


I also made this modification but there was no improvement neither decrease in the volumen. (The volumen remains the same)


These are the E Cores of the Hitachi 30.48 Inductor that I could not find.

I haven´t change the timers, maybe they were damaged because of the 3 to 8 pin connection.

The question.
How can I make it louder?

Without knowing the capacitance of piezo and inductance of all Lks and resulting fo, and Q (f) , and desired output, it’s pointless to guess. a stepup transformer can be used if impedances are known.

Without knowing the capacitance of piezo and inductance of all Lks and resulting fo, and Q (f) , and desired output, it’s pointless to guess. a stepup transformer can be used if impedances are known.

Thank you Tony Stewart....The inductance of L1 must be is 1mH but the capacitance of the piezo I don´t have the tool to measure it. The only data that I have of the piezo is 500W 105dB but the seller told me that is not really a 500W but a 100W. The frequency that produces the whole circuit is adjustable from 5KHz to 25KHz. In my case the tweeter that I bought only reaches 20KHz

This is the components list

“Sounds like” a 4 ohm tweeter. Have you tried an stereo amp….? Then rewire the inductor as a 1:10 stepup transformer.

Thank you Tony.
I haven´t tried it with an stereo amp. The idea of the step up transformer it seems has a future. I have tried different inductors with different resistances and when the inductor has a resistance around 8 Ohms the piezo sounds if it has less resistance let´s say 2 Ohms does not work and if it is for example 20 Ohms doesn´t sound either. Another point that I didn´t mention was that when the circuit is turned on and the piezo is producing sound the voltage taken just before the piezo is 23V.
What do you think of the modifications that I made and what about the timer connections of pin 3 to 8?

It’s an over complicate dual 555, which can be replaced with a Schmitt inverter with a push pull driver https://www.grc.com/tqc/TheQuietCanine.htm use a pot for feedback R but the 1mH inductor readts with the piezo approx. 0.3uF at resonance. Otherwise to flatten the response don’t use the inductor

Tony Stewart.
I really appreciate your time and help. The circuit in the link that you gave me is a simple one and I like that.... and the fact that was developed by many people gives me a sense of confidence in it.
Thank you very, very much!!!! Have a good night!!!