Questions about Electronic Sound of Chirping Canary circuit?

[samy555]

Hi
From: **broken link removed**

**broken link removed**​

Q1) How do I know that my audio transformer is 1K : 8R? Is it by simply measure the DC resistance?

Q2) If I wanted to use a ferrite core, how much should the number of turns for the primary and secondary coils, and will this core be simply a rod or one removed from a computer power supply?

Q3) How the above circuit operates? I know that the transformer is for impedance matching between the transistor high impedance and the low one of the 8 ohm speaker. Also I know that the transistor operates as an oscillator and I understand that the 47K resistor biasing the base of the transistor to start oscillating. Finally I know that the R1+C1 have a close relation to the tone frequency,,,, But what I don't know is the function of the two small caps 10n and 22n and why they have a very small capacitance related to the other two 100u caps.
Thank you very much

 

[chemelec]

Q1, Measure it with an Impedance Meter. Not an Ohm Meter.

Q2, Ferrites are used for HIGH Frequencies.
Probably wont work I this Circuit.

Q3, The 10n Provides the Oscillation Feedback.
I Assume the 22n helps to shape the Tone in the output.

 

[samy555]

Q1, Measure it with an Impedance Meter. Not an Ohm Meter.

OK
I have not an Impedance Meter but i'll experiment with my audio transformers.

Q2, Ferrites are used for HIGH Frequencies.
Probably wont work I this Circuit.

No, I think it would work
I see some chinees circuits using ferrite core transformer as audio transformer

Q3, The 10n Provides the Oscillation Feedback.

is it negative feedback (from collector back to Base)?

Thank you

 

[chemelec]

Samy555, I Don't know Where you Saw this, But FERRITE TRANSFORMERS Will NEVER Work at Audio Frequencies.
It would need to be a Really HUGE Ferrite Core to Get that type of Impedance in the Audio Range.

That Looks Like Positive Feedback.

 

[Audioguru]

The transformer has a center-tap that is effectively grounded through the power supply. Then when the collector voltage goes up the base voltage goes down, or when the collector voltage goes down the base voltage goes up which is positive feedback.

A ferrite transformer might be able to drive a high impedance piezo squeaky sounding transducer.

 

[samy555]

Samy555, I Don't know Where you Saw this, But FERRITE TRANSFORMERS Will NEVER Work at Audio Frequencies.
It would need to be a Really HUGE Ferrite Core to Get that type of Impedance in the Audio Range.

That Looks Like Positive Feedback.

not at all
Please look here at the cycle buzzer:
https://reprap.org/wiki/Scratchbuilt_Piezo_Printhead
and here:
https://reprap.org/wiki/File:Cycle_buzzer.jpg

the transformer is a ferrite core,, I have one in my house for my child
thank you

- - - Updated - - -

The transformer has a center-tap that is effectively grounded through the power supply.

Yes

Then when the collector voltage goes up the base voltage goes down, or when the collector voltage goes down the base voltage goes up which is positive feedback.

Unfortunately, I did not understand the idea!
In common Emitter configuration it is natural when the collector voltage goes down the base voltage goes up and vice versa??!!!!

A ferrite transformer might be able to drive a high impedance piezo squeaky sounding transducer.

Yes you are right
Thank you very much

 

[Audioguru]

Your photos show a normal transformer with a laminated iron core, not a ferrite core.
An oscillator needs to have positive feedback. The common-emitter transistor produces 180 degrees phase shift from base to collector and the center-tapped transformer also produces 180 degrees phase shift for a total phase shift of 360 degrees so there is positive feedback.

Will you use a high impedance piezo transducer instead of an 8 ohm speaker? The piezo can probably be driven by a ferrite transformer, but a laminated iron transformer can also be used.

 

[samy555]

Hi
This is the first time I heard that:

and the center-tapped transformer also produces 180 degrees phase shift for a total phase shift of 360 degrees so there is positive feedback.

pleas give me a page link that explain that point more.

Your photos show a normal transformer with a laminated iron core, not a ferrite core.

No it is a ferrite core. Now I hold it in my hand and I see it with my own eyes it is a ferrite

Will you use a high impedance piezo transducer instead of an 8 ohm speaker? The piezo can probably be driven by a ferrite transformer,

Yes it use a high impedance piezo transducer instead of an 8 ohm speaker.
thank you guru

 

[Audioguru]

In a center-tapped inductor (the coil on your transformer) if the center-tap is held at a constant 0V or other voltage and when one end goes positive then the other end goes negative and vice-versa, that is 180 degrees of phase shift. Look in Google for Center Tapped Transformer.

 

[samy555]

In a center-tapped inductor (the coil on your transformer) if the center-tap is held at a constant 0V or other voltage and when one end goes positive then the other end goes negative and vice-versa, that is 180 degrees of phase shift. Look in Google for Center Tapped Transformer.

Yes I supposed to understand it but I rushed not thinking about it a little.
Thanks GURU

 

[Audioguru]

You need an ordinary audio piezo transducer, not the ultrasonic printhead piezo in your link.