When I say noise I mean crackling and hissing from speaker, maybe it's because 10k resistor needs connecting to pin three instead of positive rail. No expert when it comes to connections on 555 timer just guessing if I'm honest. I have got a scope can check out signals tomorrow, what should I be looking for. Had scope on earlier very jagged peaks frequency over 40kh.

 

A 555 is not an amplifier in the normal sense. Why did you choose this circuit to learn about audio amplifiers?

A 555 can mimic an amplifier, but trying to understand amplification or gain with a 555 is il-advised.

 

Would a resistor between the collector of the transistor and +V help? I don't remember the 555 having a pullup on that input.

The control input is tied directly to one tap of the internal three-resistor divider string, so there is 5 K to Vcc and 10 K to GND.

Part of the problem here is that we don't know the amplitude or quality of the audio at the control input.

ak

 

The first thing I would do is disconnect pin 5 from transistor and ground pin 5 thru a 10n cap.

Then look at the signal at pin 3. Make sure carrier F can easily bypass the speaker. (thru C4 and C5) And check for 555 current consumption. Not all 555s can supply the same amount of current. In this setup, pin 7 can be configured to help with the current requirement, I believe.

Then with the wiper of a pot, vary DC voltage on pin 5, and watch and listen to the output. This will give you some idea of what your dealing with.

Even with everything adjusted properly, it will still be a terrible audio amp.

 

Had another look at circuit today and found bad connections on speaker.
After resoldering the distortion is not as bad however I still can't amplify voice.
Bit confused as when I tap the mic or blow across it the speaker amplifys the sound.
Why then can it not carry speech?

Have got the circuit wired as shown on talking electronics website, link in post 14.
Took some measurements with oscilloscope and found 64khz 11.20v RMS at pin 3. 10hz 8.20v RMS at pin 5 and 10hz 5.60v RMS at pins 6,2,7, all linked.
As requested I removed link to pin 5 and added a 10nf cap then measured the output and got the following results, 63.5khz vrms 10.80v, vmax 11.80v, vmin 5.40v. the current drawn was 11.11ma, hope this is of use.
Appreciate any advice would like to get it working then move onto some other types of amplifiers.

 

Had another look at circuit today and found bad connections on speaker.
After resoldering the distortion is not as bad however I still can't amplify voice.
Bit confused as when I tap the mic or blow across it the speaker amplifys the sound.
Why then can it not carry speech?
Have got the circuit wired as shown on talking electronics website, link in post 14.

You might try playing around with the value of the 680K resistor that goes from the positive supply down to the base of the BC547. It's possible that the circuit is biased "right on the hairy edge" of working, and making that resistor either larger or smaller might put it in a more functional state.

Appreciate any advice would like to get it working then move onto some other types of amplifiers.

Frankly, I would just move on, and not bother making this circuit work; at best, it's going to be a "kinda-sorta" amplifier that works only in a half-baked fashion, and it is definitely NOT a use for which the 555 timer chip was intended. As BR-549 said, even when adjusted properly, it's going to be a lousy amplifier.

 

Re-check your circuit for proper configuration. (all pin and component connections) Pin 7 is floating.

Check for proper resistor and capacitor values. Don't get mixed up in your two circuits.

Be aware of the current warning on this configuration.

I still recommend starting at the beginning, bread boarding these circuits.

By the time you get to this circuit, you get a feel for how these pins interact.

It's a great device, it's just not an amplifier per se.

 

Hi guys, came across a website named circuit digest. It shows the same circuit I have built but doesn't claim to amplify speech. Think it is just meant to prove weak signals can be amplified, they recommend blowing across mic to test it out, even have a video posted showing this. Couldn't post link, easy to find if interested.
Anyway think enough time has been spent on this time to move onto something else, thanks again for replys.