Analogue Dub Siren

[audioguru]

The circuit in post #101 does not have a capacitor in series with R1 so its frequency response goes lower than earthquake frequencies and includes amplification at DC. Therefore for higher gain you can simply reduce the value of R1. But The input offset voltage of an opamp is DC and it also gets amplified. For audio frequencies the capacitor value in series with R1 depends on the value of R1 for good low frequency response. Therefore for more audio gain it is best to increase the value of R2 if the circuit does not have the high stray capacitance of a solderless breadboard.

Trimpots are linear only. Real potentiometers are either linear or log.
An OPA2134 is a good dual audio opamp with the same pin numbering as the LM358. I have used TL072 dual opamps for many years on audio circuits but the OPA2134 is newer and much better.

 

[spec]

The circuit in post #101 does not have a capacitor in series with R1 so its frequency response goes lower than earthquake frequencies and includes amplification at DC. Therefore for higher gain you can simply reduce the value of R1. But The input offset voltage of an opamp is DC and it also gets amplified. For audio frequencies the capacitor value in series with R1 depends on the value of R1 for good low frequency response. Therefore for more audio gain it is best to increase the value of R2 if the circuit does not have the high stray capacitance of a solderless breadboard.

Trimpots are linear only. Real potentiometers are either linear or log.
An OPA2134 is a good dual audio opamp with the same pin numbering as the LM358. I have used TL072 dual opamps for many years on audio circuits but the OPA2134 is newer and much better.

AG the circuit of post #101 is only a test circuit and all of your observations are already known.

We have not arrived at a final circuit yet- one step at a time.

But we have got an amplifier working- or so it seems.

I too like the OPA 2134 and one of its advantages is a very low input bias current and operation down to 5V, but it is not at its best below a 20V (+-10V) supply lines in my experience anyway.

One thing that is unknown at the moment are the input levels and output levels which are fundamentally important to get to a final design as are the source impedance and output load impedance.

In view of the application I would imagine that a large dynamic range would be beneficial to preserve the sound of the dub siren.

spec

 

[Rorut]

testes to replace the 1K with 470ohm and 150ohm. Barely hears any difference. Also tested to replace the 10K with a 220K, a bit higher but not much at all...
But when increasing to 220K sound is getting a bit wierd. Guess it is because of what you described earlier.

But with 1K and 10K circuit is the most stable so far of circuits tested Im positive and looking forward to the strip board

 

[spec]

testes to replace the 1K with 470ohm and 150ohm. Barely hears any difference. Also tested to replace the 10K with a 220K, a bit higher but not much at all...

Hy Rorut,

Can you measure the voltage gain with a battery on the input.

Measure the voltage on the wiper of the potentiometer with respect to 0V (to get Vin) then measure the output voltage (Vout)

The voltage gain (A) is then Vout/Vin

As I mentioned before, the ear is a very poor judge of gain.

spec

 

[Rorut]

Hi
With 1.5v on input and replacing 1K with 470ohm and measuring on the wiper of the (volume) pot I get 1.5v on max rotated pot.
with this measuring the output i get 10.8v with pot at max and 0.161v with pot at lowest.
Did I do it correctly?

Doing above with 1K I get same results

 

[audioguru]

With a 12v supply, the output of an LM358 cannot go higher than about 10.8V so your gain measurement is incorrect. You must turn down the volume control at the input so that the output goes no higher than about 10V. Then you can measure the amplifier input level at the output of the volume control and compare it with the output level at the output of the amplifier.

 

[Rorut]

With a 12v supply, the output of an LM358 cannot go higher than about 10.8V so your gain measurement is incorrect. You must turn down the volume control at the input so that the output goes no higher than about 10V. Then you can measure the amplifier input level at the output of the volume control and compare it with the output level at the output of the amplifier.

Thanks AG, I will test doing that later today

 

[Rorut]

with 10v measured on the output of the circuit I have 0.9v on the output on volume pot (wiper).
with 1K. 10/0.9=11.1

With 470ohm
10/0.45=22.2

So is it correct now? Feels wierd to have gain if you cant hear the difference
Confusing, I really need to start reading some books about basic stuff...

 

[audioguru]

What kind of sounds does it produce where you cannot hear the difference in gain? The siren? Then the output level might be as high as it can go (the output of the amplifier might be clipping) which causes sounds something like a buzzer. Many sirens sound like buzzers.

 

[Rorut]

It produces a lot of variatons depending on combination of the three switches. I noticed it sounds a bit strange when amplified on the deeper tones, pulsating (sounding with pauses). But I think that disappeared a lot on this new version (no buzzer sound). The amplification is doing pretty good from the circuit but when chaning resistors I dont hear much difference. How do I know if it is high as possible ?

 

[audioguru]

Which of the 130 posts says what the three switches do?
When the output level of an amplifier goes as high as possible then the loudest sounds of music and speech sound distorted. A smooth sinewave sounds like a buzzer squarewave because the output of the amplifier is clipping.

When it plays a continuous deep tone (low frequency?) you say the sound pulses with pauses? Then there is a problem that is cutting off the output called "motorboating". Is the schematic in post #101?

 

[Rorut]

In post #5 I linked to the product. There is a soundclip and a description.
"4 different types of siren sounds can be selected as well as various modulation speeds and pitch setting. All these parameters are changed by using the 3 onboard rotary switches."

The motorboat-thing got better with the latest schematic on page #101.

(It was not my intention that it would be such a long thread of more than 130 posts.
Rehashing this makes atleast that I learn something. I apologize to those of you who are feeling bored and of course I appreciate all the help I get)

 

[audioguru]

The siren sounds like a squarewave variable frequency buzzer so when fed to an amplifier that has its output as high as it can go (clipping) then it sounds almost the same.
I can't play the entire video because I was told to stop the noises.

 

[Rorut]

LOL , same in my house. "Turn of that noise"..

It can make three types of waves I think. It is an pretty good improvement with the latest stable amplifer. Just thought it could be higher.
But it is better than before so will definitely continue somehow with this.

 

[Rorut]

Maybe there is a completed circuit I can buy that are doing what im trying to achieve? Tried to google it but had problems find anything. Any suggestions on getting me forward is appreciated

 

[spec]

Maybe there is a completed circuit I can buy that are doing what im trying to achieve? Tried to google it but had problems find anything. Any suggestions on getting me forward is appreciated

Hi Rorut,

A wise move.

Yes, there are many amplifiers available, and quite cheap too. I and, no doubt others, will have a look for some suitable amplifiers.

spec

 

[Rorut]

Hi Rorut,

A wise move.

Yes, there are many amplifiers available, and quite cheap too. I and, no doubt others, will have a look for some suitable amplifiers.

spec

Thanks!
No need for it to be in a box, just a completed pcb. Or a diy kit. Thanks!

 

[spec]

Thanks!
No need for it to be in a box, just a completed pcb. Or a diy kit. Thanks!

OK Rorut,

A well layedout PCB will circumnavigate the layout problems that you have been having.

As I said before, opamps have got a phenomenal voltage gain and just a sniff of unwanted cross coupling can cause all sorts of problems- I speak from experience.

spec

 

[Rorut]

OK Rorut,

A well layedout PCB will circumnavigate the layout problems that you have been having.

As I said before, opamps have got a phenomenal voltage gain and just a sniff of unwanted cross coupling can cause all sorts of problems- I speak from experience.

spec

I dont argue about that, got some experience from doing (trying) this myself and much time spent...
I'm tempted to solder the first circuit AG and you helped me with on a PCB board to give it a try, but I hope that someone could link to a completed product

 

[spec]

I dont argue about that, got some experience from doing (trying) this myself and much time spent...
I'm tempted to solder the first circuit AG and you helped me with on a PCB board to give it a try, but I hope for someone could link to a completed non-inverted board

Yes, very valuable experience- there are standard rules about laying out a high gain (open loop) amplifier. The thing is that it is fairly pernickety and perhaps boring.

It does not matter if the amplifier is inverting or non inverting for audio amplification.

What is needed now is a description of the input signal and source and the required output signal and what is to be driven.

We do know that 12V supply lines are desirable.

spec