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4069 Noise Generator

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prprog

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I am experimenting with noise (synth drum sounds). I built this 4069 noise generator. Noise is generated as expected...but it generate a hum sound. First I built it on a breadboard...noise and hum ....since it is very simple I built it (on a small perforate board and solder the components)....noise and hum again....how can I do to get rid of the hum?


Thanks,
 

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Are you operating it from a battery or from a mains source?

Do you have bypass capacitors (a 100 nF and a 100 UF) from Vdd to Gnd?
 
What an odd circuit.

The input is connected to 0V.

Each amplfieir has a gain of 10, making 1000, in total, I don't see how the amplifier is noisy enough to generate the noise you desire.

Why no go for the traditional zener diode generator?
 
What an odd circuit.

The input is connected to 0V.

Each amplfieir has a gain of 10, making 1000, in total, I don't see how the amplifier is noisy enough to generate the noise you desire.

Why no go for the traditional zener diode generator?

To answer ljcox - I am operating it with a 9V battery. No I dont have the capacitor bypassing . Do I need two capacitors, both from + and GND?
To Hero999 - I found this on a Patent circuit , so I give a try, and it work...well beside the hum.
 
What an odd circuit.

The input is connected to 0V.

Each amplfieir has a gain of 10, making 1000, in total, I don't see how the amplifier is noisy enough to generate the noise you desire.

Why no go for the traditional zener diode generator?

The first stage is configured as an oscillator
 
To answer ljcox - I am operating it with a 9V battery. No I dont have the capacitor bypassing . Do I need two capacitors, both from + and GND?
To Hero999 - I found this on a Patent circuit , so I give a try, and it work...well beside the hum.

If you're using a battery, then you only need the 100 nF.

The oscillator has a 10M resistor and a 1 nF capacitor as the timing components.

This means a time constant of 10M * 1 n = 0.01 second.

Thus its frequency will be < 100 Hz which would account for the hum.

As Hero said, it is an odd circuit.
 
If you're using a battery, then you only need the 100 nF.

The oscillator has a 10M resistor and a 1 nF capacitor as the timing components.

This means a time constant of 10M * 1 n = 0.01 second.

Thus its frequency will be < 100 Hz which would account for the hum.

As Hero said, it is an odd circuit.

I add the capacitor, hum still there, no difference. .....can I raise the frequency (timming)?...what will be the values to eliminate the hum?

Thanks
 
I add the capacitor, hum still there, no difference. .....can I raise the frequency (timming)?...what will be the values to eliminate the hum?

Thanks

I did not expect the 100 nF would stop the hum, it is necessary with logic circuits as a precaution against instability.

If you read what I said above I wrote
"Thus its frequency will be < 100 Hz which would account for the hum"

I don't know why yhis circuit is supposed to create a noise. It is simply a low frequency oscillator followed by 2 CMOS amplifiers.
 
The first stage is configured as an oscillator

Are you sure?

Where's the feedback?

There isn't any unless it's poorly assembled and parasitics are causing oscillation.

Some types of ceramic capacitors are piezoelectric and will act like a microphone picking up acoustic noise.
 
Are you sure? Yes, this is an oscillator config I've used many times. Normally I use a Schmitt Trigger package such as the 71C14.

Where's the feedback? Via the 10 M resistor.

There isn't any unless it's poorly assembled and parasitics are causing oscillation.

Some types of ceramic capacitors are piezoelectric and will act like a microphone picking up acoustic noise.

The attachment shows an example of one of these oscillators.

They are also mentioned in the National Semiconductor Data Book (that I was given many years ago) together with the maths necessary to calculate the frequency of oscillation. I can scan a page or two if you wish.
 

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No, it isn't an oscillator, it's a linear amplifier.

I suggest you compare the two circuits.

Hint: note the difference between a Schmitt trigger and a standard NOT gate.
 
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I know the difference between a Schmitt trigger and an inverter.

But my recollection is that I've seen oscillator circuits where they have used an inverter in this way.

Personally, I would use a Schmitt as the threshold levels are defined and they have regeneration.
 
A normal inverter can't be used as an oscillator on its own, there needs to be two or more stages.

A normal inverter will go into the linear region when a resistor is connected between the input and output and stabilise at roughly half the supply voltage.

A Schmitt trigger has no stable state so will oscillate if a resistor is connected between the output and input.

To build an oscillator with the CD4069, you need to use two gates.

This circuit is not an oscillator, it's a linear amplifier, the idea seems to be to amplify the noise generated by the first stage 100 times but it doesn't seem to work because the ambient 50/60Hz mains hum is much stronger than the noise generated inside the IC.
 
I did a Google search for 4069 oscillator and a host of results appeared.

I could not find one as in th OPs circuit, but there are single inverter LC & Crystal oscillators. I've attached an example.

However, I think you're right about doing it with a single inverter as in his circuit because I can't see how you can get 180 degrees phase shift with a single RC.

Its just that I have a vague recollection that I've seen it done.
 

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Yes, it's possible to use a single gate with an LC oscillator or crystal, I didn't mean to suggest otherwise.

Yes, you're right, it's not possible to make a simple RC oscillator with a single gate.

The only way I'm aware of is by using three resistors and capacitors but it looks nothing like the circuit with the Schmitt trigger.
 

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Yes, it's possible to use a single gate with an LC oscillator or crystal, I didn't mean to suggest otherwise. I did not think you did.

Yes, you're right, it's not possible to make a simple RC oscillator with a single gate.

The only way I'm aware of is by using three resistors and capacitors but it looks nothing like the circuit with the Schmitt trigger.
He said he is running it from a battery.

I find it difficult to believe that he is picking up mains hum unless his prototype has long wires.

Given that he has not posted a photo of the prototype, we are left to guess.
 
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