DR-55 Noise Generator - not wanted hum noise

[prprog]

I built the noise section of the DR-55 drum machine. It is generating noise (white noise which is OK) along a hum sound which I don't understand where it comes from since I am using batteries (6v) . I am connecting the output to a set of computer speakers that are AC powered (could this be the source of the hum noise?). How do I get rid of the hum noise? Also can you please tell me what is a 22/10 capacitor ? I try various values in the circuit but none get rid of the hum noise.


Thanks

 

[ericgibbs]

I built the noise section of the DR-55 drum machine. It is generating noise (white noise which is OK) along a hum sound which I don't understand where it comes from since I am using batteries (6v) . I am connecting the output to a set of computer speakers that are AC powered (could this be the source of the hum noise?). How do I get rid of the hum noise? Also can you please tell me what is a 22/10 capacitor ? I try various values in the circuit but none get rid of the hum noise.

hi
A 22/10 is a 22uF at 10V working voltage

How is the Noise Gen connected to the main amplifier and which point on the main amp ground/0V line is the Noise Gen battery -V connected.

It sounds like a 'ground loop' problem.

 

[prprog]

Thanks a lot for the interest - I connect the negative of the battery to the negative side of the plug . The output is the tip of the connector to the amp.

 

[Hero999]

I can't think what to suggest.

Try AC coupling the noise generator to the sound card's input?

 

[audioguru]

If there is hum when the battery is disconnected from the noise circuit then the cable from it to the amplifier has poor shielding.
If the noise circuit is built on a breadboard then long wires on it are antennas for picking up mains hum.
Maybe the ground connection in the cable from the circuit to the amplifier is broken.

 

[prprog]

If there is hum when the battery is disconnected from the noise circuit then the cable from it to the amplifier has poor shielding.
If the noise circuit is built on a breadboard then long wires on it are antennas for picking up mains hum.
Maybe the ground connection in the cable from the circuit to the amplifier is broken.

Hum is not present when the battery is disconnected. It occurs when the circuit is power up. Yes it is on a breadboard the only long cables are the Amplifier/Speaker cables. White Noise and hum are generated at the same time. If I touch both ends of the capacitor the hum is reduce considerably....Maybe a resistor in parallel with the capacitor will fix it...but anyway why does it produce hum?

 

[audioguru]

If the circuit is made on a compact pcb or stripboard then it won't pickup the mains hum that the wiring of the breadboard circuit picks up.
Each row of contacts on a breadboard and each wire are antennas that pickup mains hum.

 

[prprog]

If the circuit is made on a compact pcb or stripboard then it won't pickup the mains hum that the wiring of the breadboard circuit picks up.
Each row of contacts on a breadboard and each wire are antennas that pickup mains hum.

That quite interesting. Is there a way to shield the circuit from the mains? I have not finished it yet.

 

[Nigel Goodwin]

Place it in a screened metal box, with the box connected to the ground rail.

 

[mneary]

If the breadboard has a metal base, connect that to circuit ground or 0V. It may help a little (or a lot).

 

[prprog]

ok. I don't have the hum noise problem. Thanks a lot. Now....how do I buit an amplifier suitable for this circuit. I will like to built one using an LM324 OpAmp. Any suggestion?

 

[audioguru]

An LM324 has very poor audio performance. It is noisy (hiss) has up to 3% of crossover distortion and cuts off high audio frequencies above a few kHz.
It is an opamp, not a power amp so its minimum load is 2k ohms.

If you want to drive a speaker then a power amplifier IC is selected by how much power you want, what is the impedance of the speaker and how many volts and amps are available from the power supply.

 

[prprog]

An LM324 has very poor audio performance. It is noisy (hiss) has up to 3% of crossover distortion and cuts off high audio frequencies above a few kHz.
It is an opamp, not a power amp so its minimum load is 2k ohms.

If you want to drive a speaker then a power amplifier IC is selected by how much power you want, what is the impedance of the speaker and how many volts and amps are available from the power supply.

Actually is to increase the output of the Noise circuit. Then...I will connect the Noise Circuit + LM324 output to an amplifier....since this is for a noise circuit then noisy (hiss) should not be a problem ...I guest....again any LM324 circuit I should considered? (I already have a couple of LM324 in my components tray)

 

[audioguru]

Don't you care that the LM324 cuts high sound frequencies?

 

[prprog]

Don't you care that the LM324 cuts high sound frequencies?

...can you give me more details.?...I want to increase the ouput volume of the noise generator...How will the LM324 "cut" of the high sound frequencies will affect the ouput? It will still be "noise" ...but I will guest filter somehow? Right?

Thanks

 

[audioguru]

The lousy old LM324 quad and the LM358 dual low power opamps have a poor high frequency response. Their datasheets don't even show how bad they are at full output like all other opamps, it is shown when the output is only 13.5V p-p when its max frequency is only 5kHz. We can hear to 20kHz and most other half-decent opamps go up to 100kHz.

TL07x audio opamps are low noise, low distortion and have a full output response to 100kHz. They are also inexpensive.

Noise that has the high audio frequencies cut sounds muffled like a telephone or like an AM radio. The high audio frequency hiss sound of noise is supposed to sound "sizzling" up to 20kHz.