Farnell E30/1 power supply, is it dual rail?

[RoboWanabe]

Sorry, my main goal is to use the circuit to amplify a sound so i can hear it on a pair of headphones. I was going to attempt it with only a bit of knowledge and a you-tube video ( who made it out to be a lot easier than it is).

I have now got the circuit working, i can see my voice on the oscilliscop and found out why i was getting -1v drop on my oscilliscope, it was because i had tied the gnd on my power-supply to the negative i'm not sure why this caused it though?.

Also my output is really fuzzy, how can i clean up the signal?

Sorry i thought this one didn't send

 

[RoboWanabe]

Ow sorry, my main goal was to make a circuit which could take a small microphone signal and amplify it so i could listen with some headphones ( This was from a you-tube video, which made it out to be easier then it is ).
I've now got distracted from the project its self and i'm just interested about learning about op-amps.

I've got my old sine wave oscillator out to do some test's. What do i need to know in order to select the AC coupling capacitor on the Input? i think that's what its called!!. Is the resistor and capacitor on the input a kind of RC circuit? or filter?

thanks

 

[audioguru]

I'm not sure how to find out the impedance of the head phones, is there anyway i can test this at home?

The impedance is almost the same as its resistance. All half-decent headphones have a detailed datasheet available. I have some Kenwood on-the-ear headphones that came with a CD player. The headphones are rated at 16 ohms (per earphone). My multimeter measures 17.3 ohms for each earphone. Use a multimeter to measure the resistance of your headphones.

Sorry, my main goal is to use the circuit to amplify a sound so i can hear it on a pair of headphones. I was going to attempt it with only a bit of knowledge and a you-tube video ( who made it out to be a lot easier than it is).

I hope it wasn't an "Instructable". Many Instructables are completely wrong. Some are made by kids who are only 10 years old and they know NOTHING about electronics.

I have now got the circuit working, i can see my voice on the oscilliscop and found out why i was getting -1v drop on my oscilliscope, it was because i had tied the gnd on my power-supply to the negative.

We think the gnd of the power supply is not connected to its circuit.

Also my output is really fuzzy, how can i clean up the signal?

If you built the circuit on a solderless breadboard with jumper wires all over the place then the high capacitance between the wire and rows of contacts cause the circuit to oscillate at a high frequency and to pickup AM radio signals and mains hum from the air.
A compact printed circuit board should be used and the input from the microphone should be connected with shielded audio cable.
Fuzzy sound can be caused by distortion which is created when the input signal level or voltage gain of the circuit is too high.

Are you powering the circuit from two 9V batteries with their junction connected to the circuit's gnd?
Did you connect a capacitor (3.3uF to 10uF) in series with the 1k resistor and gnd?

 

[audioguru]

The amplifier has a 100k resistor to gnd on its input. If you want a coupling capacitor to pass frequencies down to about 30Hz then the capacitor value is calculated with 1 divided by (2 x pi x R x C). I calculated a capacitor value of 0.05uF but a 0.1uF (100nF) film capacitor can be used. Remove the electret mic and the 5k resistor that powers it. The output will clip when the input signal is about 0.07V peak.

 

[RoboWanabe]

Thanks for your help Audio Guru , I will use this conversation has a reference, thank you.

However i think my oscilliscope is broke. I'm using an old phillips PM 3215, I think it uses an old electron beam inside. The signal only shows up on one half the screen and when i change the x position it goes into a ball of light in the center of the screen. Also the ground refrence keeps changing, I think, becuase i keep having to zero it and then set it again?

I have recently been doing my work in the garage and maybe the harsh conditions have broke it.

I can't real'y do any more digging without an oscilloscope .

Has any one experienced this before?
Is it worth taking it apart? maybe one of the magnetic plates, which direct the beam has got stuck!?
Do you know where i can buy a cheap but modern oscilloscope?

Thank you

 

[audioguru]

The oscilloscope has a cathode ray tube with the electro-static plates inside it. When a plate is positive then it attracts the negative beam of electrons towards it.
A problem in its vertical amplifier could cause the ground reference voltage to change the position of the trace on the screen.
A problem in its horizontal amplifier or its scanning oscillator can cutoff the left side or the right side of its trace on the screen.

Maybe there is computer software available to use your sound card for a 'scope.