Well not so much of a problem but what i am trying to do is have a little filter fun, i have posted the circuit i am playing with, it is the filter section from a colour organ i found online consisting of 3 channels (filters) bass, middle and treble, i have only built the middle filter and replaced R8 with a 10K pot set to around 5K, the circuit works, as i turn the pot the output varies as the filter changes which is what i wanted but why do i only have the top half of the waveform appearing at the output?

My input signal into R7 is 1kHz at 1.75V AC coupled and is seen in the yellow trace, my output is the purple trace.

I have got so far and now i'm stuck, i was expecting the full sinewave on the output, the collector of Q3

 

i was expecting the full sinewave on the output, the collector of Q3

If your goal is to see a sinewave on the collector, then the transistor needs to be turned 1/2 way on with no signal.
Add a resistor that pulls down on the base to turn on the transistor. The bottom end of the resistor can go to ground, or it could just be B-C of the transistor.

 

If your goal is to see a sinewave on the collector, then the transistor needs to be turned 1/2 way on with no signal.
Add a resistor that pulls down on the base to turn on the transistor. The bottom end of the resistor can go to ground, or it could just be B-C of the transistor.
View attachment 367076

All that did was increase my current consumption and my output waveform disappeared altogether with a 4K7 resistor.

 

It is just a colour organ. The LED should be lit as the amplitude of the sound signal increases. You don’t need the negative half of the signal.

 

It is just a colour organ. The LED should be lit as the amplitude of the sound signal increases. You don’t need the negative half of the signal.

Thanks....yes that is what is happening, i will accept my circuit is working.

 

I've just been giving that circuit some thought and i can now see why only the top portion of the signal is needed....the proverbial penny has dropped

I should think about the theory behind my circuits before bothering you people....sorry for being dumb

 

All that did was increase my current consumption and my output waveform disappeared altogether with a 4K7 resistor.

Not 4K7 but, maybe 22k or 33k or 47k.

 

The transistor is biased as a Class-C amplifier. That is all that is needed. It is more efficient and runs cooler than Class A, AB, and B.

 

Also, you don’t need to reproduce the audio signal faithfully. What you need is the amplitude envelope.