Audio circuit problem - help needed

[Nirodha]

Audio circuit problem

Hello,

I have a circuit that uses a phototransistor to convert a light signal into an electrical signal. I amplify the voltage of the signal with another transistor. The circuit works when plugged into a laptop recorder, but when I replace the laptop with a simple 9V speaker/amplifier from radioshack, the output vanishes.

Do I need to convert my output to AC, or do I simply need to amplify the current by some amount to drive the speaker?

Thanks in advance.

 

[IanP]

Re: Audio circuit problem

It looks like you need to boost the audio signal a little bit ..
Goto this site:
**broken link removed**
Find the pre-amplifier circuit (also attached) and change the gain to, say, 5 ..

Av = (R4+R5)/R4 (on the cartoon R4->100Ω, R5->10kΩ)

Rgds,
IanP