that really helped alot. Pinouts of my transisors are correct because I
measured their HFE's on my DMM.

One question, about the mains hum - I am using a 1,5V cell. Will I still
hear the hum if I use this cell instead of using a mains PSU? And if so,
why?



"Andrew Holme" wrote in message
om...
"pil" wrote in message
...
I built the amplified ear found at
http://www.electronics-lab.com/projects/audio/023/

I do get some noise out of it that sounds a lot like one of these
listening
devices but thats it. No sounds are picked up by the mic.

What could be wrong. All trannies have hfe's of 140-180.

1. You should hear mains hum (buzz) if you touch the input with your
finger.

2. Check orientation of semiconductors.

3. Test the diode.

4. Test the diode junctions in the transistors (BE and BC).

5. Check gain using your multimeter by measuring resistance between C
and E whilst applying a wet finger between C and B.

6. Measure voltages at all circuit nodes and post to
sci.electronics.design

The semiconductors must be removed from the circuit for 3, 4 and 5.

Test 4+5 will also confirm that you have the correct device pinouts.