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.

I used a condensor microphone taken from an old panasonic tape recorded. It
has a blue and a red wire. I also swopped them around. Nothing.

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

Also, what does the dashed line between C6 and SW1 in the circuit represent?
I don't have such a connection in my circuit.

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.

pil top-posted:

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?

You'll hear it when you touch the input point, because your body is
picking up the 60Hz power freq that's everywhere. Also, your circuit
itself could be acting as that antenna.


"Andrew Holme" wrote in message
"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.

--
Cheers!
Rich

pil wrote:

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?

I built that circuit, and played around with it trying to get the AVC to
work a bit better, but with little success. The bias on that stage is
very low, and may be part of the problem. As the input to the mic
changes, so does that bias, so it's difficult to tell what the votlage
should be. But with the input at minimum, the circuit should have
maximum gain.

Also, I used an earpiece out of a telephone handset instead of a
headphones. It's louder, and uses less battery current.

[snip]

Hi,


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.

Use the specified transistors, they have higher h_fe.


--
Regards,
Soeren

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