my amplified ear wont work!

[pil]

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.

 

[Zorknob]

"pil" <pil@webmail.co.za> wrote in message news:<l7OdnTZVlpD-um7d4p2dnA@is.co.za>...

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.

You probably have inadequate supply voltage for the microphone you're
using. You need a microphone that'll work at ~1v. Beyond that, the
usual stuff: check your wiring, etc. etc.

The dashed line indicates a mechanical connection, in this case it
shows that the on/off switch and volume control are are a single unit
where you turn the volume down until you hit a click stop, then
turning it further shuts power off.

Obviously you can do this with the volume control separate from the
power switch.

 

[Andrew Holme]

"pil" <pil@webmail.co.za> wrote in message news:<l7OdnTZVlpD-um7d4p2dnA@is.co.za>...

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.

 

[Sam B.]

"pil" <pil@webmail.co.za> wrote in message news:<l7OdnTZVlpD-um7d4p2dnA@is.co.za>...

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.

Well, the noise tells you that your headphones are working, and that
you are getting some amplification of (possibly) transistor noise.

But if you mean that you used a true "condensor mic", don't those
require a high impedance input stage, like a FET? They may not work
at all with the bipolar stage that you are using. If you used a
regular electret mic, the microphone actually incorporates the FET in
with the element, if I remember correctly. But whatever you do, don't
clean them, unless you know that they are resistant to solvents. A
lot of them will be damaged when cleaned. Also, a lot of them are
quite sensitive to heat, soldering leads to the mic will destroy it,
unless you are quick, and use the proper amount of heat. Static
discharge can will also damage certain types. If everything else
looks good in the circuit, them just replace the mic. Before I did
this kind of thing for a living, I used to scavenge old cordless
telephones for the mic elements. Even regular corded phones will
have these as long as they are not very old. The local thrift stores
seem to have an endless supply of this kind of used stuff.

It's also possible that you may need to adjust your bias to the mic
(R1). But that's just a guess.

Best Regards,

Sam

 

[pil]

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" <ajholme@hotmail.com> wrote in message
news:966757eb.0407150510.3fb8ea57@posting.google.com...

"pil" <pil@webmail.co.za> wrote in message
news:<l7OdnTZVlpD-um7d4p2dnA@is.co.za>...
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.

 

[Rich Grise]

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" <ajholme@hotmail.com> wrote in message
"pil" <pil@webmail.co.za> 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

 

[Watson A.Name \"Watt Sun]

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]

 

[Soeren]

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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