Someone that already have armed and made work the audio amplifier circuit of the book Getting Started in Electronics by Forrest Mims , p.
Already I have made the following revisions:
After this now I hear a strong =A1hummm=A1 but not sounds from the microphone.
Is this what I should hear or what I should hear? Something missing? Thanks in advance for any comment
Mm... Don't have the book just like many others so you'd better provide a copy of the design for serious conversation. Meanwhile, the hum may be
50/100Hz or 60/120Hz from the power supply when not carfully smoothed. Other possibilities are lang power lines, especially when not decoupled correctly, long (unshielded) signal lines, bad solder joints, incorrect grounding and may be some other things I forgot. If you touch the input with a finger the hum should increase, otherwise the amplifier does not work at all. May indicate an open in the signal path.petrus bitbyter
Well he did say what book it was from. And this is his second thread on it, it would have been better if he'd just kept to the same thread, and Forest Mims himself made a visit to the newsgroup to say there were no errors in the schematic in the book.
Michael
Hmm, lets see, i don't think i have ESP.. i just can't seem to see how it would or would not work!. maybe if you would supply us a schematic of what your using it could help greatly!
On Mon, 17 Jul 2006 22:31:43 +0200 in sci.electronics.basics, "petrus bitbyter" wrote,
Schematic at
"David Harmon" schreef in bericht news: snipped-for-privacy@news.west.earthlink.net...
Well, no big problems in the design. Are the +9V and the -9V equal? When using 9V batteries, the +9V will have a heavy load compared with the -9V. A difference of some tenths of a volt may rule out the 386. (The offset of the 741 may do the same when amplification is set too high.) You can check by measuring the output of the 741. The DC voltage should be around 0V. +/- 0.1V may be acceptable, +/- 0.5V is fatal. Is the microphone a dynamic type? Electret micophones may work well but the ones I know, require to be powered. Once more, you should hear the mains hum when touching in input of the amplifier (both sides of the input capacitor.) You should hear some hum also when touching the input (pin 3) of the 386. If not, disconnect the volume potmeter from the output of the 741. If still no hum, your 386 fails. (Blown 386, wrong or defective components, wrong wiring, bad solder joints etc.)
petrus bitbyter
Jamie wrote in news:53Wug.90$ snipped-for-privacy@fe02.lga:
From what I can see, the problem is operator error...
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Make sure you take ground from the junction of the two batteries. And make sure it is a dynamic mike - an electret requires power and the circuit does not provide it.
Ed
One thing that I would like to add: The 386 is an audio amplifier IC that I have found typically used with single (as opposed to split) power supplies and typically used with lower voltages of 6-12 volts. In a circuit with a 386 and +/- 9V split supply, make sure the 386 is only getting the full 18V if the circuit designer intended that. The circuit may intend the 386 to get 9V and other parts of the circuit to get
18V. Also, in a circuit with +/- 9V split supply and a 386 getting 9V from one but not both of the 9V (positive and negative) supply rails, expect highly unequal current consumption from the positive and negative supplies. If these are 9V batteries, expect high probability of one but not both to have a good chance of bearing the brunt of powering the 386 amplifier IC, meaning that the two 9V batteries have a faior chance of being drained highly unequally. I would check that both 9V batteries are good and are up to supplying at least a couple tenths of an amp.- Don Klipstein ( snipped-for-privacy@misty.com)
I see two problems with the design. The first is that the only DC connection I see between the +9 V, -9 V and ground is through the 386 amp. The ground should be connected to the junction of the two nine volt batteries.
The second problem I see is that output of the 741 is referenced to 0 volts because the noninverting input is tied to ground. This means that the output will go above and below 0 volts. Since that output is DC coupled to the 386 amp, the input will be dropping below the negative supply voltage (0 VDC) and will cause severe distortion.
jgreimer
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