Re: Audio amplifier circuit does not work as expected

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


"Don Klipstein" <don@xxxxxxxxxxxxxx> wrote in message
news:slrnec86bt.kio.don@xxxxxxxxxxxxxxxxx
In article <44bc9eee$0$18927$e4fe514c@xxxxxxxxxxxxxxxxxxxxxxxx>, petrus
bitbyter wrote:

"David Harmon" <source@xxxxxxxxxx> schreef in bericht
news:455187bd.382701421@xxxxxxxxxxxxxxxxxxxxxxxxxx
On Mon, 17 Jul 2006 22:31:43 +0200 in sci.electronics.basics,
"petrus bitbyter" <pieterkraltlaatditweg@xxxxxxxxxxxxxxxxx> wrote,
Mm... Don't have the book just like many others so you'd better provide
a
copy of the design for serious conversation.

Schematic at http://i2.tinypic.com/20a4c2d.gif


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.

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.

<SNIP details of the 741>

- Don Klipstein (don@xxxxxxxxx)


.

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