Hi Bob,
Finally, I got it !.
It is related with the RC network connected between the output pin 5 and
ground, required to keep the amplifier stable at high frequencies at
different loads, as you mention on your previous post.
I checked the RC network and I even installed a new one: same
Hi Paco,
Great detective work, glad to read that you tamed the beast. Hi Hi
I am in the process of trying to model the LM386 circuits using LT spice
( program free from Linear Technologies web site SWCAD III) to try to
understand the feedback mechanism that results in these amplifier's
Paco,
Thanks for posting the solution to this problem. I feel sure there are
a number of us who read about it with interest but did not comment.
Good to know the answer to the problem!!
73 de dave
ab9ca
Francisco Barros wrote:
Hi Bob,
Finally, I got it !.
It is related with the RC
Hi Dave,
Thanks to you.
IHope Bob can tell us, with the modeling of the LM386, why this strange
behaviour.
From the knowledge point of view, the technique try and error is not the
best way, we would like to know more... .
Now, my KX1, at the LM386's speaker output, pin 5, has the original RC
Hi Bob,
Hate to say it, but it has the same behaviour with the new value of 4.7k for
R21: the audio signal shows the parasitic oscillation just on the negative
peaks, even with a 10 uV RF level.
In any case, many thanks !.
73,
Paco
Hi Paco,
Sorry to read that it did not work for you.
LM386 amplifiers can do strange things when over driven. There is a lot
of available gain.
If the amplifier is operating properly, the Idle DC voltage with no audio
signal on the output pin 5 should be half of the DC voltage measured on
the
Paco,
That certainly sounds like the strong station is overdriving the LM386,
and that the overdrive point changes depending on the load to the
LM386. Try reducing the RF gain to see if the condition is improved.
The LM386 characteristics are different than the LM380 AF Amp used in
the K2,
Hi Don
First of all, thanks for your answer.
Well, I have checked it also with a signal generator: the output signal at
R3 (AF Gain) R5 junction is always a clean 2,2 Vpp 600 Hz tone, with RF
levels of 10 uV till 500 uV, except at close or maximum volumen. I this
case, even with a 10 uV RF
Try changing the value of R21 from 2.7K to 4.7K
I had a similar problem with load sensitive parasitic oscillation of the
LM386 with a Norcal 40
When this happens it can block the receive signal because of the agc
action.
The (high frequency rolloff) feedback may be causing enough phase shift
to
Hi to all,
The scope shows a superimposed high frequency oscillation just on the
negative peaks of the audio signal.
It produces a distorted and annoying audio when the signal peaks, specially
when listening a loud station on the external speaker.
This happens when the volume is close to or at
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