Re: B40 LM386 and µB TDA2822 and that 470µF Cap

Thomas Sharka

On Thursday, March 1, 2018 11:12 PM, Vince Vielhaber <vev@...> wrote:

So you're saying that if I want to use a pair of stereo headphones I
have around here I should cut the connector off of it and wire it up to
a mono plug?  Yeah...  I'll get right on that.


On 03/01/2018 10:49 PM, Tim Gorman wrote:
> If you insert a mono plug into a TRS jack the ring terminal of the
> jack is almost always shorted to ground (i.e. the sleeve). If you wire
> the output of the 2822 to both the tip and ring terminals and then
> insert a mono plug there simply isn't any doubt that you are probably
> going to short the output of the 2822 to ground. Bad things will
> happen.
> There is no reason to wire the output of the 2822 to both the tip and
> the ring terminals. If you have a stereo headset then wire both headset
> leads to tip of the plug and only wire up the tip lead on the socket.
> Then if someone inadvertently plugs in a mono plug you won't short the
> output of the 2822 to ground.
> I agree that the large charging current going into the 470uf cap could
> stress the 2822, perhaps only causing a failure after a number of
> on/off cycles. That's something that would be hard to diagnose!
> I have modified my schematic to show using a 47uf cap being fed with a
> 1 amp fuse from the 2822. If I ever get a chance to actually finish up
> my ubitx it will be interesting to see if the 1 amp fuse is sufficient.
> tim ab0wr
> On Thu, 01 Mar 2018 15:39:50 -0800
> "Jerry Gaffke via Groups.Io" <> wrote:
>> And subsequent replies have suggested this may not be sufficient.
>> Some seem to fry when plugging something into the headphone jack even
>> if there is no short to ground involved. Or when powering up the rig.
>> Our best guess now is that there are significant currents involved
>> when that 470uF cap suddenly has to charge up to Vcc/2 And that some
>> clone TDA2822's may be weaker than mainline manufacturers.
>> On Thu, Mar 1, 2018 at 03:31 pm, Christopher Miller wrote:
>>> One of the first replies suggested not wiring the ring, and using a
>>> mono to stereo adapter cable if stereo headphones are required.

  Michigan VHF Corp.

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