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

Tim Gorman
 

Vince,

You missed the point. If you wire the tda2822 to both the tip and the
ring and then plug in a mono headphone you *will*, in almost every
case, short the output of the tda2822 to ground via the ring lead.

You will melt the tda2822 sooner or later by doing so - plus get
nothing in the headphone.

tim ab0wr

On Thu, 1 Mar 2018 23:22:48 -0500
"Vince Vielhaber" <vev@...> wrote:

Ever cut the connector off of a pair of them and try to wire on a new
one? The point, that you obviously missed, wasn't that headphones
are cheap, it's that there's no reason to do what Tim was suggesting
and that you can wire up to the tip and ring and have it work with
both stereo and mono headphones.

Vince.



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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.

Vince.


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" <jgaffke=yahoo.com@groups.io
<mailto:yahoo.com@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.



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