RE: Howzat work then?

[Kevin Hawkins <tivo@xxxxxxx>]

With a decent psu you <should> be able to get exactly the=20
same quality as a battery. They are always invaluable anyway. M*****s=20
did d  a very useful multi regulated unit once (probably when they=20
were still an electronics store rather than a toy shop).
Are there any other wires attached t  the transmitter that go=20
t  other electrical devices eg your audio sources - there is a=20
possibility of earth problems. With any transmitter good earthing is=20
essential. A wall wart should have a totally 'floating' output that=20
needs to be brought t  chassis earth on the transmitter, as probably=20
do all other inputs. If the transmitter becomes unstable you would=20
see nothing.
. RF pickup is als  potentially a problem but usually only at=20
high power levels. A ferrite core on each cable will help fix this.=20
It may all get better when it is in the metal (grounded) box.
I don't know how the frequency is fixed in the transmitter -=20
if it is crystal controlled or derived from a synthesiser then the=20
input voltage should have little effect however other methods may=20
well cause frequency instability if the supplied voltage varies at=20
all eg at 50Hz.
I assume als  as you say it takes a wide ranging voltage=20
input that there is on board stabilisation of the supply so I am=20
surprised you are seeing this problem. It would imply that the=20
troughs in the wallwart 12V supply voltage are dropping below the=20
regulators threshold yet it works fine on a 9V battery. Unregulated=20
wall warts tend to output way too much usually and rely on the=20
(known) load to reduce them t  roughly the right level. Maybe the=20
drawn power is too high for the wall wart. What is the current=20
consumption of the transmitter ? I assume the psu feed and the 9V=20
feed used the same wires ? (not bypassing the regulator for the=20
battery usage ?)

Kevin

>I think that's the answer - I just did some testing with various other
PSU=
's
>I had lying around, - one from a one-for-all IR repeater =3D same
result, =
one
>from an old Sony Discman, =3D well it sort of worked! - the audio
transmit=
s,
>but it is of a drastically lower quality than when running off the
battery=
.
>
>Does this mean the problem is due t  poor quality rectification of the
AC
>sinewave t  DC? - could the el-cheapo wallwarts be doing half-wave
>rectification only? If that's the answer, then presumably my Sony
Discman
>PSU must have been doing full-wave rectification, as the circuit works
whe=
n
>using this one, but it's a bit worrying that the audio quality was s 
poor=
,
>- is this likely t  occur with a "decent" PSU as well? - I'd
hate t  g  ou=
t
>& spend =A320 on a decent regulated PSU only t  have the same
problem!
>
>Paul G.
>
>
>
>>From: Mike Griffiths <mike@xxxxxxx>
>>Reply-To: ukha_d@xxxxxxx
>>To: "'ukha_d@xxxxxxx'" <ukha_d@xxxxxxx>
>>Subject: RE: [ukha_d] Howzat work then?
>>Date: Mon, 2 Jul 2001 09:43:28 +0100
>>
>>I think Keith has the answer then as it does say Regulated PSU
under
>>circuit
>>testing :-(
>>I must admit I would have pugged up a wallwart t o
>>
>>Mike
>>
>>Sent from Home
>>
>>-----Original Message-----
>>From: Paul Gordon [mailto:paul_gordon@xxxxxxx]
>>Sent: Mon 02 Jul 01 09:38
>>To: ukha_d@xxxxxxx
>>Subject: RE: [ukha_d] Howzat work then?
>>
>>  >Paul
>>  >Does the  wall-wart work anything else?
>>
>>Tests OK with the spare bulb from my Maglite.... (in fact I've got
a blin=
d
>>spot right in the middle of my vision 'cos it was s  bright!!!)
>>
>>  >What happens if you run it at 9v?
>>  >
>>
>>The same, - the LED on the PCB comes on as it should, so the
circuit has
>>power t  it, but ****-all is being transmitted...
>>
>>Paul G.
>>
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