A) Allong with the TV sound, it blends in the strongest AM station in
town. The amplifer module I bought just has 5 unshielded wires
coming out of it, and for the input, I used 20 inches of lamp cord
connnected to a 1/8" phone plug, which plugged into the earphone jack
of the tv. I guess the fix most likely to work is to replace the
lamp cord with co-axial shielded cable. Right?
Excellent first step... and the Kemo data sheet for this amp
specifically says that the input cable must be screened.
If you've got AM incursion, you should also try to "choke" the wires
coming into, and out of the amplifier. You can get small "clamp-on"
ferrite RFI blockers - they're similar to the tubular ferrite cores
that you find on many USB and video cables, but they come in two parts
in a plastic shell so you can clamp them onto an existing cable. Use
one on the input cable, one on the power cable, and one on each
speaker cable... this should keep the AM signal out of the amp.
B) It's probalby much too loud. I have to turn the tv volume down
from a maximum of 50 to about 15. Then let it get amplifed again by
the amp. I'm figuring the TV output has less distorition, and that
using it at low volume which then gets amped by this thing introduces
distortion. (Though I caouldn't tell because the AM radio was too much
of a distraction.)
The remedy for this seems to be to change wall warts. Right now I'm
using a 12VDC, 500mA adapter, which I chose mostly because it was the
first I saw in my box that had the end, the tip, cut off already.
The spec says it can use 4.5 to 12VDC
Reducing the voltage will probably reduce the *maximum* volume (before
it distorts) but probably not reduce the volume at any specific TV
volume setting (that is, it won't reduce the amplifier's gain).
Yeah... I just looked at Kemo's web page and it says that this amp has
an input sensitivity of " 80 mV". That's not much voltage at all.
Your TV set is almost certainly "overdriving" the input with too much
voltage, and could be forcing it into distortion quite easily.
Kemo's data sheet shows the use of a 10k potentiometer (presumably an
"audio taper" type) as a volume control. I'd suggest that you get one
(Radio Shack or similar) and wire one up as the data sheet shows...
this will let you adjust the gain. See
http://www.kemo-electronic.de/datasheets/m031n.pdf
I paid no attention to polarity, since it's a monaural output, but
when I put in a shielded input, I could make sure that the shield is
conected to what the instructions say is the ground, if it matters???
Yes. Do as they say.
Unlike their drawing, I don't have the pot wired into the input,
because the TV is 9 feet away from the bathtub. Rather it's in the
wires that go to the speakers, from a 1930's record player, mounted
above the tub (for the last 30 years.) .
You should have a pot (or a simple two-resistor fixed attenuator) in
the input circuit, so that you don't overdrive the amplifier and force
it into distortion. You don't need to remove the pot you have placed
in the speaker wiring... just add a 10k pot as the data sheet says you
should do, use this to "turn down" the amp's sensitivity to the point
where it's acceptable, and leave this pot at that setting.
--
Dave Platt AE6EO
Friends of Jade Warrior home page:
http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!