Homemade, powered by small 13 vct transformer from an old boom box and LM317T regulator (ps seems capable of 14v clean power, easily). Sounds like it's picking up the nearest AM station, especially loud and clear when I touch the volume and gain control shafts. Touching the heat sink behind the 317 with a fingertip _quiets_ the interference, though.
Causes? Fixes? Thanks.
"Father Haskell"
** Lemme guess - you have the IC in a plastic box with no shielding of any kind ?Ideally, there needs to be a metal box that is connected to the negative supply, pin 4 of the IC plus the metal parts of any pots. Alternatively, connect the metal fames of each pot to the negative rail ( pin 4) and add a cap of about 2200pF across pins 2 and 4 to bypass radio frequency energy.
The volume pot wiper needs to be de-coupled from pin 2 by a series combination of a 4.7 kohm resistor and a cap of about 0.1 uF. This stops DC voltage from pin 2 appearing on the pot and helps with RF suppression.
.... Phil
The cause is simple rectification of the AM signal at the input to the amplifier. One method of reducing RF pickup is to insert bypass caps at the input(s) that form a low pass filter. A bypass cap from Pin 7 to ground will also help. Very long leads is a bad idea. A 0.1uf bypass between power (pin 6) and ground (pin 4) should help. I can't offer a more specific solution without seeing a schematic and photo of the construction method.
You might want to repost your question (with a link to the schematic and photo of your construction) to sci.electronics.design newsgroup which is better at offering design and construction suggestions.
any
Wooden box, open, power supply board and transformer laid on workbench and connected with jumpers. Testing that everything works before final assembly.
aEasily fixed by covering the inside of the box with foil duct tape.
ps DC
"Father Haskell" "Phil Allison"
Wooden box, open, power supply board and transformer laid on workbench and connected with jumpers.
** RFI heaven.Pun intended......
Easily fixed by covering the inside of the box with foil duct tape.
** Maybe so, but making reliable electrical connection to such foil is not so easy.Nuts, bolts and solder lugs are essential.
..... Phil
put it in a die case box and use some chokes on the inputs.
Jamie
That would be a die Cast, not case box.
Jamie
Heck, a plain old Bud mini-box will do.
any
e ,dd
y.
t 8 x 1 sheet metal screw with wire end bent 180 and clamped between two washers. sSo you control volume by controlling input?
"Father Haskell" "Phil Allison" > "Father Haskell"
8 x 1 sheet metal screw with wire end bent 180 and clamped between two washers.So you control volume by controlling input?
** You after help is just like picking fights ?Cos you are being damn rude.
.... Phil
f
ive
ly,
not
ops
.Or a bit weak with electronics and thankful for everyone's advice, including yours. No reason to get your hackles up.
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