Taking the 'hummm' out of a circuit

[anonymous]

Im working on a power supply for some musical bits. Unfortunately its
producing a great deal of "hum" in the circuit. Is there any way to filter
out residual AC in the DC line?

What I have:

+18V (wall wart) ---->3500uF
(electrolytic) ---->.22uF--->7809--->.1uF--->out
|
| |
ground
ground ground

the ground is common between the wall wart and all components. There are 4
7809s in parallel at the output.

 

[Bill Bowden]

"anonymous" <anonymous@catfarm.com> wrote in message news:<hkZ9d.212267$MQ5.19587@attbi_s52>...

Im working on a power supply for some musical bits. Unfortunately its
producing a great deal of "hum" in the circuit. Is there any way to filter
out residual AC in the DC line?

What I have:

+18V (wall wart) ---->3500uF
(electrolytic) ---->.22uF--->7809--->.1uF--->out
|
| |
ground
ground ground

the ground is common between the wall wart and all components. There are 4
7809s in parallel at the output.

Looks like you are trying to get too much from the wall wart.
What is wall wart current rating at 18 volts and how much is
the load current?

-Bill

 

[tempus fugit]

So your amp is also plugged into the same power strip?


"anonymous" <anonymous@catfarm.com> wrote in message
news:lCcad.215994$MQ5.49226@attbi_s52...

"tempus fugit" <toccata@no.spam.ciaccess.com> wrote in message
news:fU%9d.336$57.170@fe51.usenetserver.com...
Is this to power guitar effects by any chance? If your components are
working properly, you might want to look into the possibility of a
ground
loop somewhere. For instance, if you have your amp plugged in one
outlet,
and your effects power supply in another one on the other side of the
room,
you're almost guaranteed to create a ground loop. Try plugging all the
gear
your plugging into into one outlet or power bar and see if the hum goes
away. Alternately, try unplugging (from the wall) each piece of
equipment
one at a time to see if the hum goes away. If it does, you've found the
problem.



yes these are guitar effects. they are all plugged into the same power
strip. they work properly (normally).

 

[anonymous]

yes.

"tempus fugit" <toccata@no.spam.ciaccess.com> wrote in message
news:f8Gad.588$57.101@fe51.usenetserver.com...

So your amp is also plugged into the same power strip?

 

[anonymous]

"under buffered"? can you be more specific?


"peterken" <peter273@hotmail.com> wrote in message
news:YxUad.276795$ih6.14215215@phobos.telenet-ops.be...

simple
as far as I see the output of the regulator is totally under-buffered
try putting an extra elco at the output of the reg, say 2200u something

 

[Bill Bowden]

"anonymous" <anonymous@catfarm.com> wrote in message news:<tDcad.215995$MQ5.98694@attbi_s52>...

Looks like you are trying to get too much from the wall wart.
What is wall wart current rating at 18 volts and how much is
the load current?

-Bill

The wall wart puts out 400 mA. For my test I was drawing ~5mA.

Well, if the input is above 12 volts DC and the load is only 5mA,
the only thing I can think of is it may be oscillating.
Use the DMM to measure AC voltage at the output. It should
be very low at 5 to 10 mV. You could try a small capacitor on the
output, maybe 1-10 uF. Maybe that will help.

-Bill

 

[tempus fugit]

400 mA should be plenty for 4 effects - most use way less than 100mA (more
like 10-20).


"anonymous" <anonymous@catfarm.com> wrote in message
news:TN2bd.460950$8_6.164900@attbi_s04...

Above I assume your wall wart is capable of delivering enough current,
but
as a side assumption :
As far as I seem to read, all 4 individual regs take appprox 400mA, thus
1.6A together
Is your wall wart capable of handling this ?
If not, input voltage will drop until a level where input ripple (lower
level) drops below 12V , thus making it impossible of regulating using a
7809



Each regulator requires 400mA just to function *at all*? I didn't know
this.
My wall wart only puts out 400mA. Where would I look up this information?
(more specifically - where did you get it from?)