[sdiy] SID 6581

[Tim Ressel]

Karl,

The hum and radio problem might me the same thing. I
take it this 'hum' is power line hum? Like 60Hz hum? 
It sounds like a high-impedance point on the board
that is licking up things out of the air. In the case
of the radio, RF can get into a circuit and be
detected (rectified) by the transistors in the IC.

I suggest a good inspection of your board. Look for
loose connections, cold solder joints, unsoldered
joints, that kind of thing. If you use sockets,
re-seat the ICs and check for damaged sockets.

One way to find a high-impedance point is to hold a
short wire in your fingers (no insulation, please) and
start touching points on your circuit. You'll know
when you hit a sensitive spot; the hum and/or radio
will increase in strength.

Sometimes the offending signals can be coming through
the power supply. Not likely with radio sigs, but if
you're near to a radio station, it is a possibility.
If it is supply related, then you have to attack. For
hum, beefier bypass caps on the supply should help.
For RF, try placing 100pf caps where the power supply
first comes onto the board. You can also try
sprinkling 100pf caps on the power supply rails around
the baord. In extreme cases, a ferrite bead or
inductor in series with the incoming power supply may
be needed.

If this all fails, I'll need to see a schematic to get
further ideas. Hope this helps!

--Tim

--- Karl Ekdahl <_nial_ at yahoo.com> wrote:
> Hello everyone, 
> 
> I've just built a paralell port controlled SID 6581
> using the schematics by Buchi, though i have some
> problems; 
> 
> Firstly it takes in radio sometimes :) Everything is
> grounded but i haven't connected the wall-ground to
> the ground in the powersupply since i'm using one of
> the AC lines as ground. Can i connect it to ground
> straight off, is it OK (i'm still lacking some basic
> knowledge i know)?
> 
> Second it drops notes while playing fast (i've done
> a
> simple vb controller program) and it doesn't seem to
> be my program.
> 
> Thirdly it takes like 30 seconds to start up and
> then
> goes "wroooooooom" for a couple of seconds.
> 
> Forth it hums. I have a ripple about 1-10mv in my
> 12v
> supply line though i thought this would be small
> enough to not make a difference.
> 
> thanks
> 
> /Karl
> 
>
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