[sdiy] filter for noisy DC power supply

[crystal]

often just a few large caps (100uF) across positive and ground will do 
the trick. (not always!)



On 10/23/2014 1:41 AM, Steve Lenham wrote:
> On 22/10/2014 10:50, David Griffith wrote:
>>
>> My gizmo is powered by an ordinary wall-wart power supply.  This supply
>> is giving a hum to the output.  There is no hum when powered by a
>> battery. Would someone please point me in the right direction of some
>> simple filter circuits to clean up the hum?
>
> I personally wouldn't assume that there is a ground fault, etc, etc - 
> some devices (esp. cheap ones) simply don't have very good power 
> supply rejection. Example: the EDP Wasp synth uses an LM386 amp IC run 
> directly from the DC power input voltage to drive the speaker and H/P 
> output. With a regulated PSU all is well, but with a "normal" 
> unregulated adaptor...hummmmmmmmmmmm. However, the line output is 
> powered from a regulated +5V and has no such problem.
>
> My favourite simple hum rejector is as follows. It will not cope with 
> massive levels of input ripple (around 1Vp-p max) but, on the plus 
> side, drops very little voltage. If you need to cope with more hum 
> then you need to look at proper regulators, but must then address the 
> issue of how many volts you can afford to lose.
>
> Connect an appropriately-rated NPN transistor inline with the positive 
> supply line (input to collector, output to emitter). Connect a 1K0 
> resistor from collector to base and a 100uF capacitor from base to 
> ground (neither of these values is hard and fast - they can be adapted 
> to what is available). Done!
>
> HTH,
>
> Steve L.
> Benden Sound Technology
>
>
>
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>


-- 
http://www.gardenofsensualdelight.com
http://soundcloud.com/user3694125