[sdiy] 'Measuring' PSU ripply without a scope [was: weird voltage regulator problem / question]

[Oren Leavitt]

Connect the PSU to a variac. Put a load on the PSU output and monitor it 
with the amp. Reduce the variac voltage slowly until ripple is heard. 
This should give an indicator of how much headroom you have.

I havn't tried this, but for the fun of it, assemble oscillators or 
other noisy circuits without the bypass capacitors. Using the amp, see 
how much noise you pick up off the power supply rails.
Then add in the bypass caps, and listen again.

- Oren

Seb Francis wrote:
> harrybissell wrote:
> 
>> The 9V should be steady. Measure the input to the regulator on AC
>> volts...
>> it should be a small number.  Usually these regulator need 3V more than
>> the output
>> voltage... minimum. You have only 5V... any AC ripple might make the
>> regulator
>> drop out.
>>
>> Solutions : Bigger filter cap, or higher input voltage (which makes
>> everything
>> HOTTER again :^). Recalculate the new power and temperature.
>>
>> If you have a scope, you can see the ripple voltage directly. If not,
>> you have
>> to rely on the meter and it is tough to know exactly how it will report
>> the
>> ripple (AC) voltage.
>>
>> This variation would usually be 60Hz or 120Hz... more an FM growl than
>> a warble, IMHO
>>  
>>
> 
> If you connect the PSU output via a DC blocking capacitor (e.g. 47uF 
> electrolytic) to an audio amplifier, you will be able to hear any ripple 
> (turn the volume up slowly, don't connect/disconnect with the volume 
> turned up or you will get a *loud* thump).
> 
> Do this test with the PSU under load (with no load there probably won't 
> be any ripple).
> 
> Seb
> 
> 
>