regulator producing noise???

someone has idea what kind of noise could generate a regulator, if input voltage is not sufficient?

I have a power supply with 12V AC rectified and regulated with a 12V regulator. the voltage drop a lot due the cheap transformer and I´m having 12V not 13V so the regulator is not working.

I´m having some spikes and a lot of harmonics 100 ,150,200,250,etc.
I think that it can be contaminating the ground of the circuit which is common . I have this noise on the B+ and on the output.

I know that I must remove the regulator, I just want to know if somebody has experience with this kind of noise.

the power supply is for 2 12ax7 heathers.
I have 6600uF before the regulator and 47uF on the output.

Do you have a schematic of your circuit?

The harmonics in your case seem to come from the AC sine, as they're a multiple of 50 Hz.

And the voltage drop... it rather comes from the rectifier diodes, doesn't it?

A regulator CAN also be noisy, but then it's rather wideband noise, like roughly said from a noisy mic or taperecorder.

Cheers,
Dominique

If you have 12Vac from the transformer, and then only 12Vdc after the rectifier under load, my guess is that you load the transformer too much. You're sure it's supposed to have the needed juice?

that power supply is similar to the g9 heather supply I just change the first cap to 6600 and the second to 47uF .

http://www.gyraf.dk/gy_pd/g9/g9_sch.gif

And the voltage drop... it rather comes from the rectifier diodes, doesn't it?

Click to expand...

the voltage drop if the trasformer regulation is bad too. if you draw current the voltage always drop a little.

the transformer is a 1A 220/12V made in China. 300mA seems to be too much for this cheap transformer.

two questions more :

- how the noise produced by a bad ground wiring must be seen?

- snubbers and freds only help on high frecuency noise isn`t?

I will try to put some graphs maybe can help to someone.

here are the graphs

Oh I see!
But that a big voltage drop at 0,3A from a transformer that is rated 1A!?
That's odd!

You could try a
* 15V transformer or a higher rated 12V transformer
* Also Schottky diodes (possibly you have some lying around) and a
* low-drop regulator could help get around the problem. The size of the
* smoothing capacitor plays a role there too, if you're using something below 1000uF, you could try something higher.

The noise:
Before the regulator the voltage isn't DC=flat, but has got some ripple...
Everytime the voltage before the regulator goes below 12V + the regulator's voltage drop, there's some irregularity in the voltage after the reg., and so when that frontier is passed upwards again, at least that's the explanation for the 100Hz noise...

Good luck!
Dominique

Many regulators can modulate the input ripple noise when they dropout.

I take off the regulator and the noise is still there. now I read 13,6 volts provably the regulator work in some way just on some wave parts.

only I have left to prove with freds and check some strange ground problem.