Anyone have a circuit to smooth out poorly regulated/filtered wal-warts?

[Rodgre]

I have a few processors which seem to be really succeptible to fluctuations in line voltage, so I'm assuming that with a good bit of regulation and filtering, they should stabilize.

Is there any secret to this, or should any simple regulator circuit and some caps do the trick?

One culprit is a 9vac adapter going to a Bellari MP105 mic preamp. I would love to quiet down this little blue beast's power supply.

Roger

[RDV]

I adapted this from Steve Daniels' small wart and it's worked wonders for all my old crappy wall warts. You could add more filtering where I've got the 1000µF, 2200µF would be really good.

HTH

RDV

[spudulike]

[Processaurus]

One culprit is a 9vac adapter going to a Bellari MP105 mic preamp. I would love to quiet down this little blue beast's power supply.

is the adapter 9v AC or 9V DC?

If you're going do regulate DC, like the two suggestions before, there needs to be a couple more volts coming in (~11v- 12v) then you want coming out (9v), otherwise the regulation will drop out and you'll get your noise back. 

Danelectro does make a regulated 9v 200mA wallwart that you can find for $10

[Rodgre]

Thanks for the tips.

I AM trying to filter and regulate a 9vAC adapter as well as some DC stuff. That one has me a little bit baffled.

Roger

[spinoza]

Cool!!

I didn't even know you could do that!

I know regulated wall warts are not so expensive, but I can often find cheap unregulated ones (1-2$ at a surplus store). I'd love to stick a bunch of them in a rack, regulate the power, creating a semi-DIY power supply.

Edit: would it work with a LM317LZ?

[spudulike]

[Transmogrifox]

As long as your 9VAC  pedal doesn't have a transformer inside, you can apply DC and it will work.  I caution you from just plugging in a DC supply without checking inside for a transformer, because the coil may have an extremely low impedance at DC and either cook the transformer, your power supply, or both.

Being an AC input pedal, I would guess that it is already internally regulated and conditioning the AC input would not accomplish much (unless it was really bad).  If you have a UPS (like for your computer), then plug your pedal power into the conditioned AC output and see if that makes a difference.  Conditioning and regulating AC requires a little bit more of a circuit than it does to regulate DC.

Poorly regulated power supplies are not the only source of noise.  I do agree that this could be the source of your problem in the case of digital circuits, though.  In either case, it makes sense to eliminate that variable.  It looks like there have been some good DC regulating circuits posted above.

[phaeton]

I asked this question exactly 30 days ago, and mr. Paul Perry pointed me to this solution, which I have yet to try

[Dan N]

I've never seen this before. Excuse the hijack, but what regulator and zener combo would get me -6.5 vdc?

[Eb7+9]

In the PSA-120T Boss gets 9.6vdc output by sticking a Si diode (1n4148) in series to ground ... in that wall-wart they use a 1000uF cap on the input (following the bridge rect) and 470uF on the output ...

theoretically speaking you can string any number of diodes in series with the ref circuit - just add the appropriate turn-on voltages per diode used : Si (0.6v-0.7v), Ge (0.2v), LED (1.2v, 1.6v, others), and Zeners ... of course, straight diodes will be oriented backwards from Zeners ...

~JC

[spudulike]

I've never seen this before. Excuse the hijack, but what regulator and zener combo would get me -6.5 vdc?

The zener simply raises the regulator floor to 4.1 volts above ground. The regulator's output is always 5 volts above ground, so you get 5 + 4.1 = 9v1.

For -6v5, you need a 7905 reg and a negative referenced input dc like this project at GGG

http://www.generalguitargadgets.com/pdf/ggg_bipolar_ps.pdf

For reg 2 use a 7905, and add a 1v5 zener (or 3x series 1N4001) between supply ground and the reg ground pin.

[Dan N]

Thanks! That's much easier than the LM337 I was going to use.