Another lunetta psu thread

[regularjackson]

I know this has been discussed before, but I couldn't find a thread that really helped me. Basically I'm building a lunetta system right now and I really don't want to use batteries. Just looking for a basic way to plug this in to the wall if anyone can help me out. Thanks.

[Psyingo]

here is a quick schematic i drew up.

as stated in the schematic, the 78xx is a voltage regulator IC. The xx designates the desired output voltage, 7812 being a 12v regulator.
You will want to have a few volts higher of an input to the regulator so it can perform its regulating magic.

On each CMOS chip you should have a 100nF decoupling cap between the +v and gnd pins; as close as possible to those pins.

The diode is there to avoid negative voltage being applied to the circuit.

[regularjackson]

Hey thanks, one question, what is JP1?

[Psyingo]

oh sorry, underneath Jp1 it says +V, but its not that clear.

Jp1 is the regulated voltage output.

[regularjackson]

oh yeah, duh. I didn't sleep enough last night. Thanks!

[regularjackson]

one other question I have pertaining to this is how to hook up a dc power jack for the wall wart? I don't know which terminals to hook up on the jack to what. I've searched around but I haven't been able to figure it out. Thanks.

[Psyingo]

usually on the wall wart it will specify if the inside is positive or negative with a little graphic... like so...





but failing that it isn't marked, you can just hook it up to a multimeter to figure out which is positive.

...like so...

[attdestroyers]

I used this same exact setup using the 7805 for my lunetta. But, I figured the decoupling caps weren't necessary on each module since this regulated power supply is decoupled already. Bad idea? My lunetta runs great with this. Think I'll have problems in the future?

I was also unsure what amperage my power supply should be. I used a 2A wall wart. Seems to work good.

[Psyingo]

well in my video synth, for example, i didn't decouple at first.. when i had everything assembled together and was testing things everything was very noisey, with very visible distortions, lines and noise on the picture... i was scratching my head for a bit. someone suggested i decouple EVERY chip and i thought 'that cant make that much of a difference...' boy was i wrong. it cleaned everything up perfectly. the image was so crisp and clean!

another example is on my drum machine... again i didnt decouple and i got tons of bleed into the drum voices from the cymbal voices... decoupled all the chips and it was gone.

DECOUPLE ALL THE THINGS

[-minus-]

Nice clear images and explanation on the psu. Looks like something you'd see in a really good book!

Yeah, I've been putting the caps on the chips for some time now. So you need them on the - pin as well? I have seen this done sometimes but haven't bothered

[attdestroyers]

ok, will do. It'll be interesting to hear how much difference it makes[/quote]