Multi-out, bi-polar PSU?

[humptydumpty]

I'd like to have one 12v+ out, one 9v-out, and two 9v+ out.

I plan on using the 7812, 7809, and 7909, but how would I wire it coming out of the transformer?

[liquids]

Transformer?  No experience there, and not sure you'd need that unless you have high current needs beyond most of the pedals here.

I would suggest you use a LT1054, and a regular PS.  check page 18 of that chips datasheet, and combined it creatively with some regulators you mentioned.

[JKowalski]

You would need a transformer with a split secondary (or two secondaries)



The center tap is grounded, so you get full wave rectification going positive and negative on either side of ground. Add a filter cap on each one (watch for polarity) and your regulator.

[R.G.]

I'd like to have one 12v+ out, one 9v-out, and two 9v+ out.

I plan on using the 7812, 7809, and 7909, but how would I wire it coming out of the transformer?

Does no one read "Power Supplies Basics" at geofex anymore? 

[Processaurus]

I'd like to have one 12v+ out, one 9v-out, and two 9v+ out.

I plan on using the 7812, 7809, and 7909, but how would I wire it coming out of the transformer?

Does no one read "Power Supplies Basics" at geofex anymore? 

No offense, but in spite of fundamental articles on pedal building that anyone interested in the subject should read, as it's grown, Geofex has become a mess to navigate, there's really several ambiguously named different places things can be hiding.  I could only find that article by googling "power supplies basics" site:geofex.com

[R.G.]

No offense, but in spite of fundamental articles on pedal building that anyone interested in the subject should read, as it's grown, Geofex has become a mess to navigate, there's really several ambiguously named different places things can be hiding.  I could only find that article by googling "power supplies basics" site:geofex.com

Well, you *could* have scrolled down the index page to 11/15/01 for the link to "Power supplies basics". 

No offense taken, and none intended. But this one is easy to find.

[humptydumpty]

actually, the first thing i did when i thought of this was search geofex for that page, didnt think of the index but i did have to search for power supply and select powersup.htm

I will read it and come back with what i got from it

[humptydumpty]

You would need a transformer with a split secondary (or two secondaries)



The center tap is grounded, so you get full wave rectification going positive and negative on either side of ground. Add a filter cap on each one (watch for polarity) and your regulator.

i do have a question about transformers though, why do i see people using 110/115/117 in america and not 120? for the primary, that is

[R.G.]

i do have a question about transformers though, why do i see people using 110/115/117 in america and not 120? for the primary, that is

You will find transformers intended for 120 as well.

However, to answer your question: the AC wall power voltage in the USA (and other places) has changed, generally risen, over the last 50-60 years.

In the 1950s, it was often 110Vac, but varied with the local power company. Some places were 112, which you will find listed on some equipment. Then it became 115 in most/many place, and finally 117. When almost all power companies interconnected, they set 120 as a standard. Fact is, the history is such that every one of these voltages was a standard at one time.

At least they're all 60Hz. For a while about a century ago, some power companies provided 25Hz. Ugh~!

[humptydumpty]

hey, thats pretty interesting, and to to think, i felt super dumb for not knowing something everyone seemed to

so is it still practical to use say a 115 or 117, they seem to be alot easier to find

[PRR]

> a split secondary (or two secondaries)

There's a 1-winding way to make pretty-good +/- DC.

Humpty hasn't said how much current is needed. But many things can eat half-wave perfectly well.

> i felt super dumb for not knowing something everyone seemed to

No, most folks have no sense of history.

> practical to use say a 115 or 117, they seem to be alot easier to find

Yes (within reason).

That "120V" is just a number anyway. The voltage at the house is NOT regulated. Here, it is regulated +/-2% at a substation 3 miles up the road. There's 0.5%-5% drop in 3 miles of wire feeding 100 houses (some of this drop is compensated at the substation). Then at my house I have 400 feet of skinny wire from the street. This alone is 1%-7% drop, and it is "my" wire so the drop is "my" problem.

I have 126V right now. Mid-day with the electric dryer it will be 114V or so. Many people have smaller variation, some have worse (I had 116V-103V in my office).

You should never apply "too much" voltage to a transformer. The internal heat is small at 100% rated voltage, fine at 110%, but it will run HOT at 120% and is liable to die at 130%. You will note that 115-117-120-125 are all within 10%; also anybody selling a "115V" part today knows it will be used in my 126V house and has that covered.

Two reasons for "115V". It is an older USA custom, and many current parts are "direct replacement" for stuff first sold in the 1950s, so the specs use the same numbers. Also Europe is tending toward a 230V standard, and dual-primary 115V+115V is 230V.

Note that if a transfo is rated 115V to 12.6V at full load, when I feed it 126V it will make 13.8V, and back in my 103V office it was 11.3V. A transformer is not a regulator, just a lever. What you get out depends what you put in. Most loads won't mind. Fussy loads will need an actual regulator, PLUS ample safety factor to cover regulator drop and 103V offices.

[PRR]

> every one of these voltages was a standard at one time

Yes, going back to Tommy Edison's 100V DC system.

> When almost all power companies interconnected, they set 120 as a standard.

No. Interconnect is done at busbar voltage. They don't let me inside the fence but usually 13,000V to 200,000V. Each company distributes in a series of lower voltages, to maybe 6,000V on your street, but power companies don't interconnect at this level.

The 100+ year trend from 100V to 125V is clear, as is the reason. If you want more than a lamp in the parlor, 100V is just awkwardly low. It was picked because insulation was terrible, and you often don't die at 100V. But 200V would let you get the same power with 1/2 to 1/4 the amount of costly copper. (Half if the wire-heat is the limit; 1/4 if voltage-drop is the limit.) You can't just switch to 200V. However for about the first 80 years, utilities had motive to run the voltage a bit high, force a little more consumption. Not so that bulbs burned out too fast, and certainly not so motors burned. But bulbs don't last a year, motors often get replaced in a decade. So about every 10 or 20 years there seems to be 2V or 4V shift in the nominal target voltage.

In countries which did not rush to electrify using lamps from Edison's system, who waited for Goodyear's good rubber, the general trend is to utilize at 200+V. A mix of politics and commerce and dart-throwing gave many different voltages. But as the world shrinks it has become important to rationalize toward a common standard, near 230V.

(On a third hand: some parts of Japan, where they used little more than a lamp over the table and maybe a radio, utilization was at 100V for a long time because it was good-enough and could be run in narrow alleys with less risk.)

> At least they're all 60Hz. For a while about a century ago, some power companies provided 25Hz. Ugh~!

That made sense for the purpose! It wasn't for small stuff. Before good transformer iron, iron-loss in large transformers was a real problem, less at 25Hz. The "natural speed" for 60Hz motors is 3,600RPM; more poles gives 1800 1200 etc but more poles costs more. The alternators for the older system were eNORmous: they were tapping Niagara Falls and vast loads were already available, huge systems. You don't want a 16-foot rotor turing at high RPM. At 25Hz the natural speed is 1500RPM, a 6-pole motor turns 500RPM, which is more managable.

Going the other way, aircraft said "ugh!" to 60Hz systems. 400Hz transformers and motors are much lighter. The problem there is that when you try to push 400Hz through many miles of wire, you have the same problem as a 100-foot guitar cord: all the highs are sucked out. Not a problem in aircraft, but even 60Hz is a problem for distribution to more than a city. When my father was young he worked on simulations to model large networks and keep 60Hz flowing well. But it is almost a non-issue at 25Hz and smaller interconnects.

If we could find a 110V 25Hz outlet today, we sure could let the smoke out of a lot of our toys. And they'd make a deep loud hum before they smoked.

[humptydumpty]

You would need a transformer with a split secondary (or two secondaries)

The center tap is grounded, so you get full wave rectification going positive and negative on either side of ground. Add a filter cap on each one (watch for polarity) and your regulator.

any ideas where i can find a transformer with 24v out split secondaries, center tapped?