How can I do 9vAC and 9vDC from one PSU?

[lowvolt]

I'm goofing together an ART mic preamp (9VAC power) with dirt box (9+VDC power) all in one enclosure .. it's a Hammond thing ... I need a balanced output as well as about 30+ db more gain so the mic pre will be used post-dirtbox for that chore.

How can I use one PSU to do this?  I'd like to keep this rig as clean and simple looking on the outside as I can.  So even doing p2p circuitry inside of the enclosure is ok (large enclosure, rotsa room).  Anyhow, I figure if I rectify a 9vac PSU the diode bridge will pull the power down too much.  So I'm guessing I can use a 12vac psu, rectify it, and might be able to use it that way to power both FX.  Tap the AC pre-bridge for the ART preamp, and tap it post bridge for the dirtbox.

Anyhow, is there some way to do this without having to use two separate PSUs (one for the 9vac and one for the 9vdc)?  I am sure the dirtbox is ok up to roughly 18vdc (an 808 variant that has all 25v to 50v caps), dunno about the ART mic pre though, it just says "9vac" near the power input.  You'd think it would be ok above 9vac, but who knows.  So that's what I was banking on by thinking of using possibly a 12vac psu.  It's high enough to still have decent voltage after the diode bridge, yet not so high that it will fry brains.  Then again, wtf do I know, I work on welding machines!

Uh .... whut?  Thanks ..

[DiscoVlad]

Use a transformer with seperate 9V, and 12V windings?

Rectify and regulate the 12V secondary down to 9V DC for the DC supply, leave the 9V sec. as is for the AC supply.

[lowvolt]

Use a transformer with seperate 9V, and 12V windings?

Rectify and regulate the 12V secondary down to 9V DC for the DC supply, leave the 9V sec. as is for the AC supply.

That's not a bad idea, but I think I'll call that "plan B" for now .... gotta try something I suppose!

[iccaros]

if you rectify 9v ac you will get 12.69 (if you use full wave )  which you can regulate down to 9v DC. Loading will depend on current draw..

[lowvolt]

if you rectify 9v ac you will get 12.69 (if you use full wave )  which you can regulate down to 9v DC. Loading will depend on current draw..

Ok, that's news to me ... the voltage will actually GO UP if I use a full wave bridge?  How so?  I mean, each half cycle is going through it's own diode, how does that make the AC voltage actually go up?  (wow, just when you think you have seen it all ....).

Please explain or could you provide a link to an explanation?

Thank you.  

[iccaros]

http://www.hammondmfg.com/pdf/5c007.pdf

[Cliff Schecht]

I tried power AC and DC stuff off of the same adapter but kept blowing up wall warts when I plugged in both my Alesis reverb unit (AC) and all of my normal 9V stuff to the same bridge rectifier/filter/regulator circuit. It took me a second but then I remembered a similar folly I had when I was trying to use the same winding on a power transformer to go through both a bridge rectifier and through a simple half-wave rectifier for my negative voltage supply (was building a 5E8A low power tweed Twin). The fix for the problem ended up being to AC couple the signal from the point where the HV secondary and either side of the bridge rectifier were (except in my case half of the bridge was paralleled 5U4's and the other half was SS diodes).

Here is a schematic for what I did. The same "fix" could be used for trying to get AC and DC off of the same AC power supply/bridge setup. You have to capacitively couple the AC off of the bridge rectifier before feeding it into any AC power effects or neither of the effects will power on. Just two caps and two resistors (after the caps to ground) to fix the problem.

[PRR]

I bet the ART _has_ +12V DC internally. Steal some.

[iccaros]

I bet the ART _has_ +12V DC internally. Steal some.

I missed the ART part..
The art takes 9vac and rectifies it. They use a voltage booster to get the tube to a voltage inside. Why they use 9v ac I do not know, I have plugged 9vdc in by accident and it worked.  in any case they boost it to 48vdc

[Cliff Schecht]

Yup, if you open something up and see a rectifier feeding a positive voltage regulator then you should be able to power it off of 12V DC instead of 9V AC. This won't work if a bipolar supply is derived from the AC input though, or if any supplies other than a single 12V DC supply is taken from said AC. I usually check schematics or at least pop stuff open before plugging in power randomly, but sometimes my inner cowboy kicks in and plug A seems to power device B just fine.

[lowvolt]

I bet the ART _has_ +12V DC internally. Steal some.

I missed the ART part..
The art takes 9vac and rectifies it. They use a voltage booster to get the tube to a voltage inside. Why they use 9v ac I do not know, I have plugged 9vdc in by accident and it worked.  in any case they boost it to 48vdc

Haahaa!  Missed the "ART" part?  Y'mean the fifth word in the first sentence of the opening post written in all caps?  That's a good one ...   You sound like me.  Slow down a bit, maybe a bit less 5hr energy.  Heheh .. kidding of course.  Thanks for the offered help.

So, since the ART already rectifies the input power on it's own, are you all telling me I can just use a single 9vdc wall wart adaptor to simply power both FX?  Just sortof "Y" off of the plug?  (As long as I am careful about the polarity?).  Since the ART seems to be actually rectifying AC anyhow?  (again, minding input polarity).

Sorry all of the more technical stuff isn't landing in my head, I really am trying though!      Not one of my better days.

And Cliff Schecht, thanks for the schemo but I simply can't see what part of it you're telling me applies to my issue.  I have all the brains god gave an onion.  I have my good days when a DIY amplifier is a piece of cake, er candy, or some such easiness.  Today isn't one of them (the VA has me on pain control meds for a spinal injury, they rob me of my intellect sometimes .. this is one of those ~sometimes~).

Thanks..

[lowvolt]

if you rectify 9v ac you will get 12.69 (if you use full wave )  which you can regulate down to 9v DC. Loading will depend on current draw..

Ok ... you said "if you use a full wave bridge" the 9vac would raise to 12.69vdc ....... you DIDN'T say "if you use a full wave CAPACITOR bridge" .... it uh, makes like a HUGE difference.

That's why I asked how a "full wave bridge" would actually raise the voltage.  Dude, you had me going there for a minute!  I thought I'd totally forgotten everything!  (Whew!).

[PRR]

> missed the ART part..

Doesn't matter. "NO" audio electronics runs on AC. There's gotta be DC in there somewhere.

While the wall-wart may output AC, internally there is surely a rectifier and DC filter.

> Why they use 9v ac I do not know

Usually (as you say!) because they want to derive multiple DC voltages. This is easy to do with AC. For example the Mike preamp can voltage-multiply 9VAC to 48V DC for Phantom power. Some of the low-price ART (and PaIa, and others) boxes jack-up low AC volts to 20V-50V to power tubes. Nearly every 2400 baud modem was a 9V AC wall-wart internally converted to +/-12V DC.

> I have plugged 9vdc in by accident and it worked

Odd. Maybe the amplifier runs on 9VDC. Maybe you were not using the Phantom feature, or a Phantom mike which works down to 9V. Maybe that particular model really uses a voltage converter and will eat either AC or DC, but they had a crate of AC supplies from a previous model.

> Just sortof "Y" off of the plug?

No. I'm suggesting opening the ART mic preamp and finding where the input AC is turned to about 11V DC, and tapping that.

If you are not confident opening, investigating, and tapping onto the guts of the ART mic preamp, your best safe approach is another supply just for the dirt-box. Yes, that's messy, but as Cliff says deriving several DC supplies from one AC supply and then running audio signals between gets very confusing and possibly smoke-releasing.

[PRR]

Cliff -- how did you do the notepad image?

http://www.diystompboxes.com/smfforum/index.php?topic=97268.msg847579#msg847579

[Cliff Schecht]

Lowvolt, if the ART box doesn't have any linear regulators or the like that require you to be a certain threshold above the output voltage of said regulator then you are probably fine plugging 9V right in, or really 12V because that's what they're most likely using inside. You can try 9V too, it will probably work just fine.

Something else that is nice about plugging DC into an AC input (when AC is feeding a bridge rectifier) is that the polarity of the adapter doesn't matter. Think about it, the rectifier doesn't care which way ground and VCC is because either way you are forward biasing the diodes on. So you don't HAVE to use a 9V negative center adapter, you can use that ONE 9V positive center adapter that we all have laying around .

[Cliff Schecht]

Cliff -- how did you do the notepad image?

http://www.diystompboxes.com/smfforum/index.php?topic=97268.msg847579#msg847579

Microsoft OneNote has a very nifty feature that I use very often. You can set it up so that when you hit Windows key + s, One Note freezes whatever is on the screen and you can use your mouse to select whatever you want off of the screen. Since I have tablet PC's laying around for school I tend to just draw things up if it's quicker than opening Eagle and drawing a schematic there.

Also Lowvolt, look again at the little pic I posted. There is a circuit in the bottom right hand corner that is used to derive -45V for biasing the power tubes in this particular amp (Fender 5E8A clone). What I was pointing out specifically to you was that the very first part in that bias is a DC blocking cap followed by a resistor to ground. You need this on both sides of the bridge rectifier to steal AC from the wall-wart. I drew a picture, let me figure out how to post it again.

[Cliff Schecht]

OK take a peek at this. The unlabeled caps and resistors can be something like 10uF and 10kOhm, just make sure the cutoff frequency of this high pass filter we are forming is pretty well below 60 Hz (it's about 1.5 Hz with 10uF and 10k). The 10k resistor can be a 1/4W resistor like we use everywhere else. You can now power your AC effects from this. The two floating wires on the right side go to either side of the power plug, the polarity of these doesn't matter so they can be flipped if need be.

[R.G.]

The root of all the trouble is the fact that a FWB alternately connects each side of the incoming AC to one of the output lines. One or the other AC lines - or both! - are alternately shorted to whatever the output power calls ground. Capacitors remove this direct connection.

You get much the same problem with two FWB rectifiers from the same AC. You can't arbitrarily connect the DC outputs, because if you do, you wind up shorting the incoming AC through an unintended diode path half the time.

Since what an external pedal wants with 9Vac is to make DC from it, you are at the mercy of what the external pedal does with the 9Vac.

The capacitors isolate the diode path OK, but they have to be big and high(ish) current capable to carry enough power.

[PRR]

Very-very often, when a box takes lo-volt AC, the internal plan is a LOT like the PAiA Tubehead seen here:  http://www.paia.com/manuals/ 

Snip:


One side of the AC goes to pedal common ground. (If not, Stop!)

The other side goes to one or two 1N4002 diodes and large capacitors. Here you find DC, usually a + and sometimes a - also.

The PAiA shipped with 12VAC wart which gives about 16VDC. This ART has a 9VAC wart which will give around 12VDC.

Tap some power here, much like where the PAiA shows "Vcc". Just tack-solder red and black leads to C1. You will often want to add an R-C smoothing filter like their R1 C2. (Aside from smoothing, a resistor reduces the chance that a mistake on your side will release smoke from wart or diodes.) For a small pedal, 1K may be a good starter value. (PAiA used 100 because they are powering three pretty hungry chips.)

BTW: if your ART is not too new, write to them with a serial number and they will email you a schematic.

[PRR]

> plugging DC into an AC input (when AC is feeding a bridge rectifier)

Perhaps redundant to R.G.'s remarks:

Yes, an isolated DC supply can feed _some_ "AC" gear. And as you say, either polarity.

But if you use a _common_ DC supply for more than one pedal (1-Spot with daisy or similar) then the "AC" pedal will always be 0.6V AC off of signal ground for the rest of your pedals.

And if it is not the simple FWB to a single DC rail (if it is more like that PAiA Tubehead), then you won't get the required rail voltages.