Okay, so I bought a SKB pedalboard, the Stage Five one. It is one of the best purchases I have made in my entire life. Absolutely fabulous, and I am having so much fun with it.
The tricky part is - the only power outlet that I have left unused is a 1.3A 9V AC. I use another one of those to power the Line 6 DL-4 pedal. All of the other outlets are being used by other pedals. The only one I have left is the 1.3A AC one.
Now, I bought the EHX Freeze (it's on it's way to me) and it sucks around 170 mA of power, so I was thinking I could convert the unused AC outlet to DC, regulate it to 9V, and feed the Freeze from there.
The whole purpose of buying the SKB pedalboard was to abandon power adapters, cables, and everything, I would hate to have to use the Freeze power adapter or to daisy chain anything (currently nothing on the board is daisy chained), so the last remaining power outlet (the 9V AC one right) is my only option. If I don't convert that successfully than I will have to daisy chain, but I would rather not do that.
So, what do you guys suggest? I am totally clueless about current rectification and all. Any existing schematics, veros, pcbs, that could get me started right away?
Thanks!
Sure there are solutions for your task. I browsed a bit and found this for a start:
http://www.tonepad.com/getFile.asp?id=111
Musicfromouterspace also have a project:
http://www.musicfromouterspace.com (browse site for power supply)
... or you can make your own i guess, just borrow parts from the schematics above. Its basically just to rectify, regulate and filter.
Cheers
Hm, I should have thought about the tonepad thing. Thanks!
Any components here that are maybe overkill and could be chosen to be smaller in value (therefore in size as well), I want this to be as small as possible, because you know...that pedalboard realestate is always a PITA :D
You can get smaller parts, especially if you go SMD, but the problem is going to be getting 9VDC from the 9VAC supply. The losses in the rectification are going to take you below 9V. You might be able to do one of the voltage doubling rectifiers, but they'll have more ripple, so you'll need more capacitance to smooth it. It would also have more current loss because you'd need to waste more voltage in the regulator.
You might be able to do it with a bit of step up transformer to get the 9VAC to 12VAC and then rectify. I've been looking for something similar for awhile and I can't find anything that will work.
There are some more complicated ways you could do it that would still be small, but I think they are all going to increase the 140mA draw of the pedal up to about 200mA or higher.
Hm. And I could swear that somewhere I've read that 9V AC would give me 12.6 or something of volts of DC. Somewhere on diystompboxes.
Man I would hate to have to daisy chain, ughh...why do I even use digital pedals ::) ;D
Quote from: RobA on July 30, 2014, 03:08:51 PM
... but the problem is going to be getting 9VDC from the 9VAC supply. The losses in the rectification are going to take you below 9V. ...
Really? I am converting 12VAC to +/-12VDC right here myself... with 7812 / 7912 regulators. I should look for the exact schematic i used, for some reason i dont know where to find it atm.
Cheers
(http://i26.photobucket.com/albums/c107/rascalseven/Alesis-typebipolarsupply.png)
... just found that from a google search. It looks pretty much just as i done it.
This...looks very easily doable. Any thoughts on why this should be a bad idea RobA? Given that you wrote just before that one can't get 9V out of 9V AC...I must say that I am confused, and I do know very little about these things...
It's not a bad idea. You just have to be a bit careful about how you set it up and what the voltage reading of your power supply means. If it's 9VAC RMS, then you should be able to do it. I would just use an LDO regulator to do it with. The problems can come from the drop out voltage of the regulator and the losses due to the diodes.
The peak voltage from your 9VAC (if it's RMS voltage) is going to be sqrt(2.0) * 9.0V. If you drop 1.1V in the diodes in the bridge rectifier, you are down to about 11.4V or so. That's fine with room to spare for an LDO regulator, but less good for a normal type. So, if you go for an LDO regulator it'll work. Just make sure you get one that can deliver more than 100mV, since that's what most can do.
If you get something like this one http://www.st.com/web/en/resource/technical/document/datasheet/CD00044919.pdf (http://www.st.com/web/en/resource/technical/document/datasheet/CD00044919.pdf) in the SOT223 and get an SMD rectifier and use some 16V SMD ceramic caps, you could make the whole thing tiny.
... now i remember i used the General Guitar Gadgets schematic to build mine (sorry for ranting about with more than one reference here, but the GGG one it was, and it is very lookalike the posted picture above. Also, the link above has a few funny voltages, as 9VAC in --> +/- 15VDC out).
RobA has a point, i just had to refresh my mind: on the first (pair of) big capacitor(s), you get ripply DC, more than 12 VDC if you feed with 9VAC. This voltage is then feeding the regulator(s), and will decrease when loaded. And when heavy loaded, it will decrease so much that the regulator will stop working correctly.
In your case though, your AC supply can deliver 1.3A and your load is 170mA (right?), which i guess (notice: guess) will keep you on the safe side.
Cheers
Yep that's where the issues are. Also, since the peak voltage out from the rectifier is multiplicative and the drop out from the regulator is always the same, you've got more room to spare with higher voltages. 12VAC to 12VDC is easy, 15VAC to 15VDC is dead simple, but 9VAC to 9VDC is on the edge of being problematic.
I've adapted the GGG circuit too for my bench supply. It works well. I've got 12VAC in from a good supply and can actually get up to 15V out from the LM317 regulators I use for the variable taps.
One other reason to think about going with the more modern LDO type regulators is that they are stable with really low ESR caps. They can be used with like 10µF or 20µF SMD ceramic caps and be perfectly stable. Doing something like that could really get the size down. If you could find the right little enclosure, you could pretty much do it inline with the plug.
Hey guys thanks for the discussion so far. I was just about to order some parts for the SpaceHarp phaser, and I ran LDO through banzai's catalog and this is what they have:
http://www.banzaimusic.com/L4940V5.html
http://www.banzaimusic.com/L4941BV.html
http://www.banzaimusic.com/LM2940CT-12.html
http://www.banzaimusic.com/LM2940CT-15.html
http://www.banzaimusic.com/LM2940CT-5.html
Would any of these serve the purpose I need it for?
Regardless of whether it would or not, I am not sure how to use it, just use it instead of lm317 in a typical tonepad power supply schematic/layout?
P.S. Vallhagen my man did you ever receive that pcb and transistor I've sent you during the PIF rounds?
Quote from: Cortexturizer on July 31, 2014, 08:41:01 AM
Hey guys thanks for the discussion so far. I was just about to order some parts for the SpaceHarp phaser, and I ran LDO through banzai's catalog and this is what they have:
http://www.banzaimusic.com/L4940V5.html
http://www.banzaimusic.com/L4941BV.html
http://www.banzaimusic.com/LM2940CT-12.html
http://www.banzaimusic.com/LM2940CT-15.html
http://www.banzaimusic.com/LM2940CT-5.html
Would any of these serve the purpose I need it for?
Regardless of whether it would or not, I am not sure how to use it, just use it instead of lm317 in a typical tonepad power supply schematic/layout?
P.S. Vallhagen my man did you ever receive that pcb and transistor I've sent you during the PIF rounds?
Nope, you will need a 2940-9. 2940 has 5/8/9/10/12/15V types.
http://www.mouser.de/ProductDetail/Texas-Instruments/LM2940CT-90-NOPB/?qs=%2fha2pyFadujrFlYti9Pu2NokJrQhkrziYISQ0GXQcq4%3d
So wait, just to make it blatantly clear for me, looking at this schematic from tonepad -
(https://lh3.googleusercontent.com/-rtzAr5I9vyo/U9oqYrj41rI/AAAAAAAACmM/8JI1ZXjeT8o/w896-h341-no/power%2Bsupply%2Bschematic.jpg)
I just stick that one in instead of the lm317 and I'm (hopefully) golden?
Quote from: Cortexturizer on July 31, 2014, 11:39:22 AM
So wait, just to make it blatantly clear for me, looking at this schematic from tonepad -
I just stick that one in instead of the lm317 and I'm (hopefully) golden?
Aähh, NO.
The 317 is an adjustable voltage regulator and the 2940 is a fixed one.
get rid of all the resistors (2x1k, 240R), D6 and the 10uF cap and it will work.
And D5 stays, right?
Can't believe I'm gonna have to order only one part and pay the shipping that could have bought 5 those parts...
Would it be particularly stupid if I was to put a 12 or 15V version (those I can get in my city) and then 7809 from there? Would 7809-ing after it limit the amount of current (I see from the datasheet that the available current is around 1A), or reintroduce ripple or something...I reckon not. It would call for another part in a low-parts-level plan, but hey...
Yes, D5 stays.
But i dont understand what you are trying to tell me with using a 12/15v version and later replacing it with the 9v version?
You cannot use a version that is designed for higher voltages as it would not be able to work with an AC input too low.
No, I meant, after using all the benefits of the LDO (it is unfortunate that I can only get a 12 or 15V version of it) regulate to 9V using the 7809. My question was, would that work. Obviously, it's a workaround, but I'm not paying 20 euros for shipping a 1,3e part.
But you have 9V AC, right ?
Can you get a 5V 2940 ? You only would need 4x 1N4001 diodes to make it a 9V regulator. I can show you how.
Yes! I can get the 5V version. Just note that I'm gonna power a digital device (EHX Freeze) that draws around 170 mA. Would your design deliver clean enough power? I surely hope it would!
Quote from: Cortexturizer on July 31, 2014, 08:41:01 AM
P.S. Vallhagen my man did you ever receive that pcb and transistor I've sent you during the PIF rounds?
Man, my man, oh i'm SORRY that i didn't come back to you when it was on the carpet (or in the mirror;) ). It got lost between things i guess, but your worth a big thanx. I shall not miss such things. Yes i received that great package! Thanx a zillion! Somewhere along the line i will come up with some finnished builds!
Cheers! And thanx again!
(and to all others; sorry for OT)
Oh come on it wasn't a big thing, no need for all the thankyou's :P I was just wondering for the longest time whether you'd got it. Cheers!
Quote from: Cortexturizer on July 31, 2014, 01:14:53 PM
Yes! I can get the 5V version. Just note that I'm gonna power a digital device (EHX Freeze) that draws around 170 mA. Would your design deliver clean enough power? I surely hope it would!
It does:-)
To bring up the reg voltage you need to have additional 4V to between the regulator and ground. To do that you only need to put 4x1N4001 in series. They usually have a forward voltage of max. 1.1V, so this should be easy.
I would meassure the Vf of each diode to be close to 1V if possible. If you cannot get the 1V you now know the princliple and try other diodes you might have. (250mA min. in your case)
Don't the 2940 types typically only give 100mA?
Are you trying to avoid SMD? How small do you want the adapter to be? How fast do you need it?
I asked that last question because I'm just about to have to place an order to Mouser myself because I just discovered I don't have the voltage regulator for the Flintlock flanger (damn!). If we can figure out what to get you parts wise, I can put them in my order and then post them to you.
Quote from: Thomas_H on July 31, 2014, 01:48:56 PM
Quote from: Cortexturizer on July 31, 2014, 01:14:53 PM
Yes! I can get the 5V version. Just note that I'm gonna power a digital device (EHX Freeze) that draws around 170 mA. Would your design deliver clean enough power? I surely hope it would!
It does:-)
To bring up the reg voltage you need to have additional 4V to between the regulator and ground. To do that you only need to put 4x1N4001 in series. They usually have a forward voltage of max. 1.1V, so this should be easy.
I would meassure the Vf of each diode to be close to 1V if possible. If you cannot get the 1V you now know the princliple and try other diodes you might have. (250mA min. in your case)
That's a good idea. You could do it with a Zener voltage regulator too since you know about the max power. They can be a bit dirty, but I saw a design a bit ago for getting clean power out of one and it was pretty simple.
Edit: Oh, and there are LM2940's I've seen that have higher current capability in the 5V types.
RoB, 2940 is a TO220 device with 1A
I personally would not do a Zener regulation for this task.
Quote from: Thomas_H on July 31, 2014, 01:58:32 PM
RoB, 2940 is a TO220 device with 1A
I personally would not do a Zener regulation for this task.
Yeah, I was looking on Mouser here and had restricted my search to SMD because of the above mentioned thought of making it tiny. You are right though, in the TO-220, you can get them with higher output current.
Mouser here does have 1A 5V LDO's using SOT-223 as well.
Normally, I'd agree with you about Zener based regulators, but this idea looked cool and came with graphs of noise figures and such, so it looked fun. :D. I'll find a link if I can and put it up just for interest.
The other thing that was in my mind that might make the Zener regulator feasible is the I think from the gut shots I saw, the EHX Freeze may have a pretty good regulator setup on it's power input itself.
My "Electronics" bookmarks section in my browser is too big. It took me way too much time to find this link. I think I need to organize.
Anyway, here's the link to the Zener based guy I mentioned. (The page has various others too). I'm not saying that this is the way to go, but it is an interesting read.
http://www.tnt-audio.com/clinica/regulators_noise3_e.html (http://www.tnt-audio.com/clinica/regulators_noise3_e.html)
I played with it and it works well. But in the end, I went with using a TPS7A49xx regulator for the project I'm working on.
Guys...this is outstanding! Thanks a million Thomas! Great idea.
This hopefully solves all my problems. Man I'd buy you a beer right now. Gonna use your design asap, probably not today though, but as soon as, and report here. Awesome.
And RobA, thanks for wanting to include the 9V version into your order, what a nice move, thanks man. I appreciate it.
Quote from: Cortexturizer on July 31, 2014, 02:50:26 PM
Guys...this is outstanding! Thanks a million Thomas! Great idea.
This hopefully solves all my problems. Man I'd buy you a beer right now. Gonna use your design asap, probably not today though, but as soon as, and report here. Awesome.
And RobA, thanks for wanting to include the 9V version into your order, what a nice move, thanks man. I appreciate it.
No big deal really and I'd still be glad to do it, but I think Thomas will have you up and running far faster than I could. Cheers and I'd like to hear what you think of the Freeze when you get to play with it. It's a tempting looking pedal.
Yeah, they've done the Super Ego as well which expands on the Freeze, now THAT's tempting.
I've expanded my board a lot lately, will show it in the appropriate thread as soon as the Freeze arrives, then it will be complete. I managed to get some more boutique stuff, like Randy's Revenge ring mod, Pigtronix envelope phaser EP-2, Zvex Loop Gate, I tend to go for those that not many players choose. Really happy with them all.
I wanna thank Thomas for being a wonderful sport and helping me get this thing done. Here it is, in a small-ish black plastic box with two 9VDC outs
(https://fbcdn-sphotos-c-a.akamaihd.net/hphotos-ak-xfa1/v/t1.0-9/s720x720/10553464_10152648718566337_3421199796058973405_n.jpg?oh=958bade49b29cd718e86fca2bf7d556f&oe=5478E81B&__gda__=1415357509_3306fcf77738917476c6e1761073b3b9)
The weird thing about it is this - my 3-in-1 build won't make a sound with this power supply, the only thing i get is ugly oscillations. Whereas my '77 EHX bass balls works perfectly. The new SpaceHarp by Haberdasher works great, and is silent as well.
I gathered the strength and courage to plug in the Freeze as well and this is what I get - https://docs.google.com/file/d/0B--6F_4JB7SYUmZ4ZTFKZG5rSnM/edit
So it works as it should, but there's oscillations happening. What to do?
Once again, kudos to Thomas for getting me this close. (http://www.muzicki-forum.com/forum/images/smilies/mfsmajli-pivo.gif)
If the output voltage level is high enough and that side of things looks to be OK. It kinda sounds like it might not be getting enough current. Is the regulator that's in there able to source the ~200mA the Freeze needs?
Some regulators are touchy about the output caps. Which regulator and caps do you have in there?
Well I followed Thomas' schematic from page 2 of this thread line by line. My 3-in-1 behaves even worse, there's oscillation only, no sound happening at all. I'll try some other pedal later, some of the digital ones and see what happens. I have one that draws 40ma and one that draws 100ma so that could be a nice test.
I didn't see the LDO package right when I looked in the photo the first time. Now I see that it's a TO-220 so that should be OK.
Here is one thing to look at from the LM2940 doc,
Quote**COUT must be at least 22 μF to maintain stability. May be increased without bound to maintain regulation during transients. Locate as close as possible to the regulator. This capacitor must be rated over the same operating temperature range as the regulator and the ESR is critical; see curve.
The curve in question indicates that for the current draw you are looking at, the cap needs to have an ESR in the 0.5 to 2.5Ω range. You might be able to meet those specs by paralleling a decent 22µF electro across the 100nF cap or if that doesn't work, try using a 22µF ceramic cap (X7R or X5R type).
Hey Rob I tried your idea with paralleling the 100n cap with a 22uF electro but that only made things worse, I could hear the oscillation even on the pedals that haven't had it before.
Oh, and I can add MXR Micro Flanger to the list of the ones who work okay with this supply. I could hear less oscillation with the Boss RV5 than with the Freeze. Boss is also digital and draws around 50ma.
Also, I took a reading from the supply while connected to the Freeze, and there was the output voltage under load at the same 9VDC.
Since the total capacitance increase didn't fix the noise, it could be the ESR of the cap that's driving the oscillation. You are using the LM2940? Check out page 14 of this doc, http://www.mouser.com/ds/2/405/snvs769i-285393.pdf (http://www.mouser.com/ds/2/405/snvs769i-285393.pdf)
You are using a film cap for the output cap? If so, I'd guess the ESR is too low. Adding the 22µF cap in parallel would actually reduce the total ESR of the combined caps. So, that would explain the oscillations getting worse after adding the 22µF even if you need the increased capacitance for stability.
To meet the spec sheet requirements, I think you'll need to replace the 100n cap with a tantalum cap or an electrolytic that's got the right ESR range. I'd guess an electro like a Panasonic FR or Nichicon PS would work, but I don't think I have an LM2940 around to breadboard and test it.
I tried a tantalum but no progress. I tried another pedal though, the micro POG and it works brilliantly. So in the end I used the power supply to power the pog, small stone and micro flanger, and that made it possible to use the out that I used for the pog so far to power the freeze and I'm all set, all the pedals on the board are getting juice now. Pog draws around 170ma, worka perfectly silently and all. This supply hasn't turned out to be perfect but I got the job done in the end so all is good.
Thanks gents.
That's seriously weird. The docs make it seem like the Micro POG is more sensitive than the Freeze, although it looks like they both use the same power supply. I'm really curious as to what's going on. The POG draws more current? Maybe that's it -- the additional current draw puts the regulator into a stable area.
It's good you've got a working solution though, even if does seem weird.