25v wall wart?

[bassmannate]

I'm looking at a preamp project that calls for 25vdc supply voltage. Does anyone know of a regulated wall wart that would provide this? I can't seem to find one on google.

[MikeH]

What about the charge pump that Rick uses for the Murder one?  With a little tweaking I'm sure you can get 25 volts out of it.

http://www.diystompboxes.com/smfforum/index.php?topic=73222.0

[RedHouse]

Jameco?

[Rob Strand]

You might have more luck with 24V DC unit.

Another option is 12VAC wall wart put through a doubler to get 24V DC unregulated (which will be more like 34V or so).

[bassmannate]

I've considered using a max1044 circuit but it doesn't put out much current. I'm not sure how much current the circuit draws.

Edit: If I were to power a max1044 with a regulated 12vdc power supply, would I then have to regulate the output of the max1044 as well?

[liquids]

Frequency - I thought the MAX1044 current output was fairly low...and every time you up the voltage, aren't you further reducing the available current?  Isn't there a point where it ceases to be practical and functional?   

How much current is even available with a MAX1044 (or even the cheaper and better LT1054) at 24v, let alone the +50v range? 

In my limited experience, it seemed like I was getting massive voltage drops with a MAX1044 doing the charge pump thing connected even to a standard load...what is your experience?

I frequently fantasize about things I'd do if R.G. and VS put out something exactly like the one spot but with 24v... 

Of course I imagine the amount of people who fry their cheapo pedals from and blame the company would make that alone not worth it for them to do, without even knowing how marketable and salable it would(n't?) be.  But I would buy one.   

[Paul Marossy]

You could also get a 24VAC wall wart, full wave rectify/filter it and then send it thru an LM317 set at 25V. You could have 1 amp at 25 volts to work with.

That's what I would do if it were me.

[frequencycentral]

The MAX gives out 20ma IIR. The LT1054 gives 100ma IIR. Never used a LT. The MAX circuit in Murder One is ~90 volts without load and drops about 10% when loaded. Easily enough for a couple of tubes' plates. The less doubling stages you use, the less voltage drop when loaded. A large cap at the output of the circuit will keep it pretty stable. TC1044 is another option. Have a look at R.G.s article, that's where I got the idea from: http://www.geofex.com/circuits/+9_to_33.htm

[liquids]

The MAX gives out 20ma IIR. The LT1054 gives 100ma IIR. Never used a LT. The MAX circuit in Murder One is ~90 volts without load and drops about 10% when loaded. Easily enough for a couple of tubes' plates. The less doubling stages you use, the less voltage drop when loaded. A large cap at the output of the circuit will keep it pretty stable. TC1044 is another option. Have a look at R.G.s article, that's where I got the idea from: http://www.geofex.com/circuits/+9_to_33.htm

I've seen that article, and also many of R.G.'s post on it since...some of which reference his being confounded as to why people would still use the MAX1044 when it is more expensive, offers less current, and need an extra connection to oscillate above audio range since the LT1054 is available with none of those issues.     That being said, the article says nothing of available current, and while it seems logical you can get infinite voltage, it only talks about going up to +33v. There is no discussion of any drawbacks of the voltage gain, such as potentially low current available at that voltage and beyond... that means that either there are none, or it's just not being mentioned. 

My 'understanding' (I hesitate to call it that!) is that ohms law, and every mass-produced voltage increasing device indicates that the more you 'charge pump' voltage, the less current available.  I'm not doing the math, I just wonder, unless for some reason increasing voltage does not affect the 10ma of available current somehow, if there's only 10ma available at 18v, will you even have enough current to power an LED dimly at 80v?   You're saying yes, and I guess I trust that, or assume that there is very little current demanded by your circuit, and/or that the tubes which are being feed by this 80v charge pump is current starved. 

That being said I'd love to hear you or others try dropping in an LT1054CP, available for $1.70 from Small Bear or 1.75 from Mouser, and see if it improves things for you, as if offers 5x more current all else being equal. 

You could also get a 24VAC wall wart, full wave rectify/filter it and then send it thru an LM317 set at 25V. You could have 1 amp at 25 volts to work with.

That's what I would do if it were me.

Lets suppose I did that...  Not knowing anything about the topic other than that it would work A) wouldn't I need/want a power supply that was regulated? B) If so, are regulated AC power supplies available?  C) Would that cause noise if it were not designed for audio?  My understanding and experience is that it's hard enough to find power supplies for audio that are quiet enough for realtime use, and those that aren't are noise monsters. 

Would rectifying a regulated DC supply, with the usual large caps from +V to ground, make any such noise negligible, or is is still advised to get a AC supply designed for audio use?

[petemoore]

Lets suppose I did that...  Not knowing anything about the topic other than that it would work A) wouldn't I need/want a power supply that was regulated? B)
  Not sure I follow the question, starting with a schematic makes it clearer what you're asking, the AC amp would require a DC Power supply.
  If so, are regulated AC power supplies available? 
  I believe the nomenclature of this question is a misnomer.
  C) Would that cause noise if it were not designed for audio? 
  What is 'that' and also, what is "it''?
  The suggestion Paul offered is safe and should put out a relatively ripple free DC voltage, put the last cap near the audio circuit.
My understanding and experience is that it's hard enough to find power supplies for audio that are quiet enough for realtime use, and those that aren't are noise monsters.  
  Get the regulator wired up right and it's hard to tell DC that from a battery = near perfect DC.
"Would rectifying a regulated DC supply",
  My computer is so jumpy I resotrtd to quotes, and can't see what I'm typing anymore, with the usual large caps from +V to ground, make any such noise negligible, or is is still advised to get a AC supply designed for audio use?


 

[Paul Marossy]

Lets suppose I did that...  Not knowing anything about the topic other than that it would work A) wouldn't I need/want a power supply that was regulated? B) If so, are regulated AC power supplies available?  C) Would that cause noise if it were not designed for audio?  My understanding and experience is that it's hard enough to find power supplies for audio that are quiet enough for realtime use, and those that aren't are noise monsters.  

Would rectifying a regulated DC supply, with the usual large caps from +V to ground, make any such noise negligible, or is is still advised to get a AC supply designed for audio use?

Yes, regulating it would be advisable. That's what the LM317 is for.
You're not going to find a regulated AC power supply, no such thing (AFAIK).
If it's filtered properly, and the circuit is laid out/designed well, noise shouldn't be an issue.
And, you don't need to rectify DC.    All you need is the typical full wave rectifier that uses four 1N4___ diodes.

[Rob Strand]

Re the voltage doublers I wasn't referring the IC's.

If you start with an *AC* wallwart you can use either of the voltage doublers on this page.  They use a different diode/cap configuration to double the voltage.

http://www.play-hookey.com/ac_theory/ps_v_multipliers.html

Devices which use AC wallwarts often have doublers either for higher voltages or to generate multiple supply rails internally.

[Zedmin_fx]

I might have a 25 volt wall wart, let me look around.

[Paul Marossy]

If you start with an *AC* wallwart you can use either of the voltage doublers on this page.  They use a different diode/cap configuration to double the voltage.

That would be a good reason to use a 12VAC wall wart. That is if you needed different voltages (generally speaking).

Devices which use AC wallwarts often have doublers either for higher voltages or to generate multiple supply rails internally.

That explains a few things. I have wondered why I occassionally see an AC wall wart on a piece of guitar related equipment.

[bassmannate]

Wow, didn't know I would create so much discussion!

I have to say that I would really LIKE to use some sort of voltage doubler with a 12v wall wart since I need to get a 12v for my Valvecaster anyway. My only concern is the current draw.

I've posted it before in other threads but I guess I'll post it again.
http://www.lynx.net/~jc/360+schm.gif

I'm gonna do a little research on some of the more current intensive parts such as transistors and such to see what kind of current draw they have. I'm also looking into the lt1054 as an option as well. The fewer wall warts the better in my opinion so if I can reuse my 12v then that will probably be the route I'll go.

[slideman82]

You can try a printer 30V supply and regulate it... they're simple, and great! And cheap too. A friend gave me a couple of those, and I'm happier now!