Anyone use Wall warts to run a gainclone

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Hi J

I'm not sure people have used wallwarts to test GCs, as they would need be dual rails, ie 15-0-15 to work properly, and most are just single rail,15-0 for example.

If you were sure they had no internal circuitry such as smoothing or regulation, you could possibly cobble two together, but the current would probably still not be sufficient to run the amp at anywhere near full power.

I would suggest you look around for electronics surplus suppliers, either locally or on the web, who could probably do you a cheap deal on a 18-0-18v 300VA transformer. This would work much better.

Good luck
 
If you can track down two old Aurora AFX slot car set wall warts in a surplus store, they might work. The big ones that came with the bigger sets were the heftiest I've seen, but unfortunately they did have a diode or diodes inside which you would have to get to somehow. I've got only one of the big ones myself.
 
I scored an old printers power supply which I believe is 20-0-20 AC and 3 Amps or something. Its not really a wall wart though as it doesn't give DC. I think its basically just an external transformer, maybe it has fusing too. I plan on using that.

Pete
 
Re laptop chargers:

Laptop chargers typically give out:

Newer Compaq units: zero and 18.5V at 65W
Not quite so new Dell units: zero and 20V at 70W.

So as you see, these are quite interesting as power supplies go. The problem is that they are not bidirectional. I suspect they are floating though, so two units hooked up the right way will double power AND give you a split supply if that is what you are after. I have a few power supplies kicking about, and have been toying with doing something like this for a while.

Petter
 
Petter said:
Re laptop chargers:

Laptop chargers typically give out:

Newer Compaq units: zero and 18.5V at 65W
Not quite so new Dell units: zero and 20V at 70W.
Petter

Laptop chargers are off-line switchers -- they should work -- but make sure to wrap the cord through a torroid -- this will stop some of the switching transients from permeating through.

You will occasionally see +/- 24 Volt Lambda linear supplies on EBay. I use one of these to test some of the LM3886 LM1876 LM3875 type amps. There was a beast which went bidless last week, starting price was $49.

You will very frequently see 24V/3 amp Power-One, Artesyn, Lucent switching supplies on EBay for dirt cheap prices -- this due to problems in Telecom.
 
JCoffey said:
Interesting. I have quite a few compaq laptop power supplies laying around. Something to look into. Build a couple Monoblocks with laptop cords connected to them.......


If you use a balanced topology (and "create your own ground"), you can get by with one PSU and won't have to worry about interference between the supplies (beating comes to mind since they are NOT running at the same frequency, but probably close).

I would add filtering at the output of the Compaq unit. Try it with a resistive load first to verify that you don't get oscillations with your chosen filter (LC or just C?). It would probably be opportune to look at the waveform to see how "bad" the output is.

Petter
 
Petter said:



If you use a balanced topology (and "create your own ground"), you can get by with one PSU and won't have to worry about interference between the supplies (beating comes to mind since they are NOT running at the same frequency, but probably close).

I would add filtering at the output of the Compaq unit. Try it with a resistive load first to verify that you don't get oscillations with your chosen filter (LC or just C?). It would probably be opportune to look at the waveform to see how "bad" the output is.

Petter

after trying different single rail voltages for balanced working ( with a resistor divider and cap to define the centre point for the i/p earth ) I came to the conclusion that 36V was about optimum.
I'm not sure if computor supplies come this high. And yes, LF common mode noise will cancel but this does not apply to higher frequencies so filtering will be necessary

cheers

mike
 
JCoffey said:
Interesting. I have quite a few compaq laptop power supplies laying around. Something to look into. Build a couple Monoblocks with laptop cords connected to them.......
Petter said:


I blew a Compaq supply and replaced with a linear one with Pass transistor for the extra juice -- CPQ wanted $90 for a new supply! Apple, btw, is worse and their laptop supplies have short half-lives.

With regard to filtering -- it's the switching transients you want to eliminate in addition to the ripple. Thus, I use a small surplus torroid on the DC line. Without it you get interference eminating back from the computer into the power line.
 
it's the connector

the connector which they use can become "undone" with a lot of use, mine became intermittent and sparked -- we have 2 Mac laptops in the house, 1 dell and 1 compaq. The Mac connector is "quirky" to say the least, incorporating ferrite shielding into the body of the casing. Compaq just uses a standard plug, Dell's is proprietary, but not as complex as the Mac to replace.
 
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