[ThermL]

Howdy, i've grown tired of using 9v batteries in my Tangentsoft CMoy so I've been researching various circuits I can use to regulate the power coming from a AC/DC power brick using the LM317 IC and found this little simple circuit http://www.discovercircuits.com/DJ-Circuits/bat-elim2.htm
 
I was wondering if it would be suitable to reduce the noise coming from my 12v power brick and also, if I could just modify the R1/R2 values to 240ohm and 3.3kohm (also removing that 15k resistor) to give the ~18v out we need for the opamp. Is this circuit adequate? Or, is there other circuits out there more suitable for my needs that I can easily throw together on the perfboard I have right now. I'm very green in the DIY audio area, and electronics in general. I've only soldered together 2 CMOY's and have never designed a circuit. I just have a rough understanding of whats going on really so try and keep the circuits simple.
 
Thanks in advanced

 

[Fred_fred2004]

Have a look at Tangent's tread design
 
http://tangentsoft.net/elec/tread/
 
cheers
FRED

 

[ThermL]

So if I understand the TREAD design correctly, since I already have a AC/DC wallwart, I can just bypass the rectifier. Now the major question is whether or not I can remove C5. I am unsure if my wallwart has a filter cap thats nice and beefy. It's just a RAYOVAC wallwart that i'm pretty sure was used for a battery charger. So should I just keep in C5 regardless? Also, since i'm just looking for 18v out, can I remove the pot at VSET and just keep the R1/R2 ratio static and avoid the use of that component?
 
This certainly is a easy enough circuit for me to make, now finding out how to arrange this thing on my bit of radioshack PCB....

 

[stixx]

 
Quote:

So if I understand the TREAD design correctly, since I already have a AC/DC wallwart, I can just bypass the rectifier. Now the major question is whether or not I can remove C5. I am unsure if my wallwart has a filter cap thats nice and beefy. It's just a RAYOVAC wallwart that i'm pretty sure was used for a battery charger. So should I just keep in C5 regardless? Also, since i'm just looking for 18v out, can I remove the pot at VSET and just keep the R1/R2 ratio static and avoid the use of that component?

 I'd leave C5 in just to be safe... and one 470uF at 25V is rather small. And yes, you can keep the R1/R2 ratio static... it even doesn't have to be very exact since your Cmoy won't care whether its fed by 18V or 19V. So you are looking at maybe 8-10 small parts to cram on your board... should be an easy task

.
 
Good luck with your project!

 

[cobaltmute]

Leave C5 in.  It will help deal with any ripple from your wallwart.

 

[holland]

You need enough voltage in order to regulate to 18v under load/use.  You'd need a source voltage, loaded (which means in use by your amp), to be about 22V.
 
For a simpler circuit, you can look at using the 7818.
 
You also didn't say what kind of a wallwart you have, an unregulated linear wallwart or some SMPS wallwart?  What is the DC voltage coming from your wallwart, measured with a multimeter.
 
Since you have a 12v supply, you won't get 18v.  Since you mentioned a power brick, it sounds like you may have a SMPS supply, which is already regulated, but not linearly regulated.

 

[tangent]

First, what holland said.
 
Second, no one's mentioned isolation yet. If your power brick doesn't have an isolated output, it will fail to work with the CMoy if you also use it with a wall-powered source, or try to use the CMoy as a preamp for a wall-powered load.  You can get away with non-isolated output with a battery-powered player and headphones, but it's still "evil" to do that with a virtual-ground design like the CMoy.

 

[TheLaw]

Wow Fred, after all the time I spent looking around on Tangent's site, I am surprised that I never ran across that. Thanks!

 

[Avro_Arrow]

The information is all still there if you know how to find it but Tangent removed
all the links.
 
Quote:

Wow Fred, after all the time I spent looking around on Tangent's site, I am surprised that I never ran across that. Thanks!

 

[ThermL]

I'm unsure about all the specs of my wallwart, but I have tested that it is isolated. I think i'll just grab a 18v wallwart off of digikey and settle all of the issues. I was looking at some more chips and was wondering if http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=5164856&cm_vc=av_uk would be a suitable replacement. I assume i'll still want a ~470uf filtering cap before the input. The spec sheet shows I should use a capacitor less than 1uf inbetween the ADJ and the Output, but I was wondering if I should put a capacitor from the ADJ to the ground also as shown in the TREAD schematic for, as tangent puts it, "This cap bypasses the regulator’s adjustment pin, increasing the regulator’s ripple rejection".
 
Edit: I decided to attach a picture showing the super simple/rough circuit. Thoughts?
 

 

[Avro_Arrow]

Fixed regulators don't have an "adj" pin. Just "in" "out" and "gnd".
Your schematic looks ok.
 
Quote:

I'm unsure about all the specs of my wallwart, but I have tested that it is isolated. I think i'll just grab a 18v wallwart off of digikey and settle all of the issues. I was looking at some more chips and was wondering if http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=5164856&cm_vc=av_uk would be a suitable replacement. I assume i'll still want a ~470uf filtering cap before the input. The spec sheet shows I should use a capacitor less than 1uf inbetween the ADJ and the Output, but I was wondering if I should put a capacitor from the ADJ to the ground also as shown in the TREAD schematic for, as tangent puts it, "This cap bypasses the regulator’s adjustment pin, increasing the regulator’s ripple rejection".
 
Edit: I decided to attach a picture showing the super simple/rough circuit. Thoughts?
 

 

[Avro_Arrow]

Your wall wart will need to be a few volts higher than the voltage
you want to get out of your regulator. This is called the "drop out voltage".
The drop out voltage for the 7818 is 2 volts.
So, you would need 20 volts in to get 18 volts out.
If you can find a 20 volt unregulated wall wort that would do.
A 24 volt unregulated DC wall wart is probably easier to find.

 

[Fred_fred2004]

Have you considered using a rechargable battery?
 
cheers
FRED

 

[ThermL]

I have considered using rechargables (i'm actually using them right now) its just that i'd rather avoid the hassle of swapping batteries while i'm gaming or other occurances. That and I figured this would be a simple project and offer some more opportunities to teach myself circuitry and audio electronics.
 
Anyways I read that wallwarts usually output a much higher voltage under light load than rated, so thats why I figured I could get away with a 18v wallwart since the CMoy most definitely won't be pulling 500mA. I mean, my 12v wallwart under no load outputs 23.4v but I figure it'd drop a lot more significantly and probably end up under 18 using the CMoy and regulator.
 
Could I get away with using a 18v wallwart for this circuit?

 

[holland]

Quote:

Originally Posted by ThermL /img/forum/go_quote.gif
 
Anyways I read that wallwarts usually output a much higher voltage under light load than rated, so thats why I figured I could get away with a 18v wallwart since the CMoy most definitely won't be pulling 500mA. I mean, my 12v wallwart under no load outputs 23.4v but I figure it'd drop a lot more significantly and probably end up under 18 using the CMoy and regulator.
 
Could I get away with using a 18v wallwart for this circuit?

23.4v??  that's quite a variation for a 12v transformer.  What's the power rating?  There are some that will output around 15v or so.  Are you sure your meter isn't broken?
 
Yes, unloaded transformers output more voltage.  The question is what is it rated for and what is the load of your cmoy?  It's not class-A biased, so it's hard to say for sure, so let's say about 20mA, which isn't a whole lot.
 
You need to put a load on it, or at least read off the label of the wallwart.  Honestly, you'll probably not notice much of a difference between 9v and 18v.
 
For a recharging circuit, you can reference the Mini3 schematic, which has a trickle charger and battery.