Howdey guys and gals,
I built the circuit in the lesson Volume 6 Experiments and since I am new to building circuitry I waned to know what, if any, modifications would be needed to run this badboy off of a wall wort with a regulator and filter circuit. I was thinking a 12v 500ma?

Thanks in advance for anyhelp.

-Romes

 

No can do unless you create a, "fake" ground at the middle of a 12 volt supply and use that for the ground symbols at the inputs of the two op-amps. Both of them require very little current, so you can just use 2 resistors and a capacitor to make the voltage at the middle hold still. Say...10k ohms each with a 10 uf capacitor connected to the most negative voltage of the wall wart.

Got it?

 

Thanks for the quick reply, let me draw up what I think you mean and post it for you to review, about ten minuets.

 

I love minuets, especially the one by Bach...Minuet in G.

 

I love minuets, especially the one by Bach...Minuet in G.

Haha, got to love spellcheck, anywho, I was thinking, what if I used a transformer and a rectifier to make a +12/-12?

 

No can do unless you create a, "fake" ground at the middle of a 12 volt supply and use that for the ground symbols at the inputs of the two op-amps. Both of them require very little current, so you can just use 2 resistors and a capacitor to make the voltage at the middle hold still. Say...10k ohms each with a 10 uf capacitor connected to the most negative voltage of the wall wart.

You forgot about the speaker ground, which takes a lot of current. For that a common solution is to use a large capacitor in series with the amp output to the speaker. A 1000uF cap will give a -3dB rolloff at 20Hz with an 8 ohm speaker. Connect the plus terminal of the cap to the amp output.

And you need a 24V supply, not a 12V supply unless you want about a factor of four reduction in the maximum output power.

 

Haha, got to love spellcheck, anywho, I was thinking, what if I used a transformer and a rectifier to make a +12/-12?

For +/- 12V you need a center-tapped 20V transformer (which gives about +/- 14V peak DC output from the rectifier/filters).

 

Oh darn. You caught me again!
That speaker is going to cause quite a lot of current.
Crutschow came up with a method, otherwise you're going to need 2 wall warts to get a proper voltage supply with a good, current carrying ground.

Here's the wrong way:

 

And, yes, a center tapped transformer with a full wave rectifier and 2 filter capacitors will work, but that's a lot different from a wall wart or two.

 

From your earlier description, this is what I came up with, but where would the -12v go?

 

Look at my drawing in post #8 and add the capacitor that crutschow described then change the ground on the speaker to v-.

Right crutschow?

I mean, you can't dump all that speaker current into a 10k voltage divider.

 

Ok disregard that last post, can you explain why you say it is the wrong way?
What if the speaker was a 4ohm?

 

My drawing did not account for the speaker current.
If the speaker is 4 ohms, double the capacitor to 2200 uf.

 

Ill give it a shot! Thanks so much for you timely help and patience for my newby self!

 

Por nada. This was a quickie compared to most of the questions we deal with here.

 

crutschow, thank you to you as well!

 

Look at my drawing in post #8 and add the capacitor that crutschow described then change the ground on the speaker to v-.

Right crutschow?
.................

That is correct.

I have an old Dynakit 120 amp (60W/Ch) which uses that output technique that I built many moons ago. Works well and still has a great transparent sound. It was one of the first quality solid-stage audio amps to be sold.

 

Here. I added the capacitor and ground changes.

 

Just get two wall warts, connect them as a standard split supply- done.

I have been bitten by phantom ground splitters before- hard to make them stiff and stable.
Once I designed this complex audio device with a single supply, and an opamp driven faux ground circuit, it worked great until the client showed up, then the faux ground went into oscillation, I had to wear a bag over my head for a week.

 

Thanks for adding the caps and pots. Your a good man.

Anywho I built the circuit, following the schematic and illustrationhttp://72.135.236.34/shares/USB_Storage/20140930_230731.jpg and all I get is a little hum, and the VR changes volume.
Ill throw up a few pics of the build, and I would really appreciate it if you see anything obviously wrong.
I know that the photos arent going to be too detailed, but I can elaborate it need be.

Again, thanks so much for the effort on your guyes part.

PS: Since posting I did chane the N on the speaker to -V and still nada