Problems with smokey amp circuit (low volume)

[docnova]

I built the smokey amp using the following schematic from http://www.beavisaudio.com. The thing is, when I follow the schematic the output vomule is extremely low. If I remove the 47uF capacitor going to the output however, it sounds just fine. Does the capacitor serve any function to protect the speaker? Output voltage is 1.12v with the capacitor and 2.58v with it removed. Sorry I know this is a total newbie question, but I would appreciate any information.

[newfish]

The Capacitor serves two functions...

Firstly, Caps only allow AC voltage through - and block DC - so any DC on the Smokey's output stops at the 47uF Cap (it de-couples the AC signal from the DC supply).

Speakers really don't like having DC applied across them - so this cap serves a valuable function here.

Secondly, the Cap will only allow a certain band of frequencies through - think of it as a static tone control.

This is why most folks put switchable input Caps on their fuzz-boxes - it allows you to dial-in more / less bass without having to keep re-soldering different components in place.

Two worthwhile jobs performed by just one component!

Please be aware that the 47uF Cap is polarised (i.e. prefers to be used in a specific direction).  It might be worth checking that the negative (-) side of your Cap is connected to the 'Speaker' side of your circuit.

Hope this helps / clears up some questions for you.

Keep at it - tiny amps like this are very handy for late-night practice or testing those after-hours builds.

[petemoore]

Does the capacitor serve any function to protect the speaker?
  Yes, direct current tends to heat/bake the coil, and of course since there's no frequency content in DC, the current only serves as a way to remove coil-smoke, not recomended.
  Output voltage is 1.12v with the capacitor
  The output should be 0.0Vdc, somehow the job of the capacitor [blocking DC] isn't being performed.
  and 2.58v with it removed.
  For these types of circuits, grabbing 2 of the larger capacitor values [and rated for >10% of measured voltage that will be applied [ie make the cap V rating larger than the circuit supply voltage]..connect +'s to -'s making a bipolar capacitor out of a couple caps [added feature: doubles the Uf value], there's no way to reverse polarize a non-polarized capacitor, and will help let more bass through if the values in question are small enough-ish to roll off bass there.

[jaki54321]

Make sure the capaitor is set right... That being said, take a look at this picture:



I do not know what kind of capacitor you are using but it should be something like that. The schematic calls for a 47uF capacitor. And the symbol is for Electrolytic which is |( the | side is the positive leg, and the ( is the negative, so make sure that pin 5 of the Amp IC is connected to the positive side because as you can see in the schematic, pin 5 of the amp IC is going directly to the | side of the capacitor in the schematic. To tell which is the positive side, the positive leg is always bigger then the negative. But if you cut the legs, one side of it is negative, if you take a look at the picture above, it has one big leg and one smaller leg, and the smaller leg has markings above it that go down toward it. Thats the negative side. The negative side of your Capacitor should be going out to the speaker.

I am no professional, i am still pretty new, but I do know that Caps block DC and allow AC, and speakers do not like DC too much, Newfish and Petemoore are right. So check the polarity of your capacitor and see if you can figure out the problem.

Best of luck!

[earthtonesaudio]

I built the smokey amp using the following schematic from http://www.beavisaudio.com. The thing is, when I follow the schematic the output vomule is extremely low. If I remove the 47uF capacitor going to the output however, it sounds just fine. Does the capacitor serve any function to protect the speaker? Output voltage is 1.12v with the capacitor and 2.58v with it removed. Sorry I know this is a total newbie question, but I would appreciate any information.

There's so much wrong here I have to suspect you have hooked something up incorrectly or you've damaged some component.

The output voltage at pin 5 should be 4.5V with the cap installed and something closer to zero with the cap shorted (that is what you meant by "removed," correct?).

I agree with the others.  Backwards cap or worse.