Smokey Amp Losing Power When Changing Volume?

[NZDavo]

Hi All

I have just setup a smokey amp on a bread board. (See schematic here - http://www.blueguitar.org/new/schem/_ss/smokey.gif)
I have added an LED (with 4.7k ohm resistor) at pin 6 so I can see its on.

This is a super simple build but I can't get it to work! I had sound very briefly and now I can't get it back. I've tried 2 different IC's and 4 Caps.
I have double checked that my Caps are the right way round. (electrolytic)
(Note I am using 2x 220uf caps like this build - http://dirtbox.net/wp-content/uploads/2010/06/Smokey-Amp-Vero-Layout.jpg )

I can hear 'static' noise when plugging into my guitar but nothing when plucking the strings.

I tried wiring the ground from the input socket straight to the battery so that I could see if the problem was at that end. Then the LED did a funny thing - if I rotate the volume knob on the guitar it glows bright at low volume and high volume but fades to nothing when the volume is near the middle - don't know if that's significant?

So I'm completely stuck - can anyone help me?

voltages are:
Pin 1 = 1.04v
Pin 2 = 0.03v
Pin 3 = 0.08v
Pin 4 = 0.02v
Pin 5 = 0.56v
Pin 6 = 8.36v
Pin 7 = 4.00v
Pin 8 = 1.02v

Thanks!
David

[Jdansti]

Your schematic doesn't show the volume pot, so we don't know how it is wired. The best thing would be to post some pics showing all of your wiring including the volume pot.

It would also be a good idea to measure the voltage at pin 6 with the volume pot in different positions.

Edit-I just noticed that the volume pot you were referring to is your guitar volume. I recommend that you don't plug your guitar into it until you get this figured out. You wouldn't want to fry your pickups. 

[NZDavo]

Thanks for your reply!

Oh dear! I hope I haven't fried anything! I tested it on two guitars too!
(Will check them tonight)

If I don't use my guitar to produce a signal what would you suggest? I could use an ipod nano maybe? Or is there another way to make some sound that I can hear through the amp?

Cheers
David

[Jdansti]

Power the circuit and check the voltage at the tip of the input jack with nothing plugged into the jack and let us know what you get. (pos probe on the tip and neg probe on the neg power).

Beyond that we need to see some photos of the breadboard and offboard connections.

[NZDavo]

Hi John

Yahooooo! its working!

Well sort of. If I stand in just the right place and face just the right direction it plays great! If I move a foot in the wrong direction it goes silent.

But that's huge progress! I used the ipod nano and got a signal when my hand was a certain distance from the speaker. So I figured that it might be the same with the guitar. Spent a little time hopping round the dining room until I discovered the right spot to make it work. (Neighbors probably think I've lost it!)

Any ideas why its so temperamental? (Could it be the fact that its on a breadboard and none of the connections are soldered?)

Thanks again for your help!

Cheers
David

[Jdansti]

[Twilight Zone theme music playing in the background].

Beats the crap out of me.     

Probably the best thing from here would be to get it on a perfboard or vero and see how it works. It's a small enough circuit so it shouldn't take much time to do this.

I'd suggest two modifications to the Smokey scheme. First, place a 1k pot between pins 1-8 to give you control over the gain/distortion (see http://www.beavisaudio.com/projects/NoisyCricket/Noisy_Cricket_Schematic.gif). You can also use a switch instead of a pot.

Also, a 10ohm resistor from pin 5 to ground (sometimes the resistor is in series with a 47nF cap) is recommended to avoid oscillation. This is also shown on the link above.

Good luck with it! 

[therizky]

For circuit this simple I wouldn't bother breadboarding especially involving 386, thing will oscillate and just doesn't want to work properly with poor connections

I would use ac adaptor to run this thing and left gain and volume control at its full.  Connect it to laptop, play some songs, and let it runs for some time. Even thought the sound was real clipped and distorted when you push the chip near its limit.