Help, trying to build an amp.

[docz]

Ok so I started out trying to make my own amp. So far I have been working on the preamp section.
I based my design off of several designs I found on the internet and the datasheet for the ICs (LM386).
My idea was to use one IC with a drive pot and to be able to switch in the other IC for a "boost" or "high gain" channel.

I am getting weird results. First the gain pot doesn't work, at 0 I get some weird weird artifact noise in addition to harsh metallic distortion. At 10 I get just the harsh metallic distortion. The knob only affects the artifacts.
Also there is kind of a gating effect, sustained notes seem to be cut off after a while in a quick fade out, and playing hard makes it go silent and drop out. Switching on the booster amplifies this effect, I get a second of sounds, then it drops out, then it comes back a second and drops out again, then it dies in the gating effect. Also when playing two strings together I get a "tremolo" effect or oscilation or what you call it

What am I doing wrong? Any ideas?

Schematic is attached,
EDIT: Noticed an error in the schematic C1 is electrolytic!

DocZ

[J M Fahey]

To begin with, S1 on the up position joins two *outputs* together, a big no-no.

[pyromaniac_]

Yeah, this schematic looks really weird if you ask me. I don't understand what the switch is so-posed to do, but it's probably wrong as Fahey said. Another thing though, why is pin 1 & 8 at IC1 connected to ground via a pot (which is wired wrong, it should be wired as a variable resistor) and a cap?

Take a look at the datasheet, and you'll see. If pin 1 & 8 is left unconnected, the gain will be 20 (no distortion then). If they are connected with an capacitor at 10uF and a variable resistor at 1.2k in series, the gain can be adjust by changing the value of the resistor from 50 (R=0) to 200 (R=1.2k). This is how the Little Gem Amp an similar works.

EDIT
Btw, just read the datasheet and now I wonder why 10uF for C2 and C5. The datasheet suggests 100nF. And C5 might not be necessary, cause IC2 is only used with Gain=20.