Replies to This Discussion

Permalink Reply by Paul Craig on February 29, 2016 at 12:36pm

Thanks.

Permalink Reply by Paul Craig on March 4, 2016 at 10:04am

Amp is wired and the circuits are verified. Just need those dang tack strips for the grill cloth.The rat's nest.

Permalink Reply by Paul Craig on March 4, 2016 at 12:21pm

Uhh  No. LOL

Permalink Reply by Paul Craig on March 7, 2016 at 9:25pm

Took the amp for a test drive while waiting for the tack strips. It has a problem. Either I'm going to need to delete Volume 2 and convert Volume 1 to Master volume or I'm going to need to do something with the inputs.

Permalink Reply by Paul Craig on March 8, 2016 at 8:04am

Maybe so, I'll be going over it with a fine tooth comb next couple of days.

Permalink Reply by Scott aka Farmer Ted on March 9, 2016 at 3:28am

Hey Paul,

Been watching this amp build from the beginning with interest. Looks like you've made a variation of the Little Gem Mk II from runoffgroove.com with the gain pot mods instead of the fixed 10uF gain caps. Nice.

What I wondered, after looking at yours and the Little Gem MkII schematics, is the absence of a capacitor for the speaker, like seen in a single LM386 circuit.

Another difference is the LG schematic replacing the 10K volume pot for a 0.22uF cap leading into the 3 and 2 pins of the twin LM386.

Curious though, what issues are you having with the amp?

Permalink Reply by Paul Craig on March 9, 2016 at 7:28am

I based this on the Ruby amp and the Tufnel distortion pedal from Beavis Audio.

Just getting hum through the output speaker. Thought that some solder may have dripped into the volume pots when I was soldering everything together, but they are okay. I think the problem may be in the input circuit(since the changes from the first amp build are twin volumes and twin inputs), that's what I'm checking next anyway.

Permalink Reply by Scott aka Farmer Ted on March 9, 2016 at 9:02am

Both the Ruby and the Tufnel have a capacitor set in line with the output/speaker+ line from pin 5. That cap isolates the dc current inside the circuit, and allows the ac guitar signal to pass to the speaker.

(Not referring to the cap and resistor off of pin 5 to ground shown on the Ruby and Tufnel diagrams).

I may be mistaken, but without the capacitor mentioned, it's possible you have ac and dc power going to the speaker.

Permalink Reply by Paul Craig on March 9, 2016 at 11:25am

I used the output circuits from this:If caps are needed before the speaker, I'll have to use 2 right? 1 for each side of the output since this is a bridged amp?

Permalink Reply by Scott aka Farmer Ted on March 9, 2016 at 1:14pm

Interesting. I think I'm going to have to make one up as shown in that schematic to see for myself.

Permalink Reply by Scott aka Farmer Ted on March 9, 2016 at 3:17pm

The LM386N-4 IC chip, based on Texas Instruments data, at 16v battery/wall wart power, can put out 700mW (0.7 watts). But it can handle a max. of 18 volts, with a 1 watt output. So by bridging two as in the diagram, at max power, it can produce 2 watts output.

And a wallwart is optimum, since this circuit would drain batteries like a hungry vampire.

Permalink Reply by Paul Craig on March 10, 2016 at 5:27am

I use a 9volt walwart rated at 800ma

I'm using the Im386N1 chips, but you can switch them for the N4's.

Thought about adding caps between the output pins and the speaker to experiment with, but never got to it. A couple of Bi-Polar film caps maybe?

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