Simple Active Tone Control For Ruby

[Nick C.]

I wasn't completely happy with the tone of my Ruby amp. Too much bass not enough highs, especially with  humbuckers. The Cricket Tone control just rolls off more highs so that didn't help. Trying out different speakers helped, but I wanted more.

Looking at some old posts I decided to try something inspired by an idea from Mark Hammer. Basically by putting a cap in the gain loop from pins 1 to 8 you increase the gain of selected frequencies as opposed to the full spectrum. I found that a .33uF cap (negative to pin 8 ) in series with the gain pot ( I used a 5k pot) now turned into a very nice tone control. Now I can go from smooth jazz/blues to bright and jangly. Yes! The drawback is the loss of some overdrive which I think can be made up with a grit control ala the Cricket.

Nick

[dano12]

That's a very nice find. I've never been terribly satisfied with the noisy cricket tone control. I'll have to give yous at try, thanks for posting.

[Nick C.]

Hey Dano

As I said above the biggest drawback is loss of drive and some volume. I'm not sure how your Grit switch works, but I was wondering if I add a pot between pins 5 and 7 that it could be another gain control?

[dano12]

Hey Dano

As I said above the biggest drawback is loss of drive and some volume. I'm not sure how your Grit switch works, but I was wondering if I add a pot between pins 5 and 7 that it could be another gain control?

The Grit mod was discovered by accident when I wired a NC up wrong on the breadboard. I don't know how or why it works. But it does.

Go figure.

You could try a pot or a pot in series with a cap to see what it does.

[dano12]

Also, tangentially regarding the grit mod, it uses Pin 7 which is the bypass pin. The function of bypass is not discussed in the LM386 datasheet so I did a bit of digging and found this gem from 1997:

http://qrp.kd4ab.org/1997/970228/0064.html

Quote:

Lots of good information there, but I was a bit amazed that you failed to
mention the use of a bypass cap on pin 7. A small electrolytic or tantalum
cap of a few uF from pin 7 to ground will isolate the high gain input stage
of the LM386 from power supply noise, hum, transients, etc. Such a bypass
cap is much more effective in this regard than the "brute force" Vcc filter
that you recommend in your note #2.

You aren't the only one to ignore this; most commercial rigs (and kits)
using the LM386 either fail to bypass pin 7 at all or use too small a value
(0.01uF or 0.1uF) to be totally effective.

So somehow by sending the output through a cap back to the bypass pin, grit happens.

The quote also suggests that the 100nf I use in the Noisy Cricket is too low a value for good stability. Hmmmm.....

[Nick C.]

I have an electronics expert friend at work who keeps saying lots of stuff we do wont work.
He's older and can't understand that yes, I really do want to push the signal way past the rails. I can sense his blood pressure rising;)