Smash Drive

[Alex C]

Hey, I recently built the Smash Drive, a very simple circuit using the LM386 IC.   This is sort a warning and easy remedy for the suggested simple output section on the layout/schematic page.
          When I first built it I chose the simple output section (just a .1uf capacitor) for the sake of simplicity.  When I fired it up, it was horribly harsh and buzzy, and it was on the verge of hurting my ears even when the volume control (from pin 5) was very low, because of the sharp, piercing treble, the kind that makes you wince- you know what I mean.  
          I tried adding a variety of capacitors from output to ground (I just used the lugs of the volume pot) to tame the highs, but even up to .1uf not much happened.  I didn't have a .22uf on hand, so I tried a .47uf electrolytic, which gave me close to the treble reduction that I wanted, but reduced the output level too much.  
          So then I spliced in a simple low-pass filter at the output - a 10k resistor in series with the output and a .1uf capacitor to ground after the resistor.  This worked incredibly well, and now it has a nice midrange smoothness, and no high-end harshness at all.  I haven't tried other values yet, I was too excited that it finally sounded good.
           Now I love this pedal, and I love playing through it and knowing that the sweet sounds I'm making when I'm rocking out are coming from very few components, sort of like in a Fuzz Face.  It's hard to believe that just a few capacitors, resistors, and semiconductors can rock so hard.  Sweet!
           Every other review/post I've seen regarding the Smash Drive had the tone stack at the end, so I never heard of any of my type of ear-splitting treble.  I have heard others say that LM386s can vary considerably, so maybe that was my problem.  Did anyone else choose the simple output section and run into this problem?  I'd like to know if it's just me (in which case I would blame it on my particular LM386, certainly not any mistake that I made).  
          I love the forum, it's great!

                                                      Alex

[RDV]

I had a similar problem, it wasn't exactly ear-splitting, but it had a lot of treble and not much bass. I didn't have the components on hand to do a tonestack so I undid it and made another Little Gem out of it.

Regards

RDV

[Transmogrifox]

I think your biggest problem is that the output is so hot it was excessively driving the input of your amp, and your amp was making the harsh trebly and buzzy tone.

I simply wired a pot to the output to taper the volume.  The simple version should include a 10:1 resistor divider.

That is what your LPF did, was it decreased the overall signal level for all frequencies...in fact, the break frequency is about 160 Hz, which is about right for the mid-rangy thing, because the input attenuates low frequencies up to about a mid rangey point... so you have your LPF attenuating far below where the input attenuates, so the highest amplitude frequencies are even attenuated....but the peak of the overall frequency response probably occurs somewhere between 600 Hz and 1.5 kHz.  I need to see the schematic again to calculate where the input 3dB frequency is to find out exactly where this peaks....

The moral of the story is
1.  The LPF (10k and .1uf cap) attenuated the overall signal level.
2.  The input leaves high gain on high frequencies, the output has low gain on high frequencies, so you have a bandpass filter with the peak in the midrange somewhere.