Another overdrive / fuzz

[will queue for free stuff]

I've been playing with the LM386 recently trying to get an overdriven fuzz tone.
I finally tried running the guitar signal into the 386 first. I had always set the 386 at the end of the
circuit and I couldn't get the fuzz to settle down across the frequency range of the guitar. Even with a filter
in place to attenuate low frequencies, the  low E string would often stomp all over the higher frequency notes.
The arrangement I have now has the 386 at high gain (pins 1 and 8 connected with a 1K log pot) driving the signal past
diodes to ground and into a circuit that closely resembles the alembic stratoblaster (in layouts gallery).
I'd really appreciate some feedback.
I'd like to post the schematic (from an eagle program I have), but I'm having an old fart attack and I can't seem to
figure out how to do it.   
Could someone help an old guy out?

[earthtonesaudio]

What I do is upload the file to the layouts gallery, then use the button (above the row of smiley faces when you're typing a post) to insert it in a post.  You just view your image after it's uploaded, then right-click and select "copy image location," and paste that between the "img" tags.

[will queue for free stuff]

Thanks!
I need to pay more attention to new technology.
Here's the layout.
I find the fuzz somewhat aggressive when the LM386 is pushed but will back off with adjustment of the 1K pot.
The overdrive is smooth and again will back right off with adjustment of the 100k gain pot.
The circuit responds well to pick attack right through highest gain settings.
Comments both positive and negative are very much appreciated.

[earthtonesaudio]

Almost. 

[earthtonesaudio]

I would suggest a current limiting resistor somewhere between the LM386 and the diodes.  Also, R1 is somewhat unnecessary because internal to the LM386 is a 50k resistor to ground.  Similarly C6 is not necessary for DC blocking (the JFET is ground referenced anyway) so you can take it out unless you want it there for tonal purposes.

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Alex,
You've gone above and beyond.
Thanks very much for both your help and suggestions.
I'll certainly take your suggestions to the breadboard.
Thanks again.
Craig.

[arawn]

I would leave r1 because of the low impedance of the 386 Maybe even consider making it larger like maybe 3m to help keep your high frequencies. Course that's just me otw it looks pretty good, I am even interested in playing with it a bit.
Always remember though High impedance in and low impedance out, Just look at the ruby, big daddy, and grace circuits, not to mention the noisy cricket, They alll have input buffers to keep the impedance up. I like your idea tho, cause they all do sound a little bottom heavy.

[Derringer]

the low input Z isn't necessarily a bad thing, it'll help tame some of the higher frequencies and quite often, that is desired.

but, if you want to have a higher input Z, no size pull-down resistor at the input is going to increase the input Z of the 386 ... which is 50K ... so you'd need a buffering stage infront of the 386 if you really wanted a higher input Z. The design probably doesn't need it though.

I would put a cap on the input though, to eliminate the chances of DC getting to the 386 input and to help shape the tone.

You could also play around with asymmetrical clipping with different diode combos if desired

Volume control ?

[will queue for free stuff]

Thanks for the replies.
They're very much appreciated.

I would leave r1 because of the low impedance of the 386 Maybe even consider making it larger like maybe 3m to help keep your high frequencies. Course that's just me otw it looks pretty good, I am even interested in playing with it a bit.
Always remember though High impedance in and low impedance out, Just look at the ruby, big daddy, and grace circuits, not to mention the noisy cricket, They all have input buffers to keep the impedance up. I like your idea tho, cause they all do sound a little bottom heavy.

I agree.......
I like the idea of R1.

the low input Z isn't necessarily a bad thing, it'll help tame some of the higher frequencies and quite often, that is desired.

but, if you want to have a higher input Z, no size pull-down resistor at the input is going to increase the input Z of the 386 ... which is 50K ... so you'd need a buffering stage infront of the 386 if you really wanted a higher input Z. The design probably doesn't need it though.

I would put a cap on the input though, to eliminate the chances of DC getting to the 386 input and to help shape the tone.

You could also play around with asymmetrical clipping with different diode combos if desired

Volume control ?

I'm pulling C6 and putting it up front, I'll try .01uF also.
I had a volume pot wired in, 100k log, but I found both pots were always maxed out........
Thanks again.
Craig

[earthtonesaudio]

One simple way to raise the input impedance of the LM386 is with a series resistor, like this:



With the 1M pot at maximum resistance, the input Z is approximately 1.05M and the input is attenuated to about 5% of its original strength (so less overall volume through the effect).
With the 1M at minimum resistance, the input Z is mostly determined by the chip (about 50k), but you get the full signal strength. 
The net effect is that if you're using a passive guitar as the input, louder settings will also have slightly reduced high frequencies, while lower volume settings will be brighter.

[will queue for free stuff]

Thanks Alex.
You'll never know how useful that tip will be to me.
I have two Gibson guitars.
One with active pickups EMG 81 / 85 and a guitar with model 59's.
Do you happen to know if pin 7 has any effect on tone if it's left unconnected (to ground)?
Connected or unconnected, I can't hear a difference. 

Derringer,
I tried asymmetrical clipping on the circuit. The fuzz is still smooth, but it shows an increased sensitivity
to harmonics, which can be very nice with the overdrive being sweet also.

[earthtonesaudio]

According to the schematic in the datasheet, pin 7 is the junction of two resistors that supply current to the differential input stage.  Adding a cap to ground there is mainly useful for reducing noise from the power supply.  Sort of like how in tube amp schematics there is the B+ voltage for the output stage but then several other (lower) filtered voltages for the preamp stages. 

There are other things you can do with pin 7, but it would be best to really understand differential pairs before you start experimenting.