LM386 based distortion help

[stoned_survival]

hi
i have been working on an LM386 based distortion/overdrive circuit for quite some time now....havent bought the components yet but have simulated the ckt on pspice.
i want to ask whther some1 has tried out either of the 2 things i am stating below:
1) if i take the distorted output of the km 386 and feed it back and add soem amount of this output to the input of  lm86
2) if i feed forward the undistorted input of the lm386 and add it in some amount to the output of lm386

even if you have nto tried this particular mod out but have worked with lm386 please pour in you valuable suggestions

thnx

[petemoore]

  Here's what I read:
  source = guitar
  guitar > input > amp > Some output output / some 'fedback' to input through feedback loop.
  'A small amount' fed back to the input can:
  cause oscillation or cancellation.
  'A really small amount' of feedback can cause:
  Re-inforcement or dampening.
  And of course depends on whether it and the original source are fed to the inverting or non-inverting amp input.

[stoned_survival]

hmmm i dint quite understand how that relates to my problem i mean therres definately no cancellation since the output and input of lm386 are in phase in the configuration i am using it in! and abotu the oscillations .....can u explain a little abotu how and y oscillations will be caused in this case and whetehr or nto thwey can be removed??!

thanx

[flo]

Feed-back will cause oscilations when the loop gain is larger than 1 and the feedbacked signal is mixed in phase with the input signal. In the other case, the feedback signal is mixed out of phase with the input signal and that will cause dampening / cancellations.
"Feed-forward" here, is just mixing a bit of unprocessed signal with the processed signal. Can sound nice depending on what you want to achieve.

> ... i dint quite understand how that relates to my problem ...
What is the problem actually?

Regards,
Flo.

[stoned_survival]

the problem is that i want to get an idea about what the 2 mods will sound like !

and eyah so basically mixing the original signal with a distorted signal(feed forward) will make the output signal "less distorted" rt??

about feedback....the closed loop gain will always be  greater than 1 ...then?? oscliations??

[flo]

Well, probably you have to try it know what is sounds like. Its very hard to describe something like that in words...
Imo, try the "feed-forward" and forget about the "feed-backward", but hey just try it! (and report results please), you never know what suprise you will get!
It can be very nice to hear a good distorted / crushed sound and then to mix in some of the original clean signal back in. Bass players do it all the time to get their low frequency sound back after processing.

> ... mixing the original signal with a distorted signal(feed forward) will make the output signal "less distorted" rt??
Not less distorted, just different, more complex and therefore probably interesting: Distorted sound layered with a nice topping of clean (fill in your own receipe here)...

> ...the closed loop gain will always be  greater than 1 ...then?? oscliations??
Nature is simple in this regard: Keep amplifying (gain > 1) the same thing over and over and it will "explode" (= start to oscillate somewhere in the frequency spectrum).

Flo.

[Electron Tornado]

I'm working on an overdrive around a 386 op amp as well. The feed forward idea sounds interesting to try. Is there a source I can go to where I can learn how a feed forward is done?

Thanks.

[anchovie]

I did some experiments on a breadboard with an LM386 once (not particularly scientific ones - just shorting things together to see what happened!). If I recall correctly, I tried feeding back the output and it went nuts and sounded terrible. A lot of gain can be squeezed out of a 386 as it is, and the ouput signal is huge.

The "feed forward" idea is basically a clean blend, which some overdrives use. http://seanm.ca/stomp/bblender.html

[Electron Tornado]

I later found a book I have by RA Penfold with a couple of examples of feed forward. He takes both signals and adds them in an IC. He adds a potentiometer to vary the amount of distorted signal allowed to reach the summing IC.

[stoned_survival]

hey!i guess u got me wrong! when i am talking about feeding the signal back into the input ...i DO NOT mean feeding the whole signal back....we can divide it by a constant value in order to make its magnitude similar to the magnitude of the original input signal...then mix these 2 signals in some amount so as to obtain a signal which has magnituede comparable to he magnitude of the original input signal...but the waveform is different...so even aftr clipping the wveform will be different! and hence the tone!!

about feed forward..... seems like every1 seems to agree on this one...though i plan to use a buffer and an adder circuit(with potentiometer) to mix signals