After some experimenting, I arrived at an amp design that I quite like.
These days I live in an apartment, so low volume (70-80dB, aka 'very loud talking') is useful to me. Hence my interest in an LM386 amp. It was hellish loud (90+dB, aka 'shouting'), so I put a power soak on it for 0.01W which is just right. Who would have thought that a 10mW amp would sound so sweet? Not me, even though I should understand how a log scale works.
Features include a pre-amp that (1) runs clean, (2) clips via the feedback loop (tubescreamer style) and (3) clips to ground (rat style). Somehow, I got it to do all three quite well. I think the 2.4k 'clip-to-ground' diode has a fair bit to do with it working quite well. The 'clip-in-feedback' is quite crunchy, even though the gain is quite low.
Anyway... here's a schematic (and vero layout of the preamp), in three pieces.
You'll need to do your own wiring of the pots, switches and diodes.
All suggestions are most welcome.
Bretto
(https://i.postimg.cc/SXKxpYx7/TL071-preamp-and-LM386-power-amp.jpg) (https://postimg.cc/SXKxpYx7)
(https://i.postimg.cc/NKB0pzhn/TL071-preamp-and-LM386-power-amp-II.jpg) (https://postimg.cc/NKB0pzhn)
(https://i.postimg.cc/hXstw1ct/TL071-preamp-and-LM386-power-amp-III-vero.jpg) (https://postimg.cc/hXstw1ct)
TL071 non-inverting input isn't biased at half-supply..!! :icon_wink:
(or I need more coffee..)
Disconnect upper 1K resistor leg from +12V/22μF cap and connect it to GND while raising 100nF cap value..
(better make resistive divider values 10k, or so..)
I'd connect a 1M, or so, resistor between 1μF cap and GND for anti-pop purpose..
A 100nF ceramic cap (disk) across pins 7 & 4 (as close as physically posible) should "clear" IC supply..
Also, a 100pF cap across 100k feedback resistor should prevent HF oscillations..
And a 100R resistor to form a LPF with 22μF smoothing cap..
P.S.
What's the purpose of two caps (1μF & 22μF) between hard clipping diode pair.)??
edit: What I mean..
(https://i.imgur.com/F22jU7h.jpg)
Brett, I'm guessing you didn't feel the need to add any kind of tone stack or eq? Also, a 2p4T or 2P6T rotary and a suitable selection of resistors would give a range of power soak settings. BTW, what power rating did you use on the power soak Rs?
Have you tried attenuating the input of the LM386 rather than power soaking the output ?
That could work if you have set up your LM386 to not distort.
Quote from: Vivek on December 08, 2022, 02:23:05 PM
Have you tried attenuating the input of the LM386 rather than power soaking the output ?
That could work if you have set up your LM386 to not distort.
I'm guessing the idea was to overdrive the 386.
If overdriving the 386 is the target here, I'ld try asymmetrical clipping in the TL071 stage.