386 idea

[Connoisseur of Distortion]

the 386 has gain pins (1 and ... as the resistance changes, the gain changes... so could you put an op-amp between the pins to amplify the signal for still more gain?? or would this cook the 386? Advise me!  :lol:

[Connoisseur of Distortion]

please ignore the sunglasses... i forgot about 8 and the parenthesis

[smashinator]

I looked at the datasheet, and my answer is "I dunno."  Please try it out and let us know how it works.

It looks to me that making a connection between pins 1 and 8 adds that component in parallel with a resistor.  Unfortunately, I don't know what effect adding a booster in there would have.

***edit*** said resistor looks to be connected to the collector of a transistor.

[Connoisseur of Distortion]

i agree that putting a connection between 1 and 8 will put components in parallel with the resistor. my thinking is very straightforward, logical, and stupid. I thank that if you boost the signal instead of weaken it (by way of pot) it will distort more heavily. i am seeing a high-gain distortion pedal with a handful of parts!  

[Peter Snowberg]

http://cache.national.com/ds/LM/LM386.pdf

If you look at the datasheet, you'll see that pins 1 and 8 have a 1.35K resistor between them internally. This resistor balances the amount of current the input section of the chip sees from the power supply versus the amount of negative feedback from the output stage via the 15K resistor internally to pin 5.

If you add a cap between pins 1 and 8 the gain goes up because the negative feedback is overpowered by the stiffer supply (lower impedance).

Another way to reduce the feedback and thus increase the gain would be to attach a cap (say 4.7uF to start) from pin 1 to ground. That will kill off most of the NFB and increase gain much more than a cap between pins 1 and 8. Add a resistor in series with the cap to reduce the boost level if you wish.

The 386 is a fun chip, but for maximum fun, use the JRC386BD.

[Transmogrifox]

The concept that you're talking about has much merit, but often times you struggle with the stability issue, ie, you make an oscillator by adding gain components around a feed back loop, not to mention the pin 1 and 8 connections form a feed back loop with your added amplifier...I think you can pull it off with a little experimentation, though.

Just give it a try and see what happens.  It doesn't pose any safety issues that will zap you.  At its worst, you'll burn a up a 386 for 50 cents.

enjoy

[Connoisseur of Distortion]

well, i guess i better get a breadboard...

a 50 cent investment in electronics seems ok, even to a miser like me  :roll:

[Connoisseur of Distortion]

got a breadboard, and now i need advice on the pin thing again... Should i boost 8 and run it into 1, or boost 1 and run it into 8? i have been looking over the data sheet, and i really don't want to mess up on something so trivial...

[javacody]

Peter said you want to run a cap from pin 1 to ground.

Peter, why do you prefer the BD chip? In my experiments, I've noticed that the D chip is more stable (its also the chip Zinky uses in the Smoky).

[Connoisseur of Distortion]

ok! the result of running an opamp in the gain loop of an opamp is nothing incredible. there is a boost in volume and distortion, but nothing i'd probably ever use. interesting note: using clipping diodes in the feedback loop of the gain loop opamp (whew) creates some smooth (albeit pretty soft) distortion. i'm considering trying the diodes in the feedback loop of the ordinary opamp, but i'm not expecting miracles.