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Old 18th November 2005, 01:38 AM   #1
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Default LM386 projects?

I built a really simple pedal based around this chip and did some toying with the core circuit in general. Seems pretty useful, simple and under exploited. Also about the best way I can see getting people started in a hobby dealing with electronics.

Anyway, the point of this thread is so maybe you dinosaurs can seduce the newbies into getting their feet wet with some simple LM386 projects. As it is, it was well over a year until one day I stumbled across a simple diagram that properly explained an op amp meaning, it labeled and worded things so a normal human being that isn't in the classroom could understand it. Technical terms mind you but unclouded with useless information and grammar.

I'm working on a simple onboard guitar pre with input buffer that utilizes this chip. It's a transistor based buffer and kills all grounding noise while removing zero tone
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Old 18th November 2005, 11:43 AM   #2
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Are you sure you have the right number?, an LM386 is a power amplifier chip, not an opamp. A nice little chip for driving headphones, or a small speaker, but not a good choice for a preamp. It's going to have much less gain than an opamp, be much noisier, and consume a great deal more power from the supply.
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Old 18th November 2005, 03:46 PM   #3
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I know it's not an op amp but it's a simple engine to get people started...I think you imsunderstood the purpose of the thread.

But as a preamp, I think it will work great. I don't understand how you say it could not have enough power though, I've seen applications where people maxed the output through a clever circuit to 5 watts.
I've got a pretty clever idea for an onboard preamp circuit utilizing this chip.
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Old 18th November 2005, 05:00 PM   #4
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Just to be clear, Nigel did not say it didn't have enough power, he said it doesn't have much gain.

The data sheet states a voltage gain of 20 to 200 is possible with external components. Are you trying to build a small PRE amp or POWER amp- two different animals... The chip would be great for a small headphone amp- it only delivers <1W @ 10% THD into 8 ohms. If you just want to shape the tone, I think a standard opamp would work better.

I do agree that it would be a fun chip for a beginner to mess around with. It will run from a battery very easily- no split rails needed. The data sheet has some fun circuits including a simple AM radio receiver....
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Old 18th November 2005, 05:17 PM   #5
teemuk is offline teemuk  Finland
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I like LM386's tone very much but i wish it would have been designed to follow a standard opamp pin configuration: I think this world already has enough of "mystery IC's" that become obsolete as the time passes and finding a substitute for them is a tough job - or in worst cases impossible. Gladly the chip used to be an industry workhorse for low power audio applications.

I never did any experiments in using LM386 as a preamp but my first thought is that even the theoretical maximum signal amplitude range of +-6V will limit the headroom quite much. On the other hand the chip will provide a nice amount of current even for "small" impedances (ie. under 600 ohms) so in some cases it would work better than many of the standard opamps.

I also know that this IC is used in some distortion pedal circuits, with or without diode clippers, and the overall comments praise it's tone. All these circuits seem to solely rely on overdriving a tube stage though.

Neither I would limit the use of LM386 to just the poweramp purpose the datasheet describes, and that's because I have bumbed into couple of other interesting (and unorthodox) circuits: One of them was LM386 in class D configuration, (this circuit was presented in DiyAudio class-D forums about a month ago) and the second one used the LM386 to replace the voltage divider/reference voltage/regulator - circuit of a typical single supply opamp based (guitar pedal) circuit. Nice idea since the output of the LM386 is always half of the supply voltage. Anyway, I think the internet is already full of LM386 circuits that look exactly alike and some originality and innovation is never a bad thing.

One point worth to mention is that there are lot's of different LM386 chips. Some of them have different supply voltage and output power ratings (from 12 to 5V and from 1W to 0,3W!!!) and some of them are just plain "mystery chips" with specs you might have to guess. The last time I bought LM386 chips i got a bunch of GL386 chips instead - which luckily are totally identical to the 1W/12V LM386. Even their datasheet seems to be a carbon copy of original LM386 datasheet.

The reason why I mention this is that one has to be extra careful when choosing the LM386 chip, otherwise he/she might end up being dissappointed when the circuit seems to operate worse than expected for no obvious reasons. This is not an ideal situation for beginners in DIY electronics since they might not have a clue about this variation between "LM386" models. Luckily, I haven't yet bumbed into any counterfeit LM - or whatever - 386 chips though.

Teemu K
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Old 18th November 2005, 05:32 PM   #6
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My design utilizes an input buffer with a 3 megohms input impedance and about 3 dB of gain. I'm pretty certain I can dumb down the LM386's performance and still get a lot of clean output and gain from it.


Underpowered?
I seriously doubt it.
I actually have used the LM386 circuit to drive a 4x12 cabinet with a 9 volt battery powering it.
Maxing the gain is easy. You slap a variable resistor between pins 8 and 1 I believe it is and you'll get 200X. My guitars are high enough output as it is so I'm not really looking to add voltage gain as much as raw volume. I think a lot of people go about things the wrong way in their design and understanding the nature of signal voltage and volume response occuring in musical instrument gear. My findings have been that fine tuning a rigs response and sustain greatly involves both volume and signal voltage tinkering.

Think of it this way, your pickups are hot enough but you want to use less dirty gain so you can get a nice smooth tone that is still fairly clean but delivers high performance suitable for lead/solo playing. Say like Santana's tone. You may find with some rigs cranking down the voltage but increasing the volume does the trick, others it may be the opposite or a combination of whatever. Personaly I think if your pickups performance, output and response is plenty dynamic, using volume to overdrive an amp rather than voltage yields a smoother tone.
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Old 26th November 2005, 01:20 AM   #7
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Default LM386 Actually Works

I know it's a power amp, and hard to believe, but I've been using this simple little circuit for a couple years now between my guitar and amp. It makes my 30W Kustom sound like it has a few more watts, and also seems to add a little quality to the tone. I do not use the input cap, and I do not join pins #1 and #8. If you join pins 1 and 8 it adds too much gain, but would probably be good for distortion pedal. I like it loud, and was running my amp at almost 100% volume. Now I run it at 40% on the volume knob. I have used it with Fender Strat and Les Paul with good results. Great little chip. I believe they are about .39 cents US$ at Mouser Electronics.
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Old 14th March 2012, 08:14 PM   #8
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fwiw, and sorry to bump a zombie, but google "dead easy dirt"...there's nothing to it, and it makes a great little distortion pedal....and easy to play with to taste. surprisingly musical!
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