Universal LM386 Audio Box - Page 1
Forum section: electronics / projects

author: jonovid
author_rank: Super Contributor
timestamp: October 04, 2019, 09:38:56 pm
content: here is a little box for the benchits a universal audio amp.if you do anything with analog audio, generally you will need a way of testing things.this little box is made from an old Dick Smith intercom.and has a DIN port for adding what ever! even if its just to use the 6 volt pin.

author: floobydust
author_rank: Super Contributor
timestamp: October 05, 2019, 01:12:46 am
content: Just a note, I was revamping an LM386 signal tracer I'd made a long time ago.It's like your circuit but the input has a blocking capacitor with diode clamp, and a 1MEG pot. I add a 1000pF cap from pin 3 to GND to stop AM radio pickup. For headphones, I add an extra 100R resistor so my ears don't get blasted.If sound quality is poor, dirty or gritty sounding - as always, the LM386 does like to burst oscillate around 13MHz. The output network 10R 0.1uF helps somewhat but the only fix I find is 2.2uF X7R ceramic cap right across Vcc and GND at pins 4,6. Without these, I've never had the LM386 behave itself.

author: jonovid
author_rank: Super Contributor
timestamp: October 05, 2019, 07:27:11 am
content: Quote from: floobydust on October 05, 2019, 01:12:46 amI know about the AM radio pickup problem. yes you are right, some fix's are needed, the circuit has a little too much gain. the odd switching is because had no space for a multi pole switch in the box, My intention is to use this, to test circuit bending & analog music synthesizer circuits.

author: 001
author_rank: Super Contributor
timestamp: October 05, 2019, 05:43:43 pm
content: Do You really use it with microphone?

author: floobydust
author_rank: Super Contributor
timestamp: October 05, 2019, 07:38:03 pm
content: I have an electret condensor mic input (no dynamic mic), not for yelling at people but to quickly test them for cars hands-free nav and PC's etc.

author: jonovid
author_rank: Super Contributor
timestamp: October 07, 2019, 05:50:42 am
content: the mic pr-amp works a good white noise generator with no input.Quote from: floobydust on October 05, 2019, 01:12:46 amnote- the power rail 220uf electrolytic is right up next to the lm386, - may need to add an nf or two here as I do with voltage regulators circuits.I have made some changes to the circuit after I tested it on a piezo but only got 50Hz AC noise.and the line out part of the circuit, failed to work properly with the 10uf at the output.did add a 2k maybe its to high, with a 600pf to clamp down the input of the mic pre-amp.yes the sound quality is hard gritty sounding, the base boost circuit in the data sheet maybe the answer here.I considered it to be too much low end boost, when looking at the data sheet. seeing the base hump, so disregarded it initially.thinking that a level flat frequency response was the best choice here.the other fix is the output 100uf is too low, no base & line out failed. more coupling on the output is needed.adding a 200uf & lowering the gain is what is needed.its problematic to remove some components as I compacted everything into the enclosurecutting wire lengths to save space.I may just start from scratch and plan it out butter on breadboard.before stuffing everything into another enclosure.all is not lost. I have a good little white noise generatorwith some limited audio functionalityif you're interested the two toggle switches , RGB color LED and the potentiometer were mounted on a sub-panelunder the top panel that was held in place with 2mm bolts, covered in self adhesive film with a top clear layer of film over the text.

author: Audioguru again
author_rank: Regular Contributor
timestamp: October 07, 2019, 05:39:37 pm
content: The output power of the LM386 amplifier IC with the 6V supply is only 0.2W before clipping which is almost nothing. The output power is less as the battery voltage runs down.The 100uF output capacitor cuts 200Hz to half the output power of higher frequencies and cuts lower frequencies much more. A tinny sound.The "bass boost" circuit actually reduces mids and highs so that the lower frequencies can use the maximum 0.2W of power.The tiny low power speaker would sound gritty and tinny anyway.

author: jonovid
author_rank: Super Contributor
timestamp: October 08, 2019, 06:20:52 am
content: Quote from: Audioguru again on October 07, 2019, 05:39:37 pmI have made some changes to the circuit .see the blueadded more caps and larger size caps.one switch, now sets the gain range, the other switch the ON , OFF and ON with Mic pre-amp.I am still the fix the output bass boost. the circuit to-date

author: Audioguru again
author_rank: Regular Contributor
timestamp: October 08, 2019, 03:13:45 pm
content: Many years ago I made a sound system for the beach. It sounded much better than the lousy ghetto-blasters that other people had.I used a 4" long throw 8 ohm woofer in a small ported enclosure and two 2.5" satellite speakers in sealed enclosures.The stereo amplifier ICs were LM2896 that had bootstrapping for a high output power when the supply voltage is low. Their metal tabs were bolted to small heatsinks. The battery was six C-size Ni-Cads producing 8.4V when fully charged. The woofer used two bridged amplifiers producing 4.3W with low distortion and each satellite speaker used 1.2W with low distortion. I did not add bass boost because it sounded pretty good without it and it would have reduced the average loudness.My home audio system had plenty of power for me to add bass boost to the 8" woofers so they sounded and felt like sub-woofers.

author: floobydust
author_rank: Super Contributor
timestamp: October 08, 2019, 06:00:23 pm
content: Mr. Carlson's Super ProbeusesLM4871but it's only a max. 6V (bridged) part 1.2W 8R, terrible datasheet and who knows what gain it's good for. The Super Probe has three extra CE amplifier stages, overall extremely high gain guessing over 1,000. I don't have a need for that though. I find gain of 200 is plenty, especially with headphones you can pick off the smallest signals.Anytime the LM386 sounds extra gritty or full of AC hum and buzz, or AM radio, it's because the IC is oscillating around 13MHz. The RF bursts show up at higher volume and radiate from the speaker wiring. I tried an output ferrite bead/Zobel helps tiny bit and best fix is a large ceramic cap right across the IC power pins. Actually, I find most of NS chip amps do this due to the Sziklai O/P stage.I kind of hate the IC because it is such a cheezy internal circuit, noisy distorted and goes back to 1976. It really needs an update. But it is convenient and OK for speech. Ali/eBay kits are $1.50 including IC, pot, pcb, DC jack etc. and hard to resist, although they are junk- have bad PCB layout and smallish 10k pot.I add two clamp-diodes to protect the LM386 input and a DC blocking cap, sometimes I'm poking around high voltages. I put a BNC to use scope probe for the input, and have an extra JFET section for high-Z work.

author: jonovid
author_rank: Super Contributor
timestamp: October 09, 2019, 06:47:19 am
content: Wow- the circuit shown in Mr Carlson's Lab video is somewhat like what Im trying to do here.but with more gain range from the highist to the low line level signals.-anyway looking at your LM386 circuitQuotenow that is bad for an audio ic, - I may need a lot more RF suppression in my project. ferrite beads.interesting to see how you have resolved the output, diode limiter,& the use of a 1M pot. -that I do not have in the right size for my project.Quotemost pre assembled LM386 amp module's sold for arduino, have a lot missing in its circuit with only a 100uF on the output.so I am stuck with a bag of cheap 4-to-15 volt LM386's off aliexpress, so the need make-do with this ic with its shortcomings.as I often copy my more successful circuits in part or in whole when considering new projects.the maximum gain of 200 for the LM386 with a 10k pot is somewhat inadequate for some of my uses, like dynamic microphones & tape heads.so I found this npn audio transistor circuit that did the job when tested running off 4-to-6 volts.its one successful white noise generator when open circuit. but otherwise will do the job for nowhowever looking at the circuit shown in Mr Carlson's Lab video, I can see how some improvements can be made to my circuitwith a little more planning within the limits of a plastic case.