I've been using the LM386 for couple years - before I saw the Ruby circuit. I installed the simple 386 circuit, without an input cap, just on the inside of my 30W Kustom guitar amp, working as a preamp. Works great. Added a lot of SPL to this amp. I was running the amp volume on 7. Now I run it on 2. Big difference for this little amp.
Cool, I love the idea as a LM386 as a preamp. What'd you use for a schematic for that?
The LM 386 I installed in my 30W Kustom, has only 2 parts - a .1 ceramic bypass cap, and a 220 uf output cap. I installed it right at the 1/4 input jack of the amp. To avoid messing with anything else within the amp, I had room in the case for a 9V DC wall wart, and 2 1000uf smoothing caps. I wired the wall wart to the AC where it comes in to the case just after the fuse. A very easy project, and added much needed extra SPL to this little 30W. I like it loud. I always run this amp volume on 7. Now I run it on 2.
Narrow minded, I accidently left out the input cap on one of my 386 preamps. But it worked great, so I quit using them. Depending on the project, a volume control can be used if needed.
This 30W Kustom is a chip amp. There's a possibility it could work differently for different amps - tube, transistor, etc. However, I've been building them in a small Radio Shack project box for family and friends as a plug-in preamp for guitars and mics. No complaints yet.
LM386 is a great little chip. I've been using it for a couple years.
Wow this is great. I've been wanting to use one as a preamp (and did for a while) but was told not to because even though its small, it is technically a poweramp chip. I was told it would do damage to my amp to run it that way. So did you basically wire it like a little gem and then instead of going to a speaker, it goes to the rest of the amp? Is the rest of it identical?
I disconnected the input jack from the amp, wired the little 386 circuit to the jack, then wired the 386 into the amp where the input jack was. In other words, I put the 386 between the input jack, and the amp. (not good at explaining things) However, this could be a problem on certain amps if the input jack was mounted onto a circuit board, and shouldn't be attempted by any newbies. I play 3 times a week at church and wanted to cut down on the number of pieces I have to carry, and with the power supply mounted within the amp, no more battery purchases.
The simplest, would be as I did before, mount it in a little box and plug into it. The circuit is so small, it could even be mounted inside a guitar if there was room for a 9v battery. But again, that wouldn't be a job for a newbie probably.
As previously posted, only 2 parts to my circuit, a bypass cap between pins 6 and 4 (pins 4 & 2 are hooked together), and an output cap. The circuit is the size of a postage stamp. In this circuit, I do not use pins 1, 8, and 7, so I just snip them off with fingernail clips and get them out of the way.
The size of the output cap can be adjusted to suit your needs. I normally use a 220uf. The larger you go, the more bass response you get.
And YES, being able to use it as a power amp or preamp, makes this little chip amazing. When at all possible, I use it, to avoid high parts count of other chips.
Wow, this is great. Could you draw up a quick schematic possibly? If you don't/can't/won't I probably will make an attempt later and see if I can get it right. I'd love to have this in the wiki, and I would like to test it some. I used my little gem as a preamp for my amp a few times (both my dean markley, and my LM3886 setup) with good results, but I was afraid of it hurting stuff. I did some research and found the voltage levels should be ok for the amp, but was worried about amps. Since you've had good luck with it, it makes me wonder. I'd love to see a solid LM386 preamp put together with 3 band EQ. It's something I'm considering working on.
No problem joecool85. I'll get a shematic drawed up and posted asap.
The ones I built for some friends, as plug-in modules, are being used as guitar and mic preamps. One plugged into a PA system for a mic, and a couple into a powered mixer. So I don't think there would be any danger in this circuit causing any damage, as they have been using them for several months now with no complaints, just compliments.
I'd also like to see the schematic. Sounds like a great idea you have going.
I'm a bit curious about the use of the fuse. Based on your description, is the fuse upstream of the wall-wart power supply?
:)
RE: Fuse
Sorry about that, I stateted that wrong. The wal-wart is wired in before the fuse, so it is fused with the rest of the amp.
Trying to send the 386 schematic, but I'm having trouble with my scanner. Always something to make one's day. Anyway, there's really nothing to it. Where the -/+ wires come in, I use a .1 ceramic bypass cap, as close to the chip as possible. I come straight in to the input - no input cap. I wire pins 2 and 4 together and hook to ground. I use a 220uf cap on the output, and that's it. On this particular circuit, I don't use pins 1,7, or 8, so I just clip them off and get them out of the way.
All the other 386 circuits you see, have so many parts, some may laugh at this one, but as previously posted, I play 3 times a week, and had this circuit in my 30W Kustom for quite some time now. If there were going to be any problems, they would have showed up by now. Also, friends using this circuit, have had no problems.
There might be applications, or guitar amps, where it might not work, or where you would need an input cap, or maybe a zobel network on the output, but so far, I've not had any problems.
Also, I'll say this again: If the amp input is sortered onto a circuit board, I would recommend just mounting the chip in a small box with 9V battery and use as you would any other effects box. Anyone reading this that didn't have the experience, could damage their amp circuit board, or maybe cause smoke !!
If I can get this scanner going, I'll send the drawing.
Cool. Sounds like what I want in my guitar. I was going to mount a LPB-1 circuit in there, but this would be even cooler. I love the LM386 chip :-)
I think Dan-o's pico cricket is what willy's talking about (bottom of page)...
http://beavisaudio.com/Projects/NoisyCricket/index.htm
Is this what you meant willy?
I was confused about where to put the bypass cap, so its not in there, where would that go?
And for people that don't know, the pins are numbered like this on a LM386:
1-XX-8
2-XX-7
3-XX-6
4-XX-5
Are you planning to stick this in front of your poweramp/chipamp, joe? I'm curious to know how it turns out. I was thinking of making dan-o's noisey cricket anyways, but it might make for a slightly more flexible and certainly a little different preamp... hmmm... I could make it easily detachable (could just sit on top) and then I'd have both a practice amp and a gigging volume amp sort of in one... just thinking here.
Yeah I am. But first its going straight into my guitar so it will be infront of any amp haha. I have used a little gem as a preamp with great results on my chipamp though. So I'm sure this will work well. I'm thinking for the version I'm putting on my chipamp I will put a 3 band EQ ahead of it.
yeah, a three band would be better than a one knobber... I gotta finish my poweramp before I can start experimenting, though... wish I had more time!
Let us know what you come with.
YES-stompin_T "The Smokey" is the circuit I've been using. To get a little more bass response, I use a 220uc cap on the output. You can tailor this to suit your needs. The single coil pickups in my Strat needed a little more bass.
Sorry Joecool, I skipped over your post.
YES, the circuit you got drawed out is the one I use.
Cool, now what about the bypass cap? You said you used a .1uF between the +/- Is that the +/- as in power, or signal?
The .1, also numbered as a 104, bypass cap goes on the power lines as close the chip as you can get it. I usually run my +/- power lines on the back side of the circuit board (underneath, the chip). Or, if you're handy with the soldering iron, you can solder the little .1 ceramic cap also on the backside of the chip from + power pin to the - ground pin.
The little preamp boxes I built for some friends, don't even have a circuit board. The bypass cap is soldered on the backside of the chip,the output cap soldered directly onto pin 5, and with a small piece of solid wire, I soldered the input pin directly onto the 1/4" input jack.
Also, I use the 3 pin 1/4" jacks, wire the 9V battery to the 3rd pin, so when they plug in, it powers up. That eliminates the need for a switch. Most of your stomp boxes are wired this way.
Quote from: willy1usa on October 08, 2006, 07:30:13 AM
Also, I use the 3 pin 1/4" jacks, wire the 9V battery to the 3rd pin, so when they plug in, it powers up. That eliminates the need for a switch. Most of your stomp boxes are wired this way.
Cool, thats how I always wire my stompboxes as well. It just makes sense.
Friend of mine had some LM380's, and I've been playing around with them. They are just as simple, and as low parts count as the LM386, but more power. And they accept the guitar with no problem. The data sheet I have says it's capable of 4 Watts. So it works as a preamp, and would also work as a small practice amp.There's a very noticable difference in power of the 386 and 380. I've just built one, and it really sounds good thru an 8" speaker. (in the tiny practice amp category of course)
My friend was a lucky dog - caught a Radio Shack moving to new location, and they sold their inventory to keep from moving it. He don't want to sell any of it, but he did give me a few pieces.
if you use the 386 as a pre you might want to add a buffer as well,
i input inpedance is fairly low if i recall correctly.
Quote from: doug deeper on December 15, 2006, 01:07:16 PM
if you use the 386 as a pre you might want to add a buffer as well,
i input inpedance is fairly low if i recall correctly.
Actually, the circuit is almost a buffer already. It might be a good idea to put a pair of 1Mohm+ resistors at the input, (voltage divider?) one to ground from input and one to V+ from input. This is a Jack Orman idea, and will set input impedance.
Quite a lot of confusion here... At least for me...
I think it might not be a good idea to put a pair of those resistors to input: This is effectivily loading the supply with 2 ohm load! Besides, I can't understand who'd wish to have an input impedance of 0.5 ohms. I'm sure Jack Orman has meant 1 Megaohm resistors or something.
Internal input impedance of LM386 is 50 kilo-ohms. Any input resistor from signal path to ground is in parallel with it. The recommendation of using an external buffer is very wise.
The power of LM386 can't toast anything if you use the chip to drive high impedance loads. (P=UI) If the quoted output power of the chip is half watt to eight ohms then the output power is something pretty small for typical input impedances (few kilo-ohms and up).
Yeah, I meant 1Mohm or higher, edited my post above to reflect that.
This circuit isn't being used to drive a speaker, in this discussion it's being used as a "preamp", but compare it to the buffers on Orman's site. In one case, the only things missing are the input resistors. If all you're looking to do is set input impedance, then that's all you should need to worry about. I would think that putting a buffer ahead of this would lead to the necessity of tweaking the circuit, there'd be a fair anount of gain on tap.
i buffer wouldnt add any gain, just raise the input impedance, and make it a lot more pedal friendly (among other things).
I guess I have to repeat myself: "Internal input impedance of LM386 is 50 kilo-ohms. Any input resistor from signal path to ground is in parallel with it."
This is fixed input impedance. If you don't take my word for that see the datasheet. Putting more resistance to the input will just lower the input impedance even further. Thus need for external buffer.
Regarding those input resistors: The inputs of LM386 are internally fixed to about zero volt bias. If you try to tie the input to half supply potential externally you disrupt the operation of the chip. If I'm correct, in such occasion it will have a negative gain. LM386 is not an opamp!
I don't know why some people refer to LM386 as a buffer. This chip has an internal gain set minimum of 20. Buffers are unity gain.
well said!