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Author Topic: Build Your Own LM386 Preamp  (Read 29252 times)

willy1usa

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Build Your Own LM386 Preamp
« on: September 28, 2006, 09:29:24 PM »
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.
« Last Edit: October 04, 2006, 10:48:26 AM by joecool85 »

joecool85

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Re: Build Your Own Noisy Cricket
« Reply #1 on: September 28, 2006, 10:28:59 PM »
Cool, I love the idea as a LM386 as a preamp.  What'd you use for a schematic for that?
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willy1usa

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Re: Build Your Own Noisy Cricket
« Reply #2 on: September 29, 2006, 06:12:14 AM »
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.

joecool85

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Re: Build Your Own Noisy Cricket
« Reply #3 on: September 29, 2006, 07:56:31 AM »
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?
Life is what you make it.
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willy1usa

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Re: Build Your Own Noisy Cricket
« Reply #4 on: September 30, 2006, 12:06:03 PM »
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.

joecool85

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Re: Build Your Own Noisy Cricket
« Reply #5 on: October 01, 2006, 09:43:14 AM »
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.
Life is what you make it.
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willy1usa

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Re: Build Your Own Noisy Cricket
« Reply #6 on: October 01, 2006, 03:38:08 PM »
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.

idle_chatterbox

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Re: Build Your Own Noisy Cricket
« Reply #7 on: October 02, 2006, 03:59:12 PM »
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?

 :)

willy1usa

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Re: Build Your Own Noisy Cricket
« Reply #8 on: October 03, 2006, 08:31:30 AM »
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.

joecool85

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Re: Build Your Own Noisy Cricket
« Reply #9 on: October 03, 2006, 08:45:41 AM »
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 :-)
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Stompin_Tom

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Re: Build Your Own Noisy Cricket
« Reply #10 on: October 03, 2006, 03:53:25 PM »
I think Dan-o's pico cricket is what willy's talking about (bottom of page)...
 
http://beavisaudio.com/Projects/NoisyCricket/index.htm
myspace.com/bestinventions

joecool85

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Build Your Own LM386 preamp
« Reply #11 on: October 04, 2006, 10:39:09 AM »
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
« Last Edit: October 04, 2006, 10:47:56 AM by joecool85 »
Life is what you make it.
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Stompin_Tom

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Re: Build Your Own LM386 Preamp
« Reply #12 on: October 04, 2006, 12:33:43 PM »
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.

myspace.com/bestinventions

joecool85

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Re: Build Your Own LM386 Preamp
« Reply #13 on: October 04, 2006, 01:05:10 PM »
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.
Life is what you make it.
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Stompin_Tom

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Re: Build Your Own LM386 Preamp
« Reply #14 on: October 04, 2006, 01:56:09 PM »
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.
myspace.com/bestinventions

 

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