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Small Guitar Amp - LM386
Small Guitar Amp - LM386
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Old 17th July 2017, 03:12 PM   #1
THRobinson is offline THRobinson  Canada
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Default Small Guitar Amp - LM386

Seen a few diagrams for these 'Smokey' Amps... Little Gem, Ruby... etc... lot's of variations out there. I have 0 background in electronics, thought one of these with a breadboard would be a fun learning project.

I have a breadboard, small bundle of jumper wires, and two LM386 chips and a little IC socket for them, plus a pair of small perfboards (I think is the name)... just need to get some capacitors and resistors.

Questions are

1) Does it matter for audio which resistors are used? series, material, brand, etc...

2) Capacitors I know some are meant for audio, though not sure if in this case it would make a big difference or not. Was looking at the Nichicon MUSE series, but for small capacitors, 0.047uF / 0.01uF for example, they don't look like cans, more like squared blobs with wires. For those capacitors, is there a Nichicon series meant for audio? or so small who cares?

3) For one of these amps... do capacitors really matter? apart from good Japanese ones vs cheap ones?

Again, thought be a fun small project... I haven't played guitar in years, but have a nephew that does so thought I'd make a pair of mini guitar amps for each of us.

Amp I will probably build is
Little Gems
or
Ruby
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Old 17th July 2017, 05:09 PM   #2
Enzo is offline Enzo  United States
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OK, I may get flamed for this, this is largely a hifi board. There are a lot of "cork sniffers" in the hifi world, and I am not going to say they are wrong...for hifi. But this is just a guitar amp, and in the guitar world there is a lot less concern over which brand of overpriced cap to use.

But the 386 projects are good projects to get your feet wet with, so to speak. And relatively inexpensive, you might build say three of them, each with different types of parts, just to see what differences it does or does not make.

As to caps, the two electrolytics pretty much have to be that type. If you find film caps of that value, they will likely be larger than the whole circuit board. The other caps are going to be film caps, they are not readily available as electrolytics due to their small size, and ceramics are best left where they sit.

This is not a high gain amp, really it is just a small power amp. And it runs on a 9v battery, so caps need not have high voltage ratings. Personally I would use any general line of film caps. The Ruby page has not only a layout, but also a photo of one made. The part selection there looks fine to me. Simple film caps, and a couple common film resistors.

In the world of hifi, the goal is for the system to be as transparent as possible, we don't want the sound to be colored. But in the guitar world, the amplifier is part of the instrument. A colorless amp would sound like plugging your guitar into the PA or worse, a hifi. A very lifeless sound. Guitar amps are made to color the sound, they add their own molding to the sound. That is why some players use a Marshall, and others use a Fender amp, the two amps sound nothing alike.

So I am not being anti-hifi, just suggesting we not apply the same hifi standards to guitar work. In other words, don't sweat the small stuff. I am sure nephew will appreciate it.
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Old 17th July 2017, 05:18 PM   #3
THRobinson is offline THRobinson  Canada
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Ya I figured pretty much that was the case... basically, get Japanese caps and beyond that don't worry about it.

I see on DigiKey they even have some CAP Kits from Nichicon ($$$) and Panasonic and some under $30CAD kits from Rubycon as well. May even be worth getting a kit so I can play with different caps and see how they change things. I think start at a 25V kit, which I assume is more than plenty for a 9V battery.

Capacitor Kits | DigiKey
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Old 19th July 2017, 08:50 AM   #4
Enzo is offline Enzo  United States
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25v would be fine, even 16v. You could use even higher voltages, but the caps get larger as the voltage goes up, so they could get crowded.
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Old 19th July 2017, 10:37 AM   #5
Ketje is offline Ketje  Belgium
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There are diff. types of LM386, be shure to use the right one.
Mona
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File Type: jpg 386.jpg (33.0 KB, 103 views)
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Old 19th July 2017, 05:17 PM   #6
THRobinson is offline THRobinson  Canada
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I forget which LM386's I ended up getting, actually bought them a while back then got busy and well, ya... kinda resurfaced the other day which is why decided to make the amp finally.

If I recall, the higher the last number is the higher the wattage for the speakers, which is why I think I went for the LM386N-3... though power wise, since using a 9V battery I think I'm safe in that sense.

Though, while talking capacitors and 16v, 25v, etc... may as well ask. I see threads where people get amps and replace the caps for better audio, also, even if keeping the audio caps the same, they often replace the caps for the power input.

What's the rule on that?

Let's say, just making a number up... you have an amp and the cap at the power source is 1000uf/12V... I've seen people mention replacing with a higher voltage, also seen people change to ones with a different uf.

What's the general rule to thumb when recapping the power input caps?

Just curious, I have a cheap eBay TPA3116 amp coming though at this point assuming lost (almost 2 months now) and was looking at a Lepai and saw posts about recapping those for the audio or at least the power cap to make it better. Power one I assumed you'd get a better cap with matching specs and that's it but, some people change the specs as well and curious why in case I end up grabbing a Lepai (not Lepy).
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Old 19th July 2017, 06:20 PM   #7
CapnDenny1 is offline CapnDenny1  United States
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And then there are some of us who want our guitar amps to sound like Hi-Fi, only also like a guitar amp?

Don't sweat the parts. Save your money for the next one. This won't be very loud at all.

But for a first project, it looks pretty cool.
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Old 19th July 2017, 06:38 PM   #8
Enzo is offline Enzo  United States
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OK, say 1000uf cap. Usually something that large is a filter cap in some supply. SOmeone may decide to use 2200uf instead, because it will be a "better" filter. That is only th case if the original value was not sufficient. If you have removed all the ripple, you cannot then go back and remove more. If the design is marginal, then maybe larger caps does help. Point being it is case by case, larger filters does not automatically improve things.


Caps, electrolytics anyway, come in a couple temperature ratings 85 or 105 degreesC. 85 degree caps tend to be a couple cents cheaper, which adds up when you are using 100,000 of them. So in SOME applications like power amps where heat can be high, someone may find 85 degree caps stock, and puts in 105s for better reliability. In something like your 386, temperature will not be a factor.

People love to fuss with their stuff. People argue over which caps are "better" than which all the time, search this forum for it. In my view, some of it is the results are better because we did it ourselves. But I will believe there is genuine improvement in their amp, at least for their ears. There might be small differences in actual capacitance value, or ESR, or self-inductance, or whatever, that could have a subtle affect on your sound.

VOltage? You can always use higher voltage caps, though they take up more space. Usually it doesn't matter. In your 9v battery circuit, it is unlikely there will be any voltage spikes threatening the 25v caps, so I see no advantage to using 35 or 50v ones, other than I may have them on hand already. Someone could argue that higher voltage ones might have more inductance or something, I guess it is possible, but how much effect that would have on power supply filters I couldn't say.

There is no "rule" about upgrading caps or other parts, other than the specs have to meet the circuit needs. When you want your circuit to be better, you need to define what better means. How is the amp lacking now? What do you need it to do to be improved?
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Old 19th July 2017, 06:47 PM   #9
THRobinson is offline THRobinson  Canada
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Quote:
Originally Posted by CapnDenny1 View Post
And then there are some of us who want our guitar amps to sound like Hi-Fi, only also like a guitar amp?

Don't sweat the parts. Save your money for the next one. This won't be very loud at all.

But for a first project, it looks pretty cool.
No... I think you misread... in addition to the guitar amp, I have an eBay amp for another project (arcade cabinet) coming which seems lost in the mail at this time so may buy a Lepai mini amp... the recap questions were more about that.

For the guitar amp, I'll grab probably the cheapest Nichicon's I can find, or, a few cheap kits online that have a few dozen caps in them from Nichicon, Panasonic and Rubycon.
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Old 19th July 2017, 07:01 PM   #10
THRobinson is offline THRobinson  Canada
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Quote:
Originally Posted by Enzo View Post
OK, say 1000uf cap. Usually something that large is a filter cap in some supply. SOmeone may decide to use 2200uf instead, because it will be a "better" filter. That is only th case if the original value was not sufficient. If you have removed all the ripple, you cannot then go back and remove more. If the design is marginal, then maybe larger caps does help. Point being it is case by case, larger filters does not automatically improve things.


Caps, electrolytics anyway, come in a couple temperature ratings 85 or 105 degreesC. 85 degree caps tend to be a couple cents cheaper, which adds up when you are using 100,000 of them. So in SOME applications like power amps where heat can be high, someone may find 85 degree caps stock, and puts in 105s for better reliability. In something like your 386, temperature will not be a factor.

People love to fuss with their stuff. People argue over which caps are "better" than which all the time, search this forum for it. In my view, some of it is the results are better because we did it ourselves. But I will believe there is genuine improvement in their amp, at least for their ears. There might be small differences in actual capacitance value, or ESR, or self-inductance, or whatever, that could have a subtle affect on your sound.

VOltage? You can always use higher voltage caps, though they take up more space. Usually it doesn't matter. In your 9v battery circuit, it is unlikely there will be any voltage spikes threatening the 25v caps, so I see no advantage to using 35 or 50v ones, other than I may have them on hand already. Someone could argue that higher voltage ones might have more inductance or something, I guess it is possible, but how much effect that would have on power supply filters I couldn't say.

There is no "rule" about upgrading caps or other parts, other than the specs have to meet the circuit needs. When you want your circuit to be better, you need to define what better means. How is the amp lacking now? What do you need it to do to be improved?
Thanks... I was wondering when it came to a cap for power input... thought if you add a cap with a higher voltage, it would let too much power in and fry stuff, but I guess the volt rating is more what it can handle than what it lets through.

I recapped my two Samsung monitors because of known issues with those (LINK) and when I bought new caps, I tried to match the specs as close as possible, and physical size, though read a higher V rating is better... wasn't sure about uf and just left that alone. Ended up matching specs pretty much for everything using Nichicon caps (one Panasonic)... when there were more than one to choose from, I looked at the ones that had the highest temperature ratings and longest life expectancy (hours @ temp).

Found a spec sheets for CapXon caps which were in there, and wasn't sure if I had the exact same series but tried my best to match specs with ripples and such...

Took WAY more time/effort than expected to replace the caps. Kinda assumed 470uF35V was the same regardless brand, but soon found out that there were different sizes, ratings, that whole ripple thing etc... pain in the butt but made me want to learn more.
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