Guitar amplifier in a can

duragezic

Lifer
Oct 11, 1999
11,234
4
81
As I member of the student IEEE chapter here, we get to see and do a few neat things every now and then. A couple of months ago, the chair presented his guitar amplifier in an aluminum can (like soup or vegatable) . It was kind of cool actually and sounded decent. It's at least some amplifier, since playing electric guitars without an amp doesn't have a good sound, but I don't necessarily want to use a large amp everytime if I'm just messing around for 5-10 minutes.

All it used was a LM386 op amp, a small, full-range speaker (he got one from Durango), and a resistor or two to control the gain, a few caps, and I can't remember if he used a pot for volume or if it was just on/off. But very simple... only a few $ in parts, best if you can get the speaker free.

I'm unsure of what op amp characteristics are important in this application. The guy said that he used a gain of 50, which produced a very slightly distorted sound. He had tried 200 but it was very noisy/thrashy. I was thinking maybe 100 might suit my style more.

Has anyone done one of these before? Or would know what op amp would be best for this? Or, what could I do to make it even better if possible? Like he just said from the LM386 datasheet, the example gain schematic was all there was to it. Like I was considering adding a switch for higher gain and lower gain, or perhaps a pot to for that, etc. Ideas?
 

duragezic

Lifer
Oct 11, 1999
11,234
4
81
It's the LM386 actually. I mixed up the numbers. The guy said that he followed the data sheet. There's a few resistors and caps and the LM386, plus a speaker and 9V, and that's all there is to it. I'm not sure what kind of mods if any I want to try against the example on the data sheet but I'll update this thread if I ever get the time to try it out.
 

BlancoNino

Diamond Member
Oct 31, 2005
5,695
0
0
Originally posted by: duragezic
Has anyone done one of these before? Or would know what op amp would be best for this? Or, what could I do to make it even better if possible? Like he just said from the LM356 datasheet, the example gain schematic was all there was to it. Like I was considering adding a switch for higher gain and lower gain, or perhaps a pot to for that, etc. Ideas?

Going in that direction would probably be too advanced. Are you really looking for a cheap, small amp to play?

http://www.samedaymusic.com/product--EPIEPABKJR

Those have amazing tone and are all Class A tube.
 

mattyrug

Golden Member
Sep 25, 2000
1,162
0
0
how's about one of these Mini-Marshall Stacks
I'd have to say to build one, you wouldn't need/want a full range speaker, probally something with a 12dB/Oct LPF starting at 6k and a 12dB/Oct HPF at 100Hz. Ever plug a guitar amp into a full range cab or into a speaker with a horn? Sounds awful, like razor blades!
 

0

Golden Member
Jul 22, 2003
1,270
0
0
Actually you can use any op amp and stage a couple of power transistors on its output to get much more power. We do this all the time.
 

duragezic

Lifer
Oct 11, 1999
11,234
4
81
Cool, thanks for the ideas.

I'm not actually looking for a mini, 10 W amp or so. Much too expensive anyway. Granted this homemade one in a can is not near the level of the mini amps, but it's more of a thing to play around with when I'm just messing around for a few minutes. Plus it'd be a cool electronics project to do, and hopefully I can make some small modifications so it's a little more challenging. And what's cool is that I have a circuit design and fabrication class this semester. We get to do a project or two where we make a schematic of our choosing, layout the board in EAGLE, and then the guy mills out the boards for us (for free, well included in the lab fee). I'll probably have to pay the $ to populate it but I can likely get all of the components for a few dollars from our IEEE lab.

Right, it wasn't a full-range speaker... it was just a small one from a vehicle that the guy got from a sounds/audio place for free by just asking for it. If I can't find that, I'll find something suitable in Mouser of the like. When I looked before, most were $2-$5 or so for something that seemed like it would work. So I want to keep this project around $10-15.

The LM1875 is a beast! The datasheet even has a layout example and considerations when laying out the components. I'll see if I can find some of these components to borrow and breadboard up a test to play around with the gain. I'll probably start with a 9V battery as the supply and see how that works. Looks like I'd get about 5 W with that.

0: Could you be more specific about the power transistors? My class covering op-amps, transistors, and diodes was a joke, thus a huge part of EE I have little knowledge of. Getting a good grade had NOTHING to do with the actual understanding of those devices.

 

ttown

Platinum Member
Oct 27, 2003
2,412
0
0
Hey!

This sounds like a cool project.
Can you post or link to a circuit diagram?

I got me and my kid a radio-shack "sensorlab" project kit for xmas; and also an electric guitar.

This sounds like a perfect rainy day project!

tia
 

0

Golden Member
Jul 22, 2003
1,270
0
0
Originally posted by: duragezic
Cool, thanks for the ideas.

I'm not actually looking for a mini, 10 W amp or so. Much too expensive anyway. Granted this homemade one in a can is not near the level of the mini amps, but it's more of a thing to play around with when I'm just messing around for a few minutes. Plus it'd be a cool electronics project to do, and hopefully I can make some small modifications so it's a little more challenging. And what's cool is that I have a circuit design and fabrication class this semester. We get to do a project or two where we make a schematic of our choosing, layout the board in EAGLE, and then the guy mills out the boards for us (for free, well included in the lab fee). I'll probably have to pay the $ to populate it but I can likely get all of the components for a few dollars from our IEEE lab.

Right, it wasn't a full-range speaker... it was just a small one from a vehicle that the guy got from a sounds/audio place for free by just asking for it. If I can't find that, I'll find something suitable in Mouser of the like. When I looked before, most were $2-$5 or so for something that seemed like it would work. So I want to keep this project around $10-15.

The LM1875 is a beast! The datasheet even has a layout example and considerations when laying out the components. I'll see if I can find some of these components to borrow and breadboard up a test to play around with the gain. I'll probably start with a 9V battery as the supply and see how that works. Looks like I'd get about 5 W with that.

0: Could you be more specific about the power transistors? My class covering op-amps, transistors, and diodes was a joke, thus a huge part of EE I have little knowledge of. Getting a good grade had NOTHING to do with the actual understanding of those devices.


check out the link below. What I'm talking about is summarized in the section called OUTPUT STAGE IN A FEEDBACK LOOP

http://www.ecircuitcenter.com/Circuits/pushpull/pushpull.htm

A matched pair of NPN/PNP power transistors will do the trick. A very easy addition to give you good power.
 

ttown

Platinum Member
Oct 27, 2003
2,412
0
0
LINK

Here's a link to the IEEE meeting notes, with the guitar-amp circuit diagram at the end

Thanks OP! Looks easy enough for a rainy day

edit: in the diagram, there's a BYPASS capacitor with a broken line ?
What is that? I've never seen that before (one semester of college electronics)
What size should it be?
 

CraKaJaX

Lifer
Dec 26, 2004
11,905
148
101
Originally posted by: ttown
LINK

Here's a link to the IEEE meeting notes, with the guitar-amp circuit diagram at the end

Thanks OP! Looks easy enough for a rainy day

Nice. :thumbsup:
 

ttown

Platinum Member
Oct 27, 2003
2,412
0
0
Originally posted by: ttown
LINK

Here's a link to the IEEE meeting notes, with the guitar-amp circuit diagram at the end

Thanks OP! Looks easy enough for a rainy day

edit: in the diagram, there's a BYPASS capacitor with a broken line ?
What is that? I've never seen that before (one semester of college electronics)
What size should it be?
*bump* to see if anyone can tell me what size the bypass cap should be, and why does the diagram show a broken line
 

duragezic

Lifer
Oct 11, 1999
11,234
4
81
Haha wow, ttown, nice find when you didn't even know what school to look for! I had deleted the email those notes were sent in a while ago so I only remembered the idea when I seen the that page posted by the elevators.

I believe the bypass cap is to block DC signals from intefering with your sound signal. Maybe the broken line means it's optional, but they are pretty common so I would use it. I would guess a 0.01 uF would work. I can ask the Chair (the guy who built and presented it) if I see him around school later today to make sure.
 

So

Lifer
Jul 2, 2001
25,923
17
81
Originally posted by: duragezic
Haha wow, ttown, nice find when you didn't even know what school to look for! I had deleted the email those notes were sent in a while ago so I only remembered the idea when I seen the that page posted by the elevators.

I believe the bypass cap is to block DC signals from intefering with your sound signal. I would guess a 0.01 uF would work. I can ask the Chair (the guy who built and presented it) if I see him around school later today to make sure.

Haha, our IEEE did the same thing a while back.

Well, a mint tin audio amp, but the same concept.
 

duragezic

Lifer
Oct 11, 1999
11,234
4
81
Yeah they did the headphone audio amp in an altoids can last year.

Btw, I had talked to the guy Saturday night about it and I think he said it was only like 1/2 W or so of output power. So ttown you might want to try some of these other ideas posted here for a more powerful amp, but even as is, it was loud enough for a small room with a couple of people listening. So I mentioned the LM1875 to him and he said he was familar with it from fixing a small, 10-15 W amp for someone and it used those.

I'm thinking the LM1875 and/or the power transistors could make a beast!
 

Seekermeister

Golden Member
Oct 3, 2006
1,971
0
0
Or, you could do as I did, and get an acoustic electric. That way you can get good sound with or without an amp. About the only time that I use the electric aspect, is to plug into the computer for tuning, or input to a sequencer. But then, I'm not a performer.
 

ttown

Platinum Member
Oct 27, 2003
2,412
0
0
Originally posted by: duragezic
Yeah they did the headphone audio amp in an altoids can last year.

Btw, I had talked to the guy Saturday night about it and I think he said it was only like 1/2 W or so of output power. So ttown you might want to try some of these other ideas posted here for a more powerful amp, but even as is, it was loud enough for a small room with a couple of people listening. So I mentioned the LM1875 to him and he said he was familar with it from fixing a small, 10-15 W amp for someone and it used those.

I'm thinking the LM1875 and/or the power transistors could make a beast!
I already have a real amp for the guitar -- so I'm really just thinking that a couple bucks worth or parts combined with a Radio Shack project kit breadboard would be a good educational experience for me and my daughter.
Just something a little more practical and fun than the blinking led or buzzing buzzer projects.

I did a little reading about bypass capacitors and came across a general recommendation to use 0.01uF caps with low power ICs, so I was going to try that. It does look like it's there for noise reduction.
I'd appreciate it if you could confirm the size. Anyway... looks easy enough to do -- so thanks for the original post!
 

nakedfrog

No Lifer
Apr 3, 2001
61,341
16,879
136
Yeah, a few years back I rigged up an LM386 on a breadboard, and used it to drive an old crappy bookshelf speaker. It sounded pretty decent for the cost (which was basically a 9V battery, got all the parts from people at no cost).
 

Special K

Diamond Member
Jun 18, 2000
7,098
0
76
Originally posted by: 0
Originally posted by: duragezic
Cool, thanks for the ideas.

I'm not actually looking for a mini, 10 W amp or so. Much too expensive anyway. Granted this homemade one in a can is not near the level of the mini amps, but it's more of a thing to play around with when I'm just messing around for a few minutes. Plus it'd be a cool electronics project to do, and hopefully I can make some small modifications so it's a little more challenging. And what's cool is that I have a circuit design and fabrication class this semester. We get to do a project or two where we make a schematic of our choosing, layout the board in EAGLE, and then the guy mills out the boards for us (for free, well included in the lab fee). I'll probably have to pay the $ to populate it but I can likely get all of the components for a few dollars from our IEEE lab.

Right, it wasn't a full-range speaker... it was just a small one from a vehicle that the guy got from a sounds/audio place for free by just asking for it. If I can't find that, I'll find something suitable in Mouser of the like. When I looked before, most were $2-$5 or so for something that seemed like it would work. So I want to keep this project around $10-15.

The LM1875 is a beast! The datasheet even has a layout example and considerations when laying out the components. I'll see if I can find some of these components to borrow and breadboard up a test to play around with the gain. I'll probably start with a 9V battery as the supply and see how that works. Looks like I'd get about 5 W with that.

0: Could you be more specific about the power transistors? My class covering op-amps, transistors, and diodes was a joke, thus a huge part of EE I have little knowledge of. Getting a good grade had NOTHING to do with the actual understanding of those devices.


check out the link below. What I'm talking about is summarized in the section called OUTPUT STAGE IN A FEEDBACK LOOP

http://www.ecircuitcenter.com/Circuits/pushpull/pushpull.htm

A matched pair of NPN/PNP power transistors will do the trick. A very easy addition to give you good power.

Isn't that just an inverter made from BJTs? I'm a digital designer and don't have much experience with amplifier design.

 

0

Golden Member
Jul 22, 2003
1,270
0
0
Originally posted by: Special K
Originally posted by: 0
Originally posted by: duragezic
Cool, thanks for the ideas.

I'm not actually looking for a mini, 10 W amp or so. Much too expensive anyway. Granted this homemade one in a can is not near the level of the mini amps, but it's more of a thing to play around with when I'm just messing around for a few minutes. Plus it'd be a cool electronics project to do, and hopefully I can make some small modifications so it's a little more challenging. And what's cool is that I have a circuit design and fabrication class this semester. We get to do a project or two where we make a schematic of our choosing, layout the board in EAGLE, and then the guy mills out the boards for us (for free, well included in the lab fee). I'll probably have to pay the $ to populate it but I can likely get all of the components for a few dollars from our IEEE lab.

Right, it wasn't a full-range speaker... it was just a small one from a vehicle that the guy got from a sounds/audio place for free by just asking for it. If I can't find that, I'll find something suitable in Mouser of the like. When I looked before, most were $2-$5 or so for something that seemed like it would work. So I want to keep this project around $10-15.

The LM1875 is a beast! The datasheet even has a layout example and considerations when laying out the components. I'll see if I can find some of these components to borrow and breadboard up a test to play around with the gain. I'll probably start with a 9V battery as the supply and see how that works. Looks like I'd get about 5 W with that.

0: Could you be more specific about the power transistors? My class covering op-amps, transistors, and diodes was a joke, thus a huge part of EE I have little knowledge of. Getting a good grade had NOTHING to do with the actual understanding of those devices.


check out the link below. What I'm talking about is summarized in the section called OUTPUT STAGE IN A FEEDBACK LOOP

http://www.ecircuitcenter.com/Circuits/pushpull/pushpull.htm

A matched pair of NPN/PNP power transistors will do the trick. A very easy addition to give you good power.

Isn't that just an inverter made from BJTs? I'm a digital designer and don't have much experience with amplifier design.


the bjts are in an emitter-follower arrangement, so they don't invert and their voltage gain is 1. They are there to boost the output current of the op-amp.
 
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