Hi!
I tried to make a simple guitar amp for starters (I'm not familiar with guitar amp building, but I'm an engineer, I have a good understanding of electronics), like the Smokey Amp or the Ruby Amp. After being over-confident and building a PCB that doesn't work, I wired it up on a breadboard but it just doesn't work. One by one I tried to change everything (bought more expensive jack socket, changed the IC, played with the caps), but it does not work, neither when the pins 1-8 are left open nor when they are bypassed by a 10uF capacitor.
I'm starting to suspect the speaker. With guitar, there is no sound, if I use my laptop's headphone output as input, I can get some very low volume sound. The LM386's output power is about 300mW, and I am trying to use it with a 2-3$ 0.35W small speaker resembling this. May it be that these speakers are no good? The Smokey Amp also uses a cheap 2" speaker like these.
Thanks in advance for your insights!
I tried to make a simple guitar amp for starters (I'm not familiar with guitar amp building, but I'm an engineer, I have a good understanding of electronics), like the Smokey Amp or the Ruby Amp. After being over-confident and building a PCB that doesn't work, I wired it up on a breadboard but it just doesn't work. One by one I tried to change everything (bought more expensive jack socket, changed the IC, played with the caps), but it does not work, neither when the pins 1-8 are left open nor when they are bypassed by a 10uF capacitor.
I'm starting to suspect the speaker. With guitar, there is no sound, if I use my laptop's headphone output as input, I can get some very low volume sound. The LM386's output power is about 300mW, and I am trying to use it with a 2-3$ 0.35W small speaker resembling this. May it be that these speakers are no good? The Smokey Amp also uses a cheap 2" speaker like these.
Thanks in advance for your insights!
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Do you have a voltmeter? Look for right-voltages on the pins. One is +9V, one is zero. Inputs on a '386 are both very near zero. Output of any single-supply-ended audio amp should be near half supply. '386 has a "bypass" which also runs near half supply. The "Gain" pins run near 1.2V and equal. That's 8 readings. Don't get your probe tip between pins, some shorts are bad.
http://www.circuitbasics.com/wp-content/uploads/2015/04/LM386-Pin-Diagram-300x221.png
Unless your guitar has active electronics the output could be pretty low, does your LM386 based amp have both a high enough input impedance and sufficient gain?
The Smokey/Ruby plans "work" with guitar. Certainly better than "no sound".
The Ruby has a JFET preamp; Smokey does not.
You are right that the gain and impedance are marginal. But he's not even getting lame sound. Something aint right.
The Ruby has a JFET preamp; Smokey does not.
You are right that the gain and impedance are marginal. But he's not even getting lame sound. Something aint right.
You need a pre amp for a guitar as they put out very low levels.
0.3 watts isn't much either, a few watts is needed for a practice amp.
I remember my first amp in 1980 was an LM386 in my electronics class.
We all made one and everyone's either blew up or at least overheated.
I think it was down to poor decoupling and no zobel on the output.
0.3 watts isn't much either, a few watts is needed for a practice amp.
I remember my first amp in 1980 was an LM386 in my electronics class.
We all made one and everyone's either blew up or at least overheated.
I think it was down to poor decoupling and no zobel on the output.
Are you sure your guitar and cable work ?
I would try a bigger more conventional speaker.
I have used the 386 many times with guitar.
It works fine.
Possibly your guitar frequencies are not passable with that speaker.
I would try a bigger more conventional speaker.
I have used the 386 many times with guitar.
It works fine.
Possibly your guitar frequencies are not passable with that speaker.
Thank you all for your answers. I'll try to summarize what I've done since:
- PRR: of course I have checked the voltages of the pins of the '386 and also of the input buffer JFET. That's the first thing I do on all my circuits (but up until now they have been RF and microwave, not audio). They were exactly the same values as you wrote, thanks for taking the time! 🙂
- The thoughts on the preamp: I thought the LM386 should be enough, given that with a 9V battery (I also tried it with a lab supply, although it should work with a battery, that's my goal) the maximum output is about 8Vpp and even with minimum gain that corresponds with a 400mVpp input, and the output of my humbucker pickups should be about 100-200mVpp, although I have not measured that. So I figured with the '386 and an input buffer I should at least hear something. I rebuilt it again today, because for simplicity's sake I omitted the shunt resistor on the input of the LM386, until now I just connected it to the source of the JFET through a coupling capacitor.
Now, the amp picks up a lot of noise with high gains, and the speaker sounds like a tea kettle. However, I changed the output to headphones with a large series resistor on the output, and my computer's output music sounds nicely, but there is still no sound with the guitar, except with the neck pickup if I strum very hardly, some faint sounds can be heard. And now, although I haven't done anything, it is again noisy (there are 220u and 100n decoupling capacitors at the supply and a 100u decoupling capacitor between pins 6 and 4) and once I even heard some radio.
The noise may be because of the jumper cables on the breadboard. I'll try using a preamp and put it on a PCB when I have more time, later I would like a more sophisticated (aux in, volume and gain control as in Ruby, maybe passive tone control, maybe diode distortion if the problem is with the gain, headphone output) amplifier for bedroom practice. If it doesn't work, I don't know what to do. I already spent 60$ worth of local currency on components for this (most of them can used for other stuff of course, except for the variety of speakers I tried) just because I did not want to buy a Marshall MS2 for 40$; plus it's a huge hit for my pride as an electrical engineer.
- PRR: of course I have checked the voltages of the pins of the '386 and also of the input buffer JFET. That's the first thing I do on all my circuits (but up until now they have been RF and microwave, not audio). They were exactly the same values as you wrote, thanks for taking the time! 🙂
- The thoughts on the preamp: I thought the LM386 should be enough, given that with a 9V battery (I also tried it with a lab supply, although it should work with a battery, that's my goal) the maximum output is about 8Vpp and even with minimum gain that corresponds with a 400mVpp input, and the output of my humbucker pickups should be about 100-200mVpp, although I have not measured that. So I figured with the '386 and an input buffer I should at least hear something. I rebuilt it again today, because for simplicity's sake I omitted the shunt resistor on the input of the LM386, until now I just connected it to the source of the JFET through a coupling capacitor.
Now, the amp picks up a lot of noise with high gains, and the speaker sounds like a tea kettle. However, I changed the output to headphones with a large series resistor on the output, and my computer's output music sounds nicely, but there is still no sound with the guitar, except with the neck pickup if I strum very hardly, some faint sounds can be heard. And now, although I haven't done anything, it is again noisy (there are 220u and 100n decoupling capacitors at the supply and a 100u decoupling capacitor between pins 6 and 4) and once I even heard some radio.
The noise may be because of the jumper cables on the breadboard. I'll try using a preamp and put it on a PCB when I have more time, later I would like a more sophisticated (aux in, volume and gain control as in Ruby, maybe passive tone control, maybe diode distortion if the problem is with the gain, headphone output) amplifier for bedroom practice. If it doesn't work, I don't know what to do. I already spent 60$ worth of local currency on components for this (most of them can used for other stuff of course, except for the variety of speakers I tried) just because I did not want to buy a Marshall MS2 for 40$; plus it's a huge hit for my pride as an electrical engineer.
Then I won't tell you which end of the nail goes to the wood.
Being an experienced builder, it almost has to be something you don't know about audio/guitar. Jack terminal layout?
There are rules which must be true for microwave but are RULES in audio. Is it turned on? Is it plugged in? Are you sure?
As hitsware says, we have had 3-page forum de-bugs only to find that the guitar or cord were bad. On pedals it seems to be common to get the IN and OUT jacks switched.
The '386 circuits *should* work for guitar. The high-gain on the '386 is 200X. A serious guitar amp should overload for 20mV in. 20mV*200 is 4,000mV or 4V, which is (past) clipping on a 9V circuit. The half-Watt output is no Marshall Major but should wake the baby. The 50K input is a heavy load on guitar treble, but lower note fundamentals are like 5K impedance at the pickup and that will drive 50K. Your speakers may not reproduce the lowest notes, but Power Chords mixing several tones in the hundreds-Hz range will throw intermodulation all up the audio band.
Your voltages suggest you did not get a fake no-good '386.
So it's gotta be a wiring mishap.
Pictures? On another forum, sharp fresh eyes sometimes spot the mis-wire.
watch the pinout of your guitar lead connector on your amp. I have seen this trick people before.
If the circuit works PROPERLY with a sound card input it doesnt leave many other culprits. (I assume you have a capacitor on the input - the omission of this could screw things up)
If the circuit works PROPERLY with a sound card input it doesnt leave many other culprits. (I assume you have a capacitor on the input - the omission of this could screw things up)
Not the same,so which one do you have?
In any case, build the smokey, let´s start with the simplest one, then we get fancy.
So, since we have lots of suspects here:
1) protoboard *just* smokey, as simple as can be.
Post here the circuit you use.
2) measure voltages as suggested above, no signal input, no speaker connected.
3) check speaker with a 9V battery or supply set to, say, 2V: briefly touching speaker terminals must make it click.
4) connect speaker to smokey speaker out
5) put your ear by the speaker: any turn ON/OFF click?
6) connect sound source to smokey input, play something.
If you want to not only hear but actually measure something, play this MP3 file into Smokey: https://www.mediacollege.com/audio/tone/files/1kHz_44100Hz_16bit_30sec.mp3
Set player to Loop or repeat one so you have a continuous tone.
6) you should hear a piercing 1kHz tone through speaker.
You should be able to get 1V or 2V RMS at speaker out.
Post results.
IF 1 to 6 succeed, plug your guitar and play, if not detail what happened.
Good luck 🙂
Agreed, I would focus on these two things. I don't think the guitar signal is making it to the input of your amp, since you obviously have a working amp past that point.
Have you tried using an oscilloscope to trace signals through your amp?
One other thing to check was also mentioned earlier by someone else: make sure plugging in the guitar isn't upsetting the (midpoint) bias on the input of the LM386. In other words, you need an input coupling capacitor - do you have one?
Good luck!
-Gnobuddy
LM386 is designed so inputs sit AT the negative rail (unlike general opamps). An input cap is optional, often omitted.
You could try coaxial wiring inside your amp on the passive components that pass audio signals. Also does your guitar put out _10db ?
It seems most humbucker-equipped guitars will put out at least a few hundred mV if you strum a chord lightly, and something closer to 1 volt peaks if you strum a chord firmly. Roughly halve that for single-coils.
On another thread, one person produced oscilloscope captures showing his ability to generate 10 volt peaks by playing a note on a single guitar string. Yes, ten volts! (Surely the exception rather than the rule, though.)
Even a couple of hundred millivolts is a fair bit of voltage, and my experience has been that if you buffer this voltage with a unity gain buffer (0 dB of gain) and feed it to a loudspeaker, it is actually quite audible. Not loud, but audible. In fact, you can clearly hear a mere 10 mV of AC signal at 1 kHz applied to a typical 8 ohm guitar speaker!
The OP described his amp as having plenty of sensitivity with his computer audio output signal, so I don't think lack of gain is the primary problem he's facing.
-Gnobuddy
Hi guys,
Sorry, I was on vacation for a week. Thank you all for your replies! I changed two things: switched the 9V battery to a 9V power adaptor, which is actually 12V somehow, and tried ALL my LM386 chips. Turns out, 2 out of 5 biases up all right, but do not work, and the 9V battery is really noisy and doesn't put out enough power. The guitar sounds wonderfully now, especially the bridge pickup (the neck pickup was always a lot weaker, even with my store-bought amp). Even my cheap speakers work, although not so well with the bass strings.
Thank you again for your helpfulness!
Sorry, I was on vacation for a week. Thank you all for your replies! I changed two things: switched the 9V battery to a 9V power adaptor, which is actually 12V somehow, and tried ALL my LM386 chips. Turns out, 2 out of 5 biases up all right, but do not work, and the 9V battery is really noisy and doesn't put out enough power. The guitar sounds wonderfully now, especially the bridge pickup (the neck pickup was always a lot weaker, even with my store-bought amp). Even my cheap speakers work, although not so well with the bass strings.
Thank you again for your helpfulness!
Wow. Counterfeit chips?
I have a Yamaha keyboard (with built in speakers) which uses six AA cells, so if you need battery operation, try that.
I used to have an older version of this keyboard, that one used six "D" cells. Apparently improvements in battery technology (and maybe reduced power consumption of the keyboard electronics) allowed Yamaha engineers to move to AA cells instead.
As you probably know, the individual cells inside a 9V battery are very small, and have quite high internal resistance, which is probably the source of the noise (instability) and lack of power that you mentioned.
Congratulations!
-Gnobuddy
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