Hi All,
I'm making a little guitar amplifier with an LM386 - based on this schematic (little gem amp). I'd like to add a second input with a 3.5mm jack so I could easily plug in an aux cable if I wanted to use this for music. Can I just wire it as below, or do I need to add some resistors or otherwise isolate the IN1 and IN2 jacks?
I recall that tube amps like a deluxe reverb or champ may have a 1M resistor between the inputs, but I don't really understand the purpose of that, or if it would be necessary in this context. Note that I don't really care if this is a GOOD sounding solution for the aux in.
Also, ideally this would be "safe" if both inputs are being used at the same time, though simultaneous use really isn't the purpose of this.
Thanks in advance.
I'm making a little guitar amplifier with an LM386 - based on this schematic (little gem amp). I'd like to add a second input with a 3.5mm jack so I could easily plug in an aux cable if I wanted to use this for music. Can I just wire it as below, or do I need to add some resistors or otherwise isolate the IN1 and IN2 jacks?
I recall that tube amps like a deluxe reverb or champ may have a 1M resistor between the inputs, but I don't really understand the purpose of that, or if it would be necessary in this context. Note that I don't really care if this is a GOOD sounding solution for the aux in.
Also, ideally this would be "safe" if both inputs are being used at the same time, though simultaneous use really isn't the purpose of this.
Thanks in advance.
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I'm curious why you use the inverting input.
Connecting two sources in parallel like you show will effectively short both of them out. That's not a recipe for success. What you need is a summing amp: https://www.electronics-tutorials.ws/opamp/opamp_4.html
Tom
Connecting two sources in parallel like you show will effectively short both of them out. That's not a recipe for success. What you need is a summing amp: https://www.electronics-tutorials.ws/opamp/opamp_4.html
Tom
Good question - I actually don't. My amp design originated with the Smokey Amp schematic (below), and I evolved it towards the Little Gem (above), but I never did switch to the inverting input. For some reason, some of these little chip amp tutorials say the inverting input is better for some reason, but things were working for me so I decided not to change it.
This is over my head, and I'm not sure how to implement this in my design. I wonder if there is some other way to do this. Maybe the easier thing is to get some sort of switched input jack for the guitar side so that when you plug in a guitar it disconnects the 3.5mm input.
You're going to get a pretty loud pop in the speaker when you unplug the source. And another loud pop when you plug it back in. A 47 kΩ from the input to ground would fix that.
Tom
Tom
Ah, gotcha. Yeah, I typically actually just use a power switch and not that stereo/switching jack, so usually not plugging/unplugging under load. But I'll take that advice for ones where I use the switching jack.
No volume- the LM386 does not have excess gain for e-guitar, the on-axe knob suffices.
The LM386 inputs are nominally at zero VDC, "no pop". Yes, they float to a few mV but after a few hot licks at the blazing half-watt level, your ear is not bothered.
Leo Fender or friend devised a marvelous input network to run one over-hot guitar (or a synth?) -or- two semi equal guitars with tolerable loading and isolation. (If you are a big star you get your own amp so your cohort can't suck your signal, but not all of us are there yet.)
The LM386 inputs are nominally at zero VDC, "no pop". Yes, they float to a few mV but after a few hot licks at the blazing half-watt level, your ear is not bothered.
Leo Fender or friend devised a marvelous input network to run one over-hot guitar (or a synth?) -or- two semi equal guitars with tolerable loading and isolation. (If you are a big star you get your own amp so your cohort can't suck your signal, but not all of us are there yet.)
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Interesting. Indeed they are. I assumed it behaved like a power opamp with fixed gain. My bad.
Tom
Tom