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Author Topic: Simple 3W amp IC? (for 4ohm speaker)  (Read 456 times)

japBLONK

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Simple 3W amp IC? (for 4ohm speaker)
« on: January 20, 2021, 03:08:51 PM »
Hey guys,
I want to build a tiny guitar amplifier and my drawer full of LM386's isn't cutting it. Are there any IC's that are currently manufactured that do at least 3W and are similarly as easy as the LM386 and ideally include some protection for overheating, etc? 

If not, maybe my best bet is to add a push-pull transistor output at the end of an opamp stage (like in the attachment) - but I don't know how I'd chose the resistor values or the transistors to get 3W safely.


joecool85

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Re: Simple 3W amp IC? (for 4ohm speaker)
« Reply #1 on: January 20, 2021, 03:21:25 PM »
Hey guys,
I want to build a tiny guitar amplifier and my drawer full of LM386's isn't cutting it. Are there any IC's that are currently manufactured that do at least 3W and are similarly as easy as the LM386 and ideally include some protection for overheating, etc? 

If not, maybe my best bet is to add a push-pull transistor output at the end of an opamp stage (like in the attachment) - but I don't know how I'd chose the resistor values or the transistors to get 3W safely.

PAM8302 or similar class D is going to be your best bet in my book.  All you have to do is use an opamp to invert one leg of the signal so you have differential audio to input into it for full power.  They are SMD chips though, so it's easiest to order then on a board already.  I've used this one from Adafruit and really like it: https://www.adafruit.com/product/2130

I'm actually designing a single ended to differential converter board to piggyback on this.  If there is enough interest, I might sell the PCBs.
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japBLONK

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Re: Simple 3W amp IC? (for 4ohm speaker)
« Reply #2 on: January 20, 2021, 03:59:58 PM »
Thanks Joe, I just put a few of those chips in my digikey cart - will include some adapter boards too.

I'm not sure I understand your need for the inverter? I see it has differential input, but don't you just ground the inverting input and send the signal to the non-inverting input? I get that it would be half the volume than if the diff input was used, but couldn't that gain just be made up in the pre-amp stage anyways?

joecool85

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Re: Simple 3W amp IC? (for 4ohm speaker)
« Reply #3 on: January 20, 2021, 08:33:12 PM »
Thanks Joe, I just put a few of those chips in my digikey cart - will include some adapter boards too.

I'm not sure I understand your need for the inverter? I see it has differential input, but don't you just ground the inverting input and send the signal to the non-inverting input? I get that it would be half the volume than if the diff input was used, but couldn't that gain just be made up in the pre-amp stage anyways?

What adapter board are you ordering?

Technically you are right about the input.  In theory you can double the output of the preamp and then send the input neg to ground on the PAM8302.  In my experience the audio quality seemed lower when I did this so I tend to like using an opamp to invert one leg.  It also allows you to use whatever for a preamp and not have an issue instead of having to build one that is extra loud to deal with the issue.
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willpirkle

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Re: Simple 3W amp IC? (for 4ohm speaker)
« Reply #4 on: January 21, 2021, 07:19:54 AM »
I’m using this TDA1517 stereo amp kit in one of my audio electronics classes. I built and tested it over Christmas and it is stable at 4 ohms. For $12 (Jameco, $27 on Amazon) it might be worth a try for your application. The output power will depend on the supply voltage and current capabilities.

https://www.jameco.com/z/MK190-Velleman-2x5-Watt-Amplifier-for-Portable-Audio-Player-Kit-6-14VDC-1A_2196588.html

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flester

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Re: Simple 3W amp IC? (for 4ohm speaker)
« Reply #5 on: January 21, 2021, 08:41:39 AM »
One reason I use LM386 is that they provide an acceptable kind of distortion on their own. Will you be able to achieve that, or will it be a clean amp?

joecool85

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Re: Simple 3W amp IC? (for 4ohm speaker)
« Reply #6 on: January 21, 2021, 08:37:47 PM »
One reason I use LM386 is that they provide an acceptable kind of distortion on their own. Will you be able to achieve that, or will it be a clean amp?

So far as I've seen, the LM386 is the only chip that functions in that way.  Most anything else you will need to obtain your overdrive/distortion sounds from a preamp or pedal.
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edvard

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Re: Simple 3W amp IC? (for 4ohm speaker)
« Reply #7 on: January 22, 2021, 10:10:02 PM »
I’m using this TDA1517 stereo amp kit in one of my audio electronics classes. I built and tested it over Christmas and it is stable at 4 ohms. For $12 (Jameco, $27 on Amazon) it might be worth a try for your application. The output power will depend on the supply voltage and current capabilities.

https://www.jameco.com/z/MK190-Velleman-2x5-Watt-Amplifier-for-Portable-Audio-Player-Kit-6-14VDC-1A_2196588.html

- Will

I second the vote for TDA1517; 2 channels, 6 watts per, though they recommend heat sinking if you try to bridge it.  I used to have a habit of finding old ISA soundcards that are loaded with TDA1517 chips, or TEA2025B for the lower-power ones.  Also check the Craigslist "Free" ads or any friends with old broken computer speakers or one of those cheap mass-produced stereos from the '90s; they often have usable power chips hiding inside. 
Or go for broke and get a handful of LM1875s.  They are rated for 20 watts, but that's edge case; at 12 volts with an 8Ω speaker you'll get more like 6-8 watts.

JoeCool85's suggestion to go with a Class D chip is solid though, much less heat to deal with.