Power Supply - Solid State Guitar Amp Board

Audioguru again

Joined Oct 21, 2019
6,758
The datasheet for the LM386 amplifier IC shows that with fairly high clipping distortion its output is only 0.5W into 8 ohms with a 9V supply or an output of only 0.25W when the supply voltage is only 6V.
With a 12V supply and an 8 ohm speaker, the maximum output is still almost only 0.5W but the IC gets very hot and might fail.
Do Not use a 4 ohm speaker.
 

MisterBill2

Joined Jan 23, 2018
18,970
In other venues I have read complaints about the sound from LM386 amplifiers. I have not used them myself, and with my damaged hearing and that sound level capability I doubt that my opinion of the distortion would be valid.
So my question is how good would the amplifier sound in a musical application?? What level of distortion would exist in such an amplifier?? That would be under ideal conditions.
 

Audioguru again

Joined Oct 21, 2019
6,758
In other venues I have read complaints about the sound from LM386 amplifiers. I have not used them myself, and with my damaged hearing and that sound level capability I doubt that my opinion of the distortion would be valid.
So my question is how good would the amplifier sound in a musical application?? What level of distortion would exist in such an amplifier?? That would be under ideal conditions.
The datasheet of every amplifier IC shows its amount of distortion. The LM386 show distortion at only 0.2% at 1lHz and at an output power of 125mW into 8 ohms with a 6V supply. With a 9V supply the output power is doubled with slightly more distortion than with a 6V supply.

My clock radio and computer speakers have similar amplifiers as the LM386 and music sounds good in good speakers when the loudness produces no clipping distortion.

Every audio amplifier produces severe clipping distortion when its input level is too high. The clipping is symmetrical and is harsh so does not sound the same as an old vacuum tubes overdrive circuit or a distortion producing pedal circuit.
 

pistolplc

Joined Oct 3, 2022
11
Hey Bucky - You left a comment on one of my old threads about LM386 amps, but it seems to have been deleted. Anyway, I have a lot of experience making amps like this, and here's the quick version.

1) LM386 amps are awesome. Don't listen to anyone telling you to use/make something else. I have everything from a 1960 tweed champ, to an LM386 amp head that I built to run a 4x12 cabinet, to an LM386 amp in a 1960s transistor radio with a 2.5 inch speaker, and I love them all. They are each their own thing. (Granted, I run all my LM386 amps at full gain, so they're basically just little AC/DC monsters. I can share some recordings of my amps if you're interested.). But these amps are really fun, and a great project.

2) 12V is fine, but the people who said 9v is just as good are correct. For LM386 chips into a 4 ohm speaker, there is really no difference in output. See the graph below - the bottom curve shows the output voltage as a function of supply voltage for a 4 ohm speaker load. Basically, no difference between 9 and 12.

1706024309735.png

Personally, I prefer 9V batteries because then I don't have to use a plug and I can put the amp anywhere. Also, you'll get maybe 25-50 hours of playing on a single 9v. (Not exact - I jus know I hardly ever replace batteries in my amps.)

3) 4 ohm speaker is fine.
1706024418260.png
I would say that half my LM386 amps run 4 ohm speakers.

4) Depending on how that amp is wired, you might end up with noise/hum from the external power supply - that's part of the reason I like 9V batteries.

Happy to answer more questions. Especially from a fellow Badger. (Class of 2004.)
 

pistolplc

Joined Oct 3, 2022
11
Oh, and:
5) The posters who are telling you to get a supply and cut the connector to find the +/- wires and wire those directly to the voltage input terminals on the board are correct. If you want to go that way. Really simple and straightforward. You can also use any of those "pass through" connectors if you want to have a removable power cord - just a little more wiring you'll have to do.
 

pistolplc

Joined Oct 3, 2022
11
Thank you for all of the information! It is greatly appreciated. What 2.5" speakers have you used? I've also set my unit on top of my 1x12 cab with a 16 ohm speaker. If I read that graph correctly, I could get more out that application if I switched to 12v power supply (vs 9v battery )?
I pretty much exclusively reuse the speakers in the radios, so they're whatever size/spec/brand came in these vintage radios. That little black one in the picture had a tiny little .3 watt 2.5 or 3 inch speaker. That's the one I take with me on business trips.

You might be able to get "more," but I really don't think it's worth it. I push my 4x12 at both 16 and 4 ohms with 9v battery and it sounds awesome. For a while I built some of these with 2x 9v batteries that could run in series to get 18v supply (this needs an LM386-4 chip), and it gives you a bit more volume and headroom, but not much. I really don't think 12v is going to give you any sound/volume advantage.
 

pistolplc

Joined Oct 3, 2022
11
Thank you for all of the information! It is greatly appreciated. What 2.5" speakers have you used? I've also set my unit on top of my 1x12 cab with a 16 ohm speaker. If I read that graph correctly, I could get more out that application if I switched to 12v power supply (vs 9v battery )?
Also, the schematic for the amp you're using shows a 220uF capacitor on the output - this gives much more bass response than the value that I use (47uF). With smaller speakers, the 220uf capacitor can be a bit too dark/farty sounding. You might find that your particular amp sounds better with the 1x12 than with your smaller radio speaker. If you want to change the capacitor, I could give you some pointers.
 

Audioguru again

Joined Oct 21, 2019
6,758
The graph in the LM386 datasheet shows that with a 16 ohms speaker and a 9V battery, clipping begins when the output p-p voltage is 7.25V producing 0.41W and another graph shows heating at 0.25W.
With the 16 ohms speaker and a 12V supply, clipping begins at 10Vp-p which produces 0.78W and heating is 0.45W.

An ordinary 10" or 12" guitar speaker in an enclosure does not produce a high fidelity frequency response. It produces no bass, no highs and a shrieking mid-range like this:
 

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LowQCab

Joined Nov 6, 2012
4,199
Using a "run-of-the-mill", throw-away, LapTop-Power-Supply,
You can have Plus and Minus ~10-Volts at 3 to 4-Amps,
that's ~60-Watts worth of Power-Supply, for little or nothing in cost,
and it's very compact, and very reliable.

Does this sound like something you'd like to try ?
.
.
.
 

MisterBill2

Joined Jan 23, 2018
18,970
Splitting a power source for anything more than a very low current is either more complex or rather inefficient For the 19.5 volt computer supply it could work with two ten volt one amp zener diodes in series, with the middle junction assigned to the zero volts point. There will also need to be filter capacitors from each side to the "zero" volts line to avoid unwanted coupling.

Of course the computer supplies are much less common because mostly they go with the retured computer, which is often entirely adequate for all except gamers. (Those playing fast video games)
 

Thread Starter

BuckyBratwurst

Joined Dec 29, 2023
10
LM386 for a guitar amp would sound like crap besides being extremely low power.
There are so many other viable solutions available I wouldn't know where to start.
Thanks for the reply. Could you please point me to some alternatives to the LM386? I'm a newbie. This was my first amp build.
 
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