#1
Hullo chaps,

I'm building a little gem of the first kind. The 1/2 watt one. What should the speaker impedance be for best results? The description says it can run a 16ohm cab, but is there a way to determine what the optimal impedance would be?

Thanks
Last edited by sashki at Feb 21, 2008,
#2
I just use what I can find (it doesn't do any damage), but it guess a matching speaker would sound better.
#3
Quote by mr_hankey
I just use what I can find (it doesn't do any damage), but it guess a matching speaker would sound better.

Erm...yeah. Matching with what? I don't know the output impedance, and I was wondering if anyone does.
#4
Quote by sashki
Erm...yeah. Matching with what? I don't know the output impedance, and I was wondering if anyone does.
It looks like that chip is best suited to an 8 ohm load. Look at the graphs on page 4 of the link.

http://www.national.com/ds/LM/LM386.pdf

It will generate more heat, internally (device dissipation) and less output on a 4 ohm load.

With a 9 volt supply and a 16 ohm load,
the power out will be limited to a little less than 1/2 watt, and it will run cool.

You'll be able to get a little more power out at 8 ohms.
You'll also generate more internal heat, than at 16 ohms, but it won't be excessive.
But heat = wasted energy.
If you're running from batteries, the life will be a bit shorter with an 8 ohm load.


This isn't rocket science. It's a dirty, funky, little amp.
Use what you can get easily and cheaply, or what you already have.
Either 8 or 16.


...
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
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#5
You can use a 4 ohm speaker, but make sure you heatsink the IC.
"Everybody, one day will die and be forgotten. Act and behave in a way that will make life interesting and fun. Find a passion, form relationships, don't be afraid to get out there and fuck what everyone else thinks."
#7
Quote by Invader Jim
You can run a 16 ohm marshall cab with one of those. You shouldn't have to heatsink the IC, should you?


Lower impedance = more current = more heat produced by the IC.
"Everybody, one day will die and be forgotten. Act and behave in a way that will make life interesting and fun. Find a passion, form relationships, don't be afraid to get out there and fuck what everyone else thinks."
#8
The need for heatsinking depends on the voltage of the power supply and the load.

With a 12 volt ps, and a 4 ohm load, you waste over a watt of power in the IC when you have an output of about 1/3 watt. 1 watt is a lot of power for an 8-pin dip. Without a heat sink, it will get mighty hot and probably fail.

16 ohms and 9 volt would be very safe, comparatively. You only dissipate 1/4 of heat and you get 1/2 watt to the speaker. A heatsink won't be necessary.

It's easy enough to figure out. Just run it a while, then put your finger on it. If it's too hot to keep your finger on for more than a few seconds, epoxy a small aluminum heatsink to it.

Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.
#10
^ JB quick to attach a heatsink? I think it would work well.
It's non-conductive electrically, but that doesn't really matter here.
You're looking to transfer heat.
a thin, continuous coating would be best.
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.