VOltage regulator works, but theres a problem - diyAudio
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Old 13th June 2006, 05:57 PM   #1
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Default VOltage regulator works, but theres a problem

I have a LM317 voltage regulator powering my LM386 microphone amp that I made to put in my car. the voltage regulator filters out 90% of the engine noise that i was thinking it would do. the only thing is that if there is any volume used to imnput in the microphone(this is the amp runnin off of the regulator) it cuts in and out really fast like its being overloaded or something, but the amp doesnt do that when i have just the power itself running the LM386 amp.

is the LM386 drawing oto much current from the voltage regulator? im thiking that may be it because i read that the LM317 has an internal protection built in if too much current is used... or what could be the problem? if it is the regulator, are there any that output more current?
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Old 14th June 2006, 09:55 AM   #2
AndrewT is offline AndrewT  Scotland
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Hi,
maybe?

Yes, there is a comprehensive protection package built into a chip regulator. Max current and max temp being two I'm aware of.

How big is the heatsink you bolted on?
How hot is the regulator (not the heatsink)?
How big are the caps on the reg output to meet peak demand from the amp?

Just starters.
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Old 14th June 2006, 10:53 AM   #3
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Hi,

Check the input - output voltages of the regulator. You should have input > output + 3v to make it work properly.

Did you use input/output small film caps (100-330nf) near the pins ?
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Old 14th June 2006, 05:19 PM   #4
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just so i wont confuse anyone i drew out the schematic. Click the image to open in full size.

i just tested it out when i built it so i didnt put a heatsink on it, yet. when i had it hookedup for about 20 seconds, the thing didnt get warm at all. it stayed 100% the temp that it was b4 it was hooked up.

the voltage difference is atleast 3 volts. when my car is running, it is at 13.8 volts and i have the output set for 9.0volts...the 5k pot is used to adjust the voltage of the output
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Old 14th June 2006, 05:55 PM   #5
poobah is offline poobah  United States
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Can you post a schem for your mic amp?
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Old 14th June 2006, 06:12 PM   #6
sss is offline sss  Israel
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its not the protection ....
when protection is activated it will cut out, and fill run again after a few secunds or a minut ... not "really fast" as u describe.
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Old 15th June 2006, 03:23 AM   #7
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alright. well ill hook a DMM to the output of the voltage regulator and hook up the amp to see what the readings are.

Its really weird because when i have my mic amp directly hooked up to my cars 12v, i can scream into it and it wont distort or cutout like it does when i talk into the amp when its ran off the voltage regulator....i dont have to scream at all, or even talk that loud into the mic for it to cut out. later on tonight ill try to take a recording of what it sounds like. right now its driving an 8ohm speaker out of an alarm clock

here is the schematic of the mic amp
http://img211.imageshack.us/img211/5...iclm3861rx.gif
Click the image to open in full size.
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Old 15th June 2006, 04:00 PM   #8
sss is offline sss  Israel
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Quote:
Originally posted by silentblackhat
alright. well ill hook a DMM to the output of the voltage regulator and hook up the amp to see what the readings are.

Its really weird because when i have my mic amp directly hooked up to my cars 12v, i can scream into it and it wont distort or cutout like it does when i talk into the amp when its ran off the voltage regulator....i dont have to scream at all, or even talk that loud into the mic for it to cut out. later on tonight ill try to take a recording of what it sounds like. right now its driving an 8ohm speaker out of an alarm clock


i think when u say "cuts out" u mean clipping ....

thats because the voltage from the regulator is too low (9V right?)
u need a lower impedance speaker .
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Old 15th June 2006, 09:36 PM   #9
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haha crap i should have thought of that...im into car audio stuff so i know about clipping, what it is and everything...i just never thougt of that on the small type of amplifiers. thats probably correct tho. i did solve the problem with a power line filter and it works now without any problem. thanks a lot for all the help and time
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