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Power supply problem/info needed

T

Techno1

Active Member
Feb 21, 2022
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New Hampshire
So i have a audio module that I bought has 8 channels that can record and play back voice or music using just a onboard mic.
The module comes with a enclosed speaker and has 3 AA batteries inside and plugs onto the module to supply 5 volts and a speaker.
record audio is great and also recording music or any sound sounds great in playback mode.

I want to enclose this in a small project box to make a watergate record for my CB/Ham radio.

Problem again sounds great with the 3 AA batteries even taking the output to an audio amp crystal clear.

When I try to use a LM7805 5 volt regulator as the power to the module it will record but playback is distorted.
I have tried a few caps and electro caps to filter any noise and still distortion.
I go back to the battery supply and crystal clear.

Something is causing this distortion when I use the 5 volt regulator.
I have other projects that I have used the 5v regulator and never a problem.
Would an isolated 5v small module help in this situation?

Any recommendations on what is going on why the distortion with 12volts to a 5v regulator to power this module why the distortion.

I will try to do a video tonight with audio so all can see what is going on.

thanks for any help
 

I made sure all pc board module and LM7805 are all grounded the same common 12 volt in power. Tried all different ways of no ground the 5v reg and the audio amp.
So when its working great on battery power I switch wires to the 12 volt in power to the 5v reg and the 5v out pin to power the module on hit play and audio is distorted.
Im thinking a 5 volt isolated supply might do it might order some and give it a shot. So the isolated 5v will just do the sound module and the LM7805 will power
the audio amp, anything to get this going.

thanks for your reply
 
Techno1 said:
I made sure all pc board module and LM7805 are all grounded the same common 12 volt in power. Tried all different ways of no ground the 5v reg and the audio amp.
So when its working great on battery power I switch wires to the 12 volt in power to the 5v reg and the 5v out pin to power the module on hit play and audio is distorted.
Im thinking a 5 volt isolated supply might do it might order some and give it a shot. So the isolated 5v will just do the sound module and the LM7805 will power
the audio amp, anything to get this going.

thanks for your reply
Click to expand...
What is the current draw of the circuit under load?
 
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The current draw is less than 1amp.

To test this im using a Astron power supply and also on my other bench a variable PS dont know the name and same effects battery powered works good but under a power supply power the distorted audio. So it seems to be the 12 volt power to the boards as it just lowers the audio a bit and then distortion.

The speaker/audio out is 2 wires and seem to be Isolated from ground need both wires to get the audio. I tried 1 wire to the audio amp and the other to ground also and distorted audio.


Here is a link from my server that you can watch the video.
 
Is it possible that the amplifier bias is unregulated and the extra half a volt is causing the distortion by shifting the operating point? Temporarily toss a 1N4004 or similar diode in series with the 7805 output to see if dropping that 5v to 4.4v solves the issue.
 
The amplifier is good for 5-12 volt in using the lm386. Been using this amp for 5 years no problem in all my other boxes that use one.
Its the recorder board that is getting hit when I try to use an external 5 volt power supply. Using battery supply is ok but an actual 12v supply to the 5v regulator is causing distorting and pulling down the audio.
 
1721930380826.png
I tried something like this and still no good.

Any better suggestions as i dont think its noise it when the external power supply ground is tied to the module it just wrecks havoc.
I ordered some isolated small module 12-5 volts and see what happens
or if a better suggestion please im all eyes/ears
 
Sure looks legitimate to me.

Any time you get dynamic behavior from what should be a steady-state circuit the oscilloscope is your best friend.

A meter can tell you a lot about steady-state things, but not so much about this kind of issue.

73
 
Thanks Nomadradio.
Again the audio amp that i have been using for the past 5 years works great nice clean audio if the audio amp and the playback module use separate power supplies.
The minute i tie them together to share the same supply the playback module audio gets distorted like bogged down.
I even tried the audio amp with 12 volt supply and the playback module with a wall watt 5 volt dc supply and works great nice clean audio. tied the both modules back together and distortion.

Again I ordered some isolated 12v in and 5v out little modules and see what happens if it will help.
I guess im looking to isolate the ground to either module and not tie them together if that makes any sense.
 

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