Need Help! LM386 with Automatic gain from 20 to 200

Thread Starter

Etronic

Joined Oct 7, 2011
127
OK --it doesn't seem as if anyone is going to jump in here, so I'll try one last time.......

The reason your circuit is not working could be for several reasons.
The HT9170 (MT8870) is looking for two tones. One from the high group, one from the low. If it detects anything other than a valid pair of two tones, it will not update the output latches.

'Other' could mean noise, non-valid alternative tones, hum, reflections from the room ambience creating false tones....or a combination of any of those things. Because your unit is working close up , but not further away, then the one thing it probably isn't, is clipping.....

There is no way that any of us can know which of those is causing your problem, without either seeing an oscilloscope trace, or listening to a recording of the audio being received at the input of the HT9170.

Readers of this thread will know I have suggested, on several occasions, that you record and upload a sample of your received audio.

You just say you can't - and then move on to your next attempt at trying something different, without really knowing if you're even moving in the right direction.....it's called 'thrashing around in the dark'......

If you really are keen to get this working - and over 100 posts suggests you are - then post an audio sample of what you're getting at the moment.

Then we can all can hear what's going on with your prototype, and maybe offer some suggestions?.

Although this may seem like a simple project, it's actually not that easy to make a high gain, low noise audio preamp -- especially only using a 5V supply -- as a beginners project....

Post an audio sample....
rogs!

Where do i connect the wire leads to the audio output of the amp or the input of the decoder.Please explain how to connect them.

I will try and record this audio signal. Thats if my PC records it.
 

rogs

Joined Aug 28, 2009
279
Connect pin 3 of the HT 9170 to the line input of your computer sound card, via (in series with) a capacitor. ( A mic input will probably be too sensitive)
Any capacitor in the range 1uf to 100 uf should do fine.

Use a free app ( like Audacity for example) to record your audio on to your computer.
 

Thread Starter

Etronic

Joined Oct 7, 2011
127
Connect pin 3 of the HT 9170 to the line input of your computer sound card, via (in series with) a capacitor. ( A mic input will probably be too sensitive)
Any capacitor in the range 1uf to 100 uf should do fine.

Use a free app ( like Audacity for example) to record your audio on to your computer.

Keeping the LMV796 amp connected to the decoder.Correct! Or disconnect it.
 

rogs

Joined Aug 28, 2009
279
Yes..keep the op-amp connected.
You're looking to record from the output of the internal op-amp in the HT9170, which is the last stage in your amplifier gain chain.
That way we shall be able to hear all of your analogue input circuitry....
 

Thread Starter

Etronic

Joined Oct 7, 2011
127
I haven't been working on this project for some time now.
I've just gotten back trying to figure out why it will not work with any audio amp.

1. My computer speakers were going dead 2. The mic seams its not getting enough gain
at different distances. so the gain wasn't high enough at a far distance so the mic couldn't
pick up the sound at that range.3 Mic is not sensitive enough to pick up tone's far away.
The tone sounds is at times to high or to low from computer speakers at different distances.
And I know for sure now its not the HT9170 DECODER CHIP.
The HT9170 tone decoder works great from connecting directly to the headphone output jack then to pin 2 on the chip.
all tones are detected all the time every time I push a key on the online tone decoder generator.

So I would need an audio amp circuit with high gain. But? Also pick up tone sounds at different distances.
but could detect soft low or high loud sounds at 15 feet away from the sound source .

There is no way I myself could build an amp like this, my audio experience is zero to get a circuit like this to work.
This is way I need someone on this site who could build and test a Audio amp circuit for me.Or already has
an amplifier that can you what I need.
 
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