rogs

Im going to try the circuit you suggested in post #15 where you stated
keep it simple by using the LM358 circuit.And subsituting it with the
LMV358 part.R3 and R4 would need to stay in the circuit
to bias the IC with a single power supply as stated in the datesheet.
But you suggest removing them. Why? The circuit my not function
correctly with out those resistors in the circuit.

http://howcircuits.com/lm358-preamp.html

If this circuit dose not give me the results i need. Maybe you got a completed circuit schematic that you
used and build for a Preamp.With these parts.

In post #15 I suggest removing R3 and R4 and then connect pin 3 directly to pin 1 (and/or) 4 of the HT9170 (as I have in my circuit sketch in post #92). This will let you use the internal 'half rail' voltage reference (2.5V) within the HT9170 to provide the bias for your opamp, rather than the resistors.
This is a much lower impedance reference than the resistors provide, and should help with any noise or hum problems that may come form either the supply rail itself, or from the high value of the resistors R3 and R4.
Not saying that will occur, but it may

As I mention in several of my previous posts, a recording of the DTMF you have manged to pick up so far would give a much better idea of what's actually happening, and hopefully give some pointers as to why you're not getting the results you need.....

 

I could not record any of the LMV796 audio's output.To check its output for any noise,hum,distortion,hissing,etc, etc.My computer will not record this data.Reason. I just don't know.


This is in reference to the LMV796 op amp that i used in my circuit.The non-inverting circuit. In the datasheet

As stated in post #93

With your non-inverting circuit you set the input impedance at 50k (the two 100k resistors connected to your non inverting input are seen in parallel from an AC (signal) point of view).
The disadvantage of that configuration is that any noise or hum on the supply rails will be subject to the full gain of the pre-amp. Hence my suggestion to record the output from your amplifier, so that you could check.

Couldn't record audio.

So lets say there is that noise and hum or distortion on the
supply rails and going into the input and coming out of the output what can i do to remedy these characteristics in the LMV796 circuit.May there is a problem with a combination of these characteristics.And thats why
i get DTMF pick-up at a maximum of only 6''.And not the 10ft i want.


Also in post #91 you made a sketch of a inverting set up circuit with
no bias resistors.
I was going to try that with LMV358.Would an inverting setup
work better then in a non-inverting set up.As in your sketch.

 

Also in post #91 you made a sketch of a inverting set up circuit with
no bias resistors.
I was going to try that with LMV358.Would an inverting setup
work better then in a non-inverting set up.As in your sketch.

Both options should work OK. The idea of not using the bias resistors was to eliminate the possibility of high impedance hum pick up, when using 100k bias resistors, or the possibility of noise pick up from the supply rail, which is then amplifed by the preamp.

It is possible that neither of these things are happening, and that your problem is elsewhere. Which is why I keep suggesting that you record the output from your existing circuit..... Without access to an oscilloscope, listening to an audio output is the next best thing to give clues on what's wrong.....
If you can't record at the moment, I would suggest that your next best step is probably to fix the computer recording problem....

 

Has any one ''else'' on here ever build an audio amp using the LMV796.

I been try to get a distance of 10ft.But having no luck with that.

The most i could get is 6'' away form my computer using an online DTMF
generator. Could it be clipping on the output or something like internal
noise.

Would any one on here who knows about audio and use op amps
willing to help if i send them a Sample of the LMV796 AMP.
To see way its not picking up dtmf tone ten feet from there computer.
Maybe an ''engineer'' on here would be willing to test this amp out for me.
i could send you an sample.the circuit im use is the non-inverting setup
on page 16 in the datasheet.

http://www.ti.com/lit/ds/symlink/lmv796.pdf

It dose work. But i'm only getting 6'' picking up the dtmf tones generated from
my computer.Maybe it needs a AGC circuit.

Ron .H

Would you be willing to have a go at this amp if i send you a sample.

 

I have no experience with this, but I think the minimum input is 27mv. Since you are using the inverting input for the preamp you lose about 1/2 the gain. So maybe a gain of 5. Another 10 in the chip so maybe 50 total. maybe a mv out of the mic at a couple of inches leaves it short. Maybe try a 200k pot on the preamp. It may never work very good at 10 feet - a lot of bounces.

 

I have no experience with this, but I think the minimum input is 27mv. Since you are using the inverting input for the preamp you lose about 1/2 the gain. So maybe a gain of 5. Another 10 in the chip so maybe 50 total. maybe a mv out of the mic at a couple of inches leaves it short. Maybe try a 200k pot on the preamp. It may never work very good at 10 feet - a lot of bounces.

Hi ronv

I'm ''not'' using the inverting input. I'm using the ''non-inverting'' input.
on page 16 in the datasheet. Figure 50.I have the mic connected to the non-inverting input.For a gain of 20. At 6'' away max i get.

What do mean by,alot of bounces.Please explain!

Which op amp would you use to get the 10ft distance.
Must be low noise,low current for battery use and high gain.
Also high slew rate and the supply voltage must be 2.7V-5.0V INPUT.

My circuit im using is from figure 50.
Why can't this circuit im using work at 10ft.

 

Hello,

What type of mic are you using?
You can decouple the mic from the main power by a resistor and a capacitor.
I have drawn them in your schematic:

This will prevent noise from the powersupply to enter the preamp.

Bertus

 

Lots of schematics.. He says as he adds one more. But you have the non-inverting one. Good.

Here is a simulation with a 60 dba spl. That's about like being in your living room listening to the TV. Maybe your tone is louder or quieter. I don't know. Anyway at that level you need more gain. So I took the bertus schematic with the filter and gained it up to where there is about 50 mv to the 9170.(see pot & resistor changes) Speaking of that what are pins 1 and 4 of the 9170 tied to now that you have the non inverting setup?
Your op amp is ok - maybe a little fast for a breadboard so I added a 100pf cap across it so maybe it won't oscillate.
By bounces I mean echos in the room from walls and furniture and stuff.
You have a 5.5 volt battery?

 

Hello,

What type of mic are you using?
You can decouple the mic from the main power by a resistor and a capacitor.
I have drawn them in your schematic:

I'm using a electret mic capsule from digikey P9925-ND. But its it been replaced with another mic don't know the part number.

 

Hello,

The following project from ESP might be an interested read for you:
http://sound.westhost.com/project93.htm

There is told how to use an electret microphone in combination with a preamp.

Bertus

 

ronv

So I took the bertus schematic with the filter and gained it up to where there is about 50 mv to the 9170.(see pot & resistor changes) Speaking of that what are pins 1 and 4 of the 9170 tied to now that you have the non inverting setup?

Pin1 and Pin 4 are connected together.As in the datasheet of the 9170.
I connected the output of the lmv796 to pin 2 of the 9170 from the 1uF capacitor on the output.The 10K and 100k sets the gain of 10 on the 9170.

How would you connect the amp to the 9170.

I have 4 x1.5V cells for my battery which is 6V. But its been use in other circuits so its drain down some.
Thats why i get 5.5V-5.6V. No! there is no battery at 5.5V.

 

Lots of schematics.. He says as he adds one more. But you have the non-inverting one. Good.

Here is a simulation with a 60 dba spl. That's about like being in your living room listening to the TV. Maybe your tone is louder or quieter. I don't know. Anyway at that level you need more gain. So I took the bertus schematic with the filter and gained it up to where there is about 50 mv to the 9170.(see pot & resistor changes) Speaking of that what are pins 1 and 4 of the 9170 tied to now that you have the non inverting setup?
Your op amp is ok - maybe a little fast for a breadboard so I added a 100pf cap across it so maybe it won't oscillate.
By bounces I mean echos in the room from walls and furniture and stuff.
You have a 5.5 volt battery?

ronv.

Which electret Mic capsule would you use.In a project like this.

I'm using a electret mic capsule from digikey P9925-ND. But its been replaced with another mic don't know the part number.How high should the
dba spl be to pick-up sound at 10ft...Is that signaltonoise ratio.

Which one would you use from digikey.com.

There is no 5.5V battery.Its a 6V.Its been used in other projects.

 

Sorry, I missed you. The wm61a should work ok. I would just raise the gain like in the schematic. Seems your hookup is ok.

 

Hi

ronv

In bertus post #107 he changed the 10k bias resistor that i had in the original circuit.To a 4.7K, and used a 10uF decouple capacitor.

In your post you have a 2.2K resistor for the mic bias and a 100uF
decouple capacitor.Is there a differance in the function on how the
circuit will react to using the different parts.

Which parts would be better to use in the circuit.

 

It probably doesn't make much difference. The 2.2k will raise the gain slightly and the 100 Ufd. will filter a little more noise out.

 

Try turning the volume up and down to see if the distance changes. If it does the gain may still be to low.

 

Hi
ronv

At 1-2'' all the tones come on.And that's at the upper sound level on my computer.
Now at the same level.I move my computer 6'' away with the highest gain
on the amp.And some of the tones only come on and some don't.
The same thing happen's at maximum distance of 12'' still some come on and most don't That's at the highest sound level on my computer and the maximum gain
on the amp.
The trimmer pot is 100K. I'm using the circuit with the added parts that you added to my circuit in, i think post #108.The maximum gain with your added parts is a gain of 212.
Now i only have a 500K and 1M trimmer pot.What values would i need to get a even higher gain.With a 500K or 1MK trimmer pot.

But? i want to know why are some tones detected and come on.And some tones don't come on.This confuses me.Why is happening.

 

I'm not sure why it doesn't work. It would only work on my telephone from about 2 inches and it was much louder than when I push a button on the phone.

 

I'm not sure why it doesn't work. It would only work on my telephone from about 2 inches and it was much louder than when I push a button on the phone.

my work up to 12'' But? some tones come on and some tones do not come
on the LEDs light up on some tones and not on others.

What happening here? Why do some tones and not the rest at 6'' and 12''. But? at 2'' all the tones work when i press each key on that keypad. And each LED comes on for each key that i pressed at 2''.

If there's anyone else out there who would know this and what could
be the problem please post to this thead.

 

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....