[Seeking advice for lm386 or similar]

Hi.

You probably missunderstoodf what i was saying.

1) I want to do a SPICE simulation of a circuit i have build.
2) This cricuit have a lm386
3) The simulator i have do not have lm386 modeled
4) Searching google for model result in no construtive hint.
5) In fact it only show that alot of ppl can't find it.
6) It is acceptable for me to substitute the lm386 IC for another one beter modelised
7) I am asking if anyone know of such similar IC
8) In the worst case senario i'll modelise the lm386 according to the datasheet
9) Internal circuit in the datasheet miss some information
10) I am also asking if someone knwo what kind of transistor is used in lm386
11) Or if anyone ever modelised a spice circuit out of a datasheet


Thanks.

[Seeking advice for lm386 or similar]

Hi. I am in the process of making an SPICE simulation of the project
Electronic Sthetoscope 2.


However i cannot found any model of lm386.
Googling at it looks like this is something alot of ppl have dificulty to find.

I am wondering if any of you know a chip that have similar utility but easier to find model. I no one know such chip or knwo how to obtain a lm386 spice...
I'll try to modelise the circuit in the datasheet.

If i do that is there anything i need to know ?
About transistor ? What are FET - CMOS.
What is used in lm386 ?

What is the part that look like a diode with a circle around it ?

Thank you in advance.

[Electronic Stethoscope]

Just seen at digikey that this particular model is in sold in package of 2000+ !!
anything else to recomand ?

[Electronic Stethoscope]

In order to keep the LM386 and a volume control from overloading, the volume control is always ahead of the amplifier.

I undestand an opamp can overload... but how can a potentiometer overload ? does it have to do with headphone impedance ? Can i use a preset voltage divider before the lm386 then a potentiometer to reduce a bit the gain ?

Cmos transmission gates

What are those ? is this a way to setup transistor ?


I've seen audio mixer .. those are opamp used in addition mode rigth ?
I really do not want to go in that route... the current setup is already complicated.
I'd rather use K.I.S.S. philosophy.
All i want is preventing mylself from damaging the expensive chipcorder or the computer soundcard.

[edit] Just seen this Fet mixer project
http://www.electronics-lab.com/projects/audio/034/index.html

so basicly all i need is to add 2N3819 Junction FET
and one capacitor / resistance ?

[Electronic Stethoscope]

As you said....
I need an attenuator to reinject chipcorder output to the LM386
I need an attenuator to (optionnally) plug the output of the electronic sthetoscope to computer mic input

Both need to be somwhere arround the volume control potentiometter.
I somehow fear that there will be too much attenuator in that region
Do you need something special to prevent the normal flow from leaking in all those attenuator ?
Op-amp buffer ?

The last thing i want would be using an hardware switch to choose between mode:
- chipcorder playback
- realtime hearing
- realtime hearing + mic output


btw can the volume control be after the lm386 ?
So you can merge the chipcorder output and the lm386 output and after that, control volume ?

[Electronic Stethoscope]

Yes, i had this question.
Can you really plug the output of the lm386 to Microphone input
Or you need to go rigth before the volume control to do that ?

Your noise sound like aluminium paper being folded near the mic.
I hope this isnt the pop and crack that is tipical to opamp audioguru last described

Good luck in your project

[Electronic Stethoscope]

from reading the small footnotes and reading other TI datasheet, i am under the impression that 7V means (Vcc+) at 7V and (Vcc-) at ground or Vcc at +- 3.5 v


how long does it take to take a 9V battery to 6V ?

[Electronic Stethoscope]

Hmm, i have one question

What do you mean by the TL074 behaving badly when the voltage dropdown to 6V ? Because i have to find some research question on the circuit, and the (Noise/distortion/whatever happen) Vs input voltage seem an interesting subject.

Or i can just test experimentally the curve Voltage/current vs input frequency wich is a bit less interesting.

Or maybee i can analyse what happen arround the LM386 without your "rectifier"

[Electronic Stethoscope]

Hi ... I have exatcly two guess to make on that topic
1st (less likely ) is the quality of the microphone


2nd ... you have inversed R6 and C4 or C3 and R5 (or R7)
making it a highpass filter that cut at 100hz instead of a lowpass filter that keep 0-100hz
Pls make sure your capacitor are at the rigth place.

I can also see you are using one led instead of two or a dual ... coud this have any impact ?


--------
to audioguru:
finally about the input voltage, i have realised that two 9V battery is quite big for the "portable" project we are trying to make. So my guess is that i'll be ok with my current pieces and draining +- 4.5 V from a 9V battery. at the worst cases the 9V will get to 6V wich is +- 3V wich is still acceptable.

[Electronic Stethoscope]

You want a lowpass filter not a bandpass filter

Well ... i sort of know what i want.
I'm building this to identify certain heart song and enphasis them thus a bandpass


Oh well i was proud of the opamp i choose as i figured it was good quality etc.
I'll wait before doing another digikey order as last one was quite expensive and it's many trouble.
The main reason i should switch is what you call the  " input bias voltage "
what are the consequences of that being unregulated ?


Well i guess you conviced me, the cricuit is mostly what i need
Do you have any reference / part number for affordable shielded cable ?

[Electronic Stethoscope]

The circuit must be re-designed to use a single supply voltage.

I am wrong to beleive that the only place where -9V is needed is at the opamp ?
Then the redisign would be in choosing resistance / capacitor values ?

In splitted voltage.. the chip i use can work at +- 8V Max recommanded
Is there an easy way to get +- 8V from a 9volt battery ?

C2 couples AC audio from the approx. +6V microphone to the 0V opamp input, so C2 always has the correct polarity.
C6 couples AC audio from the +4.3V output of the LM386 to the 0V connection for the headphones, so C6 always has the correct polarity.

Those two, i understand now...
I guess C5 is like C6
C4 ... is grounded so i understand also
but what about c3 ?

You have a capacitor in the LM386's circuit which boosts its gain to 200. A two-resistors attenuator is needed to reduce the output level of the playback chip to match the very sensitive input of the LM386.

so the attenuator is basicly a voltage divider to fit the need of the LM386 input. good to know.

---------

thank you for your help
I have one last question....
Do you have anny comment on the two "filter cricuit" I decided to adopt ?

[Electronic Stethoscope]

The input bias voltage of a transistor or opamp circuit is its most important requirement. Opamps usually have their input bias voltage set at half the supply voltage which is ground when a positive and negative supply is used.

Now, how exatly i assure that the input bias is correctly configured ?
If i have ground and 9V... the input bias is 4.5V ? meaning that i need to keep at least 4.5volt anywhere in the circuit ?
If so ... i may switch to your positive / negative power source.

C2 and C6 are polarized and couple audio in this circuit. The audio never causes the polarity to reverse across the capacitors so they pass audio fine.

Sorry to be a noob but what exatly you mean by couple the audio ?
You mean that between C2 and C6 the sound alwais go in the sema direction ?
Will this still be true if we change the central filter to target otehr frequency ?
What are the advantage of using such polarised capacitor instead of normal ones ?
Is it only a matter of electrolytic capacitor being easier to find at high value (1000uF)?

Also considering other chips i have my input source is more likely to be 2*AA (3V)
Than 9V .... does it makes any major difference ?

It won't work with a 3V battery that drops to only 2.0V over its life! A 9V battery voltage drops to 6.0V.

Well the electret work from 1.5V and so does the current opamp i have choosen.
one of my problem is that the recorder chip work at a very low voltage and it's the more expensive part of the circuit so i tougth i'd keep everything low.

Even if they do work at only 2V, the voltage swing will be reduced to nearly nothing due to losses.

Please explain this.  For the headphone at the end is it the voltage or current wich is important ?

The recorder probably needs an input level control, so can record the output of the LM386.
The recorder can playback into the circuit's volume control if a switch and attenuator for it is added to the circuit.

a switch will be added .... what do you mean by attenuator .. resistance, opamp used as a buffer ?

Thank you for your quick reply

[Electronic Stethoscope]

Thanks you, well i'll see for my quad opamp ... i may change it latter.
Is the noise twice as it's a quad versus a double ?
If not do you have any quad you recommand ?
What do you mean exactly by inbut bias ?
I see that you are using some electrolytic capacitor in your circuit.
Aren't they polarised to only one direction, a bit like a diode ?
If so ... doesn't the sound need to go in both direction as it have +- v
Also considering other chips i have my input source is more likely to be 2*AA (3V)
Than 9V .... does it makes any major difference ?

I need to put a recorder chip in the stetho... Is there any place you suggest me to *plug* the recorder input and the playback output ?

[Electronic Stethoscope]

Hi everyone
Tanks for the interesting reading (20 pages is A lot ! )

Like many others I have, chosen this stethoscope as a school project.
My particular study in the team is about different heart frequency, and thus i need to have multiple optional filters... e.g. No filter, low pass, band pass.

After recording different stethoscope song I have arbitrary found those values:
Low pass 640 Hz (song in higher frequency sounded too much like noise)
Band pass Fc = 160Hz, Width = 160 Hz. (about 90 to 300 after rounding pieces value)


I have found that a professional 3M Littman e4000 have those frequency:
Extended range 20-1000
diaphragm 200-500
"precision" 20-100 <- the current circuit fit this category which is good ;)


I initially tough I could do this using only opamp but after reading I