Sound level detector circuit

[audioguru]

A dynamic microphone has a pretty big diaphragm, much bigger than the tiny one on an earbud headphone.
But they are both dynamic (coil and magnet). The earbud mic will probably have a very low output level so the preamp will need more gain and the resistor that powers an electret mic must be removed from the preamp.

 

[Harshana Umesh]

What is the use of D1?
There is a current loop along D1 and T1 C-E and reduce the T1 bias current.

 

[audioguru]

What is the use of D1?
There is a current loop along D1 and T1 C-E and reduce the T1 bias current.

When the output of the opamp goes low then the base-emitter diode of the transistor causes the coupling capacitor to charge. But almost nothing discharges the coupling capacitor when the output of the opamp goes high so the capacitor charges higher and higher until it does not couple the signal to the transistor anymore and the transistor stops working.
The diode D! was added to discharge the coupling capacitor on each cycle of the waveform.

 

[Grossel]

A dynamic microphone has a pretty big diaphragm, much bigger than the tiny one on an earbud headphone.

What is the definition of a diaphragm? Is it some kind of dB plot?

 

[audioguru]

A diaphragm in a microphone is its "cone" that sound causes to vibrate and it moves the coil.

 

[MrDEB]

Well the results are in
The H bridge amp w/ H bridge mosfets outputs the loudest sound.
Used this circuit for testing outputs of the different output configurations
https://www.instructables.com/files/orig/FX5/67GS/FLROK12R/FX567GSFLROK12R.gif
Tried just a transistor as well as the amp with the 4 Tip/31,31 transistors, H bridge configuration (too much possiabilities of heating)
Now just need to change the 1 k resistor to 330 ohms and get the Mosfets (TO-220 pkg) outside the enclosure (I think I only need to put the two P channels mosfets on heat sinks.
Is there a method of mounting the two Mosfets on same heat-sink but isolated from each other. I recall something about ceramic ? or other insulator but it transfers heat.
need to redesign PC board to allow the Mosfets to be mounted outside the enclosure unless someone has a better idea?

 

[audioguru]

You can buy insulating kits for little power transistors. They come with a shoulder washer so the bolt doesn't short the transistor to the heatsink. The insulation passes heat but does not conduct electricity. Also use a thin coating of thermal compound.

 

[MrDEB]

Will look into them insulating kits
THANKS

 

[MrDEB]

H bridge alternative?

Audioguru, you are the reason behind using the attached schematic but IYO will a SN754410 perform as well without the problems of heating and a lower parts count.
Hopefully it will but having no experience using or even using an H bridge to begin with.

 

[audioguru]

The SN754410 has an output voltage loss of from 2.1V to 2.9V p-p which will make it get hot.
The Mosfet circuit has a very low voltage loss.

 

[MrDEB]

How to arrive at 2.1 to 2.9 voltage loss ? I realize a transistor loses aprox .6v
Wonder just how hot and will a heat sink prevent?
Vcc1=5v
Vcc2 = 12-14v
tried locating heat calculations ??
computer having issues of browser being hijacked due to Google-analytics.com (issue w/ Firefox)

 

[MrDEB]

Decided to measure the current draw of entire unit
little confused but using the 20A scale I read .01A (I blew the fuse on the 400ma scale)
so I guess 1 amp draw?

 

[audioguru]

Decided to measure the current draw of entire unit
little confused but using the 20A scale I read .01A (I blew the fuse on the 400ma scale)
so I guess 1 amp draw?

I would guess that the h-bridge driving a piezo transducer would draw no more than 50mA which is 1/20th of 1A.

 

[MrDEB]

I have a fuse on the power input that I will check what amperage.
That .01 is high you say?
wonder why?
Maybe a current limiting resistor would help? but then it would make the sound not as loud.
Trying to configure a heat sink for the mosfets. May have to go a 2x board or ?

 

[MrDEB]

mosfet selection? perhaps I need a closer match for the P channel mosfet?
one I am using is .41 ohms, 6.7A drain https://www.electro-tech-online.com/custompdfs/2010/10/FDP55N06.pdf
maybe a closer match? .12ohms 17A drain current.
https://www.mouser.com/Search/ProductDetail.aspx?R=FQP17P06virtualkey51210000virtualkey512-FQP17P06
not sure what to look for to find a complementry component.

 

[audioguru]

Your datasheets do not show a Mosfet with an on-resistance of 0.41 ohms.
The FDP55N06 has a max of 0.022 ohms which is about 0.031 ohms when it is hot.
Then its heating for DC is (100mA squared x 0.031 ohms)= 0.31mW which is nothing. The Mosfet is turned off for half the time when the other side of the bridge conducts so its DC heating is half at only 0.015mW. At high frewquencies the capacitance of the Mosfets slow them down so they ramp slowly instead of switching quickly if their driver has any resistance. Then they get hot.
Also, both the upper and lower Mosfets are turned on for a moment as one is turning off when the other is turning on then the fairly high current in them heats them.

 

[MrDEB]

not sure what I am looking at to pick a complement mosfet (close match)
The present mosfets I am using are FDP55N06 and FQP7P06
I was wondering if a FQP17P06 would be a better choice for the P channel as the data sheet shows RDS(on) =.12
the FQP7P06 has RDS(on) = .41
thinking if the P channel was a closer match to the N channel the circuit might not get so warm.
At present I am planning on mounting the TO-220's(maybe just the P channel) on the outside of the enclosure on a piece of channel aluminum w/ slits for cooling and painted flat black

 

[MrDEB]

Ol Be80Be has found a component that might work?
**broken link removed**
looks like it might work but need your valuable input.
Have samples ordered

 

[audioguru]

The MAXIM audio amp IC has a very low output power to drive headphones or tiny piezo speakers in a laptop pc that are very close to you.

 

[MrDEB]

In other words it won't perform as well as the mosfet amp?
What about the substitution of the FQP7P06 for the FQP17P06
what ever forward transconductance is?
9.3S vers 4S
is this related to the capacitance you are referring to as to a reason the P channel gets warm?
the N channel mosfet hasgFS(max/min) = 33S