Hello,

The following project on elliots site might interest you:
http://sound.westhost.com/project93.htm

At the bottom of the page you can see how to connect the mic and eventualy how to modify it.

Bertus

 

R2 will probably need to be a much higher value (e.g. ~ 1MegOhm).

There are some useful examples of values for base and collector resistors here:


http://ee.old.no/library/

The EE1003 manual contains examples using silicon transistors, the EE20 has germanium if anyone fancies a trip down memory lane.

 

What type of biasing is used for T1 and T2? I think it's common-collector for T2. right? What about T1?

For the AC signal both of this transistors work as a common-emitter amplifies.
If you have time try read this
http://forum.allaboutcircuits.com/t...is-for-voltage-drops.85763/page-3#post-616893

i

What are the usage of R4 and R7 and R8?

R4 - provide a negative feedback, the part of a output signal is feed back into the input.
R7 - provide a path to ground for C3 right plate. So when we disconnect the load. We don't leave our output (C3) floating. So we use R7 as a pull-down resistor. So we can conclude that this resistor is not always needed.
R8 together with C5 form a low pass filter for decoupling purpuse.

 

The picture of your circuit shows many long insulated wires. These wires act as antennas and pick up stray signals from power line wiring creating hum. In addition, the long wires can couple to each other causing feedback and oscillation.

I would recommend using short wires that are flat against the solderless bread board. Also, the resistors and capacitors should have the leads cut short so that they are against the SBB when installed. I always use the leads cut from the resistors and capacitors for my jumpers. Using un-insulated wires encourages using short wires.

How about one of these types of soldering?

You are talking about this type of wiring?:

Connected two pins of microphone together and measuring the output pin to see does it has any noise.

A bit confused. How exactly? should I use a circuit like this:

Thanks guys

 

Hello,

The first construction you show looks like a dead bug type of construction.
The mechanic stability will not be very good.

The second type is called manhattan style construction.
The mechanical stability will be pretty good.

The last is a breadboard construction.
That will not work well with RF circuits.

The mic circuit shown is a minimalistic circuit to use a electret mic.

Bertus

 

Hello,

The first construction you show looks like a dead bug type of construction.
The mechanic stability will not be very good.

The second type is called manhattan style construction.
The mechanical stability will be pretty good.


Bertus

The dead bug method is great for proving a concept.

If I can't be bothered doing a stripboard assembly, I make a dead bug/ Manhattan hybrid - the ground rail can be secured directly to the ground plane, as much support as is needed is provided by attaching copper land pads to line up with existing points.

My E-cig charger is still a dead bug because its very small and simple and doesn't seem to be suffering any of the usual vulnerabilities, but if and when I revise the design, it will probably get a more permanent structure.

 

I know you head is swimming with all this information, but here's another good tutorial on the single bipolar transistor amplifier that might be of interest:

http://thesignalpath.com/blogs/2012...ion-of-a-single-transistor-bipolar-amplifier/

 

New circuit. R8=100 Ohm ==> Gain=7600, Vin(ampl)=0.375mV.

 

New circuit. R8=100 Ohm ==> Gain=7600, Vin(ampl)=0.375mV.

View attachment 88442

This circuit sounds se*y to me.
But I don't have 2N2905. Can I use one of this: 2N3906,2N3904,BC548,BC557,BC338,BC327,BC337,BF199 ?

Please attach the files you simulate in LTspice.
Thanks

P.S. I have to wait to recieve some components. a bunch Caps and resistors. out of stock!

 

Use the transistor BC557.
Today I can't prepare files for LTspice (sym, lib, asc).
I'll do it tomorrow morning (I am in Minsk, now I have 16:10).

 

Use the transistor BC557.
Today I can't prepare files for LTspice (sym, lib, asc).
I'll do it tomorrow morning (I am in Minsk, now I have 16:10).

Fine. Thanks.

 

I have measured the output of headset jack of my PC and it was 3.3v.

Thanks but 70mv isn't enough. I want to get the output between 0v-3v3. any seggestion?

You can use a TL431 programmable zener instead of the transistor - it has huge gain if you AC shunt the feedback path as someone posted an example for the transistor.

My TL431 electret booster was published in Elektor a couple of years ago.

Start by connecting the TL431 anode to GND and cathode to Vcc via a 2k2 resistor. Connect the electret directly from Vin to GND.

Connect a 1k2 resistor to cathode - a 47k pot from the other end of 1k2 to GND - adjust 47k pot for about mid point voltage on cathode (the TL431 can't pull lower than 2V, so you could take that into account when calculating the voltage swing).

When you have the cathode (output) about mid point - take out the pot - measure it, and replace it with the nearest fixed resistor.

Now you have a junction between the 1k2 and the resistor that replaced the pot - shunt that to GND with a capacitor.

My first prototype had a very tired looking 100uF I found rolling about on the bench, and it worked beautifully.

A subsequent build had all new components and turned out to be prone to picking up random radio stations - the old shunt capacitor had a lot of ESR and probably self inductance too, it didn't shunt the HF nfb and the booster didn't pick up radio. You probably need 100uF for good LF response, but you could try a 100R preset pot in series with it so you can roll off the HF end.

The one built with new components had a good AC shunt cap, so it shunted HF nfb as well - the amplifier frequency response was only limited by the TL431 frequency limit.

 

Gain trim amplifier gain.

 

Ian field.
It is easier to draw a circuit.
This is not a description of a patent.
I would have done so.

 

You can use a TL431 programmable zener instead of the transistor - it has huge gain if you AC shunt the feedback path as someone posted an example for the transistor.

My TL431 electret booster was published in Elektor a couple of years ago.

Start by connecting the TL431 anode to GND and cathode to Vcc via a 2k2 resistor. Connect the electret directly from Vin to GND.

Connect a 1k2 resistor to cathode - a 47k pot from the other end of 1k2 to GND - adjust 47k pot for about mid point voltage on cathode (the TL431 can't pull lower than 2V, so you could take that into account when calculating the voltage swing).

When you have the cathode (output) about mid point - take out the pot - measure it, and replace it with the nearest fixed resistor.

Now you have a junction between the 1k2 and the resistor that replaced the pot - shunt that to GND with a capacitor.

My first prototype had a very tired looking 100uF I found rolling about on the bench, and it worked beautifully.

A subsequent build had all new components and turned out to be prone to picking up random radio stations - the old shunt capacitor had a lot of ESR and probably self inductance too, it didn't shunt the HF nfb and the booster didn't pick up radio. You probably need 100uF for good LF response, but you could try a 100R preset pot in series with it so you can roll off the HF end.

The one built with new components had a good AC shunt cap, so it shunted HF nfb as well - the amplifier frequency response was only limited by the TL431 frequency limit.

Thanks Ian for nice suggestion. how about this circuit:

Gain trim amplifier View attachment 88495 gain.

Thanks. that's perfect!
What's U2? How can I change the Gain? with R6?

Ian field.
It is easier to draw a circuit.
This is not a description of a patent.
I would have done so.View attachment 88497

Thanks. that plot(curve) confused me. does it mean that it cannot work for the frequency higher than 1Khz?

 

Another circuit:

Source

 

I have fell in love of TL431.
I have found some descriptions about it and its principles in amplify bias here. this part:

Figure (5) shows a DC voltage component with a TL431 amplifier, amplification of this circuit decided by the R1 and Rin, the equivalent of the op amp’s negative feedback loop, and its quiescent output voltage determined by the R1 and R2.
The advantages of this circuit, it is simple, the accuracy is good, can provide a stable static characteristics. The disadvantage is less impedance, Vout swing is limited.

Figure is the exchange of the amplifier, the structure and the DC amplifier is very similar, but have the same advantages and disadvantages.

Due to the datasheet(you can download here), I think it's the main circuit:

But somethings ain't clear. For example:

1- How much is the input impedance?
2- How much is its Gain? or maybe at first it's better to say "Is the gain of TL431 limited or not?
3- What parameters(factors) are important for TL431 in amplify mode? for example for Op-Amps some factors like Temp drift, input offset,... are important.
4- Could you please compare TL431 and transistor(BJT) and Op-Amp for me and tell me what are the differences between these three components in amplify mode?

Thanks in advence

 

Thanks Ian for nice suggestion. how about this circuit:

Thanks. that's perfect!
What's U2? How can I change the Gain? with R6?

Thanks. that plot(curve) confused me. does it mean that it cannot work for the frequency higher than 1Khz?

That's one way of doing it - not a very good one though.

The circuit as shown has no compensation for device gain or thermal drift. You fix that by taking the Vin bias from the cathode, my idea solves the problem of that bias resistor reducing gain by also providing AC nfb; by splitting the bias resistor and shunting the tap with a large capacitor.

The Vin pin will self regulate at 2.5V, that's slightly higher than the optimum 2.0V for most electret capsules, but in practice it works very well. So in my design the capsule is connected directly to the Vin terminal where it gets its electret supply and forms the lower part of the bias network.

In theory - you should connect a 47k pot from cathode to Vin and set the operating point for every different capsule. In practice; once I'd established a resistor value, it worked with every other capsule I tried.

 

I cite my research amp LTspice system.

 

Fine. Thanks.

Another way you can go about boosting an electret mic with a bipolar transistor; use the grounded base configuration.

Picture the classic textbook common emitter stage, both collector and emitter have a resistor to their respective supply rail, and the base is fed by a potential divider across the rails.

The bit that changes it from common emitter to common base, is simply moving the bypass capacitor from the emitter resistor to the lower resistor in the base divider.

The first thing to do is look up the recommended voltage for the electret capsule - its usually about 2V. The B/E junction will drop about 0.7V, so the voltage divider should be set to feed the base; 2.0V + 0.7V = 2.7V - now; simply replace the emitter resistor with the electret capsule.

If you can get hold of the exact right data sheet for your electret capsule, it should tell you the current for it, if not most are similar so any data sheet will give you somewhere in the right direction. If you can't get the spec for current, replace the collector resistor with a 100k pot and adjust for best operating point.

The common base configuration will give you plenty of voltage gain, but the current gain will be a tiny bit less than 1 - an emitter follower hung on the output will soon sort that out.