Preamp doesn't work?

[Bob Scott]

One of the guys who ran sims could try shorting base to collector and see if the results are similar to the measured values.

Don't need a simulator.

With TR1 base and collector shorted, TR1 becomes a diode with cathode connected to C3, an AC ground.

TR2 now has less than 6DB of gain (amplification factor <2) to the output. 10mV in: maybe 17mV out with an impedance of ~8K, and that's without the TR2 "diode" shorting the signal to an AC ground.

Maybe the second circuit is copied exactly, short and all?

What do the spice simulations say?

There sure is a lot of response to this $2.00 problem.

Bob

 

[mvs sarma]

For a quick check I ran a DC test on your amplifier using a 12 volt supply. I used 2N2222A transistors so things will be a little different. The numbers in pink boxes are the DC voltage.

The AC frequency response shows that it has an “audio” frequency response.

Ronsimpson,

Can you try with the feed back connected as per original schematic, i.e., at Emitter Q1 in your schematic, instead of Q2.

Thanks in advance.

 

[mvs sarma]

My simulation result shows a "flatter" frequency drop off response at frequency >10KHz.

Maybe it is the different transistors being used. Anyone wants to try this the .asc file is attached.

Perhaps you need to terminate the output with a load of say 1K (equivalent to Line out impedance)or something for the simulation to be effective.

 

[zlatkoA]

Uh what a complication ok...
remove R9
remove R4
remove C6 then in this place put resistor with 470k
remove R7
change R5 to 680 ohms
change C3 to 47 uF
change R1 to 2k2
use voltage 6 to 12 volts max 15Volts

 

[zlatkoA]

Are you remove elements like i said
do this and will work
tesla...

 

[zlatkoA]

Dont trust el simulators ....

 

[audioguru]

Who will draw this completely new schematic of the changes suggested by ZlatkoA?

 

[mvs sarma]

Who will draw this completely new schematic of the changes suggested by ZlatkoA?

With this mod the performance would suffer I fear. Same collector feeding both bases.
However the modded schematic is attached.

 

[eblc1388]

The suggested changes failed to work as one transistor is now fully saturated.

 

[audioguru]

Even if the transistors are re-biased correctly the circuit changes by ZlatkoA wouldn't have anywhere near enough gain to be a mic preamp.

 

[mvs sarma]

The suggested changes failed to work as one transistor is now fully saturated.

Hai, L.chung,
I was requesting you to try to change the feed back line to Q1 Emitter (as per your diagram)and try, last week in the original schematic. any comments Please.

 

[eblc1388]

Hai, L.chung,
I was requesting you to try to change the feed back line to Q1 Emitter (as per your diagram)and try, last week in the original schematic. any comments Please.

No you didn't.

 

[mvs sarma]

No you didn't.

Sorry, Sir. It was regarding a post of and aimed for Ronsimpson. He tried simulation but he connected the feed back to Q2 as per his diagram while it was to be connected to Q1.

Don't mind for the mistake.