How can i make this audio preamp circuit work?

Thread Starter

Iwt

Joined Oct 29, 2022
11
Hello! I have this uni project to design an audio preamp with tone control but I don't know what is wrong with this one and how can I make it work.
1668336805466.png
 

Thread Starter

Iwt

Joined Oct 29, 2022
11
Hi lwt,
Please explain in what way it does not work.?
E

What is the purpose of R15.?
I am pretty new to this so I am as confused as you are as why R15 is there. I found this circuit in an old book somewhere on the internet and tried making it work. As you can see the tone control part has 0V all over it and the output is 0 as well. The simulation:1668338234761.png
 

WBahn

Joined Mar 31, 2012
27,925
Is this your design? If so, walk through the stages and describe what each is supposed to do and how it is actually behaving compared to what was intended.

If not, then it's even more important and valuable that you do this.
 

Thread Starter

Iwt

Joined Oct 29, 2022
11
Is this your design? If so, walk through the stages and describe what each is supposed to do and how it is actually behaving compared to what was intended.

If not, then it's even more important and valuable that you do this.
It is not my design. I am pretty new to this and I don't think I would be able to design something similar from scratch.
 

LesJones

Joined Jan 8, 2017
3,905
You start of by saying that you have to DESIGN the preamp but then you post a circuit from the internet that someone else designed. Show us the circuit that YOU have designed and explain how it works. (Or the way you think it should work. The circuit you have posted will attenuate the input signal. Not amplify it.

Les.
 

Thread Starter

Iwt

Joined Oct 29, 2022
11
You start of by saying that you have to DESIGN the preamp but then you post a circuit from the internet that someone else designed. Show us the circuit that YOU have designed and explain how it works. (Or the way you think it should work. The circuit you have posted will attenuate the input signal. Not amplify it.

Les.
Would love to be able to design a circuit all by myself. Unfortunately I don't have the knowledge for that.
 

ericgibbs

Joined Jan 29, 2010
16,808
Did it! Am I wrong or that is a gain stage? but why is it oscillating between 3.350 and 3.295?
hi lwt,
I don't wish to sound blunt, but if you don't know why Q1e is swinging between these two voltages when there is an input on Vin, your chances of understanding the remainder of the circuit is in doubt.

Note the Vin 1kHz 100mV sine wave on this simulation

BTW: if I have drawn the circuit correctly and used the displayed component value, you can see the circuit does not work.

Please post a link to the original source of the circuit.

E
EG57_ 201.png
 

Thread Starter

Iwt

Joined Oct 29, 2022
11
hi lwt,
I don't wish to sound blunt, but if you don't know why Q1e is swinging between these two voltages when there is an input on Vin, your chances of understanding the remainder of the circuit is in doubt.

Note the Vin 1kHz 100mV sine wave on this simulation

BTW: if I have drawn the circuit correctly and used the displayed component value, you can see the circuit does not work.

Please post a link to the original source of the circuit.

E
View attachment 280577
This is where I found the circuit: Tone Control Circuit Schematic Circuits: electronic auido circuit , Tone Control Circuit - Schematic Circuits Elektropage.com
 

ericgibbs

Joined Jan 29, 2010
16,808
hi lwt,
This is the original source data, it works according to their specification.
Note what it says about the V gain less than unity.

E
EG57_ 203.png
 

LesJones

Joined Jan 8, 2017
3,905
Why did you change the value of R12 from the value in the original circuit ? With the original value that stage would provide some gain. With the value that you used it would attenuate the signal.

Les.
 
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