I'm constructing a audio amplifier in LT spice, some good starting points?

Thread Starter

ZimmerJ

Joined Dec 9, 2020
55
Hello, i'm new here on AAC. I've seen alot of interesting topics, questions and answers here, so i would like to be part of it.
Question:
It is for a school assignment, and i'm choosing to build a multistage amplifier (Pre-amp and Power-amp). What is a good starting point when choosing values for components and such?
Instinctively, my first thought is to start from the output, thinking that i want to achieve for example a certain power for my speaker, and then work from the "results" that i want from this audio amplifer. Frequency spectrum should be between 20 Hz - 20 kHz and say i wanna power a 30 W speaker. Where do i start off?
And what other things should be considered when constructing an audio ampifier? I know there is alot if it's suppose to be professional work, but if there is a way to keep it somewhat basic and just achieving the frequency spectrum and output power, that would be great.

I have done a layout, with the connections and the components.

I have basic knowledge of circuitry and components, but calculating the values of each doesn't seem too easy when doing a more complex circuit like this. I feel like i don't really know where to start. I maybe i should make it a single-stage amp for my level of experience?

Appreciate any answers, eager to learn. Thanks
 

Papabravo

Joined Feb 24, 2006
16,492
I would start on the input side. Take a low level source and amplify it with one or two stages. This building block can then be used as a standalone pre-amplifier. Then look at a power stage for driving the speaker.
 

Audioguru again

Joined Oct 21, 2019
3,316
Starting from the output:
Did you select a 4 ohms or 8 ohms speaker?
Calculate the RMS voltage across the speaker that produces the needed 30W.
Then calculate the peak-to-peak voltage which a DC power supply is needed to produce. Add a few volts tor the amplifier output voltage loss.
Calculate the maximum peak output current then select suitable output transistors.
The calculations use simple multiplying. 2 x 3= 6.
 

Thread Starter

ZimmerJ

Joined Dec 9, 2020
55
Starting from the output:
Did you select a 4 ohms or 8 ohms speaker?
Calculate the RMS voltage across the speaker that produces the needed 30W.
Then calculate the peak-to-peak voltage which a DC power supply is needed to produce. Add a few volts tor the amplifier output voltage loss.
Calculate the maximum peak output current then select suitable output transistors.
The calculations use simple multiplying. 2 x 3= 6.
Neither, but i guess i will start with that. Thanks for the advice, i'll give it a try.
 
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