Audio Levels

Thread Starter

aac044210

Joined Nov 19, 2019
127
Hi:

I want to understand audio levels. If I build for example a 5 watt (real power) amplifier that
requires a 70 mV input to produce the 5 watts, is that going to require another stage of
amplification in order to work with a cd player, a microphone or an fm tuner? I have no idea
what sort of output level these devices generate.

I have attached a schematic as an example.

aac
 

Attachments

Alec_t

Joined Sep 17, 2013
10,901
A typical microphone output would be in the 5mV rms region, so would need a microphone pre-amp stage.
The CD player would hopefully have a line-level output of ~ 0.5-2V rms, or a headphone output of ~ 150mV rms, either of which would be ok to feed directly to your input pot.
 

Thread Starter

aac044210

Joined Nov 19, 2019
127
A typical microphone output would be in the 5mV rms region, so would need a microphone pre-amp stage.
The CD player would hopefully have a line-level output of ~ 0.5-2V rms, or a headphone output of ~ 150mV rms, either of which would be ok to feed directly to your input pot.
Thanks Alect_t. I guess the fm tuner could be fed directly into the input pot as well?
 

Audioguru again

Joined Oct 21, 2019
857
The amplifier you show has a gain that depends on the output impedance of the signal source.
It also has its value of RE2 too low depending on the hFE of Q2.
Attachments:
Amplifier 1= With a low level mic input from a low source resistance, the gain is much too high.
Amplifier 2= With an input resistor added to fix the gain, the output shows that the input is biased wrong.
Amplifier 3= The value of RE2 was increased to match the high hFE of Q2.
 

Attachments

Top