Electronics > Beginners

Pre-amp to connect microphone to speakers

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Zero999:
That module looks good for small headphones, but its output, with low distortion, is only specified as 80mW into 8Ω, so won't be very loud if you use it to drive speakers.

Audioguru:
The MAX9812L is a mono mic preamp and the TDA1308 not made anymore was a stereo headphones amplifier. Maybe ebay is selling old ones or a Chinese knock-off. The TDA1308 has its output power (typically only 40mW) spec'd with a 5V supply and 32 ohm headphones. Its output power is much less into 8 ohms.

SoundFan:
I've also noticed the low-power output of this module. I won't keep this module for the final version of my project anyway but I would like to reverse-engineer it to get a better understanding of why it works. Afterwards, I would like to modify the circuit to use some better suited ICs.

Zero999:

--- Quote from: Audioguru on December 03, 2018, 02:04:00 am ---The MAX9812L is a mono mic preamp and the TDA1308 not made anymore was a stereo headphones amplifier. Maybe ebay is selling old ones or a Chinese knock-off. The TDA1308 has its output power (typically only 40mW) spec'd with a 5V supply and 32 ohm headphones. Its output power is much less into 8 ohms.

--- End quote ---
No, the output is higher in to 8 Ohms than 32 Ohms.

EDIT: You were right. It's current limited, so reducing the load impedance below 16 Ohm will reduce the output voltage when clipping occurs, see my post below.
--- Quote from: SoundFan on December 03, 2018, 04:15:01 am ---I've also noticed the low-power output of this module. I won't keep this module for the final version of my project anyway but I would like to reverse-engineer it to get a better understanding of why it works. Afterwards, I would like to modify the circuit to use some better suited ICs.

--- End quote ---
Try searching for the data sheets for he ICs used on Google. I doubt you'll be able to replace them with other ICs because they'll be specifically designed around them.

There isn't that much which can be learned from looking at these modules because all the ICs are black boxes. If you want to learn you're better off looking at older discrete audio amplifier schematics.

SoundFan:

--- Quote from: Hero999 on December 03, 2018, 09:14:26 am ---No, the output is higher in to 8 Ohms than 32 Ohms.

--- End quote ---
Yes, since power (W) = U²/R


--- Quote from: Hero999 on December 03, 2018, 09:14:26 am ---There isn't that much which can be learned from looking at these modules because all the ICs are black boxes. If you want to learn you're better off looking at older discrete audio amplifier schematics.

--- End quote ---
I don't just want to look at them (you're right, that would be totally pointless), I would like to look at the gain range used and at the circuit in general, I just want to find the difference between the method described in this topic and the way the board is designed, so that I can try to make a better working circuit.

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