Using 3 terminal regulators as audio amplifiers -

https://electronicsforu.com/electronics-projects/voltage-regulator-audio-amplifier-2

https://www.electroschematics.com/6684/lm317-audio-amplifier/

https://www.electroschematics.com/6704/1-watt-stereo-amplifier-with-voltage-regulators/


Regards, Dana.

 

Thank's everybody, now i know i'm way more clear on what to do.

I know the design is bad, I delibirately chose the most simple design I could build, to learn through experience. Obviously i'm going to end up a completely different design, i just want to understand the basics.

But are the speakers realy already amplified? the website says "This power is driving the two 2.25″ paper cone speakers (code 273488004), which Bose calls Twiddlers.They are the same speakers used....", it refers to them as speakers twice, and before it talks about an amplifier board that drives the speakers.
I disasembled the broken bose sounddock, and now have the speakers, so do they realy only need to be connected to a pre-amp circuit, and then will work?

If you took the raw speakers out of the bose units, then they are indeed speakers, but you didn’t tell us that before. Why ate you not using the amplifier boards, are they broken?

Bob

 

there are variety of pickups used https://ehomerecordingstudio.com/best-bass-pickups/
your pre-amp somewhat has to account that /// related : Google in images → https://en.wikipedia.org/wiki/Guitar_wiring
. . . assuming a passive magnetic pickup . . . the output impedance varies from 10-s of kΩ to 100-s : https://www.diystompboxes.com/smfforum/index.php?topic=39559.0

 

there are variety of pickups used https://ehomerecordingstudio.com/best-bass-pickups/
your pre-amp somewhat has to account that /// related : Google in images → https://en.wikipedia.org/wiki/Guitar_wiring
. . . assuming a passive magnetic pickup . . . the output impedance varies from 10-s of kΩ to 100-s : https://www.diystompboxes.com/smfforum/index.php?topic=39559.0
View attachment 184976

Curious, why do you have to have a variable Zin, why not just a fixed Hi Z input
OpAmp follower for any pickup ?

Regards, Dana.

 

some pickups' outputs are variable (not the amp's inp.)
__________
↓↓ just a stupid falstad simulation illustrating the voltage amplifier principles
(the .txt attachment needs to be dropped to MENU > FILE > Import Form Text... )
. . . ↓↓ "Basic Simple"
~ ~ ~ ~ ~ ~ ~ ~ ~ ~
__________
if more amplification is required (10·10=100x in the below case)-- the 2-ble inverting stage :
the GAIN is trivial → both I & O are referred to the half supply - so that 10:11 input = 1:11 output e.g. output = (10:11) input / (1:11) = 10x input . . . need a different gain just adjust the resistors' ratio to other than 1:10
---------
+ a power output stage https://ludens.cl/Electron/audioamps/AudioAmps.html ( with falstad's Q.C. ↓↓ )
---------
+ about decoupling different amp stages ... see at the end of

 

If you still want to experiment with a single transistor amplifier, you need to increase the impedance that the transistor sees as a load. In order to do this, add an impedance matching audio transformer to match the impedance of the 8Ω load, i.e. going from about 2kΩ to 8Ω.

View attachment 184902

The last time I used an audio transformer in an amplifier was 55 years ago in a class AB vacuum tubes amplifier. The transformer had almost no DC current in it.

A normal class-AB amplifier (LM386) powered from 9V has an output of about 0.5W into 8 ohms. Your 2k transformer amplifier will produce an output of only 0.04W which is almost nothing unless the supply voltage is about 100VDC.