how to increase this audio circuit

Veracohr

Joined Jan 3, 2011
694
Do you want to increase the voltage, or current capability, or both?

To begin with:

- Remove R3, it does nothing useful
- If you remove R2 and connect RV2 directly to the battery you can adjust the gain over a much larger range
- Increase the capacitor sizes to about 47uF if you want the circuit to be useful over the whole audio range
- Add a small resistor to the emitter of Q1. Or better yet, add a larger, partially bypassed resistor to the emitter of Q1 and increase R_ear

What kind of output level do you want?
 

Thread Starter

paldep

Joined Mar 3, 2016
41
Thanks guys. I Will try the veracohr suggestions. This Circuit comes from a spy ear toy. I wanted to have much gain. I am working to a hearing empaired project :)
 

ian field

Joined Oct 27, 2012
6,539
Thanks guys. I Will try the veracohr suggestions. This Circuit comes from a spy ear toy. I wanted to have much gain. I am working to a hearing empaired project :)
My TL431 electret capsule booster was published in Elektor a few years ago - someone here has a link to an online copy of the article.

The device is based on a 2.5V reference, so 5V would be cutting it fine - but might work well enough with 32/64 Ohm earphones.

With 12V supply it runs slightly warm loaded with an 80R speaker, its "comfortable" with a 140R telephone earpiece.

The TL431 can be had in TO92, SMD, 8-DIL and SOIC-8. With a small handful of passives you can be up and running. You can use a logic level MOSFET for more output drive, but biasing is easier if you use an interstage coupling transformer.
 

wayneh

Joined Sep 9, 2010
16,153
I know how, as a beginner, it seems easier to use discrete components. This is not true, and I encourage you to look at integrated circuits. Yes they are complex on the inside, but that is not your problem. They are designed by teams of experts to do exactly what you want, and you usually have to do little but power them and connect inputs and outputs as described by the data sheet. You will get so much farther, so much faster, once you accept that. Designing your own transistor amplifier is challenging, and you'll never match what the pros have already done for you.
 

#12

Joined Nov 30, 2010
18,167
MikeML is a wizard with the TL431 so he got me curious. There is a low level amplifier in the datasheet.
I'm thinking about a 1000 ohm to 8 ohm audio transformer I bought at Radio Shack. Too bad most of them are closed now.:(
Oh well. If you have to go to an internet vendor to buy an audio transformer you will be more likely to get one that is right for the job instead of making the job right for the transformer.
 

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Thread Starter

paldep

Joined Mar 3, 2016
41
I have some problem to Connect this device with one single battery. I think the problem is on the connection of the max4466 electret. It has a common ground and it make me impossible the connection with the pam 8403 that have separate ground. Audio- and battery -. How can i Connect it properly? Maybe a diode?C__Data_Users_DefApps_AppData_INTERNETEXPLORER_Temp_Saved Images_circuit.jpg
 

Thread Starter

paldep

Joined Mar 3, 2016
41
No no. The problem is not in the output, but in the input. If i use a battery For each single chip. It Works.. How to Connect properly the pam8403 and the electret max4466? It's seems so easy.
 

ian field

Joined Oct 27, 2012
6,539
I know how, as a beginner, it seems easier to use discrete components. This is not true, and I encourage you to look at integrated circuits. Yes they are complex on the inside, but that is not your problem. They are designed by teams of experts to do exactly what you want, and you usually have to do little but power them and connect inputs and outputs as described by the data sheet. You will get so much farther, so much faster, once you accept that. Designing your own transistor amplifier is challenging, and you'll never match what the pros have already done for you.
The TDA7052 I suggested in an earlier post uses the absolute minimum of external components.

Literally; a supply, a decoupling capacitor, a speaker and a volume pot.

The A suffix part I mentioned has DC volume control, so the pot varies the DC bias on the control pin instead of dividing the input signal voltage.

Being a BTL amp, it also works well down to 5V.
 

Thread Starter

paldep

Joined Mar 3, 2016
41
Hey Ian field can you give me some suggestion to isolate the ground of power supply to the ground of audio?. I posted an image before.
 
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