# Beginner:Two circuits with the same battery. No way.

#### paldep

Joined Mar 3, 2016
41
I have an audio amplifier that use 3volt to power on and a preamplifier mic that use 1.5 volt. The preamplifier mic inputs in the amplifier through jack 3.5. When i try to use the same battery source the two circuits power on but it seems that there's inverse current flowing.What can i do? I'am a beginner. How can i isolate the two power input from each other ? When i use two different batteries all is going very well. When i Connect the circuits in parallel nothing happens! Thanks

#### blocco a spirale

Joined Jun 18, 2008
1,546
What do you mean by "inverse current flowing"? A schematic would be useful.

#### Dodgydave

Joined Jun 22, 2012
11,347
Wtf#, how can you have inverse current with one battery, post a circuit....

#### paldep

Joined Mar 3, 2016
41
Sorry, i'm bad in english. I can post photos of the pcbs front and retro. Can i?

#### nerdegutta

Joined Dec 15, 2009
2,684
I can post photos of the pcbs front and retro. Can i?
A close up, in focus, picture of top and bottom.

#### paldep

Joined Mar 3, 2016
41

#### ScottWang

Joined Aug 23, 2012
7,413
The connection of the Amplifiers and battery should be like this.

#### paldep

Joined Mar 3, 2016
41
thank you Scottwang -i want to connect the circuits with a single battery of 3,7 volt. how to do this?

#### Dodgydave

Joined Jun 22, 2012
11,347
You can put a couple of diodes in series with the microphone circuit to drop the voltage down.

#### paldep

Joined Mar 3, 2016
41
i have in407 diodes. how to wire them? two diodes to ground(-) and positive?

#### ScottWang

Joined Aug 23, 2012
7,413
If the 3.7V is means that the lithium then when it full charge will be up to 4.2V, and its lower voltage is 3.2V, you could adjust the R1 values to match the current you want.

#### paldep

Joined Mar 3, 2016
41
i used the circuit posted by Scottwang but the audio from the preamplifier does not pass in the amplifier. If i use separate batteries for each circuits then it work very well. it's very strange

#### ScottWang

Joined Aug 23, 2012
7,413
i used the circuit posted by Scottwang but the audio from the preamplifier does not pass in the amplifier. If i use separate batteries for each circuits then it work very well. it's very strange
Could you check the ID number of transistors for two amplifiers and labeling them in two parts and their position in the circuit.

Labeling the bjts from left to right as :
Preamp : Q1 , Q2, ...
Audio Amp : Q1, Q2, ...

Maybe you can draw the output circuit of the preamp and the input circuit of the audio amplifier.

#### paldep

Joined Mar 3, 2016
41
i made a reserch and found the schematics of my preamplifier. . the amplifier is based on a ka2209 ic. ,four 103k 100 v, one224k 100sg, two 104 cap, a 0.47uf and a 220uf10v and a led for the on off. sorry but i'm a beginner.

#### ScottWang

Joined Aug 23, 2012
7,413
If you have the capacitors as 1~10uF/10V~16V then in series with the output - C of Q1(2N2904), put the positive(+) with C of Q1 and the negative to the input of audio amplifier.

#### paldep

Joined Mar 3, 2016
41
i will try. Thanks!