Preamlifier for dynamic micro

[eak]

Hi guys,
I have been working on a preamp for my dynamic micro, based on 2 npn, i made a pcb etc, but it doesn't work whereas on a bread board using BC546b it worked just fine, at least one stage, i didn't try to test with 2 transistors. Since i have not any scope, i just mesured the working point, it is about 7V with 9V vcc, it have shifted a litle bit. In theory i calculated the resistors to have 5V (~Vcc/2).. i can't understand why i have nothing on the output. I put some pics of the pcb and schematic if you want to see them.   

[amspire]

Hi guys,
I have been working on a preamp for my dynamic micro, based on 2 pnp, i made a pcb etc, but it doesn't work whereas on a bread board using BC546b it worked just fine, at least one stage, i didn't try to test with 2 transistors. Since i have not any scope, i just mesured the working point, it is about 7V with 9V vcc, it have shifted a litle bit. In theory i calculated the resistors to have 5V (~Vcc/2).. i can't understand why i have nothing on the output. I put some pics of the pcb and schematic if you want to see them.

I haven't checked your board layouts, but a few things. You said two PNP transistors - I assume you meant two NPN transistors.

In your circuit diagram, C1 and C4 are around the wrong way.

The best way to get help is to post the circuit with measured voltages on the base, collectors and emitters.

[eak]

2amspire
Ops, i think you're right about capacitors! I measured it, at Vcc=9V both have :
Vb = 2.8V
Ve = 2.15V
Vc = 6.85 V

PS yes these are NPN, thanks

[amspire]

2amspire
Ops, i think you're right about capacitors! I measured it, at Vcc=9V both have :
Vb = 2.8V
Ve = 2.15V
Vc = 6.85 V

PS yes these are NPN, thanks

That all looks good. How does the ground fills connecting to the emitter 1K resistors connect to the rest of the ground fill? The images are a bit big to easily see without downloading, so I haven't looked at all the images.

Edit: I just realized the connection is under the transistor. It looks like it should work. Have you tried attaching a precision calibrated signal injector (ie your finger) on the transistor bases and see if you get an output? It sounds to me like there is something is shorting out the signal somewhere in part of the circuit isolated by the caps (ie not directly connected to a transistor. Perhaps on the volume input.

[PA0PBZ]

The images are a bit big to easily see without downloading, so I haven't looked at all the images.

I click on the link to the picture, my viewer then scales the image.

Edit: I just realized the connection is under the transistor.

Yes, you might be right. Otherwise the Ve of 2.15V would not be possible.

The only thing I can come up with is that pin 1 of your potmeter is connected to ground. It certainly looks a bit suspicious on the PCB, and that would effectively kill the signal without showing any strange voltages on the transistors.

[eak]

2amspire
Yes the ground is under the transistors. I changed the orientation of C1 and C4, i tried to touch the base with fingers, nothing.. I even shorted C3 , because i noticed that C3 and C4 in series would give only 5uF..nothing changed. So i give up, i will test it with a scope at university.   

[eak]

it works ! there was an open circuit  thanks to all