BM800 LCD Audioimprov Mod, low output

[Jakub W]

As the schematic on the AudioImprov site shows (quite clearly, i would think), the following points connect to ground (which also connects to the mic chassis and/or the ground of the audio board):

- one end of L2 (100uH)
- one end of C8 (27pF)
- anode of D4
- one end of C11 (10-100nF)
- one end of C20 (10-100nF)

So, I assume, this is meant by the schematic, right?

 

[Khron]

So, I assume, this is meant by the schematic, right?

Now compare that to the AudioImprov schematic.

Why is the 27pF (only) in series with the 150uH inductor?

Why is the 8.2pF "only" between the transistor base and emitter?

Or rather, why is the transistor emitter connected between the 8.2pF and 150uH?

Why is the 680k resistor connected between the transistor collector and emitter (and not between collector and base)?

 

[Jakub W]

Why is the 27pF (only) in series with the 150uH inductor?

I could have drawn it not accurately. The 1 nf cap goes to one leg of the 27 pf cap, and both of its legs are connected to the inductors respectively (Leg 1 27p => 100 mh, Leg 2 27p => 150 mh)

Or rather, why is the transistor emitter connected between the 8.2pF and 150uH?

I actually wanted to achieve connection to the 150 mh inductor this was, but I think, I see my mistake (wrong leg)

Why is the 680k resistor connected between the transistor collector and emitter (and not between collector and base)?

I recreated the drawing from memory. In fact, it is connected between the base and collector. I attach, how I connected it

 

[Jakub W]

Here is an improved version after your remarks. Did I miss something else? Please do understand I have no educational background in circuit design and electronics.

 

[Khron]

Here is an improved version after your remarks. Did I miss something else? Please do understand I have no educational background in circuit design and electronics.

Is this just a drawing, or a representation of the (non-working) physical circuit you have right now?

Regardless, I would recommend you try to recreate the original circuit, with the connections the way they are represented in the schematic, including all the ground points connected together, AND to the mic chassis / circuit ground of the audio board, and take all the guess-work out of this.

Perhaps hand-draw a schematic at the same time as you solder components together? It should make it easier to keep track of things, perhaps..?

You don't need to (re)design anything, that's already done for you. Sadly none of us can help you physically connect the correct component legs together / to the right spots, but that shouldn't take any electronics knowledge as such, just being able to read some drawings and take instructions (thinking of the transistor datasheet here, and correctly identifying the base / emitter / collector, clearly shown in its datasheet).

 

[Jakub W]

including all the ground points connected together, AND to the mic chassis / circuit ground of the audio board, and take all the guess-work out of this.

Thanks, I am aware it's not rochet science, but the common ground symbol caused the guess-work for me.

(thinking of the transistor datasheet here, and correctly identifying the base / emitter / collector, clearly shown in its datasheet).

I checked the datasheet and ensured with the Diode test of my multimeter, so it should be correct.

I will get back to you after I have checked the connections.

 

[Khron]

but the common ground symbol caused the guess-work for me.

All the nodes connected to ground, need to connect to ground - simple as that. No other nodes should be connected to ground, except the ones that are, you know, supposed to be

 

[Jakub W]

All the nodes connected to ground, need to connect to ground - simple as that. No other nodes should be connected to ground, except the ones that are, you know, supposed to be

I re-assembled the whole thing, watching out for bridged connections and tested it by ear. It seems to work, but I had to mess up the connection. What I noticed is, that the PCB started picking up sound instead of the capsule. The polarization signal is sent to the ground terminal of the capsule

 

[Khron]

The polarization signal is sent to the ground terminal of the capsule

The polarization voltage is a DC voltage, not a signal as such. And the capsule doesn't have a "ground terminal". You can apply the polarization voltage to either side of the capsule, as long as the other side connects straight to the JFET gate.

 

[Jakub W]

The polarization voltage is a DC voltage, not a signal as such. And the capsule doesn't have a "ground terminal". You can apply the polarization voltage to either side of the capsule, as long as the other side connects straight to the JFET gate.

So this is not the issue I had, but I think I redid the mistake from before. This is how I assembled it.

 

[Jakub W]

This is how it supposed to be

 

[Khron]

This is how it supposed to be

Is it, though?

I don't think one end of the 1nF capacitor is supposed to go to ground (but to the 27pF/8.2pF/150uH node).