Champ Stamp - Trimmer / Biasing

[Idlebeach]

I just built the Champ Stamp and while it functions and sounds pretty good I have a couple questions about the trimmer/ biasing the J201

Has anyone else built the Champ Stamp and happen to know what the trimmer should be set to? It seems to be biasing a transistor other than the J201. I don't know if the transistor it's changing can get to 4.5 so I'm not sure what to set it to.

Also, does the J201 need to be biased? I would've assumed it should just be 4.5 but I'm not sure which resistor I would need to swap out to make that happen.

Thanks for your time everyone!

 

[Robert]

The trim pot is biasing the BC547B (Q1). I'll get a voltage measurement from the original tomorrow.

The J201 (Q3) is a source follower, no biasing is required.

 

[Robert]

Q1 (BC547B)
Collector - 5.65V
Base - 0.76V
Emitter - 0.12V

 

[Idlebeach]

Q1 (BC547B)
Collector - 5.65V
Base - 0.76V
Emitter - 0.12V

Thanks a bunch!

 

[Robert]

I'll have the schematic posted shortly. I have a ton of them to export.

 

[Haz]

Hello I've got Champ Stamp together but get no sound.
With oscilloscope and function generator I get signal until volume pot from input. From output lead to the drive pot. I would need a schematic
I've tested all transistors with component tester and they seem to work. Tried also another ones.
I have no voltage on central 4,7uF electrolytic cap tho on pcb it's rated to minimum +25V. Others are fine.

Any clues?

Maybe somebody has some pics of unpopulated pcb? I can no longer see values under components. Good idea take pics before populating but this seemed an easy build..

 

[Haz]

I get voltages right with trimmer on Q1 (BC547B)

 

[MichaelW]

Hello I've got Champ Stamp together but get no sound.
With oscilloscope and function generator I get signal until volume pot from input. From output lead to the drive pot. I would need a schematic
I've tested all transistors with component tester and they seem to work. Tried also another ones.
I have no voltage on central 4,7uF electrolytic cap tho on pcb it's rated to minimum +25V. Others are fine.

Any clues?

Maybe somebody has some pics of unpopulated pcb? I can no longer see values under components. Good idea take pics before populating but this seemed an easy build.. View attachment 34538

Probably best to start your own Troubleshooting thread for this.0