First Build: Bass Overdrive v1

[Anonymous]

I have had a couple kits boxed up for several years and finally decided to start building yesterday.

I started with the Bass Overdrive v1 kit that I have. I made wire error placement on the 3DPT board that I corrected. I have power running and the switch is switching in and out. I am not passing signal across the main overdrive board. I checked resistor values as I was installing them and they were in the ballpark of the rated value. I don’t have the prettiest solder joints but I believe they are all connected.

What should be the first place I start for diagnoses. I can take multimeter measurements and additional pictures. I have not made an audio probe.

[Billy]

Check you get 9v to the main pcb 9v and ground pads  Ray

I think you’re saying you are but we’d need to know if the main pcb is getting 9v you’d get bypassed signal regardless of power getting to the main pcb

Also remember with the enclosure the wrong way up in would be on the left again you’d get bypass with your in and out cables going to the wrong jacks but no effect

It is a common error to plug in to out and visa versa with the enclosure upside down

Did you use MPF102 transistors and a 5457 and where did you get them I’m assuming you followed the biasing procedure

All component values and orientation that I can see look correct can’t see R1 and 2

[Anonymous]

I am getting 9v to the main board.

I now feel dumb, I did have it plugged in backwards. Flipping the connection it is now passing audio. There is a massive amount of boost occurring but there is a constant hum.

I did use MPF102s and a 2N5457. They came in the kit from Pedal Parts and Kits. If I understand it correctly to set the bias voltage I measure between the Drain and the Gate, is that correct? Q1 and Q2 are at 5V. Q3 won’t drop below 7.45V.

Upon close inspection it looks like I melted the corner of C6 not sure if that is the issue.

 

 

[Barry]

Try switching the 2N5457 to Q1 and put a MPF102 in Q3. Then try to lower the voltage.

Voltage at Q3 is too high.

You will have to redo all voltages starting from Q1 again. Go for 4.5v at Q1 and Q2 if you can.

You measure between Drain and any ground.

Only use 2 known, good cables and pedal, nothing else. No chains.

Report back.

[Anonymous]

Switched Q1 and Q3. Q3 came down to 5V but now Q1 is up at 8V.
I will have to check how it sounds tomorrow as my daughter is in bed.

[Barry]

That little test tells me what I need to know. I think?

I need to know what transistors you have now in Q1, Q2 and Q3. Your previous statement does not give me that detail.

With component tolerances and biasing circuits it is not always going to be an exact science.

Let me know what transistors in what position you originally used and verify which one is causing the voltage to be raised.

[Anonymous]

For the first set of bias numbers Q1 and Q2 were MPF102 and Q3 was the 2N5457. For the second set of the measurements I switched the transistors between Q1 and Q3 so that Q1 is the 2N5457 and Q2 and Q3 are the MPF102.

[Barry]

Yep, that is what I thought.

You need an MPF102 for Q3 as well if you do not want to desolder anything.

Making Q3 an MPF102 will not modify the tone either. It will allow you to bias though.

Send me a message using the Contact Me if you need assistance in getting another MPF102. I will be glad to help.

[Author]

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