Guitar Bass Driver v3 No Sound (solved)

[Chris S]

I’ve got a Guitar Bass Driver v3 kit that’s all wired up, But I get no sound when activated.

LED works.

I’ve used an audio probe to trace the schematic, when I probe to the first pin of Q1, I can hear the input signal between R3 and Q1 and I can get signal from pin #2 on Q1, but after that I don’t get signal to the input of Q3.

What I did notice is that if I take my audio probe, and place the ground wire of the audio probe on the input signal, I can hear signal again with the other wire on pin #2 on Q1. With the audio probe’s ground lead connected to the hot input, I can hear sounds all the way to the output.

How does this happen where the audio probe works with the ground connected to the input?

When I try to bias the transistor using the trim pot, I don’t get anything more than 0.1 V from Q9

 

 

 

[Chris S]

[mybud]

Have you tried gently tapping or wiggling the socketed transistors? Sometimes they don’t make a firm connection.

[Playsforfun]

Hey Chris. Using your meter and schematic make sure all your ground connections, on and off board, all have continuity. There are a lot of socketed transistors. It’s important to know the voltages at each leg of each tran along with the input voltage. This is a starting point. Mybud is definitely on to something. I use cheap sockets, cause I’m cheap,  and sometimes have looseness issues. It may be important to share some good pics of your soldering too. Did you test each component before install? Does your meter have a transistor checker? I’m going to go thru all the color bands of the resistors and put a second set of eyes on what I can. You have great photos so far but there are connections we can’t see. BTW Hooray for having an audio probe.

Update: I think you mixed up R27 and R29. That should fix you maybe. I can’t see R1 or R8.

[Chris S]

I swapped R27 and R29 and it came to life!

Expected

R27 – 33K

R29 – 47R

Actual

R27 – 47R

R29 – 33K

Looks like R29 is in the power section of the schematic, I’m guessing the 33K was preventing the transistors from getting powered correctly?

I typically measure every resistor before soldering, the instructions had a lot of listed modifications (ex. 22K sub for 33K) So I socketed (what I thought was) those pins and must have mixed them up the next day when I went to solder the rest of the components.

This is my 21st kit build and I’ve never run into a misplaced resistor (that I know of). My last build that didn’t work I had the triangular mount transistors rotated incorrectly, so I was “biased” towards thinking it was a problem with the transistors.

I’ll look into getting a transistor checker, I was a bit afraid that one of the 9 was defective and I wouldn’t be able to measure it, in addition to really wiggling the transistors and making sure they’re in there tightly.

Thanks mybud and Playsforfun for your help!

[Playsforfun]

Glad it was so easy, Chris. Your work is really good but it’s bound to happen sooner or later. Enjoy.

[mybud]

Only a pleasure, Chris. Glad you got it working.

[Author]

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