Epic fail recovery (L4 functioning)

[mybud]

So after the L5 clean and L5 legacy builds, I was looking forward to building the L4 bass version. It's quite a bear of a build with some specialised parts, as below.



All seemed to be going according to plan but no dice when I fired it up. I had checked the voltages beforehand and they looked kind of off but I thought that this would come right in the wash.

Silly hubristic me. It didn't.

I haven't the chops (or the heart TBH) to try to troubleshoot this but it seems clear from the really silly voltages (0.678 on IC1 for starters) that I've somehow managed to bork the voltage converter. The rest is (a resounding) silence.

I'm trying to be philosophical and not yield to disappointment and self-blame for a change. This hobby is a learning curve after all.

This goes into the box of shame and I'll try again with a fresh board later, I think.

So the real question is how does the hive mind deal with abject failure if and when such occurs? I'd really like to hear from others on how they deal with this.

Disclaimer: this is not the complete assembly. The one I tested was fully populated.

 

[mybud]

Don’t let my disappointment deter anyone, though. By all means do it if you’re up for it

Ok, so in the cold morning light I did some simple voltage testing and it turns out that Va is 5V and Vb -26V. If I understand the schematic and Kevin's build notes correctly, Va and Vb should be roughly equal to 15V positive and negative. The skewed voltages surely would prevent the circuit from functioning correctly and the L4 has received very positive reports from the build reports I've checked in the meantime.



Some other strange symptoms are a susurrus noise on both channels with volume dimed (suggesting some stray DC is floating about where it shouldn't be) and once again the compressor pops and clips in peculiar fashion. I'm going to chalk this one up to experience as above and try again with a fresh board in the summer.

Given these problems, it seems hardly fair to claim disappointment with a circuit that is functioning less than optimally due to my own ineptitude. It has potential to be fab as a brief run-through with my P-Bass has shown.

 

[lowpitch]

Ok, so in the cold morning light I did some simple voltage testing and it turns out that Va is 5V and Vb -26V. If I understand the schematic and Kevin's build notes correctly, Va and Vb should be roughly equal to 15V positive and negative. The skewed voltages surely would prevent the circuit from functioning correctly and the L4 has received very positive reports from the build reports I've checked in the meantime.

View attachment 98178

Some other strange symptoms are a susurrus noise on both channels with volume dimed (suggesting some stray DC is floating about where it shouldn't be) and once again the compressor pops and clips in peculiar fashion. I'm going to chalk this one up to experience as above and try again with a fresh board in the summer.

Given these problems, it seems hardly fair to claim disappointment with a circuit that is functioning less than optimally due to my own ineptitude. It has potential to be fab as a brief run-through with my P-Bass has shown.

Can you share your vero layout and wiring from/to the DC jack? Kind of peculiar that the converter output is offset by 9V.

 

[mybud]

Can you share your vero layout and wiring from/to the DC jack? Kind of peculiar that the converter output is offset by 9V.

Sure @lowpitch, and many thanks for responding.

I battled like hell getting it to work and eventually connected the common output of the Traco to the main circuit ground, which seemed to work. I connected the Va and Vb taps direct to the board: IOW, didn't replicate the connections to the four 100nF and six 22uF caps since these are already in place. Perhaps those components also need connecting to ground?

 

[lowpitch]

View attachment 98179
Sure @lowpitch, and many thanks for responding.

I battled like hell getting it to work and eventually connected the common output of the Traco to the main circuit ground, which seemed to work. I connected the Va and Vb taps direct to the board: IOW, didn't replicate the connections to the 4 x 100nF and six X 22uF caps since these are already in place. Perhaps those components also need connecting to ground?

Common to circuit ground is correct, but is there continuity between common and the ground terminal of the DC jack? If there isn't, maybe the converter references the wrong voltage which causes the offset of the +/- outputs in relation to chassis ground. A fix would be to run a wire from the common on the vero board to the DC jack.

 

[mybud]

Common to circuit ground is correct, but is there continuity between common and the ground terminal of the DC jack? If there isn't, maybe the converter references the wrong voltage which causes the offset of the +/- outputs in relation to chassis ground. A fix would be to run a wire from the common on the vero board to the DC jack.

Yes, there is continuity between the ground terminal and the common connection on the PCB. Similar for the PCB to PSU board connection.

 

[mybud]

Ok, so after rewiring the daughterboard and correcting a cold solder joint on the frequency pot (!) as pointed out by @Nic, it’s finally fully functional. I’m going to put this thread to bed and compile a build report. It’s by no means pretty, but it works.

Once again, my thanks to all who supported this exercise. I’ve learned a lot from troubleshooting this beast and do think it sounds pretty cool, especially nice in combo with my P-bass.