[Resolved] My first preenFM2 metal case .. trouble shooting no audio

[horridus]

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[horridus]

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[Xavier]

Everything looks good. Digital sample data reach the DACs.
This is the Biggest mistery in the whole preenfm2 history   

You can use your oscilloscope to follow the audio path.
Clear the default Combo preset (MENU>SAVE>Default>clear). REBOOT. so that we know you have a "sounding" preset.
Set the voice number to 1 for the current instrument and 0 to the others to maximize the voltage output of the preset.
Play a repeating note from you sequencer, loop it,  and be sure the instrument show up on the display.

Now put your oscilloscope on the output of the DAC.
Bottom left pin on the gerber1.png
http://ixox.fr/forum/index.php?topic=63509.msg65620#msg65620

If you see your analog waveform, Then try to continue the audio path. 1.8K => 3.3nF => 8.2k => opamp => 68 => 22uF => pot.

If the output is FLAT at the direct output of the DAC, try to unsolder the 1.8K resistor and try again the DAC output.

[horridus]

I'll give this a try 

[horridus]

Here is some audio from an MFB Step64 sequencer playing the preenFM2 over midi DIN ... I traced the audio path with the oscilloscope all the way to the phone jacks and recorded this audio sample at the same time. Also, the leds flash on the preenFM2 as midi is received, I reset to the default instrument on the preenFM2 as instructed. The audible pops are in a different pattern (matching notes from the sequencer pattern), but similar to what the chime on boot sounds like in terms of final audio product. There are some "extra" artifacts that blast occasionally that are not native to Audacity with no signal input during a recording (tried this to make sure it was not a ghost in the machine saying hello :>) ... Sorry for the harsh noise! Please make sure and turn your audio output down before playing the files.

The signal as read by the oscilloscope appears all the way to the phone jacks, but it is obviously not the audio we are hoping for. The 3.8v at the DAC output and the 4.02v at the 68 ohm resistors are still the strongest indicators of the underlying problem I think. 

[horridus]

audio from chime for comparison

[Xavier]

OK So there is actually a sound. That's not a no audio problem 

Forget what i said about the 115K resistors.
Can you double check the resistor values 1.8K and 115K ?

[horridus]

I am quite dyslexic and color blind (short list), but I will definitely check again right now.

Here is some video of part of the test too: https://youtu.be/JXA-8qQG5RE

[horridus]

I read both just now ... the 115k positions read 103.8k ... and the 1.8k positions read 1.788k

[Xavier]

Congrats...
You're the winner of the contest : the unfixable preenfm2 
Your prize : a new PCB and its components.

Send me an email to preenfm1@gmail.com and let me know if you already have some of the IC sockets, resistors, capacitors, diode in your stock...

Time to go to bed for me

[Xavier]

One last question, have you tried to power it with a real 9V wall power supply ?

[horridus]

I did ... a great deal of the first rounds of tests were done with a known to be good 9v power supply. The audible pops have always shown up on boot or with midi coming in  ...

Good night Xavier sleep well  .. thank you again for your time and tutelage

[served]

You should send the unit back to xavier.
I bet he would be thrilled to actually see what happened.

[Xavier]

Horridus, your new PCB is on it way.
Served is right, in the meantime if you can send me back your faulty preenfm2, i'd love to take a look.

Thanks,

Xavier

[horridus]

that can be done ... just returned from a seattle noise show ... i ended up playing as a last minute fill in ... great fun