X0XB0X VCO Tuning and Clicking problem

[shawnsick]

Hello, I am new to this forum and this is my first post. I have been following this forum for quite some time as I have built multiple x0xb0x kits (all supplied from x0xsh0p.de) Up until now I had been able to successfully build every kit I have put my hands one with only a few minor issues that I was able to solve myself or via research on the net (mainly through the adafruit forum).

For the past few days I have been ripping out my hair and I haven't been able to sleep due to the fact that I cannot seem to accomplish my latest kit without a very strange VCO tuning issue (and know a clicking issue). The first problem appeared as soon as I had completed assembling the kit, I put the machine in keyboard mode and I immediately noticed that on the middle octave setting (C2 to C3) all of the notes were out of tune as I expected but the last three notes on the note scale ( A, B, C,) were/are way out of tune, the other octaves are out of tune but the last three notes don't drop like they do on the middle octave mode. As soon as I noticed the problem I tested C1 to C2 and C3 to C4 and C4 to C5 and I realized that the problem didn't occur on the other octaves. I soon started checking for defects or wrong components etc and I discovered that C22 was installed the wrong way round (reversed polarity) so I replaced that capacitor with a new one to be safe. After replacing the the capacitor the problem was still present so I looked for other problems on the board and I eventually noticed that I had installed A 20K resistor at R89 instead of a 200K, after I replaced the part the problem was still there. After checking the board for bad solders and other parts without any coming across any problems I decided to connect the machine to ableton via midi to see if the problem was still there if the machine received midi notes from an external source, the problem was still there and all of a sudden in midi mode every note started clicking so loud that the notes couldn't be heard. After inspecting the board over and over again I suspected that IC9 may have been damaged so I replaced it with a brand new part but the clicking and tuning problem is still there (even in keyboard mode not just midi). After checking voltages with my multimeter on IC9 and IC11 and IC12 here is what I get: P.S \_/ Indicates the orientation mark on the top of the IC

IC9-------------------------

IC 9 (V) without pressing any notes:...IC 9 (V) after pressing and releasing C2:...IC 9 (V) After pressing and releasing C3:
5,33\_/5,33....................................5,33\_/5,33........................................5,33\_/5,33
5,33| |5,33....................................5,33| |5,33.........................................5,33| |5,33
0,01| |0,01....................................5,02| |5,02.........................................5,02| |5,02
0,01| |0,01....................................5,02| |0,01.........................................0,01| |0,00
5,33| |5,33....................................5,33| |0,00.........................................0,00| |0,00
0,01| |0,01....................................5,02| |0,01.........................................0,00| |5,02
5,33| |5,33....................................5,33| |0,00.........................................0,00| |5,33
0,00| |0,01....................................0,00| |0,00.........................................0,00| |5,03

IC11-------------------------

IC11 (V) Without pressing any notes, machine turned off and back on again after pressing notes for previous test:
4,53\_/11,82
5,33| |5,33
5,33| |5,33
0,00| |4,95

IC12-------------------------

IC12 (V) Without any notes pressed:IC12 (V) C (middle octave):.IC12 (V) D (middle octave):.IC12 (V) E (middle octave)
0,00\_/11,82..............................0,00\_/11,82.................. 0,00\_/11,82...................0,00\_/11,82
0,01| |10,78..............................0,00| |0,02.....................0,00| |0,02....................0,00| |0,02
0,00| |9,91...............................0,01| |9,91.....................0,01| |9,91.................... 0,01| |9,91
0,00| |5,33...............................0,00| |2,50.....................0,00| |2,70.....................0,00| |2,90
10,7| |5,33...............................0,02| |2,50.....................0,02| |2,70.....................0,02| |2,90
0,04| |5,33...............................0,04| |2,50.....................0,04| |2,70.....................0,04| |2,90
0,00| |4,95...............................0,00| |2,30.....................0,00| |2,50.....................0,00| |2,70

IC12 (V) F (middle octave):.....IC12 (V) G (middle octave):.IC12 (V) A (middle octave):.IC12 (V) B (middle octave):.IC12 (V) C:
0,00\_/11,82............................0,00\_/11,82....................0,00\_/11,82...................0,00\_/11,82................... 0,00\_/11,82
0,00| |0,02..............................0,00| |0,02.....................0,00| |0,02.....................0,00| |0,02.....................0,00| |0,02
0,01| |9,91..............................0,01| |9,91.....................0,01| |9,91.....................0,01| |9,91.....................0,01| |9,91
0,00| |3,00..............................0,00| |3,20.....................0,00| |2,11.....................0,00| |2,32.....................0,00| |2,42
0,02| |3,00..............................0,02| |3,20.....................0,02| |2,11.....................0,02| |2,32.....................0,02| |2,42
0,04| |3,00..............................0,04| |3,20.....................0,04| |2,11.....................0,04| |2,32.....................0,02| |2,42
0,00| |2,80..............................0,00| |3,00.....................0,00| |1,97.....................0,00| |2,16.....................0,02| |2,25

If you look at the voltage of each note on IC12 you will notice that the voltage drops on A B C (middle octave only) Here is what I got after trying C1, C2, C3, C4 and C5:

IC12 (V) C1:............................IC12 (V) C2:......................IC12 (V) C3:.....................IC12 (V) C4:....................IC12 (V) C5:
0,00\_/11,82...........................0,00\_/11,82.....................0,00\_/11,82...................0,00\_/11,82...................0,00\_/11,82
0,00| |0,02.............................0,00| |0,02......................0,00| |0,02.....................0,00| |0,02.................... 0,00| |0,02
0,01| |9,91.............................0,01| |9,91......................0,01| |9,91.....................0,01| |9,91.....................0,01| |9,91
0,00| |1,25.............................0,01| |2,50......................0,01| |2,42.....................0,01| |3,65.....................0,01| |4,91
0,00| |1,25.............................0,01| |2,50......................0,01| |2,42.....................0,01| |3,65.....................0,01| |4,91
0,00| |1,25.............................0,01| |2,50......................0,01| |2,42.....................0,01| |3,65.....................0,01| |4,91
0,00| |1,15.............................0,01| |2,31......................0,01| |2,25.....................0,01| |3,40.....................0,01| |4,57

I have also tried replacing IC12 but the problem is still there, I have access to an oscilloscope and a frequency generator and a transistor tester if necessary.
Both wave forms appear to be working and all of the LEDS and the tempo potentiometer and the LEDS above the note keys are also all working. I have tested the machine in with DIN sync and Midi (send and receive) and all of that appears to be working. I would really appreciate any sort of help as this is really starting to touch my nerves.

[mmm]

For the past few days I have been ripping out my hair and I haven't been able to sleep due to the fact that I cannot seem to accomplish my latest kit without a very strange VCO tuning issue (and know a clicking issue). The first problem appeared as soon as I had completed assembling the kit, I put the machine in keyboard mode and I immediately noticed that on the middle octave setting (C2 to C3) all of the notes were out of tune as I expected but the last three notes on the note scale ( A, B, C,) were/are way out of tune,

This is about as far as I needed to read.
Your problem is that the highest bit is probably missing. If my theory is correct the G# from one octave transposed up will have the same frequency as the lowest C (transposed one octave down).

Please play the notes G# and A in the non-transposed octave and measure the voltage at the following points:

IC9, pin 11 and 10

IC11, pin7

[shawnsick]

Hello, thank you for your reply, here is what I have found after trying what you said:

IC9 G#
Pin 10: 0,00v
pin 11: 0,01v

IC9 A
Pin 10: 5,33v
Pin 11: 5,03V

IC11 G#
Pin 7: 3,31V

IC11 A
pin 7: 2,11V

[mmm]

I'm not home right now so I don't have the schematic in front of me.

The measurements show that the highest bit makes it to and through IC9 but not to IC7 (or not with the right voltage). This points again at the resistor network.

I think the relevant resistors are R88, R89 and R90. If you measure across R88 or R89 you should get 100k, not 200k.

My guess is that there are a couple more wrong resistors within the network. All resistors between R74 and R90 must be 200k; and for all resistors in parallel you should measure 100k.

[shawnsick]

Hi, i noticed that R88 was poorly soldered, after soldering everything is as it should be but I am still having the clicking problem, If I press I note in keyboard mode without releasing the note comes through but there is a really loud thumping/click noise at the beginning of each note. Any ideas?

[antto]

it would help if you record the issue and post a little sample

[shawnsick]

Okay, I left the machine running and the error went away, I didn't touch the machine and left it for another 10 minutes and the error came back and then went away again, could this be a heat related issue?

[shawnsick]

Here are some sound recordings of the problem when it occurs:

clickproblem1.mp3.zip

(134.61 KiB) Downloaded 157 times

clickproblem2.mp3.zip

(224.62 KiB) Downloaded 135 times

[antto]

first audio looks like you didn't had any oscillator/filter signal going out at all, and what's left is some DC-offset, being amplified with the volume envelope in the VCA..

second audio: ouch...
in the beginning of each note, the oscillator is pulled out of the picture and then appears a bit later with oscillating pitch and cutoff (this is probably warbling on the 5.33 and/or 12V lines)

why is the osc pulled out is a difficult question, one reason could be strong DC-offset in the beginning of notes
i can only guess here

[shawnsick]

Bare in mind that both audio samples are recordings of the same problem, one of the samples is the machine playing in random mode and the other is when i hold down the notes in keyboard mode. The problem comes and goes, when it goes there is no clicking and the machine works and sounds beautiful. I'm starting to wonder if it could be a short circuit but I've looked almost everywhere with a magnifying glass and I can't find any problems. When the problem occurs I can still hear the differences between both waveforms when I hold down the notes in keyboard mode.

Forgot to mention that when the problem occurs the clicking can still be heard when the machines volume is set to zero.

[shawnsick]

Any ideas?

[antto]

i don't have any better ideas
if i were you, i'd get the voltage map and start measuring here and there..

[shawnsick]

Do you know where I can find a complete voltage map for the X0XB0X, I can only find one for the VCO section.

[antto]

http://forums.adafruit.com/viewtopic.php?f=12&t=12453

[shawnsick]

After hooking up the machine to and oscilloscope I have been able to look at the thumping/popping noise on the scope, it does look like a DC offset issue, it reminds me of the VCA offset on a juno 106. I was able to measure the voltage of noise and it seems to be aprox' 5,33V. I removed all of the IC chips in the VCO and the noise still appears, I tested the envelope to make sure everything is working correctly and it all appears normal. I am starting to wonder if the problem is coming from the VCA, I have already tried changing the LA4140 but that changed nothing. I am starting to wonder if the gate is bleeding into the VCA??? I have tested the gate and it works (0 and 12V on north of D35 and right of D34) I can recall accidentally reversing the wires 1 and 3 on J6 when the machine had been built, could that have caused any problems? Also on D35 I am reading 0V on the south side of the diode but looking at the voltage map my reading appears to be wrong (It should be reading 2,63V). On a lot of places around the mixer and VCA circuit I am reading a lot of wrong voltages, aprox' 1V less than what is shown on the voltage map. Any ideas or advice?