euro journeyman built - TUN calibration

[Pav]

Hi Tony,
finally got the euro Jman built.

Pre calibration checks suggested it was all fine, but I am not seeing anything like 17Khz tweaking TUN.
(freq and res pots full cw, cv2 and drive off as per instructions.
I max out at 3.56Khz. Min is @ 100Hz I then checked the voltages on the trim pot +11.6v and -11.something on the outer pins suggest power on pins 1,3 is ok.
I set pin2 to 5V anyway. Self oscillates fine but not infinitely ear splitting at full clockwise.
fyi - i skipped scale calibration.. SCL trimmer left centered for now.

What might i check to increase the frequency ?

[Synthbuilder]

i skipped scale calibration.

I'd check scaling first. How it scales will give us a clue whether the problem is CV gain issue, or an offset problem.

[Pav]

Ok Scaling step has been completed. Tun reset to -5v (i had misread 5v first time ) yet maximum self oscillation reading 4.6khz .
I reflowed and checked voltage reaches R18. checked Freq Knob voltage at R17. Turning ccw I cannot hear with my ears self oscillation after 10oclock position.

[Synthbuilder]

Turning ccw I cannot hear with my ears self oscillation after 10oclock position.

I'm a little confused here. So it's self-oscillating at higher cut off settings but not below 10 o'clock. Or do you mean you can't hear anything after turning clockwise past 10 o'clock?

And is this a maximum resonance problem rather than the range of the cut-off frequency itself? If so, what affect does the RES trimmer have on the range of self-oscillation?

[Pav]

Sorry to confuse.

>>>So it's self-oscillating at higher cut off settings but not below 10 o'clock.

Yes. Erm... well we might still have non audible self oscillating below 10. i cannot hear it or measure it...so yes.

I believe I am not achieving the "maximum useful" frequency of self oscillation (you state as 17kHz).
In addition, I only begin to hear the sine wave when frequency knob reaches 10 o'clock position. (7-10 is silent)
This might be relevant to the issue , a different issue, or expected I ask.
[PAV EDIT - Since found my 5U Jman does not start until 11.5 oclock]

>>>And is this a maximum resonance problem rather than the range of the cut-off frequency itself? If so, what affect does the RES trimmer have on the >>>range of self-oscillation?

The range of frequency I get when self-oscillating.
(FYI The Res trimmer was previously set so that self oscillation starts when the Res pot is at 2o'clock with Freq pot at maximum setting)

Calibration step 4 asks you to
"adjust TUN to set the cut-off frequency to be 17kHz when the Frequency pot is set to its maximum setting."

I cannot achieve 17kHz.
I am inferring from your alternate calibration technique that -5V should equate to approx. 17Kz with Freq and Res full and Drive and CV2 off.
Using alternate calibration technique I successfully set pin2 of TUN trimmer to read -5V.
Yet I only see 4.x kHz.

[Pav]

Follow on...Just checked my 5U Journeyman ..and I cannot hear the self oscillation until 12 o'clock so that answers that question.
The maximum frequency of the 5U is ear splitting ..unlike my euro version which is not.

[Synthbuilder]

I cannot achieve 17kHz.

Just to clarify, as I understand it, self-oscillation on the module in question only occurs with the FREQ pot between 10 o'clock and fully clockwise, and that oscillation frequency varies from 100Hz to around 4kHz. This would suggest there is a problem with the gain structure of the CV pathway. However, since you can scale the oscillation it could mean that R17 on the main board is wrong - maybe too high a value.

If this is the case, you should be able to increase the oscillation frequency beyond 4kHz with an external CV. But if you can't increase frequency with an external CV the problem could be the wrong value for the zener diode D5.

[Pav]

Solved by changing D5 - wrong way around - my bad.
fyi I did not have the exact part for D5 but used BZY55B6V2 500mw 2%. Would a 1% percentage make a difference ?
I can tune it fine now.

Thanks for the guidance.

[Synthbuilder]

Solved by changing D5 - wrong way around - my bad.

Easily done, the little blighters are really tiny.

Would a 1% percentage make a difference ?

Not in this application. The zener diode is acting as a simple voltage clamp to stop the drop in gain when you try and push the cut-off frequency too high.

I can tune it fine now.