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Buchla 252e voltage anomaly on changing preview display mode
MUFF WIGGLER Forum Index -> Buchla, EMS & Serge  
Author Buchla 252e voltage anomaly on changing preview display mode
Hi everyone.

I discovered strange voltage anomaly in my 252e :(

During changing display preview mode from first 4 modes
to 5th mode which shows all modes superimposed to see
which cells are empty and which are occupied the voltage anomaly happens.
The master clock slows down and the sound going a little bit out of tune :(

What can it be? I am asking for support.

My 252e is mounted in original boat in Lem 3 Spider set.
Music Easel is controlled by 252e.

I attached screenshot with comparison of waveforms
and a video sample from action:

Help please :(
I'm wondering if the LEDs are the cause. I can't imagine that little bit of additional voltage would be too much for the power supply but just to be sure create a very simple pattern on a single channel so that the same LEDs will be lit in both modes and see if you get the same result.

That's the first thing I would try.
I will do some tests like you sugested.
Moreover I discovered strange discrepancies in voltages which determining changing the rings.
Also I will test it on different ways and will describe it.

Thank you very much for advise.

Mattson Mini Modular
I did tests and noticed that the more cells are voltage programed the clock (BPM) slows down more.

Moreover I noticed that during changing display preview mode the programed voltages changing too.

In the case in video below you can clearly see that except changing BPM the arrangement of a rhythm also is changing.

Further tests showed changes in programed thresholds of voltage value witch determine changing the ring to the next.
On CV out 2 I programed 7 cells - one in each ring to change the ring to the next after one cycle:

0.2v 1.1v 2.0v 3.0v 3.9v 4.8v 0v

After a few changes of voltage values on other CV outputs the thresholds of voltage values on CV out 2 witch determine
changing the ring to the next also have changed so I had to correct voltages to these:

0.4v 1.3v 2.2v 3.1v 4.0v 5.0v 0v
0.8v 1.7v 2.6v 3.5v 4.5v 5.4v 0v
0.7v 1.6v 2.5v 3.4v 4.3v 5.3v 0v

Because of this, it is impossible to control my 252e precisely.

Mattson Mini Modular
Do you have this behavior in any sync mode or only in time scale mode?
Good question.
Master BPM slowing down behavior is on cycl mode and non sync mode.
Changes in programed thresholds of voltage value are on all modes.

Mattson Mini Modular
I did a couple of tests, too.

In on1 mode, I have a very slight change in tempo when all LEDs are white. It is barely noticeable and when I use the 252e as a master I wouldn't really notice it.
I usually have it synced to MIDI clock and it works perfectly fine.
The on cycle mode didn't show any of that behavior at all.

In time scale mode (I guess this is what the manual calls it), things look different. Buchla USA told me that the problem is the scanning of the CVs, which could actually change the tempo for each clock for every clock tick. Since the mode is based on more experimental drifting clocks and not the main feature I'm good with what it is.

However, I couldn't recreate any of the other CV issues.
I checked the CV outputs with a multimeter and they didn't change at all.
The same is true for the CV inputs.
The threshold for the rings always stayed the same. (of course it was skipped if that ring was already in use by another clock.)
Another important thing to know is that pushing the assign button will not necessarily jump to the ring you chose at the moment you pushed the button. It will only initiate a change to another ring. Which ring it will jump to is based upon the knob setting and the CV input once it reaches step 1.
I'm not a tech but I'm betting it's a power issue. Maybe a component is going.

Disconnect the other modules in the case and see if that helps. If it does that suggests the power supply is straining.
PDT thank you very much for your time and the tests. Your observations have made a lot in this matter. Now I'm sure about unstability voltage tresholds in my unit. I'm going to stress out further my Lem 3 Spider system by driving with more outputs, inputs of 252e and 225h, 226h which are integrated part of Lem 3 S. I will present the results. One more think I'd like to ask you and other users of 252e - about sharing thresholds of voltage values witch determine changing the ring to the next. It seems to me that this valuse should be constant in all modules. Precarious thank you for your tips - I'll deffinietly to do it.

Mattson Mini Modular
I had all manner of weirdness happening until I ditched the switching psu and got a linear supply. Now my 30u system is rock solid.
Lem 3 Spider system i closed in the smallest
Buchla boat which is powered with the same
power adapter like the Music Easel.
I tested Lem 3S on both power adapters.
iBat, did you ever sort this out? I am having issues where each of the 6 CV outputs output a different voltage even though they are all set the same. Anyone else?
Hi tmade,

Could you check with the multimeter each of the 6 CV outputs and compare it with the numbers on the display of 252e?

In mine 252e the multimeter shows differences between voltages in CV outputs when the unit is not programmed. I try to reset CV out 1 to achieve a near-zero voltage on output - I can't. The voltage in CV 1 output is near 0.02 V while on other CV outputs the voltages are near zero.

In addition in play mode the CV edit display shows strange values that in stop mode but the multimeter shows that programmed output voltages match the values displayed in the stop mode. This anomaly occurs on both low and high voltages on all rings and cells.

Mattson Mini Modular
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