Plog data input with negative voltages unexpectedly controls toggle

Eurorack
#1

I picked up a Plog module last week (a supposedly brand new one), and it’s working as expected except for one strange behavior that is making it difficult to use the toggle flip-flop and the data flip-flop at the same time.

I am trying to make a random gate by sending a clock signal to the clock input and random S&H signal to the data input. When I do this, it acts like the data input is normalled to the toggle input and causes the toggle to start flipping on and off. But it’s not just normalled: It happens even when something is plugged into the toggle input. So I can no longer use it like a toggle (at least not a toggle that I control via its input). Additionally, once this happens, if I unplug everything, sometimes the toggle is now in clock mode and continues to toggle on and off at regular intervals.

I can’t imagine this is the expected behavior, but I’m wondering if any other Plog owners have experienced anything like this?

I was looking at the jumpers on the back of the module and there are 3 pins (two positions) for the toggle input normal: Out B and N/A. There are no jumper cables on the back of my module, so I tried adding one to the N/A pins for the toggle normal, hoping this would disable any normals to that input, but it did not have an effect.

I spent a while investigating and determined this is happening because the data signal (the S&H signal) is bipolar. If I use an attenuator and offset signal to put that S&H signal in approx the 0V - 8V range, then everything seems to work as expected.

As an experiment I have a Duatt plugged into the data input. The Duatt has no input so it’s sending constant voltage. In unipolar mode, everything works as expected and does not affect the toggle. In bipolar mode, quickly turning the Duatt knob into the negative and back will trigger the toggle. This happens even with no clock input. If I turn the Duatt knob into the negative for about 1 seecond, the toggle goes into clock mode. Another strange detail is this doesn’t happen if I turn the knob very slowly. So it’s like there’s some “sharp edge trigger” detection happening.

In other words, it appears sending negative voltages to the data input acts like a toggle button press. Why is the data input even influencing the toggle? Is this by design or is my module somehow unintentionally “bleeding” signal between inputs? Why only negative voltages?

I guess I can be careful about sending negative voltages, but that’s not something I want to worry about and would like to disable this behavior if possible.

#2

I don’t have Plog in my case at the moment so I can’t replicate what’s happening in your system but in the manual: NOTE: All of the logic and trigger inputs are expecting 0-5V signals (i.e. logic level pulses/gates/ clks). However the inputs all have negative and over voltage protection. Also each input employs a comparator with a threshold of approximately 3V. This means you can still use non-square wave signal sources as long as they exceed the comparator threshold.

#3

Aa far as the toggle acting like a clock if you press and hold the button for 1 second it will act like a tap tempo clock generator. The jumper on the back is to link output B to the T input

#4

This raises the question: What does “negative voltage protection” actually do? I assumed a negative voltage would act like 0V. But it’s causing the data input to unexpectedly affect the T input. Conceptually, I don’t understand why these jacks would be linked in terms of the features of the module. It’s not a useful behavior IMO. And there’s no jumper to link the data input and T input (unlike the B output and T input, which are designed to be optionally linked via their jumper).

I suppose everything is connected in the circuitry and I should be prepared for strange behavior with negative voltages? This is probably unlikely but I was wondering if a spare bit of solder could accidentally connect things that shouldn’t be connected and cause “cross talk” between jacks that shouldn’t normally happen. I imagine that would cause much more obvious malfunctions though.

This may all be a quirk of how Plog’s negative voltage protection works. I’m really curious if anyone else can reproduce this behavior.

#5

I can’t speak for the designer :sweat_smile:! but I personally really like the way the module is designed. It’s basically meant to be used with clocks and triggers. The manual is short but everything is well explained. I usually use the data input with a clock division of my master clock and use the output to open the gate on a vca with some other signal. I see the flip-flop section of Plog like a latched gate generator and a basic clock divider.

#7

Ok so I connected Plog and it does exactly what you said. So maybe someone from Intellijel could help.

#8

Thanks for checking!

Honestly, it’s not a big deal. Everything works flawlessly if I use signals in the correct range of 0-5V (or even 0-10V seems fine).

Part of the fun with modular is plugging things in the “wrong” way, so I’ve plugged LFOs into the DATA input. When I send a clock signal to the CLK input, it “samples” the LFO and the OUT D goes high when the LFO is above about 3V or so. In other words, it converts the LFO to a gate signal. That’s all expected behavior.

But then I was really surprised that a bipolar LFO causes the OUT T signal to change. The first time I ran into this, I had something hooked up to OUT T and it started activating unexpectedly. I was really confused for a while. My intuition was the DATA input would have no effect on the OUT T behavior. I thought something was wrong. It makes me feel better to know yours does this too.

Now that I know what’s going on, I’ll remember to use unipolar signals. Or maybe find a way to “abuse” this behavior for creative purposes :slight_smile:

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