Hi guys. I built two of the Barton Simple Quatizer’s and am having a problem finding a module to feed into it. I have contacted Michael and he said
“Does the LFO you’re using’s output go positive and negative? The quantizer’s range is only 0 to +5V, if you’re inputting a negative voltage to the input, that can temporarily cause strange behaviour like setting it to bypass mode where it just outputs the input.”
For this reason I have been trying to calibrate the 1145 VCLFO (without much success). I am still getting negative voltages out of the positive output on the LFO. Anywho what other module can you recomend to feed into the Quantizer?
Since the analog input pins share their connection with a digital input, they have reverse biased ESD protection diodes to VDD and VSS. The analog input, therefore, must be between VSS and VDD. If the input voltage deviates from this range by more than 0.6V in either direction, one of the diodes is forward biased and a latch-up may occur.
The circuit could benefit, then, from some external protection diodes. A Schottky (e.g. 1N5817) from the input pin to ground and another from the input pin to the +5 V rail, together with a suitable series resistor, would brutally truncate the input voltage but would presumably prevent that “strange behaviour”.
Indeed I made the Positivizer to condition input into my own quantizer module. Be aware it not only shifts the CV to make it positive but also halves its size (a -5 to +5 V signal becomes 0 to 5 V). So you probably would not want to use it on a 1 V/oct signal, it would turn it into a 2 V/oct signal. But it’s fine if you want to quantize some CV whose amplitude isn’t crucial.
You could insert a (full bridge) rectifier between the LFO and the quantizer … Then you still have an oscillating signal albeit that it will not get any negative values (which is what you are trying to prevent).
I have an idea for a Positivizer On Steroids (or P.O.S., hmm, yes, that’s an excellent name, isn’t it?) which I might build one of these days but here’s the core of it. If you want, for instance, a 0–5 V ramp wave but your LFO can only give you -5 – +5 V, you just plug it in, flip the input side switch to ±5 V and the output side switch to 0–5 V, and voila.
I haven’t actually even breadboarded this, but how can it possibly not work?
Is there any reason to use REF02 (0.3% tolerance, 15ppm/°C, 6 EUR) instead of something like LM4040CIZ-5.0 (0.5% tolerance, 100ppm/°C, 0.60 EUR) apart from the main specs, like tolerance and temperature coefficients?
If you have a module that accepts only positive input voltages, but your source supplies an AC voltage, a bridge rectifier is not always a good solution as it will seriously distort you input signal. A better solution might be to raise the AC input signal to a certain DC level and maybe attenuate or amplify it a bit. I built a module for this called Offset-O-Matic.
Such a module is a universal utility.
It can be used as
an attenuator with variable gain
an inverter with variable gain
a buffer circuit or impedance converter
an adder allowing you to add or subtract a DC offset to a signal
combinations of the above
I invariably use it in combination with an AR, ADSR or envelope follower. These devices produce a timed sequence of voltages but they often are not at the right DC or AC level to drive the next module.
So I choose the timing using the AR’s, ADSR’s or envelope follower’s controls and determine the gain (or attenuation) and DC offset using Offset-O-Matic and connect the outout of that to the next module.
Simple things like controlling a CV-input that is based on a VACTROL get much more versatile. The LED in the VACTROL will not light up unless you input a certain ‘rather high’ voltage of maybe 2.5 Volts and only then the variation of the signal will influence the module it is in. So if you have a low input signal the VACTROL will probably not allow you to control the module it is in.
If however you use a circuit like Offset-O-Matic, you can start giving the vactrol a DC offset of e.g. 2,5 Volts so that the LED starts giving some light and then you will see that the low level signal will have an effect. To make this effect bigger or inverse the effect, Offset-O-Matic has a gain from -2 to 2 and can add whatever voltage between -5 V and 5 V. For people familiar with tube or transistor circuits, what Offset-O-Matic in essence is used for in this example is biasing the vactrol.
Note: in the schematic U2.1 and U2.2 were added to get some visual feedback through some LEDs. That part of the circuit is not essential, but to me it makes it much more clear what the circuit is doing to the input signal which makes it more easy to understand how to control the module it is plugged into. The leds show what the attenuation or gain does to the signal and whether the adder moves the signal to a positive or negative DC level.
But that messes up the waveform. For a ±5 V triangle wave it doubles the frequency and for a square wave it turns it into a DC level. If instead you added an offset and rescaled it would give you the same waveform.