Noise source and sample & hold

No modular is complete without a noise source. I use noise quite often when I make music, so I really wanted to add a nice noise generator in the modular. The noise generator is inspired by Eric G with some changes. My version outputs White noise, Pink noise, Red noise, and Blue noise. None of these outputs are really perfectly Pink or Red etc, but they are filtered noise which reduces the need of external filtering. The noise are based on a 1N759a zener diode.


Noise generator

When the noise source were finished I had some space left on the faceplate, so I added a sample and hold unit to extract random voltages from the white noise. Many thanks to Magnus Danielson for ideas and discussions! The sample and hold is based on René Schmitz’s circuit, and the built in LFO is based on the ASM-1 LFO. The sample and hold has controls for LFO speed and CV range, and outputs for CV and Gate.


LFO and S&H

This design works rather nicely. However, when making the pulse to the sample and hold (i.e. the FET transistor) short enough so the S&H doesn’t leak between samples the indication on the LED is very short leading to low light level and the output Gate is rather a short trigger. Therefore the pulse width of the LFO should be changed, by removing the 1N4148 diode and the 2k resistor. This would however decrease performance of the S&H why the circuit need an additional Gate to trigger circuit converting the square wave from the LFO to a short trigger pulse to the S&H, for example this one by Ken Stone.


Doepfer A-110-1 VCO

Deopfer A-110-1 Standard VCO

Deopfer A-110-1 Standard VCO

As for all other Doepfer modules I’ve bought, the A-110 VCO comes in cheap bubble wrap with the mounting screws in a small zip bag. No manual is included, but a decent manual is downloadable as a pdf from Doepfer’s web site. The A-110 has a very sober layout, maybe a tad towards too neat-German-precise-engineering-sober, but never the less it’s a simple and understandable layout. The front panel is anodized aluminum with black text and Doepfer-grey knobs. Inputs are placed on the left side, controls on the right side, and outputs at the bottom. To me this makes a clearly arranged and lucid layout. However, the position of the input jacks makes the VCO a bit less easy to work with, since the input patch cables might be in the way for easy knob tweaking. Despite the fact that the A-110 VCO is a cheap VCO the module feels great, robust and sturdy. The controls have a good feeling, even if the 5-position Range rotary switch rather has 10 positions (feature or failure?).

The A-110 VCO is 10 HP and is easy to mount with the two supplied mounting screws. Patching it up is easy enough, with inputs on the left and outputs at the bottom. There are two CV-inputs for frequency control (CV1 and CV2), two PWM-inputs (PW CV1 and PW CV2), and one Sync-input (Sync) for hard sync. Additionally there is the (supposed to be) 5-position octave switch (Range), a fine tune control (Tune) that covers about +/- six half tones, a pulse width control (PW) with a range from 0 to 10, an attenuator for CV2 and an attenuator for PW CV2. The outputs are for Sawtooth, Square wave, Triangle wave, and Sine wave, and all of these can be used simultaneously.

According to the Doepfer manual the A-110 VCO might need up to 20 minutes of warm up time before fully stable. The oscillator is then stable over (about) four octaves. This is certainly not great, but good enough for most applications. It is worth mentioning that due to the sawtooth core of the VCO, neither the square wave nor the triangle wave is perfect, neither the sine wave is good but rather a rounded triangle. Furthermore, I do miss the possibility to choose between linear and logarithmic frequency modulation. The A-110 has exponential frequency modulation that, besides changing the harmonic content of the sound, also affects the fundamental frequency of the tone in an (probably) unwanted way. Additionally, the A-110 VCO lacks the possibility to choose between hard and soft sync. The A-110 has hard sync, which completely resets the slave waveform when the master waveform completes a cycle.

To summarize, the A-110 VCO is a low price but nevertheless rather competent VCO with many enough functions that make it a good buy to be the workhorse in a modular system. But for the high end applications there are more advanced and expensive VCOs.

Ratings (1 = poor, 5 = excellent)
Build quality: 4
Functionality: 3
Audio quality (if applicable): 3
Ease of use: 3
Cost/Bang for your buck: 4

Comparison chart
Category: Sound sources
Controls: 1x Range (rotary switch), 1x Tune, 1x CV 2 (attenuator), 1x PW, 1x PW CV 2 (attenuator).
Inputs: 1x Sync in, 2x frequency CV in, 2x pulse width CV in.
Outputs: 1x Sawtooth out, 1x Square wave out, 1x Triangle wave out, 1x Sine wave out.
Size: Width: 10 HP, Depth: 55 mm
Power consumption: +12 V = 70mA, -12 V = not specified, +5 V = 0mA
Price: 140.00 € / $199.00