I built this nice through-zero VCO from Weston Precision Audio.
Features:
Thru-Zero Linear Frequency Modulation
5 wave shapes: Sine, Triangle, Sawtooth, Square, & Pulse
Extremely good tuning linearity (<+/-5cents over 10 octaves)
Built-in high frequency compensation
Hard Sync input (reset type)
Built in VCA for modulating Linear FM signal with an envelope
Wanting to add more analog oscillators to my collection, I recently bought a Joranalogue Audio Design Generate 3. The Generate 3 is also a through-zero design. Together with the Dannysound EN129 TZ Oscillator, I now have three different analog through-zero oscillators. The features of the TZ0 are similar to the EN129, except that the EN129 offers a log FM input with attenuator, and the TZ0 adds an internal VCA for depth control on the linear FM. TZ0 has a hard sync input. My version of the EN129 has no sync, but a soft sync was added in 2020.
Construction
I got the panel and 3 PCB set from Synthcube. The matched transistor pair and tempco resistor come preinstalled as SMD components. The rest of the project is through hole. The BOM supplied by Weston Precision Audio (in .xlsx spreadsheet format) contains Mouser.com part numbers, which simplifies ordering. There is a mistake in the BOM. R102 is called out as 86.6k 15ppm, which is wrong. The correct value is 82.5k 15ppm (as discovered from the build guide and schematic, which agree). I ordered the wrong value, but substituted an 82.5k 1%.
The build guide, which you can download ahead of time, is very useful and contains a theory of operation and full schematic diagram. Also included are color photos of each board to compare your work against. With three stacked PC boards, this modules is specified as 48mm deep.
I substituted Davies clone knobs for the small ones though I did get the specified large Coarse tuning knob. I also respected the knob color scheme. Frequency knobs are light gray, through-zero controls are yellow, and pulse width controls are black.
Three boards
Board A is the rear-most PCB and contains the power header, soldered to the back. These are photos of my build. Notice the thermal tape covering the SMD transistor pair and tempco resistor.
PC board B, in the center, is photographed with the 11mm standoffs that attached it to the other boards.
Board C is the front board that holds the pots, jacks, and LEDs. Notice that on all of these boards I have soldered the integrated circuits, not using sockets. I’ve been convinced that this is the most reliable method, and I use it whenever the quality of the PC board is high in case one needs replacement (which is exceedingly rare).
The only hiccup during the build, I soldered the LEDs backwards. Here the build guide could have been clearer. The short lead goes into the square hole.
Tip: Leads from one of the jacks hit the trimpot on the middle board, preventing full seating. Just clip off those leads.
Look for TZ sounds from this module soon! I may do a comparison of the three through-zero oscillators as well.
