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User Manual
BOM
Schematics
Build Instructions (pro)
Build Instructions (noob)
Calibration

Building Steps

Split PCBs with a cutter and the edge of a table. Do not attemp to break it appart without putting it to an edge!
On components PCB: solder all 10k resistors (6 pieces) in. Careful not to confuse them with 18k!
solder all 18k resistors (2 pieces) in. Careful not to confuse them with 10k!
solder all 12k resistors (2 pieces) in.
solder all 2.2k resistors (3 pieces) in. Do not confuse with 2.2m or 22k!
solder all 100k resistors (2 pieces) in.
solder all 2.2m resistors (2 pieces) in.
solder R36 with 150k in (replace this with a different value to change PWM control scale, leave this out and add a 200k precision trimmer if you want to add the PWM Scale Trim Mod)
solder R10 with 1M
solder R1 with 1k
solder R16 with 20k
solder R9 with 22k
solder R15 with 27k
solder R24 with 390R
solder R7 with 47R
solder R18 with 5.1k
solder R8 with 820R
solder R2 with 2k. (replace this with a 330ppm 2k Tempco if you use Transistors instead of the THAT340)
solder the two 1N4001 diodes in. Careful with the orientation! The white stripe needs to be oriented right!
solder D1, 1N4148 in. Careful with the orientation! The black stripe needs to be oriented right!
solder the 16 Pin IC sockets. Solder one leg first, solder the rest once you made sure everything is straight. Orient them right to avoid mistakes when putting the ICs in later.
solder the 8 Pin IC sockets. Solder one leg first, solder the rest once you made sure everything is straight. Orient them right to avoid mistakes when putting the ICs in later.
solder all bypass capacitors (100nF ceramic)
solder C1 with 1nF. Careful – do not confuse with C3!
solder C4 with 47pF
solder C2 with 10n
solder C3, 1n Styrofoam/Styroflex/Glimmer. (This Capacitor is for tuning and should be somewhat stable with changing temperature).
solder the Transistors Q3 and Q4, 2N3904. Careful to orient them according to the silkscreen.
solder the precision voltage reference LM4040-10.0 in.Careful to orient according to the silkscreen.
solder the electrolytic capacitors C6 and C7 with 10uF. Careful with the orientation. The white stripe needs to go to the round pad. The longer leg goes to the square pad. Make sure they are flat with the PCB otherwise you will run into problems later.
On the top side of the PCB solder the two polyfuses (print says R005 BJ6S)
turn the PCB around and solder one leg of the power connector to the bottom of the PCB. Make sure the opening is pointing left.
On the bottom side of the PCB solder the 100R Trimmer (print says 101) in. Make sure it sits firmly on the PCB.
On the bottom side of the PCB solder the 50k Trimmer (print says 503) in. Make sure it sits firmly on the PCB.
On the bottom side of the PCB solder the two 100K Trimmers (print says 104) in. Make sure they sit firmly on the PCB.
Take the Pots PCB
resistor R3 (2.2M) is not needed, bridge the contacts with a piece of wire (solder it there)
solder all 100k resistors (4 pieces) in.
solder all 1k resistors (2 pieces) in.
solder R11 with 1M
solder R6 with 2.4M (or 2.2M if no 2.4M available)
solder R35 with 330k
solder R32 with 1.8k
solder R33 with 3k
solder C2POTS with 220nF
If your pots have a small metal piece, break it off with pliers (twisting usually works well).
Do not solder: push in the green pots (except PWM_CV)
Do not solder: push in the Jacks
Do not solder: push in the pot with plastic shaft
Put the Panel onto Pots and Jacks. Screw it on with the fingers
solder Pots and jacks (make sure everything sits tightly, before soldering the first things). Be careful not to apply too much solder at the jacks.
Take of the panel again
Split the two 5-pin headers (2x male and 2x female) into four 1 pieces. Use a cutter first and then split it with two pliers.
stack both boards with the pinheaders inbetween and solder the pinheaders together (if you are not sure they are straight, only solder one pin)
Put the ICs into the sockets (watch for the orientation! you may have to bend the IC legs to make them fit)
Put the Panel back on, screw everything into place
Assemble the Powercable. Be careful about the orientation of the red stripe on the ribbon cable! Always measure the cable with a multimeter before using it!
Push on the knobs. If the knob is too loose, put a little piece of paper, isolating tape or plastic on the shaft, before pushing on the knob.
If you have a lab power supply (with the possibility to limit current), try your module with limited current first

Page 1 (Manual)

The TH-VCO1 is a voltage controlled oscillator, with a triangle Schmitt-Trigger Integrator core designed by Thomas Henry.

This core yields is a very stable Oscillator capable to output triangle (SYMBOL), sine (SYMBOL) and pwm (SYMBOL) waves. The base oscillation frequency of the oscillator may be changed via the Coarse and Fine Frequency knobs.

The Pitch of the VCO1 can also be controlled with an Control Voltage (CV) present at the V/OCT input. This input tracks with 1V per Octave and does so accurately for at least 8 octaves if the mdoule is calibrated well.

There are two FM Inputs with exponential (SYMBOL) and linear (SYMBOL) characteristics. Try plugging one of the outputs or the output of a second VCO back into a FM input and turn up the according Attenuator.

With the PWM Knob the pulse width of the PWM Output may be shifted from 0 to 100% (see diagrams to the right), resulting in a change of overtone structure. There is a PWM Input (SYMBOL) which enables voltage control of the Pulsewidth.

Pages 2-4 (BOM)

See DIY_Manuals/th-vco1_diy_manual.ods

Page 5 (Components Top)

Solder in this order to avoid trouble with part heights:

Solder Resistors first (R)
Solder Sockets for ICs
Solder 100n, 10n, 1n, 47p Capacitors
Solder 1N4001 or 1N4004 and other Diodes
Solder Q3 and Q4 Transistors and Polyfuses (F1, F2)
Solder LM4040, C6 and C7 (careful with polarity!)
Place Female Pin Headers (don’t solder, they shall be soldered in the end)

If you don’t have a THAT 340 you may also use Transistors to replace it. For ideal results glue together the transistors with the R2 2k Tempco with some heatconducting glue

Page 6 (Components Bottom)

Turn around solderd Components PCBs:

Solder all 4 Trimmers
Solder Power Connector

Page 7 (Pots Top)

Take next PCB and solder in this order:

```
Solder all Resistors first
```
```
Solder 220nf Capacitor
```

12.1 Place all Pots and Jacks into the holes (without soldering) 12.2 Fit all Pots and Jacks through the Panels. If you have a plastic shaft Pot, place it in place at the PWM_CV Pot 12.3 Put panel over pots and jacks and loosely tighten the screws with your fingers only 12.4 Solder pots and Jacks with panel in place (be extremely careful not to apply too much solder!) 12.5 Remove panel again

Page 8 (Pots Bottom)

Turn PCB around:

13.1 Put male Headerpins in their place (do not solder) 13.2 Stack Pots PCB onto Components PCB (connect male and female header pins) 13.3 With everything in place finally solder the male Headerpins to the Components PCB and the female Headerpins to the Pots PCB 14. Screw on the frontpanel and push on the knobs 15. Cut ribbon wire, make sure the connectors are placed right and press them in

Page 9 (Schematic Components)

Page 10 (Schematic Pots)

Page 11 (Circuit Explainations)

The core of the VCO-1 produces a clean triangle wave which is “shaped” into a sine from which a pulse/rectangle with variable width can be derived. The core functions by the principle of a Schmitt Trigger Integrator. This is a feedback loop between a Schmitt Trigger and an Integrator with an LM13700 OTA as a “variable resistor” to change the frequency of the oscillation.

A Schmitt Trigger is a circuit which turns an discrete input signal (=analog voltage) into a sort-of-digital “On-Off” voltage. The VCO-1 Schmitt Trigger (on the right side of the schematic) is a built up with two 2N3904 Transistors and switches on with a rising and off with a falling voltage (see oscilloscope traces).

The output of this Schmitt Trigger is fed back into the Integrator (TL072 chip in the middle) via the LM13700. The Integrator integrates the current coming out of the LM13700 and creates an Triangle which is again used to feed the discrete Schmitt Trigger: a classical Feedback loop which produces a very nice and clean triangle wave.

The C3 1nF capacitor can be changed to achieve lower or higher frequencies (10nF would turn the VCO into an LFO etc.). The Schmitt Trigger could potentially be replaced with an IC or an opamp based Schmitt Trigger, however the discrete Schmitt Trigger is claimed to have superior speed (which is important to produce accurate tones at higher frequencies). In simulation this VCO achieved an output frequency up to 80kHz without any degrading of the waveforms (~20kHz is the upper limit of human hearing). Also note that the discrete Schmitt trigger is driven by stabilized ±10V from the voltage reference and not from the ±12V rails, to further improve pitch stability.

Page 12 (Circuit Explainations 2)

The LM13700 in the core of the VCO can be seen as a “current controlled resistor” (reality is a bit more complicated). However: if you change the current on Pin 1 of this LM13700 you change the frequency of the oscillator (and therby the pitch). The current needed for this is tiny (a few μA).

The relationship between this current and the change in frequency is by default linear. This means if we add 1V to the input voltage we also add a certain number of Hz to our frequency. But pitch is perceived exponentially. Therefore in the eurorack world we usually want to have a exponential relationship: if we add 1V the input voltage, our frequency doubles. A doubling in frequency is the step of one octave.

The schematic on this page displays the exponential converter which takes the THAT-340 monolithic NPN-PNP transistor pair as a basis. The general idea is that the collector current of a transistor is exponentially related to the input base-emitter voltage. Unfortunately, something called the emitter saturation current creates a deadly temperature sensitivity and could easily cause the unit to go way flat or sharp as things warm up or cool down – this is the reason to use two transistors. Because of the way it’s been configured, the error current within the first transistor moves in the opposite direction. If the two semiconductors are closely matched in performance, then most of the temperature dependence is canceled out. Obviously a high quality pair makes a difference, and also the mechanical bonding, this is why the (sadly expensive) monolithic THAT340 is used.

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