- [x] Polivoks Power Header Orientierung raussuchen für Konsistenz! (siehe DIY_Manuals/
- [x] Hilfe für alternative Bestückung mit Transistoren anstatt THAT340 (Grafik für Manual erstellt)
- [x] dreamer> on the 1st page it says 'Lin FM' with both FM-inputs
- [ ] Gotchas für Profis
- [ ] Fotos von fertiger Platine (mit richtigen Bauteilen)
- [ ] Pot PCB: R3 fehlt in Liste, Wert richtig?
- [x] Nichtelkos haben Polaritätsanmerkung in Liste – durchgehen! (C1, C2 and C4 are mislabeled on the BOM as electrolytic)
- [ ] Pinheader passen nicht!
- [ ] Anleitung Kalibrierung
- [ ] Ergänzung Pots: Potis muss man diese kleinen Metalldinger abbrechen
- [ ] Ergänzung Tempco: wenn du anstelle des that 340 gematchte transistoren benutzt, muss
r2 dann auch wirklich ein tempco sein und sowohl u$1g$3, u$1g$4 und
r2 müssen in thermischem kontakt stehen, wie im bild hier (foto von
th 555 vco diy expo)
## 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:
1. Solder Resistors first (R)
2. Solder Sockets for ICs
3. Solder 100n, 10n, 1n, 47p Capacitors
4. Solder 1N4001 or 1N4004 and other Diodes
5. Solder Q3 and Q4 Transistors and Polyfuses (F1, F2)
6. Solder LM4040, C6 and C7 (careful with polarity!)
7. 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:
8. Solder all 4 Trimmers
9. Solder Power Connector
## Page 7 (Pots Top)
Take next PCB and solder in this order:
10. Solder all Resistors first
11. 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.
