Diy vco schematic

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Diy vco schematic

An Oscillator in electronics generally refers to a circuit which is capable of producing waveforms. This waveform can either be of Sine, triangle or even a saw tooth type. Some of the most common oscillator circuits are LC circuit, Tank circuit etc. A Voltage Controlled Oscillator is an oscillator which produces oscillating signals waveforms with variable frequency.

The frequency of this waveform is varied by varying the magnitude of the Input voltage. For now you can imagine a Voltage Controlled Oscillator VCO to be a black box which takes in Voltage of variable magnitude and produces an output signal of variable frequency, and the frequency of the output signal is directly proportional to the magnitude of the input voltage.

We will learn more about this black box and how to use one in our designs in this tutorial. There are many types of VCO circuits ; a very basic one can be built by just utilising a capacitor, inductor and resistor to make a tank circuit. Also Op-Amps, Multivibrator, transistorstimers can also be utilised to build oscillating circuits. In a RC oscillator the frequency of the output wave depends on the value of the capacitor used in the circuit, since the frequency is given by the formulae.

Hence in this case the frequency of oscillation is inversely proportional to the value of capacitance used in the circuit. So now to control the output frequency and to make it work as a VCO we have to vary the capacitance of the Capacitor based on the value of the Input voltage. This can be achieved with the help of varactor diodes. These diodes change the value of capacitance across them based on the voltage applied. A sample output graph of a VCO is shown below. Let us assume the control voltage to be Vc and the output frequency as fo.

As the input voltage control voltage is increased the output frequency increases and the vice versa is also possible. There are many types of VCO circuits used in different applications, but they can be broadly classified into two types based on their output voltage. Harmonic Oscillators: If the Output waveform of the oscillator is sinusoidal then it is called as harmonic Oscillators. These types of oscillators are harder to implement but they better stability than the Relaxation Oscillator.

Harmonic oscillators are also called as linear voltage controlled oscillator. Relaxation Oscillator: If the output waveform of the oscillator is in sawtooth or triangular form then the oscillator is called as Relaxation Oscillator.

These are comparatively easy to implement and hence most widely used. Relaxation Oscillator can further be classified as. There is some dedicated IC which has the ability to generate oscillations based on the input voltage. One such commonly used IC is the LM from national semiconductor.

This IC is capable of generating both triangular and square wave and the nominal frequency of this wave can be set by using an external and capacitor and a resistor. Later this frequency can also be varied in real time based on the input voltage supplied to it.First, the datasheet design. The datasheet design uses pretty much all the features of the chip, and shows one or two of its quirks too.

The CEM is extremely unusual in that it offers both Hard and Soft Sync inputs pin 6 and pin 9and neither of them work the way you might expect. However, the datasheet does offer alternative circuits for synchronization which can give you the classic sync effect, and manufacturers seem mostly to have gone with variations on this instead.

diy vco schematic

Sometimes people just want what they know and love. One of the quirks of the CEM is the waveform outputs. For a start, these are all different levels. Usually this would just be grounded, but it could be taken to the negative supply. Most synths compensate for the differing levels in the following waveform mixer stage. This is easily done by changing the input resistors in an inverting op-amp mixer.

Another quirk is the supply voltage.

Logic Noise: 4046 Voltage-Controlled Oscillator, Part One

Curtis dealt with this by adding a zener diode to limit the negative supply connected to pin 3 to The zener diode needs to be protected from over-current, so you typically see a current limiting resistor hanging off pin 3 R with V in the datasheet circuit.

The circuit breaks up into various functional units quite neatly. Starting numerically at Pins 1 and 2, this is the temperature compensation circuit. This works by generating a temperature-dependent voltage which is then multiplied on-chip by the incoming CV. There are still some minor errors from the multiplication process hey, this is analog, after all but the datasheet gives details of how to trim those out too if you can be bothered.

Pins 4, 5, and 6 are inputs and outputs all labelled above, so no need to discuss those. Pin 7 is more interesting. The lower half of the preset resistor serves as a resistor to ground which converts this current to a voltage, and the upper half and the series resistor 1M feed a small portion back into the Frequency CV input at Pin Pin 11 is the next important one.

Use a good quality capacitor here, with low leakage and low tempco. Pin 13 is the Linear FM input, with an associated bias network. Pin 15 is the Frequency CV input.

This is a virtual ground summing node, and you usually see a bias network as shown K, R, 10nalthough often with the values tweaked, followed by the summing resistors coming from the various CV sources. In addition there are Ground and -5V power connections. The recommended value is 1. You can argue about the relative merits of one versus the other, but the fact is that they were having tuning problems, and using the CEM helped them solve them.

diy vco schematic

Notice the sync circuit. Also note that this is Oscillator A, the Sync Slave. There are several differences to note from the Prophet 5 design. The Triangle output is used, and the Sync circuit has been altered, no longer using the Soft Sync input, but still using a transistor to reset the triangle core.

The Pulse Width mixer has also gained a few extra components.

DIY Synth Series Part 1 - The Exponential VCO

Imagine trying to tune six Minimoogs all piled up together! A three oscillator polysynth with Moog filters! This amp has x2 gain, so it boosts the triangle to V, the same range as the Ramp wave. One thing to notice is that the Moog design uses three trimmers, whereas the Sequential designs manage with only one.

Probably it compensates for the synth warming up the Memorymoog had a fan to keep it cool!When using these on the YuSynth VCO PCB which is designed for standard LM pinout, you need to cut pins 1 and 8 off, and shift the IC up in the socket- pinout below explains it all - well we thought it did but Bob B asked for clarification as to which is pin 1 as it is confusing with those red blobs. We agree so armed with a meter on the diode range revealed that the small red dot is next to pin 5.

The notch in the case is at the top of the chip. Here is an explaination for the reason why they are there.

Considering that the 78L15 and 79L15 require an overhead of 3V to give the right voltage why are these for in this circuit? Could not one just suppress them?

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As a matter of fact, because of the lack of voltage overhead and the low current draw they will rather deliver something like This helps very much in increasing the stability of the VCO. As such, all the circuit of the VCO core was designed considering the voltage drop through the regulators, and it is a very important point. In conclusion, they are there for a good reason. Make sure that when the printed face of mylar is in contact with the copper side of the PCB, the lettering can be read normally.

Components and building details. Thermal coupling between the tempco resistor and the transistor pair of the exponential converter is an important condition for insuring a good stability of the VCO. The following pictures show how to install these critical components on the PCB. The tempco resistor R12 is not installed on the PCB. It is directly soldered to pins 4 and 5 of the LM These pins are connected internally and then can be used to connect R The tempco resistor is directly glued on top of the LM Thermal grease must be used to improve thermal coupling.

Bend the 2SC legs as shown. Install and solder the 2SC first. Then add some thermal grease on the 2SC Then install and solder the tempco resistor in bridge over the 2SC such that there is a close contact between the body of the resistor and the 2SC This mod is described as well as other mods in a PDF file located at the end of this page in the Gallery section.

Thanks Mariano! You may even add a switch on the front panel in order to select between the two hard synch modes. Update : may 19th, It is the heart of the system, the module without which a system cannot be called a Music Synthesizer.

The design of such a module is not easy and building one with good accuracy, low drift and good thermal stability is not simple. I have tried various architectures and eventually came up with quite a classical design.

The second design uses a Japanese 2SC dual transistor which is much cheaper. The third design uses a pair of hand matched BCB.

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Printed circu it boards and component layout. LMN fast comparator. Thermal coupling Thermal coupling between the tempco resistor and the transistor pair of the exponential converter is an important condition for insuring a good stability of the VCO. Solder them to the PCB. Apply thermal grease on the body of the transistors and solder RThe objective of this Instructable is to show you one method of turning DC values, such as those from a thermometer, pH sensor, or pressure sensor into a frequency which can be used to send information over the microphone band of an audio jack to a smartphone.

Did you use this instructable in your classroom? Add a Teacher Note to share how you incorporated it into your lesson. Breadboard Parts 3. You can use an oscilloscope. Why: There are many designs of VCO, but we chose a hysteretic oscillator, which is a type of relaxation oscillator. If you're interested in oscillator design, this website has good information. Theory: The comparator an op-amp, in our case generates a positive feedback loop between the positive and negative voltages.

This feedback charges the capacitor when it draws from the positive voltage, then once the capacitor fills, it discharges, switching the power draw from positive to negative. This process repeats to oscillate continuously.

The frequency of the oscillation is thus dependent upon the size of the capacitor and on the input voltages.

Practice: Values should be selected so that the frequency output will be in the audio range, approximately 16 Hz to 20 kHz. Power the op amp according to the values on its data sheet. Theory: We are currently modulating voltage with a potentiometer.

If the frequency is altered based on this change in DC voltage, a change in DC voltage from a different source should also modulate the frequency.

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Practice: You want the voltage from your sensing circuit to match the voltage range you identified by sweeping voltages above. If your sensing circuit voltages are higher or lower than that range, you will see clipping. If the range of your sensing circuit voltage output is very small, your readings will have low resolution. Plug in your sensing circuit output in place of the potentiometer.

How to Make a Voltage-Controlled Oscillator

Different output frequencies of your VCO will correspond to different voltages inputted by your sensor. Congratulations, you can now send information to your phone over an audio jack! Would it be possible to use the output from a Theramin instead of the wave generator successfully? In the old days, before digital they were used to make signals that could be recorded on tape. Industry used 9 channel tape for recording data using different freq. VCOs so that several could be recorded on each channel, if I remember right you could record 24 different data streams on each channel.

They were also used to tune radio transmitters and receivers. Interesting project. This turns anything that can control a voltage into a signal that can be used as sound right? I'm guessing it's not 1 octave per volt or anything particularly musical, but the idea of making analogue events generate audible tones or digital signals has all kinds of interesting applications. More by the author:.This document is intended for A users who want to learn a little bit about the technical details of the A We will start with some electronic basics and introduce at first the most important electronic parts used in the A circuits.

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Then we will show how some basic circuits like attenuators, amplifiers, mixers, inverters and so on can be realized with these parts. The following paragraph will show some simple modifications of A modules: e. This page starts September New items will be added little by little.

diy vco schematic

If you have any suggestion for this page please send your ideas to hardware doepfer. We will try to fulfil all wishes, providing they are possible and will not contain confidential information. Additional information about technical details e. A Technical details A Mechanical details The A service manual is available only for A customers see price list for current price. The words - mainly building, testing and adjustment notes for the manufacturer - are in German but the schematics, silk screen and bill of material are international.

Electronic Parts For some parts different signs are shown. A resistor is determinded by these parameters:. For the value and tolerance of a resistor normally a color code is used should we add the color code at this place?

Potentiometers are available as rotary potentiometers or fader types. Normally, a potentiometer has 3 terminals: two end terminals and a slider terminal upper picture.

The slider touches a resistance surface that is located between the end terminals. Sometimes the second end terminal is not shown lower picture if only one end terminal is required, e. A potentiometer is determined by these parameters:. MOhm power. This parameter describes the connection between the rotary angle resp.

Sometimes special characteristics are used e. S-type law but these are not very common. For audio attenuation normally logarithmic potentiometers are used as the human ear senses the loudness of an audio signal in a logarithmic way too. The same applies to potentiometers that are used to control time parameters e. For attenuation of control signals normally linear potentiometers are used. For special functions inverse logarithmic potentiometers are used e.Basic oscillator design specifications often require a given output power into a specified load at the design frequency.

The drive level and bias current set the fundamental output current and the oscillation frequency is set by the resonator components.

Transistor selection of the transistor should consider noise, frequency, and power requirements. Based on the particular device, the design may account for parasitics of the device affecting resonator components as well as nonlinear performance specifications. All the VCO schematics presented below were practical build using the Infineon SiGe transistor BFP, and any of them can be re-tuned for different frequency ranges changing varicaps and LC tank values.

VCO Specifications. VCO Design Recommendations. Nonlinear Effects in VCOs. Oscillator circuit nonlinearities cause low-frequency noise components to be up-converted and to appear as noise sidebands on the VCO output. Although this statement is intuitively obvious, quantifying this mechanism is much more complex.

Second-order nonlinear distortion determines the degree of noise contamination of the oscillator output for instance.

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Therefore, second-order distortion in the oscillator should be minimized. The degree to which any oscillator accomplishes this goal can be judged based on the second harmonic output level of the oscillator. A good oscillator should exhibit 2 nd harmonic levels on the order of dBc.

Another useful indicator of good oscillator design is the change in oscillation frequency versus DC bias reduction. A slow reduction of the supply voltage from nominal to the point at which oscillation just ceases, should result in a very small frequency change for example, should be on the order of about of 20 kHz for a well-designed 2 GHz oscillator.

The oscillator excess open-loop gain which is necessary for initial oscillator build-up should be minimized in order to prevent amplitude fluctuations from being converted into significant frequency fluctuations.

The 2 nd harmonic currents in the oscillator sustaining stage can appear in phase quadrature with the fundamental current, thereby worsening the conversion of AM noise to PM noise. Ideally, the 2 nd and 3 rd harmonic frequencies should be placed well above the f T cut-off frequency of the oscillator sustaining stage transistor, thereby minimizing this effect. A change in the RF voltage amplitude across the tuning varactor normally affects the observed tuning capacitance value in the resonator, thereby providing one substantial AM-to-FM conversion mechanism in the oscillator.

Other VCO impairments including injection locking, load pulling, and power supply frequency pushing can cause serious oscillator performance degradation, particularly in phase-locked systems.It works by having a voltage-controlled oscillator VCO inside, and driving the VCO with a voltage signal that depends on the frequency difference between the internal VCO and the external signal.

So far so good, by changing the voltage of the internal VCO depending on how out of sync it is, you can sync up the internal and external waveforms.

When the one-fourth speed VCO signal is synced up to the input, the straight VCO signal is running four times as fast as the input. The voltage input for the VCO is on pin 9, and the output is on pin 4. And finally, the frequency range is controlled by selecting the capacitor on pins 6 and 7, as well as the frequency and optionally offset resistors on pins 11 and 12, respectively.

A capacitor of 10nF and a frequency-selection resistor of K works just great. Since the product of these two controls the center frequency, you could also use a nF 0. According to the datasheet, any value resistor between 10K and 1MOhm works just fine. The offset resistor has to be larger than the frequency-selection resistor above, but otherwise can be infinite.

This would be a great place for a 1M or 10M potentiometer. Now all we need is a voltage source to control it. First up, a potentiometer hooked up as a voltage divider.

The fun in putting synth parts under voltage control is making up wacky sources of control voltage. Turning a knob with your fingers is great, but handing that duty over to some circuitry is better. And that, in a nutshell, is what brought the synthesizer out of the laboratory and gave birth to the modern synthesizer as musical instrument. In the video, we solve this problem two ways.

First, adding a capacitor to the voltage input of the VCO holds on to the last voltage for a while. This lets the last note continue to play even after removing our finger from the keys, or the croco clip from the VHS tape, as it were.

And mixing the two results in a pitch that slowly decays. As a quick aside, you can make a rudimentary keyboard with just a bunch of push buttons and voltage sources.


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