# Simple oscillator circuit

• posted

I want a simple oscillator circuit that will give 30 kilohertz.

Which of these components do I change to achieve this?

What values should these be?

If I want a little variance (~10 percent) it should be the resistor, right?

What other opamps can I use?

Thank you.

• posted

The opamp needs to be able to feed the lamp, so you need a high-output one. Then bild it, check frequency against the value of C, change C accordingly. The lamp makes sure of a stable output without distortion.

• posted

"Gone Fishin'"

** The formula for frequency is:

f = 1 / 2.pi.R.C

So with the values shown, oscillation is at 159 Hz.

Change both R values and both C values together and do not go under 1kohm for R.

Many other op-amps could be used, but the NE5534 is a good choice.

.... Phil

• posted

I calculate 50pF with 100K gives 31.8KHz.

But which of the C do I change? The one connected to ground? Which of the R is part of the RC circuit? (The circuit is a bit confusing because it uses 2 identical R & C values.)

If I want to make the RC variable, which R do I replace with a pot (or fixed

• pot)?

Also, this op amp (LF155) is specified as dual-supply type. I need a single supply op amp. Will the R-C connection to ground of this circuit be connected to -Vcc regardless if it is a single or dual supply op amp?

Thank you.

• posted

So changing both R to 50pF and leaving both R at 100K will give 31.8KHz?

• posted

"Gone Fishin'"

** You must reduce the two R values to a few kohms at most and then pick C to suit. 2.2 kohms and 2.2 nF is about right.

Fine adjustment can be done with a pot of about 10% the value of R in series with one of them.

.... Phil

• posted

Thanks Phil. Much appreciated.

• posted

You change them both, both circuits have to balance at the wanted frequency. Changing only one will degrade oscillator quality. If you can lay your hands on a tuning cap, they often contain two sections, and make testing rather easy.

• posted

Could you use a single supply with a voltage divider to set a virtual "ground" node without causing distortion of the output waveform, or would it be necessary to put a voltage follower there?

• posted

I need some advice regarding the grounding of the parallel R & C.

The LF155 is a dual-supply amp. I need a single-supply amp.

I presume that in this circuit the ground is chosen because it is the mid-point between the dual supplies (ie, +/-15). With a single-supply amp, this point is not mid-point but rather it is the "negative supply" point.

How should this circuit change for use with a single-supply amp?

Thanks.

• posted

Gone Fishin' Inscribed thus:

Sounds like home work !

```--
Best Regards:
Baron.```
• posted

It is... of my own making.

I've been out of school for 30-plus years, now.

Do you have any suggestions re. a solution?

Thanks.

• posted

Gone Fishin' Inscribed thus:

Oops. :-)

```--
Best Regards:
Baron.```
• posted

This TI app note describes a single-supply wien bridge oscillator, which helps me with a partial solution:

<

The note does not describe specific op amp P/N's. Should I limit my design to a single-supply op amp? Or can a dual-supply op amp and a single supply be used here?

Thanks.

• posted

Take a look here:

--- news://freenews.netfront.net/ - complaints: snipped-for-privacy@netfront.net ---

• posted

```--
Does the output have to be sinusoidal?

Does it have to be centered around zero volts?```
• posted

Among conventional op-amps, there isn't much that really makes a single-supply op-amp special. Often the only thing about an op-amp that inspires the manufacturer to call it a single-supply op-amp is the fact that the common mode range (the input) includes the negative supply. At least that's my take on it. More to the point is that your APPLICATION appears to require a dual supply. Almost any old op-amp will do, like the one Phil named or even a good old

741. You need a central reference point for that circuit, as indicated by the ground symbol. It's actually not hard to take a single supply and effectively split it in two. You need a voltage divider and a voltage follower. The voltage divider is two resistors in series connected across your power supply that creates a voltage reference at the midpoint between Vcc+ and Vcc-. But it has high impedance, which means that drawing current from it will drag the voltage up and down, something you don't want. So you put a buffer in there, a voltage follower. If you get a dual op-amp you can use the spare op-amp as the voltage follower. To use an op-amp as a voltage follower you connect the non-inverting input to the voltage divider, and connect the inverting input to the op-amp's output. The op-amp's output is then a low-impedance source at the midpoint of your power supply. It's like taking a 12 volt battery and magically turning it into two 6 volt batteries in series. You can also use a bjt as a voltage follower.
• posted

Approx 30 KHz, sine, distortion not terribly important. Centered around zero? Don't know. It's to be the input to an amplifier module like one of these?

Thanks.

• posted

"Gone Fishin'"

** The link is to an LM1875 audio amp.

One could use that as the oscillator.

..... Phil

• posted

There seems to have been a mix-up. The link should be this one:

This is an audio amp. The oscillator will be the input to this.

Thanks.

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