# Problem with NE566N VCO

#### El Zu

Joined Jan 13, 2016
28
Hi!

I'm trying to make the Thomas Henry 566 VCO, the same from here, but have no luck with it. I use MFOS PSU with -15v, +15 and ground for power supply. I measure the voltage coming out of the 741 and 566 and it seems to be alright. It has non-changable strange oscillation from pin 4 and has no sound from pin 3 at all.

I have no oscilloscope, so I connect speakers to the pin 4 of the 566 to hear triangle wave. Is it correct to do like this?
If the problem is with bad 566 chip than how to figure it out?

#### GopherT

Joined Nov 23, 2012
8,012
The NE566 is not designed to drive such a low resistance load as a speaker. Check the DATASHEET, it should show maximum current output. Use your supply voltage and ohms law to calculate.

You could use an old-school crystal headphones as an improved option or, better, feed the output of Ne566 into a preamp of some sort (let us know what is available).

#### El Zu

Joined Jan 13, 2016
28
The NE566 is not designed to drive such a low resistance load as a speaker.
Oh, my fault! I use amplifier, I connect it to the amp and than goes speakers.

#### hp1729

Joined Nov 23, 2015
2,304
Hi!

I'm trying to make the Thomas Henry 566 VCO, the same from here, but have no luck with it. I use MFOS PSU with -15v, +15 and ground for power supply. I measure the voltage coming out of the 741 and 566 and it seems to be alright. It has non-changable strange oscillation from pin 4 and has no sound from pin 3 at all.

I have no oscilloscope, so I connect speakers to the pin 4 of the 566 to hear triangle wave. Is it correct to do like this?
If the problem is with bad 566 chip than how to figure it out?
I don't remember the 566 being rated to go to + and - 15 V. Maybe + and - 12 V.

#### Alec_t

Joined Sep 17, 2013
12,818
Yup. Datasheet says max supply voltage is ±12V.

#### El Zu

Joined Jan 13, 2016
28
Yup. Datasheet says max supply voltage is ±12V.
My datasheet says it is up to 24V. %)

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#### Sinus23

Joined Sep 7, 2013
247

#### El Zu

Joined Jan 13, 2016
28
Plus minus 12V =24V :/
It doesn't work at 12V, anyway
Did you notice that the schematic has unusual power supply, and it should work at 15V, somehow. Look at the thread with schematic.

#### Alec_t

Joined Sep 17, 2013
12,818
The failure to work is probably due to a poor contact somewhere on the breadboard, assuming everything is wired exactly as per the schematic.

#### hp1729

Joined Nov 23, 2015
2,304
My datasheet says it is up to 24V. %)
Yes, +24 and ground or + and - `12 V.

#### El Zu

Joined Jan 13, 2016
28
The failure to work is probably due to a poor contact somewhere on the breadboard, assuming everything is wired exactly as per the schematic.
I breadboarded it twice without any luck. Probably, it is bad chip. I will try to get a new one. Let u know.

#### hp1729

Joined Nov 23, 2015
2,304
I breadboarded it twice without any luck. Probably, it is bad chip. I will try to get a new one. Let u know.
Normally I would try to duplicate the circuit, but you choose a chip I don't have. I have worked with the 566 in the past, but they are long out of production it seems. Current price is about $10 and that is "used". Do you have a better source? Thread Starter #### El Zu Joined Jan 13, 2016 28 Normally I would try to duplicate the circuit, but you choose a chip I don't have. I have worked with the 566 in the past, but they are long out of production it seems. Current price is about$10 and that is "used". Do you have a better source?
Yes, it is a discontinued chip. I will buy it on eBay this time.