Maker Pro
Maker Pro

Will this synthesizer work?

j4cobgarby

Sep 18, 2018
49
Joined
Sep 18, 2018
Messages
49
I've attached an image of the schematic for a synth I'm designing.
The basic principle is that I have three 555 timers, each generating a square wave whose frequency is controlled by the resistors R1, R9, and R13. Each timer's output can optionally be converted to a sin wave or left as a square wave based on a switch on the output of each timer. The three different timer outputs now are summed together at U2, but are weighted according to R5, 6, and 7. The resultant waveform is then sent through the speaker at the bottom. The whole thing is powered by a 9V DC jack.

I have two main questions:
  • Are the 555 timers wired up correctly? This is my first time using them like this.
  • Will there be a problem with audio impedance at the speaker? I have little understanding of impedance in this context.
Thank you in advance!Screenshot from 2019-01-27 15-31-30.png
 

BobK

Jan 5, 2010
7,682
Joined
Jan 5, 2010
Messages
7,682
You cannot connect the discharge pin to Vcc, this is a short when discharge is low. There may be other problems.

And, no, you cannot drive a speaker directly from an op amp. You need an audio power amp.

Bob
 

j4cobgarby

Sep 18, 2018
49
Joined
Sep 18, 2018
Messages
49
You cannot connect the discharge pin to Vcc, this is a short when discharge is low. There may be other problems.

And, no, you cannot drive a speaker directly from an op amp. You need an audio power amp.

Bob
Why can I not connect discharge to Vcc? How else will I get a 50% duty cycle? Or.. Just a low value resistor instead of shorting it, perhaps?
 

BobK

Jan 5, 2010
7,682
Joined
Jan 5, 2010
Messages
7,682
Why can I not connect discharge to Vcc?
Because it shorts the power supply.
How else will I get a 50% duty cycle? Or.. Just a low value resistor instead of shorting it, perhaps?
You cannot get a 50% duty cycle with the standard astable circuit. Connect the pot to the output pin to get a 50% duty cycle.

Bob
 

Audioguru

Sep 24, 2016
3,656
Joined
Sep 24, 2016
Messages
3,656
Please look on the datasheet of a 555 how to make an oscillator.The rectangular output of the 555 sounds awful like a buzzer.
Your filters are so simple that they do nothing at low frequencies and reduce the levels at high frequencies before the waveform is near a sinewave.
You are using adjustable series resistors instead of using them wired as volume controls, and they should be log type, not linear type.
Your speaker is shorting the output to ground. A proper power amplifier would feed the speaker through a coupling capacitor to block the DC at the amplifier.

The opamp has positive feedback instead of negative feedback.
 

Audioguru

Sep 24, 2016
3,656
Joined
Sep 24, 2016
Messages
3,656
A Cmos 555 can produce a perfect squarewave with the simple circuit using the output pin.
 

j4cobgarby

Sep 18, 2018
49
Joined
Sep 18, 2018
Messages
49
Please look on the datasheet of a 555 how to make an oscillator.The rectangular output of the 555 sounds awful like a buzzer.
Your filters are so simple that they do nothing at low frequencies and reduce the levels at high frequencies before the waveform is near a sinewave.
You are using adjustable series resistors instead of using them wired as volume controls, and they should be log type, not linear type.
Your speaker is shorting the output to ground. A proper power amplifier would feed the speaker through a coupling capacitor to block the DC at the amplifier.

The opamp has positive feedback instead of negative feedback.

How, then, would you suggest converting the square waves to sine waves?
 

Audioguru

Sep 24, 2016
3,656
Joined
Sep 24, 2016
Messages
3,656
Years ago I converted a high frequency squarewave to an oversampled sinewave. Instead of the 16 stage shift register shown here, I used a simple 5 stage CD4018 counter with 5 resistors creating 10 steps. One of the counter outputs is the squarewave and the counter is fed from a 10 x the frequency variable clock oscillator. I also used a switched capacitor lowpass filter IC that had its frequency changed by the variable clock oscillator. The sinewave was good at all frequencies and its level never changed.
 

Attachments

  • digital sinewaves.png
    digital sinewaves.png
    39.6 KB · Views: 4

BobK

Jan 5, 2010
7,682
Joined
Jan 5, 2010
Messages
7,682
For a synthesizer, you really don’t want sine waves. They sound absollutely boring, not like any instrument because they have no harmonics. A softened square wave, i.e. with a low pass filter to round the edges, sounds vaguely like a woodwind. A sawtooth sounds vaguely like a bowed string.

Also, the envelope is critical to get sounds that are unstrument like.

Bob
 

j4cobgarby

Sep 18, 2018
49
Joined
Sep 18, 2018
Messages
49
For a synthesizer, you really don’t want sine waves. They sound absollutely boring, not like any instrument because they have no harmonics. A softened square wave, i.e. with a low pass filter to round the edges, sounds vaguely like a woodwind. A sawtooth sounds vaguely like a bowed string.

Also, the envelope is critical to get sounds that are unstrument like.

Bob
How would I make an envelope for the sound?
 

BobK

Jan 5, 2010
7,682
Joined
Jan 5, 2010
Messages
7,682
You would need a lot more circuitry than you currently have.

It all depends on what you are trying to achieve,

There is plenty written about analog synthesis out there.

Personally, if I wanted to make a replica of the old Moog or ARP type of synthesizer, I would do it digitally with a microcontroller.

Bob
 

j4cobgarby

Sep 18, 2018
49
Joined
Sep 18, 2018
Messages
49
You would need a lot more circuitry than you currently have.

It all depends on what you are trying to achieve,

There is plenty written about analog synthesis out there.

Personally, if I wanted to make a replica of the old Moog or ARP type of synthesizer, I would do it digitally with a microcontroller.

Bob
I was thinking of doing it with a microcontroller but this is more fun, in my opinion.

I believe I've come up with a final design (attached)

I changed the wiring of the 555s, and made the frequency be controlled by a piano-like input, instead of a potentiometer, and I've added an audio amplifier IC to power the speaker!
 

Attachments

  • Screenshot from 2019-01-31 18-59-48.png
    Screenshot from 2019-01-31 18-59-48.png
    434.1 KB · Views: 9

BobK

Jan 5, 2010
7,682
Joined
Jan 5, 2010
Messages
7,682
I think you better start simulating or breadboarding before you proceed.

Bob
 

Audioguru

Sep 24, 2016
3,656
Joined
Sep 24, 2016
Messages
3,656
I do not know what you are doing because you do not know what you are doing.
 

Attachments

  • synth with errors.png
    synth with errors.png
    87.8 KB · Views: 6

davenn

Moderator
Sep 5, 2009
14,240
Joined
Sep 5, 2009
Messages
14,240

Audioguru

Sep 24, 2016
3,656
Joined
Sep 24, 2016
Messages
3,656
Here are the important coupling capacitors and negative feedback for the mixer.
 

Attachments

  • audio parts of synth.png
    audio parts of synth.png
    38.3 KB · Views: 5

Audioguru

Sep 24, 2016
3,656
Joined
Sep 24, 2016
Messages
3,656
I found the 555 wiring from this website: https://www.electronics-tutorials.ws/waveforms/555_oscillator.html
The diodes are there so that nothing weird happens because I want all of the 555s to share the same resistor
That website (in India?) does not work right now.
If the diodes allow the 555 ICs to work then they will almost play the same frequency. Why use three oscillators when one will work much better?

Use an audio mixer circuit to mix three oscillators together. Since they play almost the same frequency then the mixed sound will flutter as the signals add in phase then cancel when out of phase. If you want to play a musical chord with three frequencies then use a musical IC designed to do it.
 
Top