New Teensy 4.1 DIY Synthesizer

[Rolfdegen]

Hallo friends

This is the control unit from Jeannie. For the button query, I use an ADC input to save output lines on the Teensy Board.

The LED Driver IC8 is controlled via the same SPI bus as the ADC chip but with a different CS line. This saves additional lines from Teensy Board.

The SPIN_1 - SPIN_4 lines on IC8 and 3 PWM lines from Teensy board are for the control of the SPIN FV-1 Effect chip.





This is a my prototype and the arrangement of buttons, potentiometers, etc. will change a bit.



Greetings. Rolf

[Rolfdegen]

The Spin FV-1 effect module is mounted on the back of the Jeannie board.



This is an old PCB version. I built it into my other DIY synthesizer "DEGENERATOR".

Here are sound examples from Degenerator Synth with FV-1 chip: https://drive.google.com/file/d/1jG6...lCWHZS45M/view

and Youtube: https://youtu.be/unN71yPqREU

Greetings Rolf

[fdaniels]

What happens if you push 2 buttons simultaneously?

[Rolfdegen]

Hallo..

This function is not intended. But the key that was pressed first becomes active.

Today I got the FV-1 chips. These are 28 pin SMD chips but it's not difficult to solder. For comparison, an 8-pin IC.



Greetings. Rolf

[Rolfdegen]

Hallo friends..

Here are complete Jeannie circuit diagram with FV-1 card. PWM1-4 and SPIN1-4 are Spin FV-1 control lines.

MCU unit


Control unit


Fx unit


(subject to change):verwirrt:

Greetings Rolf

[fdaniels]

What about an Audio IN so you can route a signal thru the Filter + FX, just like the Shruthi. Maybe you could even Sample?

[Rolfdegen]

Hallo Daniel

That is not provided in Jeannie. We want to build this synthesizer very small and inexpensive with good sound.

But maybe in an XT version with many pots ans knops :mit den Augen rollen:

Gruß Rolf

[fdaniels]

Hallo Daniel

That is not provided in Jeannie. We want to build this synthesizer very small and inexpensive.

But maybe in an XT version with many pots ans knops :mit den Augen rollen:

Gruß Rolf

Why dont you then use the internal Audio Systems Effects for "small and inexpensive"? Adding a simple circuitry for mixing audio input would allow to use it as an FV-1 FX/Filterbox additionally, which is a huge advantage. Then, sampling is just a ADC away.... You already add 10€+ of parts just for the effects, thus leaving the "small and inexpensive" world (btw, the Display also isnt "small" or "inexpensive"), so aditionally 1€ for an TL074 and associate Parts wont make it unsellable....

[Rolfdegen]

Thanks for your good ideas. There is hardly any space left on the circuit board.

It's open source and you can change it if you want

[Rolfdegen]

Hello friends


It is progressing. Corona also has something positive. You spend more time at home and on your computer.
Before I start laying out the boards, I want to know if everything works. I may be there
a bit old fashioned. But setting up an experiment on the breadboard always involves contact problems
and disturbances connected. I prefer to solder and am sure that there is at least no contact
problems are.



The right board becomes the optional Fx board. The board will turn out a bit smaller and over later
a contact strip on the back is connected to the motherboard.


Greetings Rolf

[tomas]

For better reliability of your MIDI IN consider 10k resistor between pin 7 and ground of optocoupler as explained here:
https://electronics.stackexchange.co...edirect=1&lq=1

[Rolfdegen]

Hello Tomas


I am using a 6N137. Pin 7 is Monitoring node and does not have to be connected.



Greetings from germany. Rolf

[tomas]

Sorry. Apparently I need to get my eyes checked.

[amensch]

Very nice sounding Rolf. I will be getting a PJRC audio shield in a project in the coming weeks and look forward to following your path.

[Rolfdegen]

Sorry.. double post

[Rolfdegen]

Hello again..


The prototype of the Fv-1 circuit is now completely soldered and works flawlessly. Will be a little smaller later because of SMD
and relocation of the power circuit (+/- 5V) to the main board.







https://youtu.be/Tq4jn6Mz5Ko

The Fx menu in the synth is almost ready. The parameter values are still missing after a program change. I still have to change that.

Greetings Rolf

[Rolfdegen]

Hello and have a nice Sunday


There are a few changes in the circuit diagram. The DAC output (PT8211) on the Teensy Board has an active 32KHz LowPass filter. This reduces high-frequency interference signals at the input of the effect chip.






The OTA (IC5a / b) for the volume control of the effect signal (MIX) has now been moved to the output of the effect chip. This means that the noise floor at the synthesizer output is a little lower at low effect levels.



Greetings Rolf

[Rolfdegen]

Hello friends..


We have started to route the boards. I'm curious how big they will be.


Fx board


Greetings from germany. Rolf

[ChrisGuichet]

Hello Rolf, fantastic work. I’m really enjoying see the progress on this.

I love how informative your display is, and how it gives the user lots of real time feedback. Do you have any advice or resources on how to achieve that? I would like to do something similar for my synth (real time visualization of synth parameters, oscilloscope, etc).

Thank you!