New Teensy 4.1 DIY Synthesizer

The 1st draft in 3D

It is progressing ..

The 3D model of the motherboard. The board is roughly the size of a laboratory card in euro format (160 x 100).

The Fx module is simply plugged onto the back.




The current prototype


Greetings Rolf :)
Hallo friends :)

The board is now ready. We thought about integrating an expansion connection (K4, K8 ) in the synthesizer for the electronics hobbyist).

It consists of 3 analog inputs (0-3.3V), as well as data lines and power supply for controlling a second 74HC595.

This means that potentiometers, switches and control voltages can be queried via two 16-channel analog multiplexers (74HC4067), for example.



Control Circuit with expansion connect ( K4, K8 )

Greetings. Rolf
Looking very good!
What will be your business model for this? Can I start ordering a a teensy 4.1 and audio board?
Thank you
Hi Daniel

The PCB boards or DIY kit with case can be ordered in future from

You don't need an audio card. An 16Bit audio converter (PT8211) is fitted on the board.

Greetings Rolf
Hello rolf! How much $ and how long until a Jeannie is in my hands here in California? I don't see them on tubeohm yet. Also, the presets seem identical to my did that happen? Are they a set of known synth presets used by a bunch of synth designers?
We are waiting for the first boards. It will take a while before circuit boards or kits can be ordered.

The Jeannie Synth-core is a little different from TSynth. It's smaller and has 8 voices, 8 banks with 64 different waveforms, Sequencer, 24-bit Fx chip for reverb, delay, corus and more. LowPass filter at the output to reduce high frequencies. Boost switch for more depth. It will be a transparent yello plexiglass case.

The price has not yet been determined. We are still negotiating with dealers in different countries.

Greetings from germany. Rolf
My friend Andre is busy soldering. I'm curious ..

Soldering the components shouldn't be a problem. I hope the SMD pads are not too small and can be soldered well. :)



Example of the first case




Greetings. Rolf
Last edited:
Hello dear Synthi friends ..

We have now checked our "Jeannie" and everything works flawlessly. Andre listened a little more closely with his trained ears and noticed distortions in the sound.

Measurements have confirmed this. The cause is a non-linearity in the PT8211 DA converter used.

Here the measurement on the PT8211 with 4x oversampling (176KHz) and 500Hz sine tone. The non-linear distortion creates new frequency components (1000Hz, 1500Hz, 2000Hz ..) which are added to the original sound.


At the moment we are wondering whether we should use a better converter in the Jeannie, e.g. PCM5102A. I have already taken measurements with a PCM5102A on the Jeannie.

Distortions and the noise floor are much better (see picture).



Greetings Rolf

Since the DAC chip (PCM5102A) cannot be easily soldered, we considered using a ready-made converter board (3-6 euros) and plugging it onto the mainboard from behind.

This eliminates the difficult soldering of the SMD components. The circuit boards are already available on the Internet for a few euros and cost almost as much as the converter chip alone.

32Bit DAC PCM5102A converter


Greetings. Rolf
I tested the 24Bit ES9023P from HIFIberry DAC+ light. It works well too.

But we will be using a 32Bit PCM5102A. It's a DAC with better quality.
Last edited:

There are a few more changes. My friend Andre is changing the Jeannie circuit board and integrating the PCM5102A DAC converter.

Like the other boards, the DAC converter is also mounted on the back as a plug-in module.

The difficult SMD soldering is no longer necessary. I have already installed the DAC converter module on my Jeannie (picture).




First sound impressions from Jeannie with a new PCM5102A DAC converter


Greetings from germany. Rolf
Last edited:
The Fx module

The Fx module is plugged into the marked socket strips on the back of the Jeannie.

It contains a SPIN FV-1 24Bit DSP with 15 effects. The first 7 effect programs are set as standard in the DSP.

The remaining 8 programs are stored in an EEPROM (24LC32A) and can be changed by the user. The software for this is freeware.



The Fx menu

With P1 - P3 the parameters for the effect can be adjusted. The parameter is selected with "SEL" and changed with "VAL".

With "Mix" the effect signal is mixed with the audio signal of the synthesizer. With "PRG" you select the effects.

A special feature is the adjustment of the "ClK" clock rate for the FX chip. The clock rate can be changed from 10KHz to 60KHz.

This enables delays of up to 2 seconds in length.

Greetings Rolf

The changes to the hardware of the Jeannie are now complete.

We had a few minor problems with the power supply and could solve that now.

Before new boards are ordered, everything is thoroughly tested again and fine-tuned new sounds.

There is a 2nd preview from Andre with very nice sounds from "Jeannie"


Hello dear Synthians :)

We have built in a small distortion stage in front of the digital filter in the software (picture).

One voice


The distortion stage consists of an AMP with an adjustable gain of 0.25 - 1.75

I placed the function in the oscillator menu and called it Overdrive (ODRIVE).

This can be used to program a distorted or screaming jazz organ, for example.


Greetings. Rolf
Hello ,
I would like to introduce myself first. My name is Andre , the man behind TubeOhm . After several projects Rolf and I are now working on the Jeannie. While Rolf does the programming/circuitry I do also the circuit design the conception/theoretical development of the synth and the circuit boards and later also the DIY kits .
I am happy to be here in the forum. Maybe someone has questions or suggestions and maybe we need your help to finish the project.

So, Rolf has just programmed the velocity dynamics.
Very useful I think. Of course I tested it immediately and made a 'little velocity song'.