Last Updated:
Syntecno TeeBee T303 (Mark I)
| Accent Pot | More Volume / VCA | Accent "Wow" | Infinite Decay | IEC Mains / Internal PSU |

Syntecno TeeBee Mark I T303  Modifications
Except for the IEC Mains Socket & Internal Transformer / PSU,
the other sound mods are from the download docs from
Syntecno's Homepage.

The idea of the Accent Pot:
Since the TeeBee is Velocity Sensitive but the original TB-303 is not...

When the TB303 plays a note with an accent, the following 3 things happen :
- The decay is set to zero.
- The volume goes louder.                        (controlled by Accent potentiometer)
- The resonance of the filter is boosted.     (controlled by Accent potentiometer)

With the TeeBee,
- Above attack velocity 100, the decay is set to zero.
- The attack velocity controls the amount of volume increase.
- The attack velocity controls the amount of resonance boosting.

In order to get “the most TB303-a-like accents” :
- Use an attack velocity of 30 for notes without accent.
- Use an attack velocity of 127 for notes with accent.

The MOD:
Replace R46 with a 50k Lin Pot

Locate R46 on the analogue (front) PCB,
de-solder & remove,
solder a 47K or 50K Lin Pot.

[Click Image to Enlarge]


On my TeeBee Mark I, I put took out the front Audio Input socket and mounted that at the back.
So I have a hole there to mount the Accent Pot.

New Accent knob replacing the Audio input Socket:


Mod2: More VOLUME (VCA Update)

The idea of the More Volume / VCA update MOD:

For making the sound larger in volume, resulting in a better signal to noise ratio.
(Also enables you to get better distortion possibilities when you want to overdrive your mixer input).

This modification makes the signal coming from the VCO larger.
Thus the signal going into the filter will be larger and also the output volume.
Because the filter will now work with higher amplitudes, a better signal to noise ratio will be obtained, also for the analog input.

The MOD:
Replace R62 (220K) with a 100k resistor.
Or solder another 220K in parallel to the original R62.

[Click Image to Enlarge]

What I did...
Instead of making this a permanent mod, I soldered a SWITCH,
so I can switch between the original and the mod.

A switch mounted next to the Tuning knob:

To be honest, I don't think a switch is really necessary. I only did it so I can compare the difference.
But in real life usage, the mod just makes it slightly louder, it isn't a very dramatic effect.

Mod3: Accent "Wow"

The idea of the Accent "Wow" Mod:
For having a more "wow" sound, when the accent is turned on.
This modification will only be noticeable when you turn on the accent.
Without this modification, an accent played on the TeeBee will not have the "wow" sound as much.

The MOD:
Replace R138 (27K) with a 68K resistor

[Click Image to Enlarge]

What I did...
Again, I added a switch, to switch between the original and the more "Wow" mod.

A switch mounted next to the Filter knob:


Mod4: Infinite Decay

The idea of the Infinite Decay Mod:
ith infinite decay, the decay would not affect the filter of the TeeBee.

Normally, when you put the filter decay at it's maximum (totally turned right), the filter of the TeeBee makes the sound to disappear. After approximately 1 minute, the sound has been filtered so much that the sound of the TeeBee fades away.
With this modification, it becomes possible to make the decay become "True infinite".

The MOD:
Place a resistor of 10R (10 Ohm) between the right side of R148 and the right side of R143.

You can place a switch in series with this resistor in order to be able to switch the decay to infinite or to have normal operation.

[Click Image to Enlarge]


What I did...
Again, I added a switch, to switch between the original and the infinite decay mod.

A switch mounted next to the Decay knob:


Mod5: IEC Mains Socket + Internal Power Supply

The idea of the IEC Mains Socket & Internal PSU Mod:
Well, I hate flying leads and I hare Wall-Wart Power Adaptors.

The TeeBee requires an external 12V DC 500mA power adaptor (wall-wart).

An IEC socket inlet can be mounted at the near end at the rear panel. 

The internal has enough space to house a transformer and a small PSU +12V stripboard, so I think it should be a good idea to mount these inside and add an IEC mains socket.

The wiring of the Power Switch on the front panel needs to be changed.
The original was wired to 2 pins on the rear PCB, so I de-soldered this original connection, and joint them together.

Mains goes to the Power Switch, then to the transformer.
The transformer I used was a Toridal transformer, (RS Part #223-7771). Rated 15VA, this transformer has 2 0-12V secondary - I actually joint them to before I feed to my PSU circuit, so I have 24V-0V-24V into my PSU board.

The output DC +12V should have enough power >1A, which can power the TeeBee, plus, i can use the original DC in socket at the back and connect to other equipments that needs 12V DC (eg one of my Midi Thru boxes).

The PSU circuit board is basically a diode bridge and then an LM-317 rectifier circuit.
It is the same as most of the +9V PSU boards I did on my other synths.

Only difference is for +12V, the resistors for the LM-317 are now 470R and 4K.
(I used two 2K soldered together).

[Click to Enlarge]

I don't do custom PCBs, instead I do most of my stuff on stripboards.

The stripboard in this case is 20x10, done on a 30x10 Maplins stripboard, it has quite a lot of space on each end for mounting.

The board is then mounted to the very left side of the 19'' rack, next to the toridal transformer.

12V DC output is soldered to the analog PCB, tapped to the underside of the original 12V DC In socket. This way, the original DC In socket can also be used as an output.

To make the IEC Mains Inlet hole, I use a screwing hand tool, which is an M10 Radius Hand Hole Cutter, 28x21mm (
RS Cat.#543-614 or or 541-501), with matching 10A Snap In PCB Mount IEC 320 Plug Socket (311-8031 or 488-191).




Home Synths

TeeBee MkI TeeBee MkI Mods