NLC Bong0 - Drum - Build notes

These are my build notes for the Bong0.
Its a Eurorack module from Non-Linear Circuits

"The bong0 is a twin-T based drum module with a LED acting as a nonlinear resistor to give it some interesting characteristics. 

 

Twin-T Oscillators (sometimes known as parallel-T oscillators) are another type of RC (resistor-capacitor) oscillator which produces a sinewave output . They require an Op-Amp, some resistors & capacitors.

They are very similar to the Wein-bridge oscillator. 

The two "Tee" shaped RC networks are part of the OP-amp's feedback loop

between the output and input of the op-amps inverting amplifier.

Note that each of the the resistor & capacitor elements are in an opposing formation

but are connected in parallel.

Because the inverting input is used there is a phase shift of the oscillator by 180 degrees.

Note the "Ladder Network" of resistors & capacitors that form this feedback loop.

This is pretty common with RC Phase-shift Oscillators.

The trigger input acts as a normal input to get your drum sound. The input marked ‘in’ can also be used, or you can jam a CV in there, or a gate or audio. You can just use the ‘in’ input without anything into the trigger.


Bong0 can also be used for basslines, drones and as a crude but useful VCO. It has about 20 passive components which are 0805 smd and 1 thru-hole TL072, meaning it is a good circuit for learning to solder smd parts and delivers way more fun than such a simple module should." (Andrew F).

More Links:
1. Muffs
2. Build notes (NLC)
3. Panel art
4. NLC Blog

 

"Not a smoking implement" - NLC words of wisdom.

The pots are linear 100K

As you can see in these pics I used a green LED.
The LED acts as a nonlinear resistor so i think the type of LED you choose is important.
I couldnt remember the specific specifications of the green LED that I used , but I found that the volume was very low if used as a drum.

I decided to bump it up by swapping the 470K resistor with a 1M.

 If you check the schematics this is the second -ve feedback loop of the 072 op amp.
Andrew reckons it wont hurt anything....except my speakers if I crank it to self-oscillate.

I'll try building this with a blue LED next and see if there is any difference.
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05/05/2018
Yes, the blue LED made a huge difference.
I kept the 470K resistor.

 

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You can find more NLC builds here.

http://djjondent.blogspot.com.au/2015/03/non-linear-circuits-ncl-index.html

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A side note regarding TT  or twin T oscillators.

Instead of using  a operational amplifier , someting like a logic gate could be substituted to provide the oscillations.

Ive seen a 4011 ic used as a tone generator.

 

The CD 4011 is cheap and includes 4 positive logic NAND gates on a single chip.

The NAND gate is a logic gate that gives a LOW output only when all inputs are HIGH

 

 

 See the RC network below.

The circuit is of a drum machine from the magazine "Practical Electronics", 1978.