Hey, now that I have my basic kosmo modular running (will share a few pictures in the next days) I started looking into drum modules. I think I will build some of the NeinOhNein boards by hexinverters, for example the snare here: http://www.hexinverter.net/neinohnein-snare
Looking at the BOM I noticed two things: one, I can not find the shift register (CD4006 CMOS Shift Register, they propose a NTE4006 as an alternative, but I can not find that one either (looking in europe/germany) and second: They use film capacitors for almost everything. Is this important or can I get away with the cheaper disc caps?
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CD4006 is obsolete, so your options are 1) buy off ebay and hope for the best, 2) redesign to use four 8-bit shift registers, 3) use a microcontroller (e.g. an ATTiny or even an Arduino).
https://electricdruid.net/tr-909-noise-generator/ has a bit of analysis.
edit: someone mentions K176IR10 (Š176ŠŠ 10) in the comments, which is a russian equivalent.
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hey fredrik! thank you! I can just use an arduino to generate the noise? basically generating random data and send it to an adc-out and then adjust the voltage? For the other option (using four 8-bin shift registers) I need to understand the circuit better, but I will look into that. Cost wise, it is probably the same as a cheap arduino clone xD.
or maybe directly use the druidnoise 1B?
The 909 noise generator is digital. The output is a stream of pseudo-random bits, generated by an LFSR, so with some care, you can generate exactly the same bitstream as the CD4006 circuit with just a few lines of code.
As for other sources, Iād suspect you get a decent snare drum with just about any noise circuit, even if purists may disagree.
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You can use an ATtiny85 chip (which is still available in DIY-friendly through-hole form.) Itās a tiny little eight-legger, and perfectly capable of running small Arduino sketches such as a pseudo-random number generator which you can send out of one of the digital outputs.
Arduino has an Entropy library for such purposes.
If you prefer to use a board rather than a bare microcontroller chip (for ease of programming, for instance) look for DigiSpark. This has onboard USB and works with the Arduino IDE.
Cool! Thank you! What about the capacitors? Film type is better you think?
Hereās a sketch I used on mine:
It takes a voltage divided pot wiper on A0 and generates two different frequencies based on that pot setting on 9&10. I think I was using it with a CheapDuino or a Beetle so if you do use an ATTiny (which didnāt give me great results because they have such slow clocks) then be ready to reassign the pins.
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I built the kick and I have extras of the 4006 as well as the ārareā transistors. You can basically find anything obsolete on eBay, but if you end up getting the board and are having trouble finding them, I could probably just pop one in an envelope and send it to you.
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Thatās a good point about the relatively slow clocks on the ATtiny range. On the face of it, I would expect 8GHz to be more than adequate for audio work (and I believe you can squeeze up to 20MHz out of the chip if you use an external crystal.) Sadly the '85 and its sisters ship with a 1MHz clock and you have to mess with the fuses to change that. Not difficult to do, but it can be intimidating for a newcomer.
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The ATTinyX5 ships with an 8 MHz calibrated internal clock, but with the clock prescaler set to Ć·8. You can turn off the divider in code (using clock_prescale_set) to get the full 8 MHz, which gives you ~25 instruction cycles for a 300 kHz bitstream. Thatās probably a bit too tight for a 32-bit LFSR, even if you write the core in assembler.
For higher frequencies you need to program the fuses, which is trivial if you use e.g. avrdude but can be a bit hairy to do from an IDE. Once youāve figured it out, getting to 16 MHz (50 cycles) is easy, and you can push it even further by messing with OSCCAL.
(On the other hand, the cost difference between a cheap Arduino Nano/Mega clone and a bare ATTiny85 isnāt that big, and the Arduinos give you 16 MHz with no extra effort.)
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The CD4006 is available for a bout 81 cents each for ten on AliExpress.
https://www.aliexpress.com/item/32903526554.html
Texas Instrument even still sells a military version for $15.69 each 
https://www.ti.com/product/CD4006B-MIL/samplebuy
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My guess is that capacitor type is really not important in this design.
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I was going through some notes and found an article by ESPās Rod Elliott that shows how to use CD4094 8-bit shift registers:
(if you want the exact same bit stream as the 909, expanding Rodās design to four registers is trivial)
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Coming back to this after some timeā¦
For the kick, they specify BC549 and BC559 transistors, but I can only find the BC549C and BC559A versions of thoseā¦ is the difference between the versions relevant for this design? I think it might, because there are also these āspecialā rare transistorsā¦
For the noise, I have the electric druid NOISE2 now and want to use that. It only outputs 5V noise though. could I use an opamp with a gain of 2 (using a 10k and 20k resistor) to get it to the āoriginalā level (which I understand is ~12V, because the 4006 output at their VCC and they are connected to 12V and GND?
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The last letter is the gain group (hFE range), and all transistors have a gain whether or not itās spelled out so āBC549ā would just mean ādonāt careā (and odds are any BC546-550 works here, and a lot of other transistors too).
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Cool, thatās good to know! thank you!
I want to build a neinohnein kick do u still have 4006 and the transistor?
I have the 4006, but not the transistors. Are you in the US?
No in france in brittany