Blog

yo,

its a new blog post and this one is a double feature. two new modules. "lets do it"....

passive attenuator

after making the lfo i realised i really needed a way to reduce the amplitude of the output. probably i should've thought of that when i designed it and added an extra pot, but it was cramped enough already and im not about to make a new panel for it. so instead i just banged out a 4x passive attenuator module that i can feed it through so i can eg. use it to automate the vcf cutoff just a little bit instead of "from one end of the frequency range to the other"

not much else to say about this other than that it's inspired by the fonotronik 5x passive attenuator, but i didn't have enough space to cram 5 pots in vertically without making the panel really cramped¹, so i stopped at 4. it works great but given it's literally just pots and jacks i'd be worried if it didn't,

mixer

often when i finish a module it leads naturally into making another that can interact with it in some way: i made a vcf, then made an lfo to control the vcf cutoff, then as i said above i made the passive attenuator to rein in the lfo output. but since the attenuator is just a passive utility module, there's not really an obvious partner for it, so i was kinda just thrown back into the wilderness of module ideas after that.

i do have a list of modules i'd like to make but wasn't really sold on any one of em in particular, so instead i played with the synth a bit² and decided that what i was missing was more modules that actually generate sound. i considered one of those oscillator banks, the 40106-based ones with 6 voices spitting out a heavy roaring drone, but the thing about those is that 6 voices = 6 pots = 1 wide as fuck module, and im running out of space in my rack, so that's a no-go right now. but during that consideration i realised i didn't actually have any way to mix audio signals³ even if i did have more than one audio source⁴, so a module to fix that felt like the obvious choice

i didn't really wanna just make a regular 4 in/1 out mixer, and it felt redundant to make a quad vca/vcm type module given i already have a dual vca module that i've so far only been using one side of, so i gave matrix mixers a look. unfortuantely they also have the same problem as the 6-voice oscillator bank i was thinking about in that they are wide as all hell. so instead i attempted to split the difference between a regular mixer and a matrix mixer and what i came up with in the end was this: an active mixer with 4 inputs and 6 outputs, with each output giving a different combination of inputs. tragically the easiest way to explain this is with something that looks suspiciously like algebra, but bear with me.... given inputs a, b, c and d, the outputs are:

• ab
• bc
• cd
• abc
• bcd
• abcd

i'm not really sure what this style of mixer is called, since i couldn't find any other mixer modules doing anything like this. i guess u could call it a "tree mixer"? that's how i've been thinking about it at least, as u can see from the arrangement of the output jacks. for lack of reference material (besides the mixer examples on doepfer's diy page) this design has ended up being all me for once. i'm sure other mixers like this do exist though, especially since this setup also lets it do some other useful things, like acting as 2 separate 2-in, 1-out mixers, or as a 1 x 1-5/2 x 1-2 active multiple. in theory it should accept dc input too since there's no caps along the signal path, but since i don't have any modules with dc outputs⁵ ive not tried it yet.

since i still only have one module that directly generates sound, basically all i've done with the mixer so far is combine the various wave shapes from the vco and either use them as audio or pipe them back into the vco fm sockets, but i've gotten some nice/scary sounds (respectively) already so i'm happy with it. and while i was working on this i realised there's a type of audio generator module that could be made extremely narrow due to lack of required controls and inputs: a noise module. so that's next up. which in turn will probably lead to a sample & hold module which can source the noise to give random voltages. and so the next chain of modules begins......

at least until i run out of space in the rack,

that's all on the two new modules. don't expect the double dose to be a common thing, it pretty much only happened this time because i just didn't want to update the synth page twice in a week⁶. as usual ive updated the synth page with the new stuff. u might notice it looks a little different: i finally gave up and labelled all the jacks, pots and switches so i dont have to memorise what everything does, or worry about other people playing with it and accidentally plugging outputs into outputs, or worry about myself playing with it and accidentally plugging outputs into outputs for that matter. it took the absolute piss to do with all the pots in the way but i think its probably worth it. i've also put the stripboard layouts for the modules on the repo, along with circuit schematics. as i mentioned last time i've been adding actual schematics to all my older modules over the last month or so, and i've finally done all of em, so check those out if u want. or dont. whatever..

ok really signing off now. til the next one!

– freya