Introducing OctaPass Eurorack module 8x fixed frequency HPF

 

 It's a eight-channel fixed-frequency switchable high-fidelity high-pass filter!

OctaPass

First things first... this is the build guide for this module.


 You've found the blog post for the OctoPass. It's an eight-channel high-pass fixed-frequency four-pole filter (alliteration!) that is a requested build. It's switchable -- there's little toggle switches on the panel that will allow the user to low-cut or not the signal.

The signal switching is done with a ton of Vactrols -- LED and LDR combos. This means very-low-noise, which may be important if you're deciding to cascade all 8 filters with all the normalling going on between all eight channels.

The build is a bit fiddly, with some pads quite close together. Use a sharp soldering iron tip, cleaned frequently, lead-bearing solder if legal, flux if necessary, and double-triple check all your joints. I did have some dry solder joints on some of the op amp legs, but besides that, all four of these I built worked just fine.

DuckMixer progress

 

There it is. I'm thrilled with the texture and pretty happy with the layout and graphics, BUT I PUT THE SLIDER POTS UPSIDE DOWN!!!!

All the arghs and dangits and facepalming. I'm always so careful to put pots the correct way around, but this just tripped me up. There's two other adjustments I had to make to make this run of PCBs work well, (resistor value changes) but other than that I'm really happy with how well they work.

PlusSnare!!

A simple module.

It's an 808 snare drum, with a few tweaks to make it simpler, reduce component count, adjust things here and there... but this adds two things:

Thing it adds 1:

You can plug in an alternative noise source. Any signal. It'll still get enveloped and filtered just like the white noise that makes up the "Snappy" sound. Good to make your snare drum sound like a laser or whatever?

Also, the white noise generator in the 808 has a trim adjustment to get the noise the Correct Amplitude, but I just designed it to be PLENTY LOUD and you can turn down the "Snappy" pot to get it quieter.

Other Thing Added To This Circuit (the "plus" part)

This has a PT2399 delay circuit built in. The "wet/dry" control is managed by an LDR/LED pair (a DIY Vactrol), so you can use a control voltage to inject snare sound into the delay chip circuitry. You know King Tubby? I spent several hours the last time I had The Influenza listening to many of King Tubby's albums. He is a reggae/dub artist, and one of his standout sounds is a reverb/delay on some of the snare drum hits, while most of the snare hits are dry. Dub does this a lot... whatsizname Martin Garrix did a bunch of reverb/effects on occasional snare hits (worked great, love some of his tracks) so I wanted that sound in my modular. 

Oh... side-note... it was entertaining to listen to this effect through King Tubby's discography. His earlier stuff used a spring reverb (twangy thin sound, but definitely reverb vs. delay) and his later stuff used PT2399-based "reverb", so either a single PT2399 or a famous Belkin Brick, which is actually three PT2399 chips on a small PCB encased in epoxy. The Belkin Brick is a lot smaller, more reliable, less delicate, "higher fidelity" reverb, but it lacks the reverberation qualities of a physical thing that allows sound to literally reverberate around. It's just three PT2399s :D

ANYWAY, King Tubby specifically, and dub generally, are great to listen to and I love that sound so I wanted it in my modular! So here we have the PlusSnare.

I printed up five of them, which needed rework.

I printed five more with the problems fixed, and they work great, and other people have them.

I've laid out the PCB better, and am about ready to get a release candidate printed. So here's the article teasing them, to which I will link with a QR code on the PCB

DuckMixer!!!

 It's a mixer! It can sidechain the main channels with ..... I just had the idea to normal the first mixer input to the duck-signal jack... okay that's done and I'm continuing this post so I can create a QR code linking TO this post so I can add it to the PCB before ordering it.

Anyway, this is what this will do. It's a 4 channel (stereo) or 8 channel (mono, but pairs of channels are linked) mixer. It accepts one or two signals to duck the incoming audio by envelope-following the duck-signal (adjustable decay) which illuminates an LED, which is paired with an LDR (light-dependent resistor) which shunts the incoming audio to ground. The input resistor is 100K, and the LDRs can get down to a hundred some ohms when fully illuminated (in my experience?) so it'll attenuate the incoming signal to hopefully less than 1% .

There's "max volume" attenuators on each of the 8 channels. There's four stereo sliders controlling the main level of the pairs of channels. There's a duck delay knob (controls how fast the envelope returns to zero) and each stereo pair has its own duck level knob, which controls how much current can go to each LED inside the Vactrol (LED/LDR pair).

There's a L out jack, a R out jack, a mono mixdown jack, and a stereo headphone-capable jack.

I'm proud of the headphone amp portion. It's a single DIP8 through-hole footprint into which the builder can install a bog-standard NE5532 op amp. These can put um... 25mA into a typical 32ohm headphone? Not a enough current to work well, there will be distortion and the volume will be low. But you can STACK OP AMPS as high as you want, four? five? SIX??? Probably wanna keep it at six or lower. But stack those babies and they'll happily drive 32 ohm headphones to Very Loud Volumes (beware the ears).

There's a gain/volume control for the final mixer amp, which really does set the gain so you can mix eight very hot signals without impossible-to-get-rid-of clipping.

Oh yeah, you can also mix the duck-signal into the final mix if you want. OH YEAH, there's a pair of send/return jacks for one of the channel pairs. They're post-sidechain, not sure that's the BEST choice... I love love LOVE me some monster reverb tails that are being sidechained by a kick drum. It's so cool.

Okay, now it's time to post this and go order five PCBs!!!

Either Way! A polarity-agnostic Eurorack header

    It's a new Eurorack header!! This will allow builders to use cheaper pin headers and plug their modules in either way without worrying about getting the polarity wrong and having a non-functional module. I always use these diodes as reverse-polarity protection, but there's no such thing with these extra pair of diodes. Exciting!

 

PRICE LIST!!!

 Hi, I should have done this a LONG time ago. Here's a price list of all my modules, which I hope to update every time I have a new module (or remember an old one) (or run out of them and decide not to get more haha)

Prices US$
First price is for complete tested module. Second is for kit. Third is for SMD-assembled PCB.

DoublePlusBass (full-featured kick drum, 11 knobs) $90 / $65 . $25
MantisLader (clean diode-ladder low-pass with some fun tweaks) $80 / $50 / $20
HungryRat (Proco Rat clone with CV-starve and treble/bass control) $90 / $70 / $25
NyquistNightmare (signal DESTROYER hard to describe) $90 / $60 / $25
909HAT (open, closed, accent, CV pitch, sample reverse) $90 / $75 / 25
909CRC (crash, ride, 808 cowbell, goodies) $85 / $70 / $25
DumpsterDelay (delay module with CV-controlled delay and DIRT in the feedback path) $80 / $55 / $25
PlusSnare (snare with integrated delay, CV-controlled wet/dry, with tails) $85 / $60 / $25

Shipping extra, send me an email at ozerik@gmail.com (or contact me anywhere you can find me) to get me to send you something!

Paypal Link make sure to tell me what you wanthttps://paypal.me/ZumbaJuanito?country.x=US&locale.x=en_US a

And thank you for your business!