Wednesday, May 29, 2019

Hammer Cocktail--Low Parts Count 4069UB based Low Pass Filter


Привет! Continuing from last month's post re: using 4069UB CMOS chips. The grunge alternative to boring op amps!!

This time, I build a low parts count low pass filter design from the mind of Russian techno master HAMMER. Good news, it's a quick build and sounds like nothing else I've heard, maybe a bit like an MS10 filter but not even that. This thing presents icy cold and then suddenly screams like a gorilla in heat. So: if you're after a pretty sounding 3320 based Chariots of Fire VCF this one isn't it. But for me, when pushed really hard the Hammer Cocktail sterilizes frogs at 20 paces. It's an interesting addition to my DIY rack-o-filters.

UPDATE!! 6-14-19 new front panel from Front Panel Express.  More here.


Front panel made using Lazertran decaling

Sound demo is here. About the demo: I pretended I was scoring a 70s US TV sci fi detective series called (of course) "Hammer". But, to not fry speakers, I toned down the really obvious distortion a bit. You can hear bits of it coming through and that's all from the filter.  No outboard distortion used.

The design:

The schematic for this VCF is way less complex than it looks--a simplified schematic can be seen at the top of this E-M post.  It's really only a few parts, and I  like low parts counts....and I hate stripboarding.



For the prototype I included 3 buffers on the PCB (the op amps on the left) since I figured something, not sure what, would have to buffered. I ended up using 2 of them to buffer incoming CV and outgoing audio.  For the output buffer I needed about 8x gain so I used appropriate resistor values--your own setup may require different buffering.

You can get the PDFs, Eagle files, BOM etc., on my website here....the PCB could be made much smaller and really ambitious DIYers could probably fit 2 of these Hammer Cocktail VCFs on a single Euro 14-18ishHP panel.


But for me, I took the easy route, and the over sized PCB was put behind a 1U FRAC panel.

Warning and an aside: I am running out of space in my studio and thus getting into Eurorack, which from a DIY standpoint is much more challenging; Euro is tiny compared to Frac or 5U and thus, space is much more constrained. That means DIYing surface mount, skiff boards, and the like. What that means: You may hear increased weeping and OCD meltdown in the coming posts as I get into this, but please note: I held off as long as I could. And BTW it's really, really, really hard to beat Intellijel. Figuring I will never be smart enough to DIY a great DSP based tap delay, I bought their rainmaker module and almost wept, because it's so bodacious. Maybe sometimes you have to let the players play?

About the Russian 4069UB chip: Hammer tells us that the Russian equivalent of the 4069UB "screams wilder" so I bought a few of them spuds from the former USSR. They showed up a few weeks later looking like the vendor forget about Peristroika. I mean these things were beat!



 

But it wasn't hard to bend them back, to me they were built a bit tougher maybe than western CMOS ICs.

Nota Buena! Hammer tells me older K561**2 chips might sound better--look for old daycodes (8712 means dec 87 I think?) and round logos--which he says are better sounding

I dropped the Russian IC into the Hammer Cocktail circuit and yep, the Russian 4069 equivalent did sound different, and maybe a bit more "Hammer Like"? Hammer says the Russian version has less distortion, perhaps allowing me to push the filter even harder before it became audibly intolerable. Hard to say, but it was only about $20US for the chips on Ebay, including shipping, so you might want to check it out.

For CV Hammer says use 0-2.5V and power from 5V DC.  I powered from 5V alright, there is a 5V reg on my Hammer PCB since Frac is just +/- 15V.  The resonance pot, which adds the insane uber MS10-like distortion, isn't linear, the interesting distortion is in the upper 15% or so of the pot's travel. I have confirmed with Hammer that for this particular version of his filter this is normal behavior. I might try replacing this with a reverse audio taper pot down the road.

OK that's it for now.  I still have a high performance EG and Lunetta circuit on the bench, more collaborative projects with other DIYers. More on those soon, I hope, but until next time, Прощай



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