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

Saturday, May 18, 2019

A Rolling Stone Gathers no CMOS--the 4069UB Chip

Time to get back into CMOS stuff, this time the 4069UB (unbuffered) IC used in an analog realm....

What got me started down this particular AudioDIY rabbit hole was an Electro-music forum user "Hammer's" 4069 VCF design--see the post here.  He also has a cool but unassuming Youtube vid of his 4069UB LP filter here. Good work! Even more intriguing: he's from Russia and writes that his creation "screams much wilder" with a Russian version of the 4069. Indeed--got to check that out.

How can something simple sound so--gnarly?  Must be those 4069s?

I dug in and found a really good Hackaday write up about 4069UB's used in analog audio work here and here. Hammer contacted me about his design, and suggests another good source about 4069s used in audio, here.

The 4069UB chip, in this get up, is configured somewhat like an inverting op amp. There's a negative feedback loop needed to do useful things--again the Hackaday article lays out how it works; I won't repeat that here.

OK, then, why bother using a 4069 at all (besides getting the equivalent of 6 op amp stages for 50 cents US?)  Why not use a damn op amp? Bing! distortion!  From messing around on the bench: them 4069UB's love to distort.  You crank down the positive rail--distortion. Crank up the incoming audio--what was that then? Um, distortion. I figure you can make a 4069UB **NOT** distort but for squeaky clean applications I'll use an op amp; when I want some grit I might consider a 4069UB. Best of all: to my ears, the 4069's distortion is a bit tube-amp-sounding and OK, sometimes I like that.

4069UB buffer! You need a 4069 with UB in the name for any of this to work, must be the un-buffered IC.

Hours of fun! Experiment with different P/P audio input voltages and DC offsets into a 4069 buffer to hear 50 shades of grunge. You can read more AudioDIwhY posts about DC offsets here and here.

Scope a dope! Purple is original ramp signal from my Siglent 1025 (Siggy plays Guitar) Yellow is the buffered signal at output.  Yes, it inverts....

Wiring up a cap in the feedback loop has some of the same vibe as an op amp active filter:

100K pot is for cutoff frequency....

And running it through more buffers might make the sound gnarlier!

The 4069 punishes that ramp signal!
Try more 4069 inverter stages for a bit more grunge during cutoff sweep. Xtra credit: put 2 of these entire filter fragments in series. Yeh!! 

OK this weekend coming up I will see if I can get this EM 4069UB based LPF to work. I laid out a prototype PCB capturing the design (since I hate breadboarding or stripboarding. If the PCB doesn't work I'll just pitch it). Got it fab'd at my usual spot.

I am wondering how this will work. Hammer feeds positive CV into N channel FETs (5457's); N channel JFETS are opened up by having their gates see voltages below source and drain right?  It's a safe bet the filter works at an elevated DC offset; all the analog 4069 designs I've seen so far do. The key: 4069UB, mind the offset.

UPDATE: I got hammer's Low Pass Filter to work! It sounds good n crazy! Details here.

That's what's fun about analog, you get to ponder these things. Nonetheless, I'll say it again: don't breathe the fumes. See you next time.

Sunday, May 12, 2019


I came home from my psychiatrist girlfriend's last night and went to bed about 9:15.  
While I was going to sleep I heard, every 10 minutes or so (it was random!) a sort of dull thumping sound, it kinda went WUMP! like someone was banging the side of my house with a stick wrapped in a rag.

I walked around and couldn't see what was making the noise.  

I made sure the front door was all the way shut (it wasn't, which didn't make me feel that good, but it was obvious there was no one else in the house).

I went to sleep but a WUMP, this time maybe a bit more broken stick sounding, woke me up a half hour later. I eventually dozed off again but the noise hit me this time at 11PM.  Now the sound was more frequent at times. WWWUMP! (wummp?)  WUMMMPP!! Mostly it was pretty dull, really sounded like someone banging wood with a stick or something, sometimes with more vigor, and it was really hard to tell where it was coming from.

I cursed but must have fallen asleep again, and by about 1AM a new WUMP, much louder, jolted me again. I was not getting consistent sleep and had a tough work day coming up. I had to do something.

But here was the problem: It was random, sometimes every few minutes, sometimes 4 wumps in a minute, sometimes maybe once every 15 minutes. I abso-frigging lootly could not tell where it was coming from; it sounded like perhaps from outside, from a neighbor's back yard.  Hard to say, but it might have been louder in the back of the house than the front. It would help a lot if it wasn't so damn intermittent!

So I stood in the dead center of my house (I was really, really tired) for 20 painful minutes waiting for the next WUMP so I could track it down. But--of course!--whatever was making the noise refused to cooperate.

So I got dressed and put on boots and found my camping flashlight, stepped outside into the surprisingly warm May 1AM morning  and meticulously went around the outside of my house, looking in crawl spaces, looking around the back of my yard, looking at the trees near my house, seeing if a homeless dude was sleeping in my crawl space, maybe a skunk giving birth under my house or anything else that could make this random WUMP sound. 


It actually took a bit of bravery to do this (well I thought it did, anyway) and I was absolutely bone dead zonked out tired at this point but in spite of going over every square foot of my house and yard with a flashlight, probably scaring the hell out of the my neighbors,  I couldn't see anything that could be making this sound.

I went back inside and got back in bed and 15 minutes later heard yet another WUMP!

Back to the dull muffled thump sound. 


Wait a minute: something on the roof? Seemed unlikely but I hadn't checked that yet!

Before doing the whole go to the garage, get the ladder thing I decided to go upstairs to look through the upper bathroom window at the back roof, then I got very lucky! when I walked by the speakers set up by my bench I heard a WUMP!

I could immediately tell what it was: the computer and DIY audio gear I have in there, which are hooked to some Mackie near fields, were the fault. Everything was powered on, and for some reason (no idea--did I leave some random patch up? Reaktor?  Youtube gone zombie?) the setup was making a random WUMP sound.  It was crazy, and it didn't sound electronic at all! 

The Wump Starts Here!

I shut everything off and it stopped.

And then I could sleep.  That was the end of the random WUMP.

I told this story to my psychiatrist girlfriend the next day and she told me, that's so geeky you should put it on your blog. So, here it is.

Monday, May 6, 2019

CGS blast from the past--Steiner Filter

Hello Again! This time, I repair Ken Stone's take on The Steiner Parker Synthacon filter.

Repaired Filter is working!

The filter design is a classic in the analog synth world, maybe not as famous as the Moog Ladder or Korg's MS20 incarnations, but it's definitely in thetop 40 anyway. Sound demo is here.

There have been a lot of commercially sold version of this filter: TipTop has one for Euro; Elby has a few incarnations for sale. (Elby took over CGS's site and sales....)  The awesome and insanely productive Osamu Hoshuyama has one w/ variations on his site. It's an unusual design, having LP/BP/HP inputs (not outputs--inputs!) and an odd buzzy harsh sound.

Back in about 2005 I tied my own CGS build--one of my first attempts at audio DIwhY.  But the filter soon broke--no audio--so I junked it and forgot about it. When I recently found it at the bottom of the junk box I asked around, no one in my Meetup synth nerd group wanted to take a crack at fixing it, so I decided to repair the damn thing myself.

My repair skills have improved somewhat I guess because it was really easy to find the issues. I scoped the BP audio all the way to the output, but there, right by the wire to the output jack, an important trace had lifted, probably during the initial build, and failed. There was enough of the trace left to solder a new wire in place. Now HP and BP work! I found another broken trace near the Low pass input. Easy repaired with a "kludge" or "bodge" wire:

You fix PC's by rebooting.  You fix audio with kludge wires.

Happy to say it's working again. To my ears Ken's CGS design has the same nasal sound the Synthacon at the local Synthesizer Museum has. OK last thing to do is record it!  Update! Demo done, soundcloud file is here. Have fun!

ProMicro HID Keyboard Emulator

Quick one this time. The Arduino ProMicro (examples here and here ) is based on an Atmel 16u4 MCU and has HID keyboard emulation ready to go...