Subdecay - Gurgle and Moan Envelope Filter

Brian M · Post by **Brian M** » 07 Jan 2008, 06:00

We made a few of these and sold them on ebay in late 2007. I remembered about it when reading another thread and OTA's came up.
I thought I'd let anyone who wants to take a look at it, build it, or do whatever with it.

download/file.php?id=25725&mode=view

I limited my self to a dual opamp, and the dual OTA because I wanted to fit it in a 1590B enclosure. Otherwise i probably would have used two more opamp stages rather than the Jfet input and especially the BJT output buffer... Or I could have just replaced the output buffer with an opamp, and used the other stage to make a reverse sweep function... lots of possibilitites, but only so much space to work with.

What the knobs do:
B100K in the upper middle left- resonance
B100K in the upper right- mix between LP and BP output
A100K range
B10K Center frequency

Known issues-
When the resonance pot is turned all the way up, it may oscillate. Perhaps adding a small resistor in series with the positive feedback would be a good idea here...
The mix pot is a bit scratchy, which should be pretty obvious. Not really loud scratchy, but if your amp is all the way up, you will notice it.
The decay is a but "gurgly" I actually kind of liked it that way with this perticular filter. Changing the 4.7uF cap to a 10uF would be more to some people's liking.

So there it is... a fairly simple envelope filter that doesnt rely on optoisolators, and sounds pretty good too.

The OTA circuit was basically lifted from the LM13700 data sheet, but I added the positive feedback for resonance.

Some known issues:

prehistoric · Post by **prehistoric** » 07 Jan 2008, 07:30

looks cool, brian.
i have a lot of respect for you guys with your low parts count circuits.
do you have soundclips?

bajaman · Post by **bajaman** » 07 Jan 2008, 08:13

hi Brian
thanks for sharing this with the World - hopefully one or more of the members here may build this and may even improve upon it

Once again - thanks for sharing it

bajaman

Brian M · Post by **Brian M** » 07 Jan 2008, 09:21

bajaman wrote:hi Brian
thanks for sharing this with the World - hopefully one or more of the members here may build this and may even improve upon it
Once again - thanks for sharing it
bajaman

Imrovements on filter circuits can be a lot of fun, and complex or as simple as you want to make them.

Taking the filter section as a building block, and coming up with different ways to create a control voltage could easilly create a number of cool projects.

This one is also probably could use some work... as noted above it was a bit compromised by the limitations I set my self up with.

A couple years ago I put a filter with 12 pots and a few switches on breadboard. It really was beyond overboard, because it would not have been all that user friendly. I tried to build a prototype, but after building the PCB with about 200 parts on it, it didnt work. I looked back at the artwork a few weeks later and realized i had merged two nets in to one, and couldnt make a fix very easilly. I still have the thing.... it's probably the most parts ive ever squeezed in to a stompbox... it looks impressive i guess

would have been nice if it had worked.

Brian M · Post by **Brian M** » 07 Jan 2008, 22:24

prehistoric wrote:looks cool, brian.
i have a lot of respect for you guys with your low parts count circuits.
do you have soundclips?

Sorry, had to search the site for them... i couldnt find it last night.

http://subdecay.com/gurgle.mp3

It's kinda long, and after listening, you'll understand why it has gurgle in the name.

I'm not 100% sure that this clip was from the final schematic... I think it was still on breadboard when i recorded it.

prehistoric · Post by **prehistoric** » 08 Jan 2008, 08:01

great clip! the gurgling is a nice effect, and one not really commercially offered as it's own feature before as far is i know.

envelope filters are really nice. i like to bury them in the middle of a chain of fuzz/octavedown/loop etc so their effect is masked but still causing a harmonic blip in the chain, can make some demonic vowelly sounds

Brian M · Post by **Brian M** » 09 Jan 2008, 07:52

prehistoric wrote:great clip! the gurgling is a nice effect, and one not really commercially offered as it's own feature before as far is i know.

envelope filters are really nice. i like to bury them in the middle of a chain of fuzz/octavedown/loop etc so their effect is masked but still causing a harmonic blip in the chain, can make some demonic vowelly sounds

Actually, after listening to the clip again, I'm not sure how great it is. Seems more subtle than i remember.

Regardless, there is a pretty useful building block in between all the compromises noted above.

When i had this on breadboard, i also tried an LFO controlled dual filter with opposite sweeps. sort of a take on the anderton antiwah. Sounded pretty good, although it was a bit of a large circuit for what it actually did.

Im more of a filter after fuzz kind of guy though... That reminds me i need to get back to an old idea i had a couple years ago....

Brian M · Post by **Brian M** » 23 Jan 2008, 00:53

Hmmm i was just looking at this schematic, and noticed that the envelope follower section was screwed up.

One of the resistors is not marked with a value. I'll post a corrected drawing soon.

briggs · Post by **briggs** » 23 Jan 2008, 12:18

The sound sample sounds pretty unique. I like it! Looking forward to seeing the updated scheme.

Brian M · Post by **Brian M** » 31 Jan 2008, 18:57

fixed version posted.

have fun with it

mhond · Post by **mhond** » 21 Jun 2010, 13:24

the links are broken.. could someone be so kind to relink it

im really curious !!

THNKS!!!!!

Brian M · Post by **Brian M** » 29 Jun 2010, 00:15

mhond wrote:the links are broken.. could someone be so kind to relink it im really curious !!

THNKS!!!!!

It got blasted when we restructured our website last year.

pedalgrinder · Post by **pedalgrinder** » 12 Jan 2012, 13:01

has anyone got a copy they could send me pm me if you do or repost it possibly cheers. thanks in advance

dauserarms · Post by **dauserarms** » 11 Dec 2012, 05:27

Sorry about digging up an old post but could some one repost the schematic?

Nocentelli · Post by **Nocentelli** » 01 Mar 2015, 12:30

rocklander wrote:
dauserarms wrote:Sorry about digging up an old post but could some one repost the schematic?
+1 ... schematic anywhere anyone?

Please note that Brian pulled this schematic:

Brian Subdecay wrote: A few notes-

This could be easily improved, as i made some minor compromises to fit it in to a 1590B case. In a perfect world the input and output buffers would be opamps.

the filter is essentially taken straight from the lm13700 datasheet, with positive feedback added for resonance, and values tweaked a bit for stompbox use.
We sold a few of these as prototypes as the gurgle and moan. it sounds good, but some tweaking could be done in the envelope follower to smooth things out a bit.

Sorry i don't have everything marked on here. I'll get to that some other time.

Subdecay - Gurgle and Moan Envelope Filter [traced]