Mods to Seamoon Funk Machine.

[TheBigMan]

I've been planning to do a Vero Layout of this, but after scouring the archives I found that there are a few issues with it.  With that in mind, I thought it'd be a good idea to address these and then do a layout for the improved version.

From Mark Hammer:- (re: Schem posted at Geofex)
The schematic shown desparately needs:
1) some kind of input buffer like the Dr Quack
2) a terminating resistor to keep that 4n7 cap at the output from popping (better yet, a pot to provide level balance for when the gain/Q is cranked
3) Some means of adjusting the envelope shape, like a variable attack control or decay control
4) A little more gain in the envelope follower section (try 2.7M instead of 2.2M)

So I'm thinking:-
1. FET Buffer like Jack Orman has added to the Dr Quack
2. Output Level Pot
3. Errmm, dunno?
4. 500K or 1M trimmer in series with the 2M2 resistor

Comments, suggestions, death threats etc all welcome.  Even if it is to say don't bother and just layout the Dr Quack instead. 

[Dragonfly]

I've been planning to do a Vero Layout of this, but after scouring the archives I found that there are a few issues with it. 

i came across the same issues...i havent had a chance to breadboard it and sort out the "mods", so i havent got around to doing a vero layout for it....but since youre gonna do one, i'll hold off 

[spudulike]

[Edit] Sorry, forgot to explain ...

I built the Funk Machine while I was on an AutoWah quest - horrible, just horrible no matter what I did to it. The 5Meg pot was a nightmare to find. I built the Dr. Quack and then the Nurse Quacky (see build report below). With a NE5532 and a BC547 it is sweet as a nut and highly recommended.

Building a Neutron at the moment ... aaaaargh.


Vero Layout





My PCB Layout




My Build Report & PCB Trace

http://www.elixant.com/~stompbox/smfforum/index.php?topic=35760.0

[B Tremblay]

I missed that original thread for the PCB layout, so I wanted to compliment you on an absolutely beautiful work of art.  Thanks for sharing your very professional work with the community.

[hank reynolds 3rd]

Nice one!! I built this and put it to one side (tl072 and 2n3904's...crappy combo by the looks of things ) as I cloned a mutron V w/ no problems...Gonna have to get me some 5532's  (has me wondering if any other pedals could do with subbing those trannies ..)

Thanks again

Sam

[Mark Hammer]

The Seamoon came from an era when we were all much more innocent, and much more likely to be seduced by the fact of having such an effect rather than by how well it did or didn't work.  I feel a bit remorseful for dissing it because it was Craig Anderton's design, but then just about everyone in your life whom you feel fondly towards is able to do at least one stupid thing, right?....at least that's what those of us who do stupid things several times daily are banking on!

You CAN increase the gain and Q of the filter in the SFM by increasing the value of that feedback resistor, but I found that it didn't take much more aditional feedback resistance to create an unusable sound.  My recommendation is to not go above 1meg.  Indeed, a 100k fixed resistor in series with a 500k pot may give just about as much range as most folks would want.

And yes, the output cap desparately needs a terminating resistor.  Given the change in output levels created when you alter the Q/feedback-resistance, that terminating resistance should probably be something like a 100k log pot so you can set volume level atthe same time as de-popping.

The trimmer to adjust rectifier-stage gain is a good idea, although I imagine simply upping the resistance to 2M& or 3M3 is suffiicient.

In liht of my recent release-time experiments, I'm going to suggest chaning the 10uf cap after the 100r resistor in the geofex schematic to 22uf.  In parallel with that, tack on a 500k-1M pot in series with a 47k resistor to achieve different release/decay times, both longer and faster than the stock value.

I'm also going to say not to drive yourself too nuts with the 13k resistor.  12k is probably fine, especially in view of changes to the resistance ahead of it should one install an attack pot.

In the end, I don't expect it to be "better" than a Dr Q or any of the variants.  It is simply a different filter topology and will have a slightly different sound and response curve to input level.

[TheBigMan]

Thanks for all the info Mark.  I'm thinking more and more that it's not really worth the extra effort/parts.  All the mods put it up to four pots plus a trimmer and if the benefits aren't really all that significant compared to the Dr Quack then that may be a better option.

[Mark Hammer]

Well if you already have one (DQ/NQ), sure.  If you're starting from square one, I can't see where implementing all those mods to the SFM would be a disadvantage.  The filter topology used in the DQ/NQ is not "better" in any way I can see.  I remember trying one out in 1976 in a store and being kind of impressed. But like I say, we were pretty easy to impress in those days.  If it made a guitar sound anywhere within 50 miles of a synth, we were impressed.

[TheBigMan]

Hmmm.  I'll give it some more thought.  I just started a new job today though, so time is a little short.  If I get a chance I'll try drawing up a modded schematic over the next week or two.

Thanks for all the info though Mark.  Your knowledge of filters never ceases to amaze me.