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I built the nautilus and it's on my pedal board right now.
It's sound good, but I'm looking at trying to make it sound closer to the original.
Things on my to do list...   Please correct me if I'm way off base with any of this, I'm a total noob.

1M rev audio for gain.  It will spread out the bunched up gain at the end of the travel

Since I can't find a 150k audio pot for peak, I have a 200k audio I'm going to try.  The 250k with the tapering resistor gets you 150k but it simulates a reverse audio taper.  Which is exactly the opposite of what you want, so the peak is all bunched up even more so at the beginning of the pot travel.

I'm going to get a capacitor tester and make sure C6 and C8 match as close as possible and also that
C5 and C7 are matched.

I used metal film resistors so it shouldn't be an issue but I'm going to match R8 and R9 as close as possible.

Currently I used the VTL5C3's but I'm going to try to make one like the original Mutron (1 led, 2 ldrs).  I bought a ton of different color LED's and 3 different types of LDR's (10 each for a total of 30).  I plan on making 3 vactrols to test, one for each type of LDR.  I'm going to measure light and dark resistances and pick the two LDR's of each type that match and track as close as possible. For each LDR type I'm going to chose the LED color that is closest to the peak wavelength for the LDR.

Setting Rx seems to be the key to getting the correct sweep and sound.  I think, in a perfect world, I'd have an oscilloscope and actually measure the sweep and set it to the frequency range that is the factory default for the LP mode (which is what I'm most interested in)..... I've googled the crap out of how to set RX to get the "correct" sweep.  The info out there is pretty slim.  I have seen reference to 400hz to 2k for the sweep in LP mode, but that's hearsay.  There's a guy who charges to calibrate the original Mutron III's and supposedly they sound great after it.   I would love to know what they are actually doing and what values they are looking for.  My plan is to use a trimmer and remove the external sweep control because I want it set and not change once I dial it in. 

Things I may or may not also try are changing the C1 and C11 to their original values and types, but this is probably just cork sniffery?  Also I've thought about removing the extra gain stage added at the end that isn't part of the original circuit, but that's just a passing thought.

This project has been great for me.  Up until now I've just really been painting by numbers.  But I've really started to dig into how this actually works.  I'm at the bottom of a really steep hill but I'm looking forward to the climb.

I just went to radio shack (ugh..) to grab a couple dpdt toggles.  But before I set down to unsolder/resolder the new ones in, I used a toothpick to scrape away some left over rosin/flux (whatever that crap is) around that area.   Is that stuff conductive?

With the gain at max I'm getting both the high and low setting on the range to give me an envelope effect.  Actually sounds pretty good.

So that leaves me with a couple more questions.

If the envelope effect and volume is working at max.  What should I expect to hear as the gain pot is decreased?  Currently mine is acting essentially as volume knob for the whole signal with the envelope strength decreasing as well.

When range is set to low should I expect the LED to completely out when not playing?  Even with the input unplugged the LED is lit, but dim.

Voltages look basically correct. I think we need a little more info. When you say it doesn't sound right, can you be more specific? You mentioned that you get a stronger signal near max gain---but, are you getting the filter effect at all? Or is it just your regular guitar signal?

With the gain set to anything below max the volume coming out of the amp is about half and the sound is very thin/trebly.  When I turn it up to max there's a definite point (probably at 99% clockwise) where the sound jumps up in volume to where it's the same as the bypassed.   I am getting the filter effect, it's very weak until the same point the volume jumps then it sounds pretty full.

To answer a couple of your questions: the LED will be on or off depending on where you have the Range switch set. When the Range is high the LED will always be on (even in bypass), and as you play it will dim according to the output of the envelope. When the Range is low, it's the opposite: the LED will be off and then light up as you play.

Ok when my range is set to high the LED is on all the time and does dim with the envelope effect (but only when the gain is set to max).

When my range is set low, the led does not turn off.  It does get fairly dim, but not off.   It gets brighter with the effect.  Also when set to low, even with the gain up full, the sound is about half as loud as bypass and very thin/trebly.  I do hear the effect a little.  It sounds the same as when the gain is down.

If you want to change the LED so it is always off when the effect is bypassed you can remove R20 from the PCB, wire from the neg side of the LED to R20, and the other end of R20 goes to the same lug you use on your 3PDT for your indicator LED.

Thanks, that sound like a great mod once I work out the bugs.

The filter effect itself is very sensitive to where the Gain pot is set. You get the most effect when it is near max, so do not be surprised if much of the travel of the Gain pot doesn't do a lot. This also depends on what type of gear you are using....you can expect it to behave a little differently with humbuckers or bass or bass with active pickups.  

But, if you are getting no swept filter at any setting, then something definitely is amiss. I'm just not sure if that's the case here or not.

Additional info:
I'm using a strat with Lace sensors.
Testing with the gain pot at max I'm pretty confident that the peak, sweep and 3 position rotary switch are working.

Given that the LED is not off when the Range is set to low and I used the mini toggles that didn't fit in the PCB, I think I'm leaning towards it being a switch issue or possibly a short/solder bridge somewhere.  I've looked over the pcb about a million times for solder bridges, so maybe just swapping out the switch will help.  

I took voltage readings from IC1 an IC2.  This was with the guitar/amp plugged in.  I wasn't strumming.  If someone could compare theirs to mine, hopefully that will give me some direction as what to look at.

IC1
1:   1.3mv
2:  -1.1mv
3   -1.6mv
4    8.8v
5    0
6  -1.6mv
7  -1.6mv
8    -0.8mv
9   1.3mv
10   0.1mv
11   -8.11v
12   0.1mv
13   -0.8mv
14    -3.7mv


IC2
1   0.6mv
2   0.6mv
3    0
4   8.8v
5   0.1mv
6   -0.2mv
7   -0.2mv
8  5.25v
9  3.514v
10   3.491v
11   -8.11v
12   0.1mv
13   2.9mv
14  2.125v

When I turn the gain up to max I get a stronger sound.  It's right at the end of the travel though.  Still doesn't sound quite right. 

Here's a link to some pics....

http://postimage.org/gallery/5yb8o4ag/

I reflowed a lot of the connections but still have the same results.  I guess I'll just reflow everything.
I suppose my hack job on the mini toggles could be an issue, but I did test continuity with my meter.  I also checked that the diodes weren't burned up. 

Let me know if you see anything that stands out.

Yes.  I tried twisting all the knobs/switches and got mostly the same results. Each control does have an effect on the sound. There's a point at the top of the sweep range that everything gets louder, but it still doesn't sound right.

How is the LED (the one from the pcb) supposed to react to input?  Does it stay lit and just flicker when you play?  Mine stays on even when the effect is in bypass (the bypass LED goes off though)
I guess in my mind I imagined it would light up and fade out with the "womp" of the effect when played.  But I don't really know.  Either way it's probably just a sympton of the real problem.

We'll see what happens after I reflow all the joints.  My first build (divided octave from BYOC) went so smooth I thought what could possibly go wrong! LOL  I guess troubleshooting is where I'll really start to learn more.  I'll definately post pics of both sides of the board, so you can take a look.

Is this true in all settings, and even with the gain cranked?

There are definitely a few settings that sound "broken" to me with the gain turned down and the sweep all the way up.

Yes, but I'm at work and will have to do it this evening.

twofootskunk: can we get a couple clear pics of your build?

VTL5C3, I put the LED + lead into the square hole for alignment.  Was that correct?

I finished my Nautilus build last night and unfortunately I must have a problem with it.

Bypass sound works.
When the pedal is on I do get guitar sound to pass through but it is reduced/weak/thin. I can tell it has a small amount envelope effect.  I triple checked that all the resistor/cap values were in the right spot.
The electrolytic caps and diodes are in the right direction.  My IC's are in the same way as madbean's pic.
Offboard wiring looks correct.   

I didn't see any solder bridges.  My soldering isn't amazing and I mixed up two pots that I had to unsolder/resolder (which was a pain!)  I had the mini toggles which didn't fit but I got those soldered in and they test ok with continuity check.

I think the next step is just reflowing all the solder joints.  What do you think about cleaning the board with isopropyl alcohol after I reflow?

A couple questions...
The Range switch makes the LED get brighter/dimmer when toggled.  Is that LED supposed to be on all the time?  It does flicker when I play.

Also, for IC1 and 2 the BOM says TL074.  I just noticed that I have TL074CN.  Does that matter? 

I'll try to post some pictures tonight or tomorrow.

I meant the LED that is "on the PCB tied to the envelope filter. It will light up when the effect is engaged to give you visual feedback on how the envelope is behaving."
That's one that's mounted between the Peak pot and the Range switch, right?

Sorry for the noob questions

For the Vactrols I'm using the VTL5C3's

I'm finishing up my Nautilus build.  My first madbean build! (only my second overall build).
The only LED's I have are the 5mm Blue Water Clear Ultra Bright LED from Tayda. 

Can I use that for the 3mm LED?  As far as I can tell it has pretty much the same specs as the 3mm ones.

Also, I apparently bought mini toggles for the two dpdt switches.  Which means the pins don't line with the pcb holes.  I was planning on just using very short hookup wire to connect them. Bad idea?

Just a heads up for anyone ordering 1n8 caps for this bom from tayda.  They may have their parts bin for this particular component mis-labeled.  The baggie the caps are in is labeled as 1n8 but the caps inside are actually 183's.  I've emailed them about it just now to see if they just sent me the wrong part or what.

cheers

I ordered from from Tayda and got the same 183J100's instead of the 1n8 caps (182J100).  Did you hear anything from them about that?  I just put in a ticket.

I need to order the rest of the BOM for the Nautilus.  Are the pots and switches in the Nautilus build PCB mount?

This is only my second build and I'm really looking forward to it.  The first was the BYOC Divided Octave. Maybe I should try to build the whole mu-tron family