Going for a Nautilus

[Natman]

Hi friends, I'm pretty new here, even if I lurk from time to time.

I have decided that I need an envelope filter and from doing my homework, I love the sound of a Mutron more than anything else out there. Of course I'm broke/cheap so I prefer to roll my own instead of spending $200 so I ordered the Nautilus PCB from Madbean. 

Long story longer, I'd love to hear your tips for this build. Are there more "authentic" options out there? Pitfalls? (I managed to score a NOS 150k linear pot for the Peak) Would there be any advantage to using carbon comp resistors?

I will continue to research up in here but thought another thread on the Nautilus wouldn't bother anyone.

Thanks!

[midwayfair]

Long story longer, I'd love to hear your tips for this build.

-C1M for the gain control will may make it a little easier to dial in.
-Consider resorting to buffered bypass. With some gear the Nautilus pops no matter what. (FTR, an original Mutron III does with my amp as well, so it's not just my Nautilus builds.) Also, some people prefer the behavior of an envelope filter when the input is buffered.
-If you want to be able to use a wide number of settings with more than a couple guitars in a live situation where unity volume for the effect is a necessity (i.e., you're switching it on and off several times throughout a song), you *may* want to have the volume control external. Personally I think it's got enough stuff to fiddle with.

Are there more "authentic" options out there?

Nope, not unless you can find a functioning copy of the vactrol used in the originals. I wouldn't waste my money ... it's just a Vactrol. Getting the right value capacitors is much more important.

(I managed to score a NOS 150k linear pot for the Peak)

Welll .. that's just a variable resistor, so the parallel resistance in the Nautilus makes the commonly available 250K into 150K. The taper with your 150K will be nearly identical in all spots to the original, but it won't change any sounds that the pedal makes. Just so you're clear on what that part is doing. Getting the right value capacitors is much more important.

Would there be any advantage to using carbon comp resistors?

More noise and less reliable tolerances!

There's a ton of gain in this effect. Use metal film.

Any sonic properties of carbon comp outside of noise performance -- meaning basically resistor distortion -- never come into play in a 9v pedal. In fact, to get any sort of "unique" performance out of them, you're looking at amps above certain wattages. (So not even small combo amps necessarily get any "benefit" from carbon comp).

Getting the right value capacitors is much more important.

[Natman]

Awesome -thanks man. Will make sure my caps are the right value. I'll consider a buffer too but I'm just as likely to have a boost in front. 

[twofootskunk]

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.

[Natman]

While I'm at it, can anyone tell me what kind of caps to get? I see box type film caps in photos, but what Voltage should they be?