Moonn Sojus 31 PTP

[comradehoser]

Alright PTP duders and dudetters, here is my last build report of the season, just for you.

Decided to tackle the Moonn Sojus 31 because I really like the demo of that and the Bagheera. I did some research and original npn silicon transistors are around 100 hfe. I had nothing like that but some germanium top hats, so I decided to bite the bullet and do the dreaded (to me) breadboarding step to see how they would sound and audition some transistors.



To my surprise, while it was still fiddly, breadboarding was actually hella fun and allowed me to audition all of my npn transistors and make some unpredictable choices, and persuaded me to add a diode clipping switch.

In this circuit, the transistors make a huge difference to the sound. After A LOT of mixing and matching, I settled on nothing around the OG specs: a 2n2222 metal can at Q1 with hfe of 157, a 2n5088 (I think) mpsa18 with an hfe of 704(!!!), at q2 and a bc547c with an hfe 561 (!!!) at Q3. TIL that 547c have an inverted pin out from my other transistors. I was wondering why they were sounding so warm and tame. At the same time, the circuit is very forgiving. I put in my 549c backwards, still sounded good, the ge clipping diode is more crazy backwards and I kept it that way.

The PTP build is very straightforward as the circuit is very linear. Lay down a ground line and a 9v line, and Bob's your uncle. My soldering was definitely not as intentional and aesthetic as previous PTP, but I was finagling stuff and decided to stay simple. 4 pots is a lot to coordinate tie ins and then I decided to get fancy with the layout and throw in a switch and a clipping LED visible on the outside as well. Probably could have planned things out a bit, but I had sussed everything out and the articulation points pretty much lined up.


I was trying for weathered Eastern bloc look to the enclosure with some forgotten cans of spray paint. Turned out a little more trippy than that, but I ain't mad at the result.




Now, as to the sounds: goes from reasonable familiar fuzz sounds with intensity down, to filthy filthy FILTHY fuzz [edit: and NASTY--i think it's lots of heterodyning/clashing]. It's really a wide ranging pedal, but it's always the SOJUS, and it always sounds like something is trying to break through while dismantling your signal from the other side. Sounds like notes and chords get so agitated they flame out and fall into cinders. Clipping options change things up with more aggravation. Ducking/sag on note onset at higher intensity and bias settings.

Love it.

 

[JohnnyCreepy]

This is nice and your p2p builds keep getting cleaner!

Good call on breadboarding beforehand. I really should do that too and give my b-board some use before making ”final” decision with p2p builds. Life’d be easier.

 

[comradehoser]

This is nice and your p2p builds keep getting cleaner!

Good call on breadboarding beforehand. I really should do that too and give my b-board some use before making ”final” decision with p2p builds. Life’d be easier.

Thanks! I actually have gotten away with not doing it until now. But yeah, it's pretty cool and I think the major step in "designing"/modding for (more) original circuits. And doable since most of my PTP are pretty low parts count.

It did kind of confuse my spatial flow/layout process, but I'm sure a couple of go arounds would solve that.

 

[giovanni]

Very cool build. I’m thinking about trying out P2P since I have over 100 PNP Ge transistors so I could make a few fuzz faces. Plus it’s always fun to learn something you. What kind of solid wire do you use for the builds?

 

[comradehoser]

Very cool build. I’m thinking about trying out P2P since I have over 100 PNP Ge transistors so I could make a few fuzz faces. Plus it’s always fun to learn something you. What kind of solid wire do you use for the builds?

I had a spool of copper wire that a jewelry making friend gave me that was doing nothing and I thought looked kind of nice, but you can use anything really. I think regular 20-22 AWG solid-core off-board hookup wire is fine. I've also just soldered trimmed component leads together for fun, but I try to just use the component legs. The only long runs will be the jack ins/outs, and depending on how you lay things out, the ground line and maybe the signal in. The circuit elements are pretty flimsy in isolation, but once you tie everything together, it becomes a surprisingly rigid structure, so you don't really need anything particularly beefy. My copper wire is a bit of overkill on the thickness, it might be 18 or 16 AWG, but again, I just use it because I have it.

Do it do it! I really enjoy it--as long as you have time and some patience--and I think the fuzz face will serve you very well for the learnings--except for the funky power issue.