Build Report: Axis

[petemoore]

Cant say whipped' but built this one today. Other than my confusion between B/C on one connection, which I'm happy to say was quickly debugged, it fired right up!!!
 Oooohhh Yeahh !!! Nice thick Fuzz !!! The test amp [RCA Victor Tube], I consider clean, [slightly OD's if pushed] Fuzzed right out, N/P.
 Cct seems quite well behaved compared to other FF [is this a FF?.. I seem to miss the feedback resistor there].
 The 'exrta' 47k parallelling the 47k [ie ~23.5l] really tightened things up. The bass was wooly getting out of hand [humbuckers]. The bass did exibit good definition with small guitar vol rolloff.
 Luck would have an NTE169, Q1's Hfe is 104, Q2, an NTE123 came in on the DMM at Hfe 148...
 Others tried were 3906 and 4403 for Q1, they showed higher Hfe's. Q2 did well with just about anything I tried [2n7000, 3904, 5088/9, 2n2222] but the definition [which I think to go for in FF's...Definition/gain..]..seemed best with the lower Hfe Q, just like they tell me.  Oh a BC108 in Q2 is hot.
 Very cool machine. Guitar vol. rolloff deal is good, great for blues, rolled of a little picking strength does big efkt changes.
 Ya know I'm a happy dog!
 Thanks guys for the excellent notes !!!

[Lonestarjohnny]

Pete,
Which Transistors did you end up useing, I'm new to pedal building but I just got my first project packaged and on my board, The Booster sounds great and I'm not gonna miss my klon,
I want to build the Axis for my next Project, I have a R/M Classic Fuzz that I like quite well, any pointers you offer will be gladly accepted.
JD

[GuitarLord5000]

I've settled on the Axis Fuzz for my next build.  Mostly because it looks pretty easy and has simple to find parts.  What are your thoughts on piggybacking a 3906 in Q1 'a la brett's Miss Piggy?  I picked up a stack of 'em, and seeing as they are the only PNP type trannies I got, I dont have a whole lotta options. Congrats on the build!

Dave

[petemoore]

It just went into a box I was havin' high gain [low amplitude whine] noise from an Obsidian in the same box on the other side of the 'bypass' through an LPB, at high gain settings.
 N/P with noise like that this go. I used a 100k pregain pot, I had a hole to fill there, and I think it's a good addition, probably just enough, a 250k pregain pot would be more for sure enough cut I think.
 I haven't tried it through SS, probly won't, I use tube amp anyway, the times I have tried FF into SS amp, It didn't work the same...
 Basically [so far] I'm finding it pretty easy to get this thing to behave, I haven't tried it through the MkII yet..can't wait to try that, it likes FF's 'sometimes'...it's kinda picky if you ask me.
 It turns out the transistors I picked for the gains I was looking for [~100 for Q1 and 150 Hfe Q2], were found in an NTE123 Hfe 148, and another NTE, an NTE 104. Just worked out that way. I like NTE but for the prices myself.
 I left room on top of exposed 47k leads, and parallel tagged a 47k to that making that resistor ~23.5k. This in particular should be tried IMO, someone suggested a pot there perhaps a Trimpot, since the guitar volume seemingly has control over a similar realm of effect. With pregain a trimpot or fixed R between 23k-33k should do nicely. I'm leaving mine fixed at 1/2 of 47k, N/P with gain.
 Someone said they only had a 1k for this build where the 2k2 is, by adding a 1k resistor between the 1k pot and ground, you should be able to go over the top of the gain sweet spot, and won't be able to turn the gain all the way down.
 I used a 10uf for the second emitter. Still tons  of bass.
 Having not a 22uf to go from + to ground I used a 100uf...do you think this is ok?

[Eric H]

 Someone said they only had a 1k for this build where the 2k2 is, by adding a 1k resistor between the 1k pot and ground, you should be able to go over the top of the gain sweet spot, and won't be able to turn the gain all the way down.

Good idea.

Having not a 22uf to go from + to ground I used a 100uf...do you think this is ok?

I always use 100uf power-supply decoupling caps, Pete, partly because I don't use batteries.

-Eric

[brett]

Hi.

What are your thoughts on piggybacking a 3906 in Q1 'a la brett's Miss Piggy?

This circuit is kinda set up for transistors with hFE up around 150 to 250 (especially with the 47k reduced to 23.5k).  So I'd say that piggybacking would be of limited use here (as compared to a fuzzface, where the circuit desperately needs hFE around 100).

You guys probably worked this out already, but concerning using a 1k pot + 1 k resistor, you'll need to take the wiper of the pot to AC earth (ie the big cap, not just to lug 3 of the pot).  Otherwise, you'll only get from 0 to 50% fuzz, not the 50 to 100% part of the range.  The circuit also seems to work fine with just a 1k pot (I used a linear) without any extra fixed resistance.  At first I thought I would be conducting too much feedback voltage to ground, and it would be too fuzzy even with the control turned down, but no, I still have to turn the control to about the 12 o'clock position before serious fuzz kicks in.

Have fun Pete.

cheers

[brian wenz]

Hello Hello-
  Check out my post on the other "Axis" thread.......
Brian.