RM AXIS FUZZ

[Hungeryhippie]

Hello, I have been looking at the RM Axis fuzz, and last night I bread boarded it up. I didn't manage to try it out through my amp, though, only played it through my little gem type thing. I didn't really seam to get much fuzz, some crunchy overdrive yes and it did sound good on chords but with the drive control maxed I didn’t seam to get floods of fuzz like I was expecting.

I have noted the voltages for Q1 (2N3906) Q2 (2N3904).

Q1, E B C =  4.5 3.6 3.9

Q2, E B C =  3.5 3.9 6.5

battery = 9.15v

How does this compare to any one else's?
does the emittor of the 2N3906 go to the 220ohm resistor or to the base of the 2n3904?

Hopefully I'll get to check it more tonight.

Peace.

[Boofhead]

I don't have one built up but....

According to simulation I gett for battery = 9.2V
Q1  E= 4.4V, B=3.8V,  C=3.2V
Q2  E= 2.6V, B=3.2V,  C=6.0V

Your measurements look off enough that something could be wrong.

Somethings don't seem to add-up:

- Your Q2 E voltage implies  Q1 B should be 3.9V

- Your Q2 B voltage implies Q2 E should be 3.3V.

- Your Q2 B + Q1 E voltages imply Q2 C should be 6.3V

- Your Q2 E voltage implies Q2 C should be 6.3V

Perhaps your meter is analog?

2N3906 go to the 220ohm resistor

Yes.

[brian wenz]

Hello Hello Hungeryhippie--
  Here are the readings from a real Mayer Axis:
    2N3906
  E-- 4.34
  B--3.64
  C--3.20
     2N3904
  E--2.68
  B--3.25
  C--5.86

  Here are the readings from my D.I.Y  build--
     2N3906
   E--4.21
   B--3.52
   C--3.04

     2N3904
   E--2.47
   B--3.04
   C--5.68

 The 220 ohm DOES go to the emitter of  the 2N3906.

Brian.

[Hungeryhippie]

Thank you to both of you, Thats been a great help.

I managed to get  quick look at it last night and i discovered the 39K was in fact 90K! not sure how that happened one of those things, but some thing else is still up i now have,
2N3906
E--4.42
B--3.07
C--3.02

2N3904
E--2.5
B--3.02
C--5.52


It sounded better but i think it needs another look those BC on Q1 look wrong still.

am i right i thinking that a transisor has 0.6v dropped across its B E when its turned on? Which would mean the bias is wrong somewhere.


I'll keep you posted as to what happens next.

[Boofhead]

am i right i thinking that a transisor has 0.6v dropped across its B E when its turned on? Which would mean the bias is wrong somewhere.

Yes on both accounts.

The base emitter voltage of Q2 is low.  To me it looks like the DC feedback is trying to pull the base of Q2 up but it runs out of range and cause Q1 to saturate - that's why Q1's B and C voltages are close.

Maybe look at the biasing resistors on Q1: 180k, 820k, 680k.

[Doug H]

According to my SPICE model, your Q1 base voltage is too low. In the model it is around 3.73V. The rest of your voltages look pretty close to the model. Check the 180k, 820k, 680k bias string that is setting your base bias of Q1 and see if there is an error there.

Doug

[brian wenz]

Hello  Hello  HH--
    What type of trannys are you using??   [Fairchilds......etc..]
I know I've had to tweak the bias a lot  on some circuits 'cuz the trannys were not the same brand as the original  [the Mayer Axis was one of 'em!]
According to the specs on the original Mayer pedal every reading came out a little "low" for my diy build and had to be adjusted.  Actually, your're not TOO far off so it should be pretty easy to bring it up to spec.
Brian.

[RDV]

Does anyone know if a 2N4401 & 2N4403 will work in this circuit?

Regards

RDV

[brian wenz]

Hello Hello RDV--
    No, haven't tried those.......seems like this would be a good circuit for putting sockets in!   I built an Axis with a BS170 in Q2 and it sounds good, so there must be a bunch of different trannys that would work as well.
Brian.

[dev]

Hi all,
When working properly on a clean amp does this fuzz have a stong octave with the volume on the guitar at 10.   Then slight octave from 5 to 8, and gets clean aroung 2and 3?  Is there a way to minimize the octave effect and maintain the sustain?  Also, how do you like to set the fuzz and volume controls on the pedal?

thanks Dev

[Hungeryhippie]

Ok well here's what I got so far.
The transistors I have the 2N3906 has a T2 printed on it, is this the manufacturer? And the 2N3904 is a new one I don’t know the manufacturer.

I have tried adjusting the bias for Q1, the 180K,820K, and 680K resistors, I used a 1M pot and tweaked it and watched the E and B voltages go up and down, and then I tried a combination of two 1M pots one in the 680K and the other in the 820K position. But I still haven’t been able to get the Q1 base voltage up with out the emitter being way to low (2.4v) or to close to the base voltage. Very frustrating.

How ever,

The 10K after the 180K, I replaced this with a pot, and with it shorted (no resistance) the voltages I got back were.

Q1,
E--3.21
B--3.6
C--5.1

Q2
E--2.7
B--3.21
C--6.7


However ( there is always something else isn’t there) I get no sound out of it, nuffin. Then turning the pot back again, it bursts into life!?!?

still its friday, I can spend a bit more time on it at the weekend. Thank you for your help so far,

[Boofhead]

However ( there is always something else isn’t there) I get no sound out of it, nuffin. Then turning the pot back again, it bursts into life!?!?

That would be normal the output is tapped off the 10k/22k junction and shorting the 10k kills the output signal completely.

At this point I  recommend you change Q1 I think there's something wrong there.  I looked at a few scenarios and could not find one which had a VBE~0.4V on Q1.  If you have *any* other pnp silicons throw one in as a sanity check.

[Hungeryhippie]

i did try different transistors in Q1, all 2n3906's, but all the same results,

the one thing i forgot to mention is, its also hard to concentrate with my other half going "blar blar blar Fuzz pedals is all you ever do blar blar blar" its even called Fuzz Pedaling, in my house (flat) now no matter what type of effect it is, I showed her the Dr Q and demonstrated it, "is that a new fuzz pedal!" hmmm. Well she is Norwegian.

Peace to you all cos i know i aint the only one who gets an earfull.

[Doug H]

Hi all,
When working properly on a clean amp does this fuzz have a stong octave with the volume on the guitar at 10.   Then slight octave from 5 to 8, and gets clean aroung 2and 3?  Is there a way to minimize the octave effect and maintain the sustain?  Also, how do you like to set the fuzz and volume controls on the pedal?

thanks Dev

Yeah, part of the whole deal is the strong 2nd harmonic which gives it an "almost octavia" sound when everything is dimed. Earlier I tried biasing it differently and etc with no luck. But now I realize that sound is all part of the fun. I've got this on the breadboard right now and when I experiment with it I rarely turn the guitar vol up to 10. I turn it up for octave feedback, swells, and other noise for emphasis, but keep it down around 5-7 for a good lead tone most of the time, down around 1-2 for cleanish overdrive rhythm sounds.

Also, this is not a good effect for a clean amp. Like most fuzzes, it sounds much better through a tube amp that is a little dirty. Then you get the synergistic effect of the fuzz and amp sound which combines into an awesome tone.

Doug

[Doug H]

Hello Hello RDV--
    No, haven't tried those.......seems like this would be a good circuit for putting sockets in!   I built an Axis with a BS170 in Q2 and it sounds good, so there must be a bunch of different trannys that would work as well.
Brian.

I agree. Experiment away with different transistors.  I used a metal-can 2n2222 for Q2 on the breadboard and that sounds really nice.

Doug

[brian wenz]

Hello Hello Doug--
 Thanks for the heads-up on the 2222....gonna have to find some of those!
I think the reason alot of people DON'T like this pedal is 'cuz they try to play it through a clean amp.  This thing was made to match up with a Marshall!
Brian.

[Doug H]

Hello Hello Doug--
 Thanks for the heads-up on the 2222....gonna have to find some of those!
I think the reason alot of people DON'T like this pedal is 'cuz they try to play it through a clean amp.  This thing was made to match up with a Marshall!
Brian.

Sounds great with my Firefly too (which is sort of like a micro-marshall ). It really does.

Also, I think people don't like it (and I didn't use to) because it's not the kind of thing where you just turn everything up to eleven and leave it there. You have to hang onto your volume control and season to taste IMO.

Doug

[nightingale]

Also, I think people don't like it (and I didn't use to) because it's not the kind of thing where you just turn everything up to eleven and leave it there. You have to hang onto your volume control and season to taste IMO.

Doug

sounds like my kinda fuzz~
especially because there really is anot ny clean on my blues deville i've been enjoying again lately... it breaks up super early... in a good way tho..
i am just geting together a BOM to breadboard this guy...
thanks doug

and brian~
i notive we have similiar tastee  as far as fuzz's, and guitars go... but i'm not a big marshall guy.. what kind of marshall do you play mostly?
maybe i'll have to give marshall another look.. the only snag is that i like to play smaller combo amps through house PA's... i lugged around twin reverbs for ever.. i'm kinda burnt on the 77lb amplifier.. are there any old jcm8 combos or anything worth looking at..

[brian wenz]

Hello Hello Ryan--
     I only use Marshalls  [early 70's 50-watters]  every-now-and-then for big gigs.  I mostly use 30-watt, class  'A' , 4-EL84 Vox type amps  [with 1-12"  or 2-12" speakers] for club gigs .   The EL-84's  give me a good "grind" at lower volumes  [I don't miss the Marshalls as much!]
A Vox or Vox-style amp sounds GREAT with most of the fuzz and overdrive circuits we like!   I've always had trouble using English-designed circuits with Fender amps.
The Axis circuit works really well with a class 'A' amp.......there's lottsa variations to be had with those two knobs!  
I switch guitars around from Fender Esquier to Les Paul Jr. to Fender Strat. to Hamer Sunburst Archtop [solid body] to Gibson Flying V....lotsa different sounds!
Brian.

[Hungeryhippie]

Am now very happy  

I spent more time working on it this weekend and now i have it.
Everything that has been said on this pedal is true, turn it up and control it with the volume control on the guitar, its so good.

I ended up with a 470K where the 680K was and the 100k on the base of Q2 is now 180K. Voltages are Q1 e-5.2 b-3.7 c-3.24; Q2 e-3.75 b-3.23 c-6.15.

Thank you for your help and assistance with this project.