Axis Face- Silicon

[Clubman35]

I just completed the Axis Face- Silicon from Fuzz Central's vero layout. I set the 10K trim pot (R6) so that the collector of Q2 read 5v on my meter with the bias pot set at about half, is this correct? Also, what does the 50K trim pot (R2) do? I turn the pot, but nothing seems to change with the effect. By the way, this fuzz sounds great, I must have done something right! Many thanks guys.

[petemoore]

I just completed the Axis Face- Silicon from Fuzz Central's vero layout. 
  I don't see any vero layouts at Fuzzcentral
  I set the 10K trim pot (R6) so that the collector of Q2 read 5v on my meter with the bias pot set at about half, is this correct?
  if the FF sounds good and your battery is around 2x the Q2collectors idle voltage...
   Also, what does the 50K trim pot (R2) do?
  I'm looking at this schematic
  http://fuzzcentral.tripod.com/axisfacesi.html
  And I see no R2 or 50k trimpot.
  Sorry I can't help but guess the 50k trimpot is a pre-gain set...?
   I turn the pot, but nothing seems to change with the effect. By the way, this fuzz sounds great, I must have done something right! Many thanks guys.

[Clubman35]

Sorry, the vero is from this site:   http://www.indyguitarist.com/torchy/    ....it's listed under the distortion overdrivsection. Sorry, i'm not very good at posting links to sites. Thanks.

[petemoore]

  Yes, trimpot used for a preset input gain, nice to have when using HB pickups to take some or most of the 'hair' from the dist tone after setting guitar volume stopped at max, just keeps it from 'overmudding'.
  The pot has two interesting connections, between the 'input' wire, and vertical black wire 'jumper' [the trimpot is inbetween the FF input and the input from switch], rotating the pot should introduce resistance between the guitar pickup and the FF circuit, this can be tested by putting a DMM across the pot.
  50k might not seem immediately evident as a change in sound, depending on what else is going on in there....

[captntasty]

I noticed over at Philip's site he uses a 100k for the silicon version 50k for the Ge version.  I guess you'd hear some difference with the larger value pot but as Pete said it's not going to make a huge difference in the overall effect - more for a hard set of the maximum fuzz amount and from what point the guitar volume cleans up from there.  Why haven't I done this one before? (runs off to find a FF clone to hack into! )

p.s. Did Philip just fall off the planet? 

[burnt fingers]

I built a variation of the axis face a while back.  I changed a few values to suit my tasts.  The 100k (on the si version) tames the input a little.  A bit like rolling back yout guitars volume.  I played with it until I found a setting I liked then just put in the appropriate value resistor (33k maybe 47k)  I wish I left the pot in though as the guitar I was using to test it had lower output pickups than my Les Paul.  (live and learn)

Anyway, I would suggest using the larger value 100k and play around.  It's not a dramatic change but it can take some of the harshness out if you got some really hot pickups. 

If you want to check out my variation to see what changes I made it's in my layout gallery
http://aronnelson.com/gallery/Burnt-Fingers-stuff/Plutonium_Fuzz

Congrats on the succesful build.

Scott

[formerMember1]

i had a 100K there, but switched to a 50K and liked it better.  I don't know why, maybe because i was able to dial in the value better or something. For a hendrix type strat, the 50K off, or on less than 10K was great, for a HB guitar, around 40K was good i think...

nice sounding circuit BTW!

[mac]

I think that an input pot larger than 100k varies to fast. I like a 50k.

Maybe a larger pot, say 250k, could be helpful with a non-buffered wah before the FF??



mac

[formerMember1]

250K for me is overdoing it. 50k should be plenty plenty enough to make a fuzz and wah compatible.

One thing i did have trouble with the Axis Face was squealing and oscillation with a wah.  I don't know why, but i was never able to get rid of it completely, if i remember correctly.  I think if you search you will find out why.. something about one of the silicon transistors or something.

I mean, wahs and fuzz squeal together, when unbuffered, but the axis face squeals i think even with a buffer or something,.. can't remember. 

[petemoore]

A bit like rolling back yout guitars volume.
 A lot like it...
 The only wiring difference is the open lug on the Pregain is grounded in guitar volume. And/or the value of the pots..
 My FF goes to pretty clean @ 8 on the dial, being a 250kA pot to ground I figure it introduces more resistance to SP [like a pregain] than whatever the relatively small increase of SP to Ground shunting increases to. I'd guess turning from 10 to 8 on the guitar introduces resistances to signal path of 50k~100k, while reducing the SP to gnd. ohmage...[something around like 250k - 80k = 170k from SP to Gnd. // 0k + 80k = 80k in SP.
 because it's an audio taper 250k, I think it gets up to say 80k on the SP pretty quickly, and that's a large increase from 0K..compared to the subtracting 80k from 250k that simultaneously happens as the knob is turned.
 For my SC and HB as source FF usages, 50k is a good number, depending on...I like the cleanup of a FF so I don't go for the Mongo Gain Mud available with say...higher gain transistors IWCase I might want to opt for 0k-100k as a pregain option.

[mac]

250K for me is overdoing it. 50k should be plenty plenty enough to make a fuzz and wah compatible.

One thing i did have trouble with the Axis Face was squealing and oscillation with a wah.  I don't know why, but i was never able to get rid of it completely, if i remember correctly.  I think if you search you will find out why.. something about one of the silicon transistors or something.

I mean, wahs and fuzz squeal together, when unbuffered, but the axis face squeals i think even with a buffer or something,.. can't remember. 

What transistor did you use as Q1, the 2N2369A? Many peolpe, myself included, posted that the 2369 pick up RF among other issues I do not remember. Maybe trying other transistors, like BD139, 2N2219A, MPSA42, 2N918, 2N1711 etc?
The best for me are a pair of 2N2219A and a pair of BDxxx.


mac

[billings]

I plugged in a pair of MPS6517s (PNP silicon) with measured Hfe's of ~140 straight into the roger mayer 18k Q2 collector + 2k emitter ckt with fantastic results, no tweaking at all.  Of course 1) that's the only fuzz face I've made so I have no basis for comparison and 2) it's completely off topic..  but it sounded good, and I haven't seen the part mentioned, so there you go.

[formerMember1]

mac,

I can't remember, I no longer have the pedal. But, i think it was the 2n2369a IIRC.  I am pretty sure i remember it making the wah squeal/oscillate, even though a buffer was in the wah, and after i chose another type, it went away or something. I tried multiples of the 2n2369a too. 

used BD139 for Q2 i think... always had the correct gain...

I eventually built and use Ge fuzzfaces though, I loved the Axis Face, but didn't sound like a true Ge fuzzface to me. great pedal though

[mac]

I bet the 2n2369 at Q1 is the culprit. Another thing I do not like about the 2n2369 is that it has the highest Vbe of all Si I tried. Someone here posted that Si higher Vbe could be one of the reasons why a Ge FF sound better, ie, a lower clipping threshold. In a Si FF Vc1 is about 1.3 - 1.5V while in the Ge version Vc1 is about 0.5 - 0.7V. I remember that a Motorola 2n2369 sit at 1.8V, too high.

Anyway, once the high end of the axis face is tamed, it is a very nice build.



mac