Hybrid Fuzz Face Transisor specifications?

[zachomega]

I built a fuzz face and wired it up PNP with 2n404 transistors with approximate gains of 70-80 for Q1 and 110-120 for Q2.  I think it sounds great but I'd like to try and get some new sounds out of it. 

I'd like to play with some silicon transistors but I'm really not sure what gain range they should fall into.  I have a bunch of 2n5087's and BC560's which fall into the 250-350 hfe range.  Are those suitable?  For Q1 and Q2? 

Also, I heard some sound clips of the Fox Rox Captain Coconut...particularly the Fuzz Foot and have to admit I'm quite taken with it.  Anybody have a more detailed idea of what is going on in that thing other than a low gain silicon Q1 and high gain germanium Q2? 

-Zach Omega

[tcobretti]

Those 5087s should work fine.  A great cure for oscillation is an Si FF is a 50-100pf cap across the collector and base of the Si transistor.  This will also cut some of the highs and make it sound a little more Ge (but just a little; there's no substitute for the real thing).

[zachomega]

Awesome...Lower hfe = better for this circuit?  I've read that higher gains sound terrible in this circuit. 

Also, any advantage of using silicon as Q1 instead of Q2 and vice-versa? 

My overall goal is to brighten up the fuzz face while keeping the germanium warmth.  I could go either way as far as needing more gain or less gain. 

I suppose I should also mention that I have a 10k trimmer on Q2's collector and a fixed 1k resistor replacing the 330/470 ohm resistor.  Next time I build one of these, I'm going with a larger resistor than 1k for even more output. 

-Zach Omega

Those 5087s should work fine.  A great cure for oscillation is an Si FF is a 50-100pf cap across the collector and base of the Si transistor.  This will also cut some of the highs and make it sound a little more Ge (but just a little; there's no substitute for the real thing).

[tcobretti]

My favorite Si or Ge FF I've built uses 2 MPSA18s which are very high gain.  Phillip from Fuzzcentral and RG have both talked about using low HFE Si transistors to mimic  Ge transistors, and by all accounts Phillip's Axis Face sounds great.  I built one very similar to his using the same low gain transistors, and it did sound really good.  However, that is not to say that you can't make a FF with high gain Si.  I have the schem for my high gain Si FF posted in my gallery (the Mondo Fuzz), as well as my Socket Face which is a FF layout where I try to describe how each component affects the sound.  I think the thing I have learned since I put those in there is that with an Si FF you will certainly want to lower the Feedback resistor to 33k-47k.  When it comes to combining Ge and Si, for me it came down to which Ge I plugged in.  Some sounded great, some less so.  That's why I designed the socket face, so I could experiment to my heart's content.

Incidentally, Roger Mayer's Stone Fuzz (also in my gallery) uses high gain Si transistors, and a 47k trimpot on the collector of Q1 for biasing.  I haven't heard it or built it (yet), but by all accounts this pedal is rad.

[zachomega]

I'm looking at your gallery as I type this.  Awesome stuff. 

Unfortunately, the only trimmer inside of my FF is the Q2 collector.  I do plan on building another in the semi-near future where I'll pretty much trimmer Q1 and Q2's collectors and the feedback between Q1 and Q2.  Any other places I should consider placing a trimmer? 

Also, I planned on something like Q1 collector trimmer of 50k, Q2 20k, and feedback 100k.  Sound reasonable? 

-Zach Omega

My favorite Si or Ge FF I've built uses 2 MPSA18s which are very high gain.  Phillip from Fuzzcentral and RG have both talked about using low HFE Si transistors to mimic  Ge transistors, and by all accounts Phillip's Axis Face sounds great.  I built one very similar to his using the same low gain transistors, and it did sound really good.  However, that is not to say that you can't make a FF with high gain Si.  I have the schem for my high gain Si FF posted in my gallery (the Mondo Fuzz), as well as my Socket Face which is a FF layout where I try to describe how each component affects the sound.  I think the thing I have learned since I put those in there is that with an Si FF you will certainly want to lower the Feedback resistor to 33k-47k.  When it comes to combining Ge and Si, for me it came down to which Ge I plugged in.  Some sounded great, some less so.  That's why I designed the socket face, so I could experiment to my heart's content.

Incidentally, Roger Mayer's Stone Fuzz (also in my gallery) uses high gain Si transistors, and a 47k trimpot on the collector of Q1 for biasing.  I haven't heard it or built it (yet), but by all accounts this pedal is rad.

[zachomega]

OKay...I just took apart my fuzz face and replaced transistor Q1 with a BC560...Supposed to be low gain low noise...hfe was probably between 250 and 350...Can't say for certain as I didn't check it.  Just plugged it in and I even guessed the pinout first try!   

Anyway, I noticed a lot more gain, and it could be my imagination, but I find the volume interaction to be overall much much brighter and more sensitive to a lower volume on the guitar...This really pleased me a lot.

I tried a second bc560 for Q2...I immediately felt it was too gainy and with the bias set in a host of positions, the thing oscillated.  Not a big deal since I wasn't really digging it. 

I didn't try Q1 as germanium and Q2 as silicon, but I'll do that in a bit. 

I went back to Q1 silicon and Q2 germanium.  I'm really digging it.  It has a lot more gain and still has the old feel...and is noticeably brighter...no noisier than before (which is pretty dead quiet). 

-Zach Omega

[tcobretti]

Two things I recommend:

If you build a Si FF, or even a FF with an Si in Q1, put in the 50-100pf treble bleed cap across the collector and base.  This will help with oscillation and keep the pedal from being to abrasive.

The 100k feedback resistor is a good place for experimentation.  As it gets lower, the overall gain of the circuit goes down, and the circuit's sensitivity to your guitar's volume knob goes up.  On one of my Mondo Fuzzes I put in a 50k pot so I could play with it, and it gives plenty of fuzz with a 50k of feedback resistance, but I can dial it down if I'm playing with a guitar with higher gain pickups.

If memory serves, Q1 Ge/ Q2 Si can be really good, because Q1 has more effect on the overall sound of the pedal.

The next FF I build is gonna have the 50k trimpot at Q1.  I haven't tried it yet, but I think it would greatly simplify trying different transistors.  Another great FF variant is the Multi-Face at runoffgroove.  That thing is hyper flexible.

[Dragonfly]

Zach...
  you might also try 2N2907's in there. Theyre readily available, and sound pretty good...

AC

[zachomega]

Well I didn't have any troubles with oscillations except when both transistors were silicon.  Then it was oscillation city if the bias control wasn't set correctly. 

Truthfully, I kind of like how it gets abrasive...but maybe I'd like it just as much with the treble bleed cap.  I'll try it both ways. 

Hmm...I guess tomorrow I'll be trying the silicon in Q2 with germanium in Q1.  I just like the added clarity/high end boost of the germanium/silicon combination.  All germanium seems to be a bit dull...as in high end cut...and all silicon is harsh and prone to oscillation without circuit modifcations...which I'm okay with except that this FF I'm working with is all hardwired except for the Q2 collector resistor.

-Zach Omega

Two things I recommend:

If you build a Si FF, or even a FF with an Si in Q1, put in the 50-100pf treble bleed cap across the collector and base.  This will help with oscillation and keep the pedal from being to abrasive.

The 100k feedback resistor is a good place for experimentation.  As it gets lower, the overall gain of the circuit goes down, and the circuit's sensitivity to your guitar's volume knob goes up.  On one of my Mondo Fuzzes I put in a 50k pot so I could play with it, and it gives plenty of fuzz with a 50k of feedback resistance, but I can dial it down if I'm playing with a guitar with higher gain pickups.

If memory serves, Q1 Ge/ Q2 Si can be really good, because Q1 has more effect on the overall sound of the pedal.

The next FF I build is gonna have the 50k trimpot at Q1.  I haven't tried it yet, but I think it would greatly simplify trying different transistors.  Another great FF variant is the Multi-Face at runoffgroove.  That thing is hyper flexible.

[zachomega]

Cool, good to know.  I accidentally stumbled across a website which claims they are the PNP equivalent of the 2n2222...I also have some 2n2904's which on paper seem like an ideal candidate with a gain range of 40-120 hfe, but the ones I have all measure in the 50's for gain...which seems way too low to use. 

Any other transistors I should keep an eye out for? 

-Zach Omega

Zach...
  you might also try 2N2907's in there. Theyre readily available, and sound pretty good...

AC

[Dragonfly]

Cool, good to know.  I accidentally stumbled across a website which claims they are the PNP equivalent of the 2n2222...I also have some 2n2904's which on paper seem like an ideal candidate with a gain range of 40-120 hfe, but the ones I have all measure in the 50's for gain...which seems way too low to use. 

Any other transistors I should keep an eye out for? 

-Zach Omega

Zach...
  you might also try 2N2907's in there. Theyre readily available, and sound pretty good...

AC

HERE'S a schematic of a silicon FF I designed using ideas from Phil, Brett, and a couple other people. It straddles the silicon / germanium sound quite nicely. IIRC, MartyMart said its one of his favorites. Anyway, you could easily "flip" the electro caps around and 9V/ground, use PNP's in a hybrid setup, and it sould sound GREAT. You may not need the .001uF cap if youre setting it up as a hybrid however.

As far as other PNP silicons...most of the ones I "like" are old and obsolete   ..the aforementiones 2907's are nice newer ones. If you can find them, the 2N4249's are cool...theyre originally the "bosstone" ones.

AC

[zachomega]

Very cool schematic.  I must have at least 10 different FF variations I'm going to end up building at this point. 

-Zach Omega

Cool, good to know.  I accidentally stumbled across a website which claims they are the PNP equivalent of the 2n2222...I also have some 2n2904's which on paper seem like an ideal candidate with a gain range of 40-120 hfe, but the ones I have all measure in the 50's for gain...which seems way too low to use. 

Any other transistors I should keep an eye out for? 

-Zach Omega

Zach...
  you might also try 2N2907's in there. Theyre readily available, and sound pretty good...

AC

HERE'S a schematic of a silicon FF I designed using ideas from Phil, Brett, and a couple other people. It straddles the silicon / germanium sound quite nicely. IIRC, MartyMart said its one of his favorites. Anyway, you could easily "flip" the electro caps around and 9V/ground, use PNP's in a hybrid setup, and it sould sound GREAT. You may not need the .001uF cap if youre setting it up as a hybrid however.

As far as other PNP silicons...most of the ones I "like" are old and obsolete   ..the aforementiones 2907's are nice newer ones. If you can find them, the 2N4249's are cool...theyre originally the "bosstone" ones.

AC