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Björn
(@bjf)
Medlem Moderator
Blev medlem: 2 veckor sedan
Inlägg: 5
2018-11-29 02:42  
Hi there,
Thank you for taking interest in the Sparkle Face project. Funny the last time I made a Fuzz Face circuit with germanium transistors was back in 1982 when a friend obsessed with Jimi Hendrix asked me to build him one, which I did.
Anyway earlier this year I found in a drawer a left over pcb from 1982 but one that housed BC108C’s. I felt compelled to get that working and made a pedal that went to a friend. Anyway it got me thinking that I have some fine germanium transistors
of the last generation when the germanium transistor finally rivaled silicon but alas became too expensive for commercial use and were mostly used in early computors and snuck into some power amps but as years went by they were replaced by all silicon.
The point is there’s no magic just parts and the way you use them. So these transistors- and really a fuzz face circuit totally relies on its transistors- that I am using for this have low leakage in fact not bad at all compared to silicon and medium gain, no pop corn noise 
and generally fairly good noise levels comparable to silicon and low temperature drift also comparable to silicon, but they are germanium transistors and have as such a lower Base to Emitter impedance referred to as hie in the four h parameters, and fairly low transit frequency. 
For use in a fuzz pedal or actually for use in amplifier in general, these two parameters give rise to lower order distortion than silicon and the transfer function is not as sharp. Now it’s a fuzz and yes you can get near perfect square wave with an emphasis on ’near’.
 
 
For musical use and as fuzz I have focused on getting the traditional sort of warm fuzz sound meaning one that does make compensation for the various strength of the strings plucked- of course that makes the wound string thick of buzz while the unwound strings can
get a more violin or organ type of tone.
Because of this certain playing styles are suggested and so I have kept to this and not made sound more modern other than ever so slightly restricted broadband noise.
 
Sparkle Face has three controls
 
Volume and for this I have used a value similar to a guitar pot at 500K Log and this so that the traditional filter effect with an orange spiral cable can be achieved.
 
Saturation and this is a control that alters what the guitar sees as in either a low impedance current input or a slightly higher voltage input- what this means for the guitarist and the sound is that some of the more complex distortion patterns can either be had or turned down with this control and since
the input can be made into a voltage input the unit can go after other pedals- of course then the interaction with guitar pick up and the low current impedance- actually what this means is that as a current input gain of circuit depends on what the source impedance is and if it is a guitar pick up then the 
most gain will be had when impedance of pick up is at its lowest which is its DC resistance. As frequency rises so does impedance of pick up and thus at higher frequencies there’s less amplification. This can also be viewed as a series coil feeding into a low shunt impedance and that forms a lowpass filter.
When guitar volume is turned down output impedance of the guitar rises swiftly and is at worst case at 8 with a 500K Log pot 250K and thus gain of circuit is reduced drastically and total fuzz level drops even further as the volume control on guitar is turned down due to the voltage division. 
 
As crude as it is then this circuit makes a lowpass filter at the input due to pick up loading and a lowpass filter at the output via the impedance the Volume control forms as source and the shunt being the capacitance in the following cable. For those inclined to compute worst case output impedance is 250K
and the typical capacitance in an (orange) spiral cable would at worst case be 2000pF.
 
I recall early reading on fuzz pedals and fuzz sounds back in the 70’s that the principal would be to lowpass filter before intense clipping and lowpass filter after. As can be seen the circuit does just that while in a somewhat uncontrolled and crude way.
 
 
Fuzz control and this sets the total gain of the circuit from something controlled to the maximum the chosen transistors can give at in this circuit hfe1 time hfe 2- only the current input restricts maximum gain when feed by a guitar as explained above.
 
With the Sparkle Face I have tried to set a sound that is in the middle and not extreme in any register- actually then making it a fuzz face type that can be employed with other pedals without resetting amp tone controls.
This is something I have always wanted because when building pedalboards for shows I’d glance at my shelves and yes I have some inspiring fuzzes………but they require certain settings on amplifiers and usually not the same as I’d use with all other kinds of dirt pedals I have so the only fuzz that made a board like that has been Snow White Fuzz and with the tone control on that I could set it so that I could use the same settings on amp as I would with all other pedals.
However I think I ended up with one setting that just softened the treble a bit and it was just fine. Keeping this in mind I have made some mild filtering and I used for testing the same settings on amp and all the test guitars to make sure that the sound of Sparkle Face would stay in the boundaries of my amp settings so it would become more another flavour, perhaps more in the way it feels to play and how certain chords and notes sound than more or less of any certain frequency.
 
 I purposely choose not to add a tonecontrol on the Sparkle Face but instead made a couple of custom filtering things.
It is balance to make the sound not too bright and not too dark.
I think the Sparkle Fuzz as is works well with both humbuckers and single coils aswell as P-90's.
That said feedback is good and yes I'd be interested in what type of tonecontrol would be useful and or wanted?
As noted in an earlier post there are ways of controlling eq in small ways with the existing controls and also output cable...
You know this is a crude circuit and for now I'd like to keep it that way.

That is to say that I might later do a version with tonecontrol or tone controls.

 
 
This is a modern design though so it has standard polarity DC inlet and a pilot LED and it’s true bypass and is housed in a typical floor pedal format like Hammond 1590B.
 
Anyway more on how this circuit works as a pedal
 
Due to the choices made the Sparkle Face has fairly decent noise levels for being a fuzz of this type.
 
As a model for the sound I envisioned a new shipment of fuzz pedals to a hip guitar store in the 1960’s and the privileged ones being there before opening hours picking the raisins out of the cake- now what would the best one sound like and play like if I had that opportunity to pick my favourite before opening hours?
 
I’d like mine to be one that could sound even but also broken at will as in a sound you can control with your hands ( this is where the Saturation control comes in btw) and I’d like when volume control turned down to get a slightly distorted sound even to a shade I might rather use instead of a dead clean sound.
I’d also like to able to use the fuzz pedal after wha and if I could wish anywhere I could think of putting it. I’d also be content without tone controls if the sound is balanced.
 
The Sparkle Face has some means of tone control with the Saturation control that,yes can set behavior from vintage to modern and it also directly affects input impedance and further tone can be adjusted via the output loading since output impedance is high when volume is somewhere in the middle- yes indeed should really supply an orange spiral chord to tune output treble.
 
Tone goes up when cable is stretched and down when relaxed:crazydude.
 
Yes I know that sounds really backwards using your guitar cable as EQ but it’s part of the design
 
I used my workshop RED CABLE which I bought a Kjell& Company- Sweden’s version of Radio Shack- for 100SEK-something like 12USD and the capacitance of that RED CABLE is 750pF at 6 meters and thus I consider it a medium cable with house standard capacitance so I know what the capacitive load is when attaching cable.
yes that helps knowing when tuning pick up systems but of course when tuning fuzzes.
 
Indeed a treble control could be hooked on if necessary although I decided to make a mild treble cut via some feedback.
 
 
 
Hm, when building things on a perfboard which I also did with the BJF Super Fuzz there’s a whole new land of oppurtunities…that’s saying I might get into variations like that for the DIY version. Speaking that I will need help with posting schematics and drawings and also if someone wants to make a kit for the Sparkle Fuzz.
 
Allright having said that I’d jump too on a Tone bender with bass and treble knobs just because and even more so if it came in a cool case with fancy knobs…..yes I’d look at gear to see if they fit the leatherjacket.
 
Now I have among my shop guitars a Les Paul Black top ( a guitar formerly known as gold top ) and it is mounted with two P-90’s Lundgren /BJF P-90’s and I also have a LP Junior with a P-90 as well as other guitars with P-90’sGibson and BJF /Lundgren, while the LP Junior I actually used in testing with Sparkle Face.
 
Yes I used the Blacktop as well when tuning the Sparkle face.
 
That is to say I hear black Les Pauls with P-90’s
 
For Sparkle Face I have made the Fuzz control so that it has across the 310° turning the resolution you’d find in the last tenth of rotation on a standard Fuzz Face and I have also custom filtered the sweep of the Fuzz control to balance out frequency changes as fuzz is turned down and so on the Sparkle Face there’s a mild treble lift when Fuzz is backed down in order to make a balanced sweep of the Fuzz control. Yes you can set Sparkle Fuzz seemingly clean if both Saturation and Fuzz are turned down and Sparkle Face then becomes a slightly nonlinear amplifier.
 
I have made some special filtering but at the settings you used in the demo you’d hear that only that eq is more balanced as in no overpowering bass and treble slightly restricted in the Hi Fi range as above 10KHz but more importantly at the settings used
’what comes into play is the working point set for the circuit and I set it so that output can go from linear amplification or very close to anyway to full on square wave and specifically with these transistors- in the Sparkle Faces used 2N1308’s- I’d like to set this working point since
that makes the decay of notes fall in a musical way. This is easily set up with a VOM by measuring the Voltage at Collector T2 at 4,5Volts with a 9V DC supply. It can be seen on a scope with a sine wave how waveform transforms from sine to square and specifically with Saturation 
at minimum you can see how square is symmetrical and remains symmetrical as Saturation is advanced. What this means in terms of sound is mainly noted in how a note decays and somewhat in the clarity of sound.
 
I’ll say that a while ago I found a pcb I made in the late 80’s and it was a leftover from a pedalboard on which the guy wanted to have a fuzz face and I built one but he went with the germanium version using AC128’s and that left the silicon version using BC108C's in a drawer from many years now a while 
ago I resurrected that and built a complete pedal for a friend and with that circuit I rather choose to put working point in the nonlinear region as it gave a much more interesting sound that way- yes I tried that with the sparkle faces but preferred the linear graduating into nonlinear over starting at a nonlinear
working point. For me that goes to show that it’s not the part but the way you use the part to get the desired sound.
 
Some of the filter techniques used in Sparkle Face has more to do with sound at lower settings of Fuzz and Saturation- in an effort to make the control range be useful shades more than allowing just one setting.
 
As explained earlier this type of circuit can be set as in the video clip to allow a whole lot of control from guitar and hands, while the Saturation and Fuzz controls on the pedal also allow for more stable sounds and allows the Sparkle Face to be driven by wha’s and such or even to be used as a preamp booster if 
that is desired and as such it can overdrive distorted amplifiers
 
Note that the sound of the Sparkle Face was set on a very clean transistor Marshall of 140W’s with no clipping from the amp but instead my angle was to set the sounds so that fuzz could be turned on and off without heavy change in eq and also that the Sparkle Face would provide a strong useable fuzz sound
into a pristine clean amp and also that Sparkle face would be a great overdrive for a distorted amplifier and that it further also should be possible to used at any position in a pedal system.
 
Yes indeed Fuzz Faces and especially ones with GE transistors can be tricky to tune and not really be that stable and they can even feel sick if you will but at any rate be temperamental and it that may lie some charm.
Oh yes I really liked an old Gibson FZ1A when I got it working and that also has a control to set various shades and that had some old GE-s in it.
Fuzz faces though I just got the interest when I found that old pcb from 1982 and restored it.
 
Right Sparkle Face is a fuzz and it’s about a fuzz sound not about transistors per see. I’d say that through the years I have rarely talked about parts I use other than when it has been an education thing.
 
Sounds and behaviour are what I always start with and work backwards and eventually use what parts can be used to meet the criteria.
 
Anyway the sound comes first while this came about backwards to me as I had restrictions set to circuit and transistors.
 
Right so the transistors Sparkle Face is using were once created for switching functions in computors- by no stretch would that promise a great sound but since this is also to be a diy project some dwelling on parts would seem appropriate.
2N1306's will do just fine and are very similar to 2N1308's and for those interested in listening to and comparing transistors you can also add sockets.
On temperature sensitivity and other quirks with old germanium transistors, I’ll say I have quite a few of these old germaniums in various shapes and casings. Most of them are more of historic interest than anything else. I actually have one or two of the spetz transistors- those have a little rubber hood over their glass casing and the story behind that is from the childhood of transistors and there even guitar amps built with these glass containers that made the amps light sensitive and so the phototransistor came about and also the rubber hood. I have had the pleasure or not to repair a number of Hagstrom amplifiers many of them with transistors. I actually slaughtered a preamp of a Hagstrom amp that was supposed to compete with Fender Twin Reverb and about the size of one such Fender too and with two 12” speakers but it was not worth repairing so the preamp became a fuzz pedal- a fuzz face type with a buffer ahead. Funnily I sold an old Farfisa organ the vibrato of which inspired me to make the MGMV, to a friend who wanted to slaughter it to make fuzz pedals- there were three AC128’s per oscillator per note and then some such as for the vibrato.

Oh yes those old AC128’s only some worked as some had too much leakage saturating the transistor and some even had a peculiar thing called whiskers from the casing protruding to the inner core making them intermittent and then some or most had the pop corn noise so called because it behaves a little like popcorn in an intermittent noise and many of them were so heat sensitive that you could change amplification by holding the case with your bare hands while others you could do the same thing with a hairdryer or a lamp.

When I took electronic class-on my own- there was this section of designing circuits with OC transistors at the last pages of one of the tube manuals and then icbo-the leakage from collector to base would be important to count with and sometimes the leakage alone would be enough to bias the transistor and the final circuit would appear not to work………unless you considered the leakage.

with the advent of silicon transistors icbo would become something that could be ignored in design for all practical purposes and only under extreme conditions ever to be considered

On beast deserves mentioning and that’s Hagstrom’s entry of a Backing Elvis model in a 4x12 combo at 130W’s and that was driven by the largest germanium power transistors I have ever seen about three times the size of a 300W silicon transistor.
These things could deliver a lot of current over the 2 Ohm speaker load of the 4x12 but would not take more than 40Volts so this amp had a power supply regulator making sure there would be no more than 40V across the trannies but this regulator had a tendency of dying itself so I asked my local submarine engineer and he produced two replacement heavy germanium transistors and also gave me permission to use his floating power supply to safely protect what appeared to me transistors worthy of being in a museum. There was no way of determining if these transistors worked other than connecting them in the circuit-they actually measured as if they had a short to any terminal from any terminal- but behold they worked and the amp eventually could be fired up after some really heavy restoration and it was totally worth it as that may be one of extremely few of those anyway not so many made amplifier that is still to this day working.

Oh yes when a couple of AC128’s and the like transistors could be found that were reasonably stabile and reasonably not so noisy and that further had some amplification enough to make fuzz pedal I can say the sound would then be great and yes still it would be very good to have access to a fridge in warm countries and especially if you want to play fuzz guitar on the porch in the midst of the Sun. 

Aleksander Niemand told me something fun about SSSR transistors in that when the way to make silicon transistors was discovered it was consider such an advance that this was kept out of commercial electronics and so the commercial electronics were instead made with the older germanium transistors and so there would be massive amounts of commercial intended germaniums that might leak out into the world.
The transistor chosen for Sparkle Face is of a later generation when they actually got good enough to compete with silicon but alas too expensive with their golden legs and many of these transistors have indeed been slaughtered for their legs. 
However they are still available since they were used in computers, the very early ones, and so crates of these were stashed as replacements-that is to say no magic just that these more modern types have much less temperature dependency on the order similar to many silicon.

Note on Sparkle Face is that it comes with a trimmer so that behavior can be set as outlined above, and this can be done with a scope or simply by adjusting Q2 Collector to rest at 4,4 Volts or half the potential that collector return sees.
 
 
Indeed there will be a schematic posted- I have no means to do so and for the moment the whole circuit exists in one unit and in my head and a thread with schematic and notes can come in good time, but first I am very curious to the sounds.
 
Mainly because I don’t think I am a really Fuzz Face guy while I really and deeply like fuzz guitar. There are things I find important in playability but I am curious also to what others think and that may spur ideas..
 
Yes this will be done differently or I could just have posted that the Sparkle —— is a fuzz pedal and it sounds like bla and behaves like bla when you bla it.
 
Yes I can relate to a fuzz pedal being a best friend.
 
 
Anyway have fun and stay tuned
 
BJ
 
” I believe the sound of fuzz guitar has had greater impact on mankind than man walking on the Moon"
 

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