Fuzz FAQ

#Q: All of my other pedals used 2.1mm but they require "tip-positive". Does that mean they're negative-ground? Does that mean they're incompatible with your fuzz pedal?

#Q: Why should I get HARTMAN Vintage Germanium Fuzz vs. one of [insert brand name here] Fuzz Face clone?

#Q: I still have questions.....

Q: Why Germanium? Why Silicon?

A: Different harmonic content. The two types of transistor distort differently. There are marked differences in the character of sound and the feel. Germanium is known for warm, almost woodwind-like mid-range detail, smooth upper register roll-off, loose feel and wide dynamic response. Silicon is frequently tighter and harder in sound and feel, more aggressive, more sizzle, more bite, a tighter low end, and requires a slightly different gain-pairing of the transistors to clean up properly when you roll back guitar volume.

Q: What is the difference between the HARTMAN Vintage Germanium Fuzz and the original Fuzz Face?

A: The core circuit topologies are identical. The component values are identical EXCEPT that we screen, test and match the transistors for the circuit, something that was not done (much that we know of) in the originals. The HARTMAN Vintage Germanium Fuzz adds true-bypass, external power supply, LED indicator, reverse-polarity protection and plated-through hole printed circuit board construction for an assembly significantly less prone to failure due to mechanical shock and trace delamination with age.

Q: What kind of transistors do you use?

A: NOS (New Old-stock) AC128s and NOS NKT275s. Our NKT275s are mil-spec to withstand 60V (standard NKT275 spec is 15v). We bench test all transistors at 70 degrees Fahrenheit for leakage, forward current transfer ratio (Hfe), noise, temperature drift, and inter-element capacitances. From the transistors that pass bench measurement, we then mate pairs for Hfe ranges of 75-100 for Q1 and 100-135 for Q2, respectively. We alter/deviate from these ranges and ratios only upon request. Leakages range from as low as 50uA to about 200uA. So far the NKTs average lower leakage than the AC128s. You can read more about the provenance of the our NKT275 stock here.

Q: Were AC128 really used in old Fuzz Faces?

A: I'm inclined to agree with Tom Hughes and Mike Piera on this. They claim they've never seen an original with AC128. Plenty have come through this shop for mods and repairs. Most with NKT, and several had AC128, but in every case, the AC128 had been installed after-market (sometimes pretty early on in the piece's history, but definitely not factory solder work). How the AC128s sound has everything to do with their leakage, gain (and a couple other things we test for), and less about the numbers on the cans.

Q: What are all those numbers and abbreviations, Hfe, uA, etc?

A: Hfe is forward-current transfer ratio. It is the amount by which a transistor's Collector Current increases for a given change in the voltage (your guitar signal!) between the Base and Emitter. It is, roughly speaking, the amplification factor or gain of the transistor. If you've ever read that 12AX7 preamp tubes have gains of 100 and 12AT7's gains of 70, well....this is analogous. uA are micro-amps--millionths of amperes of current. When a transistor has no voltage applied at its Base, you want to see, in a perfect world, zero leakage. Nothing's perfect, but the screening process is designed to limit imperfection. The fewer uA leakage, the better. Germanium manufactured in the 1960s had leakage all over the map. Manufacturing processes have improved over the years: current-production Germanium have leakages in the 10's of uA. Silicon is often <10uA.

Q: What about temperature?

A: There is an appreciable difference in the behavior of a Germanium transistor from the moment you turn in on up to about 5-10 minutes in. The good ones reach equilibrium and maintain it, drifting only slightly when heat is applied either from external source or from internal power dissipation. We test each transistor for about 15 minutes, or until a clear equilibrium is established, whichever comes first. We map leakage, Hfe and capacitance over time and reject the ones that drift or go into thermal runaway. We test Silicon for leakage and gain too, but they set up in fractions of a second and drift almost not at all. Time and heat are less of a factor.

Once a good Ge transistor warms up it will remain relatively stable even with signal running through it. Sudden, dramatic temperature changes--outdoor stages with the sun beating down on the box, sudden temperature drops in the desert at night, etc., can mean your sweet spot will drift somewhat on the dial. If you're likely to be playing in these conditions, consider a bias control, below.

Q: Does the fuzz clean up well with guitar volume?

A: Exceptionally well as long as the gains of the two transistors are not excessively high. NKT275s tend to get a cleaner sparkle than AC128s when you roll back, but both types allow you to have your clean and dirty tones within a few degrees of each other on the guitar volume knob. Some players leave the fuzz on all the time and use their instruments to control the intensity of the effect. The circuit is incredibly sensitive to the player's attack and touch, as well as to the guitar's electronics and the position of its controls. The BC108 Silicon transistors we use require narrower gain selection to achieve good cleanup. As much as they're a technical improvement over their Ge predecessors, and more consistent in terms of their sound, they're less forgiving when it comes to mating good pairs for cleanup. Go figure.

Q: What is Bias and why isn't Bias Control a standard feature on the Vintage Germanium Fuzz?

A: Speaking about the Germanium for a moment: the bias of the transistors of the fuzz circuit establish headroom (and thus its complement, breakup) in much the same way bias does on a tube amplifier. In both cases, the bias, or operating point, can be set permanently with a resistor soldered into the circuit board, or adjustably, with a trim-pot or knob. The original Fuzz Face established bias with the permanent/resistor method. It is worth noting that since every resistor has a tolerance (we use the same 5% carbon-composition resistors used in the original circuit), and no two Germanium transistors are alike, that you cannot mass produce Fuzz Faces with this bias method because each unit must have its transistors selected to bias correctly with the components on-board. HARTMAN Vintage Germanium Fuzz are built by fixing resistor values and selecting the transistor values. Again, not the only way it can be done, just the way we happen to do it.

If the Ge transistors selected are stable, in range, and pedal gets used in "normal" conditions, bias only decreases the amount of fuzz available. It does not significantly alter the character of the fuzz in quite the same way it does on the BC108 Silicon models (which is why it IS a standard feature on those). It's a "less-is-more" thing: one less component to fail, one less knob whose setting you have to worry about, one less gimmick.

Q: And one less thing for you to build?

A: Sure, but with a bias control our unit costs would actually go DOWN because we would be able to use a wider range of transistors that would otherwise fall outside the range of tolerance stated above and simply compensate for the variance with the bias control. Germanium transistors are hard to find, expensive, and many of each batch we buy get rejected.

Q: But doesn't Bias Control let me get tones I couldn't get otherwise?

A: On the BC108 Silicon yes, which is why we build it in standard. Tonal change on Ge is relatively small--nothing that can't be arrived at through use of guitar volume and pedal control.

Q: What's the Input Trim (Fuller) Mod?

A: With this mod, you get an additional knob ("Level") to control the amount of input signal that gets through to the Fuzz. You still get the standard volume knob, which controls the output level of the Fuzz. It is roughly analogous to using your guitar volume to clean up the fuzz, but shades the fuzz a bit darker and smoother, and because it's NOT your guitar volume, you retain USE of your guitar volume knob's range (which as you know can affect your guitar's tone quite a bit). If this were a channel strip on a mixing board this control would be pre-fader trim. It can be quite useful if you're trying to tame an overly hot input signal (e.g. guitar with hot pickups/over-wounds, humbuckers, active preamp signal, etc.).

Q: What does the Mayer-Hendrix Mod do?

A: This mod squeezes a little more gain out of the second Ge transistor. You get a slightly hotter output signal (a bit of overdrive behavior) and more fuzz, especially at the upper reaches of the fuzz dial. Calling it the 'this-one-goes-to-11' mod would not be putting too fine a point on it.

Q: Does the Mayer-Hendrix Mod alter the character of the fuzz?

A: Not especially--though as Germanium's fuzz is increased in intensity it also gets brighter, and wilder; the highest settings have a more sizzle and cut-through than the stock circuit, and introduce some snarl and grind that hints of Silicon.

Q: Isn't external power a no-no with fuzz pedals?

A: Different types of batteries, different ages of batteries, and whether you use a battery or a wall-wart power supply will all affect the sound of the fuzz somewhat. Which is better is a matter of taste. We ship each unit with a new 9V carbon-zinc battery since there seems to be a consensus these sound better than alkaline. The differences can be subtle, however, subtle enough not to throw the baby out with the bathwater, so we kept the power supply in. There's no penalty for having it and not using it, though we can omit it from your fuzz design upon request.

Q: What does PNP mean and what's the deal with the "positive ground" power supply I hear about?

A: PNP and NPN are designations for describing transistor pin polarity. The original Fuzz Face was designed using PNP (positive-negative-positive) Germanium transistors. The design called for the positive pole of the battery (or power supply) to be connected to signal ground (the sleeve of the guitar cables you plug into the pedal is the ground--the tip of the jacks is the signal). The battery snap in our Ge pedals is connected to the circuit in just this way, as is the external 9VDC jack. The Ge pedal 9VDC jack requires a "tip-positive" (sleeve negative) 2.1mm supply jack.

The BC108 Silicon transistors are NPN. Ground is negative, just like most other pedals in the known universe.

Q: Then how in the world do you run PNP Germanium and NPN Silicon together in the SFZ?

18 volt power supply. Ground is in the middle of the 18v range. The 9v above ground (i.e. ground is the more negative of the two poles) is reserved for the Silicon circuit, the 9v below ground for Germanium.

Q: Isn't that prone to oscillation?

Nope. Switching is configured so the two circuits never know the other's power supply exists.

Q: All of my other pedals used 2.1mm but they require "tip-positive". Does that mean they're negative-ground? Does that mean they're incompatible with the Vintage Germanium Fuzz pedal?

A: Negative ground and positive-ground pedals get along just fine as long as they do not share a battery or power supply transformer. Read that twice. Several commercial power supplies have multiple internal isolated transformers to allow serving both polarities simultaneously. If you're using batteries, you don't even have to think about this issue. If you're using wall-warts--just be sure not to daisy chain negative- and positive-ground pedals off the same power line EVEN WITH THE LITTLE POLARITY FLIPPING ADAPTORS ADDED, it just won't work that way. Won't hurt the pedals (usually.....) but your transformer might get a little warm, or die.

Q: Why should I get HARTMAN Vintage Germanium Fuzz vs. one of [insert brand name here] Fuzz Face clone?

A: We'll assume you already know that the Dunlop Fuzz Face reissues use recently manufactured Germanium transistors that sound nothing like their older cousins. One difference you may encounter between our pedal and other brands using NOS Germanium is craftsmanship. We take great pride in doing it right. And after going through our share of guitar pedals, we're sensitive to--and wish to studiously avoid--the empty promises and poor quality control that so often accompany mass-market and even, sadly, some boutique devices.

Another difference is price. With prices in the vintage market quickly skyrocketing beyond the reach of working musicians, our objective is to provide the real deal--historically accurate tone--along with craftsmanship and customer service of the highest order, to the people who need it, at a price you can afford. Old stock components are used in our pedals for the sake of accurate sonic reproduction when necessary, but we're not luddites. Where technology has progressed and can provide an advantage without detracting from the authenticity of the sound, we'll use it!

The idea is to create the best tools for the job where nothing is sacrificed for the sake of expediency, but without raping your wallet. In addition to the pedals we build, we repair and modify quite a few other brands. We see what works and what lasts, and what doesn't. It keeps people's pedals working, and it exposes us to the best practices of those who have gone before--the things worth keeping. If it ain't broke....

Q: I still have questions.....

A: That's a good sign. Thanks for sticking with me this far. Email mailto:info@hartmanelectronicstore.com or call (415) 652-8260. We learn as much from hearing our customers' needs as we do staring at temperature/gain curves on our test bench. If we don't pick up the phone, it's probably because we can't hear it over the '68 Super Reverb we use for auditioning the pedals before we ship them, out at a gig, or (rarely) actually sleeping. In either case, if you leave a message, please leave your number twice in case of bad reception if you're calling from a cell phone. We get back to most inquiries within a day.