#screnprinting

In the last entry, I discussed my motives and possible mods and tweaks of the Fuzz Face-circuit. This part will be about the process of screenprinting a pedal and the right choice of transistors in the Fuzz Face-circuit.

Screenprinting

My standard procedure of painting enclosures is the use of decal-paper (also called waterslide-decal). For this project, I wanted try something different: Screenprinting. I’ve getting into the method of screenprinting in the last months, producing sacs to ship my pedals in, and also some bags. The reasons for screenprinting a pedal rather than using decal-paper has aesthetic and practical aspects on the up- and downside.

Screenprinting (once you’ve mastered the process) is a convenient and fast process for the mass-production of pedals. Earthquaker Devices from the USA screenprint all of there enclosures (at least as far as I know their massive catalogue). In Germany, KMA Audio Machines are a great example for the incredible use of screenprinting on pedals with beautiful results. In the last few years, the supply of colored enclosures from different sources has been growing continuously, resulting in an incredible variety of colors and therefore nearly unlimited creative possibilites in an acceptable price-range. Meanwhile, companies like Siebdruck Versand or Siebdruckland produce products and tutorials for screenprinting textiles at home, which can easily be applied to pedals as well.

The downside of screenprinting, compared to the use of waterslide-decals, is the massive amount of preparation and time. In most cases, preparing and exposing the frame isn’t really worth the effort for one pedal. Also, the process has to be very exact and doesn’t allow much tolerance. For example, I had to recoat and expose the frame three times to get it right, which takes about two hours each try. A “mass-production” (I’m talking about batches of 20+ pedals here) with reliable, high-quality results needs some trial and error and a steady hand. So far, I’m happy with my first success that you can see above. Another aspect that limits the possibilities of screenprinted pedals is that photos, photorealistic motives and motives with more than one color are much harder to do than with decal-paper. You’d need some skills in the photo-editing software of your choice and the look won’t be that of an actual picture. With decal-paper, you’ll be able to make pretty much any design, even the ones that you could do with a screenprint. It doesn’t really work the other way around. Nevertheless: Once mastered, the looks and haptics of screenprinted pedals are significantly different and are more preferable to some people.

Transistor matching

This section will deal with the right transistors for the Annapurna Fuzz and the process of selecting appropriate types from my stock. I will also write about how different people tend to match these together.

As I mentioned in the last post, I bought a bunch of different transistors and very old ICs a few years ago. Lots of these are germanium-type, which got this project rolling in the first place. The transistors used in the Fuzz Faces that were built over the years were mostly used because of practical reasons a company can face: price and availabilty. The two main-types definitely are three NKT275 and AC128. Analogman, who’s been building a boutique-pedal based on the Fuzz Face for years now, actually gives some information on the different transistors and their tonal qualities on his website.

The semiconductor industry was new back then, and had not developed the technologies that let us make cheap, reliable, identical-as-peas-in-a-pod devices like we have become accustomed to.  R.G. Keen on the quality of germanium transistors

The important thing about germanium-transistors is their inconsistancy. No one transistor is like the other regarding their electrical values. Also, these values tend to change with variing temperatures. This means, that your pedal could sound totally different in your cool rehearsal space than on a sunny open air stage just because the temperature changed by 10°C. These facts make the right choice of transistors a hard one. And there are different approaches how to select the proper combination of transistors. As R.G. Keen writes in his article on the Fuzz Face-circuit:

Don't get too hung up on the exact numbers - they'll change in a second anyway as the device heats or cools. Look for low leakage, and approximately the right gains. The right *real* gains are from 70 to about 130. Within that range, people report the best sounds. Some people prefer equal gains, others prefer having a lower gain of 70-100 for the first transistor and 90 to 130 for the second.

As R.G. Keen mentions here, the key values for a good Fuzz Face-transistor are the gain/hfe and the leakage. To measure these, I bought a transistor test-kit on ebay (Search for GM328). But to a large extend, your ears are the best instrument at your proposal to decide if a transistor is actually fit to be used. The combination that I chose as my favorite includes an ASY11 as Q1, and a Telefunken AC122 as Q2. Here’s what I measured from my favorite combination (see pictures below): Q1: ASY11 / hFE: 49 / leakage: 160uA Q2: AC122 / hFE: 96 / leakage: 280uA

The gain is quiet low in comparison to the Keen’s proposal while the leakage is in an accpetable range. These are actually the transistors/pedal you can hear in the soundsample from the last entry.

What can we conclude here? For my part, I decided to go with a combination of measuring and listening to find the best matches for the Annapurna Fuzz. I have at least seven different types of germanium transistors here with various gains and leakages. In a first step, I measured every single transistor and wrote down the hFE- and leakage. The next step will be a test in the (to be build) prototype-pedal. I will only build as much pedals as I find good combinations, so let’s hope for the best.

What’s next?

So I finally got into screenprinting!