Built a Dallas Rangemaster clone

[Dacious]

Sort of. Off the GEO FX site. I always wanted that screaming lead tone - get close with the Tele with 4-way through my VR, but just lacked sustain. Now I know the secret of Clapton and other dudes with single coils. Tried tons of overdrives, compressors, different pedals. I either got harsh tones, feedback or both.

This thing has a super-simple circuit I built on a tagstrip - yes, a PTP solidstate effect with a germanium chip and one dial! Took some sorting through 3 or 4 transistors to find one that works out of the packet of obsolete Seiko 2SA182s, and jiggering with bias resistor values as they aren't quite the right parameters gain-wise. I've ended up outside the 'pure' parameters of a Rangemaster, a little higher voltage off the collector. Because germanium chips are prone to leak DC it is trickier to set up than your normal solid-state.

Mine is probably a little thicker-sounding than the sound clips of real ones I heard online. The good thing is: it clips and sags a lot like a guitar amp - adds a lot of sustain as the note dies and acts like a compressor to keep it ringing. But the clip is seemingly a soft-clip, not a hard, square edged buzz. Even at low settings you get a nice drive up top. It is not tubes, definitely, but is a smoother, rounder, softer tone than the normal buzziness you get from solidstate effects. For those slow-bend, single string riffs, it just sounds excellent. When you add a little finger-vibrato it keeps a note ringing nicely.

The other good thing is on large settings it thickens everything up, but mainly boosts above 2 khz, so you get a nice db boost from about the middle of the fretboard and up, either from about the third string up, or the 4th/5th fret.

I've just added bypass and buffer resistors to the original circuit.

I think I'll build a Fuzzface next - local electronics online vendor lists the OC44 chips as available!

[Lance]

I built one as well built on the goofy tag strip. Since the tone is very dependent on the caps used in the circuit, I got a handful and experimented. I finally settled on two values I liked. I drilled another hole in the case and hooked the caps on either side of a DPDT to allow selection of the two tones. Maybe my transistor was so-so...but it wasn't my favorite homebrew.

My fuzzface turned out to be another lame attempt. While the circuit does work, I just never got a strong fuzz out of it. At least nothing like I've heard on the Fulltone '69 samples.

[mr_hankey]

I've built a couple, and they've always sounded great. My fuzz faces never seem to turn out right.

[Dacious]

The secret apparently is the adjustment of the bias - the germanium chips vary wildly in gain and leakage, and a conventional DMM won't give you an accurate gain figure because it will read the DC leak as gain. All of them leak a little and therefore are relatively low-efficiency, but that is the reason they sound like they do - another happy sonic accident. Dallas set many units up with strange resistor and even pot values to make them work.

Back in 'the day' people went through crates of Fuzz Faces to find the few good ones, and Roger Mayer was in much demand to mod them up. Many of the boutique makers have apparently gone through all the stocks of the specific chips and got the 'good ones' as they aren't making anymore. But there are modern replacements, and large stocks of NOS small-switching diodes of other types in similar values.

The good news is, it seems the type of chip is secondary to the right values - people like Mike Fuller of Fulltone (his 69 pedal is a Fuzzface, basically) have reverse engineered the good ones and there's a set of parameters with the two bias resistors, the 33K and 8.2K you have to get right. Outside the range and the pedal will pretty much sound like dog-do.

You need low-leak chips with a voltage gain factor of between 50 and 100 for both the Rangemaster or Fuzzface. On the GEO FX site, Mr Keen shows how to accurately measure the chip, then tells you how to measure the voltage gain once it is in the circuit - I used trim pots on alligator clips to determine the bias resistor values. I ended up driving my chip a bit harder, which is probbly why it boosts everything a little more.

http://www.geofex.com/Article_Folder...ace/fftech.htm

[mr_hankey]

I've got trimpots on the actual circuit board. I can set the bias right, but it still doesn't sound good; and the bias gets thrown right off when there's a very minor temperature change (pedal sits too close to the amp, sunlight comes through the window etc). Maybe these new AC128 transistors just don't sound good (like Mike Fuller and many others claim).

[Dacious]

Maybe that's just how they sound? I can't say for sure, mine sounds pretty much like the soundclips I've heard, thicker than some, thinner than others but then I don't know what is being used as an amp and guitar on those clips or how recorded, pickups etc. It sounds great to me. I think if you like a more modern, crunchy distortion sound it isn't for you - more like a classic rock tone. Mine sounds great to me through my Mini 57 Twin, Princeton Reverb or Vibrolux. Can even get a nice crunch on rythym.

If you don't sort them for gain you might still have something outside optimum, even if you get bias in the circuit right. If it varies a lot, that would tend to suggest an unstable chip, and as they're a glass/epoxy envelope it's very temp-sensitive and easy to kill with a soldering iron.

There's no new AC128s being made, or OC44s. They're all old ones. The repro chip is the NKT275, although NTE is making germanium new chips. As I said, I've used NOS 2SA182s.