atreidesheir wrote:That is really encouraging.
What is Sherwood Forest pedal pirates? Sound like our kinds of people.
grrrunge wrote:How about the reverse biased diode from base to emitter? Does it have any significant effect on the sound, or does it just stabilize the temperature sensitivity of GE transistors?
grrrunge wrote:I tried to build a NPN Fuzz Face a couple of nights ago - without much luck. Perhaps it's the layout?
I built two emulators from a set of 2N3904's and a set of BC550's and hFE was easily controllable. Using my multimeter i trimmed one to 70hFE and the other to 120hFE, and built them into HBO's supposedly working NPN Fuzz Face vero layout.
Result: Almost no sound. I managed to get some sputtering decaying notes across, but nothing pretty.
Step 1 from here is trying the emulators in a NPN rangemaster build, just to verify they're actually working.
Step 2 is creating a new FF board layout from Madbeans Hipster schematic. I trust that schem is verified
I remember Mictester writing something about a diode or resistor from base to ground to simulate leakage, which should help turn modern non-leaking transistors on, but i can't remember where. That might be important as well as emulating leakage has got to be part of the GE-sim circuitry, right?
Any other great tips on biasing, or verified schematics of NPN fuzzes are greatly appreciated. I'm determined to get those pups to make some real noise!
induction wrote:What you describe sounds like a mis-biased transistor (Harald does really good work, so I suspect the layout is fine, but I haven't tried it).
induction wrote: I forgot to mention that the 2.7k resistor in my build was chosen by trial and error to give me the bias range I wanted on the collector of the Q3/Q4 piggyback.
induction wrote:If you're using this layout, then adjust VR1 until you get the bias you want (a 10k trimmer should be enough, but if not, try a bigger one). You want something near 4.5V for classic fuzz face sounds, but you can adjust it to taste or use a pot in series with a fixed resistor (like I did) to give you a range of useable sounds.
induction wrote:If that doesn't work, try my layout, or try IvIark's, which has onboard trimmers for dialing in the piggyback gains.
induction wrote:With a battery, the pedal is very quiet at all settings. With an adapter, it hums more than my other dirt pedals. For some reason, the hum jumps up a lot when the guitar volume is rolled all the way off. I haven't figured out how to solve that yet, so I just use a battery.
induction wrote:induction wrote:With a battery, the pedal is very quiet at all settings. With an adapter, it hums more than my other dirt pedals. For some reason, the hum jumps up a lot when the guitar volume is rolled all the way off. I haven't figured out how to solve that yet, so I just use a battery.
With an unregulated 9V adapter, the increased hum at zero on the guitar volume goes away with a small resistor in series with the input (I just turned up the Smooth knob a tiny bit, so I'm guessing about 100 ohms should do the trick), but otherwise the adapter hum is unaffected.
Last night I breadboarded a regulated and filtered 9V DC supply (using an unregulated 12V adapter, a 7809, 22 uF on the source voltage, 22 uF and 100 uF on the output voltage). The Javelina is as quiet with this supply as it is with a battery, at all settings.
atreidesheir wrote:Could I get a similar effect with a 2n3440 low gain (@50hfe) silicon transistor with a 1n34a tied to the base and collector to simulate leakage?
That turned out to be correct in concept, wrong in detail. I forgot the internal rbe of the transistor junction. What a bipolar transistor base-emitter junction does that a diode junction does not is to have an equivalent nonlinear resistor arising from the transistor action. This internal resistor causes the working junction to have a higher voltage at the same current as the dummy junction; looked at the other way, the dummy junction eats more current than the working one at the same voltage.
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