Not overly bright, but visibly. I recommend you replace the Q2 diodes with LEDs if you play bass, the Q3 diodes with germanium if you play guitar. So let’s talk about the mods I’ve added here: Well the holy grail of BMPs is generally considered to be the Green Russian. These tend to emphasize highs and provide moderate compression. Here’s what I came up with for my prototype build: There are two switches hidden in the fluff there. I built some sampling boards where I could use dip switches to quickly test various diodes: Each of the two identical boards at the bottom are used for just one pair of diodes. There’s nothing wrong with them, but it’s fun to experiment and here’s a spot where you can completely change the sound of the pedal very quickly. VERY worth doing if you play a lot of bass. This calculator is used to determine resistor values for the basic shunt feedback transistor circuit to set the proper DC operating point. This mostly works by massively overloading Q1, but if you bring the Sustain control up a bit, you get increased compression via the negative feedback loop on Q2, resulting in more and more of a square wave and increased compression on the extra noise generated at Q1 between notes and it all gets very overblown and wild. They work nice on Q3 if you’re playing guitar though. They’re functional equivalents. If you’re playing solo, or your band only has one guitarist, this is a great sound. But I tried a few here. Luckily, the trimmers didn’t necessitate making the board any bigger, and the spacing is correct to just install a resistor instead of a trimmer, so it’s no loss. The Hfe and leakage of the transistors will be important to the calculations. This group can fairly commonly have voltage thresholds from around 500 mV to nearly 1V, though most fall in the 600-700 mV range. Each transistor's emitter of the gain stages of the Big Muff is linked to the ground by a resistor (either 100R or 390R, R12 & R16). The Vbe values are the voltage drop across the transistor junctions. The Electro-Harmonix Big Muff Pi pedals from the 1977–78 period can command big bucks. Silicon is actually a fairly broad group. That’s just what I like. There’s a drop in frequency response across the mid-range, which causes the bass and treble to be accentuated. Everyone knows what the BMP is and rather than re-hash a bunch of boring history and probably get half of it wrong, you should go read this page if you want history. If you find your BMP a little too congested, that will help, though you’ll be doing a bit of dead bug wiring to make it happen. It’s two fewer resistor swaps than the emitter mod, and it doesn’t remove the bright, harsh assault that the NYC provides. AMZ-FX Home Page The only place you won’t find that is on a very modern heavy metal oriented amplifier where boosted mids are popular and that’s a story for another time. If you do the feedback loop mod, you need to do this one. Would repeat, depending. The 1N914/1N4148 pair is actually pretty good. The Big Muff Pi (π), often known simply as the Big Muff, is a fuzzbox produced in New York City by the Electro-Harmonix company, along with their Russian sister company Sovtek, primarily for use with the electric guitar.It is used by bassists as well due to the Big Muff's squeaky frequency response. The two mods are highly interactive, and the noise suppression mod will not only allow you to get some of the higher feedback guitar tones without the noise between notes, but it also slightly changes the tone you get from the feedback loop. Guitar Effects Blog Or some combination. So we’re going to use a switch. If you have a really bright single coil, like a Telecaster or a Stratocaster, these can sound really cool. There’s a feedback loop mod that connects the collector of Q3 to the base of Q1. It’s just a prototype. ©2015 Jack Orman So let’s look at what I built, which mods I selected, and what I learned in retrospect. Yeah, the off-board wiring could be neater, but there are 4 pots, 2 toggles, and the 3PDT so come on, eh? It’ll do the same thing. LEDs are yes, the same kind that indicate whether the pedal is on or off. And yeah, they actually do light up as you play notes. If you mismatch within a pair, using two diodes from different classes as listed above, you get asymmetric clipping. Lab Notebook Main Page Its impact on tone is way more noticeable with the feedback loop active than without it. The diodes in an old perf board Triangle I own measure 0.481 - 0.487V, and diodes in a 1971 Big Muff measured 0.560 - 0.572. I get confused thinking about tapers and I haven’t tried it yet myself. If you have two guitarists using pedals like this, they’ll blur together. If there's no emitter bypass capacitor, the gain of a correctly biased single transistor stage is determined by the ratio of the collector resistor to the emitter resistor - it's … It’s warm, thick, but the highs are still clear and pronounced. Right. So it can be VERY nice to bring back some of those mids. That lasted for a short time, then everybody wanted longer and longer sustain, so I built another transistor on the front end, and I called it the Mark II Tone Bender, the Professional Mark II." So let’s put a 100k trimmer in there, and we’ll have one of the On positions add another 100k on top of that, while the other just connects to the trimmer directly. You’ve got two opposing orientations at Q2 and Q3, so potentially, 4 different diodes. (see below). All Rights Reserved The BMP has 2 stages of negative feedback clipping. This group can fairly commonly have voltage thresholds from around 500 mV to nearly 1V, though most fall in the 600-700 mV range. If you have trouble getting the proper settings. The primary difference between the Green Russian and every other version is in the emitter resistors. I’ll build you one with the mids control and you’ll still have a fat wad of cash left over. Doing so without adding another pedal adding more gain and more noise and more tone suck is best. Feedback loop. This is often described as “more tube like”, because tubes are inherently slightly asymmetric in their clipping. Regardless of whatever else you do, you should do this mod in every BMP build you do. To tame that a bit, it’s recommended to use a resistor in the negative feedback loop, but values from 0 to 100k or higher have been recommended so how can we choose? Germanium diodes are too dark for a bass guitar with this circuit. The semi-completed main PCB is shown above it. Instead of just an on/off switch, we can use an On/Off/On SPDT toggle. When it’s all the way left, there’s a 1M resistor in series and the effect of the feedback loop is essentially eliminated.
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