Build the World’s Wickedest Overdrive
(for less than $30)

"Who are you callin' ugly?"

UPDATE: My thanks to reader William Badjek, who found in error on page 31 of the v01 project file, which would have prevented the tone control from working properly. (The schematics, however, were correct in v01.) If you’ve encountered that issue, please revisit that page of the v02 project file, now available at the link below. My apologies to anyone who got stuck on this!

Hey, DIY victims fans!

Here’s the project file for Tonefiend DIY Club Project #4: the Fiendmaster, a fab-sounding update of the Dallas Rangemaster, the circuit that put the punch in so much classic British rock. If your record collection includes a lot of albums from around 1970 featuring skinny guys with long hair and flared trousers, you need one of these!

It sounds incredible. It’s a relatively easy build. And unlike strict clones, this version runs on a regular modern power supply like the rest of your pedals. It also includes a knob that fades between the original’s bright, snappy Brit blues sound, and the humungous sludgetone that spawned Sabbath. You can round up all the parts from the usual suppliers for less the 30 bucks, or just order a pre-assembled kit from Mammoth Electronics.

View a brief demo video of the final product here. Learn more about the circuit’s significance here. And fill your cranium with everything you need to know about germanium here. Happy soldering!

128 comments to Build the World’s Wickedest Overdrive
(for less than $30)

  • Roger Moore

    As I said in my email earlier today, Thanks so much for the great projects! I’m ordering the Mammoth kit in a day or so. This one looks and sounds (from the video) like a great build.

  • Dirtbagg

    Joe, so which cap should i try for the Iommi sound  :satansmoking:
    I will probably use that and switch to the stock one.
    I have an extra DPDT laying around :what:

    • joe

      Oh, the 104 will put you right there! 

      If you’re using two caps with a switch, maybe try a 103? A good choice if you’re not in love with that bright, Bluesbreaker sound.

  • Dirtbagg

    Awesome, I am going to try that.

    • joe

      You probably know this already, but…

      …with a DPDT, you attach the input to one center lug, and the output to the other center lug. One cap goes through the two upper lugs, and the other through the two lower. It’ll work great.

  • Keith Parks

    So, if I want to use an NPN transistor, I just reverse everything that has polarity?  Diodes, electros, etc?  
    Also, I would suggest, even though it is a pain, to go with a  socket because germanium transistors can’t take the heat of soldering like a silicon can.  Unless you are a practiced and precise solderer (is that a word?), you could easily be out $5 – $7 from wrecking the tran with heat.  Just my opinion because I am a practiced but often less than precise solderer.  I will go with the premise that it is indeed a word.

    Looking forward to building this one – thanks

    • joe

      Yes, Keith — that’s the basic idea with the PNP-to-NPN conversion.

      There’s a NPN schematic on page 7 of the project PDF — just follow that. If you have a good transistor, it’ll sound killer.

  • Roger Moore

    Hello fellow Fiends! I am a long time guitarist/brand new DIYer who is here to learn a bit about FX circuits. My newness means, I of course, have little to share when it comes to building little electronic wonders, but while experimenting with Project #1 (the Bad-Ass distortion) I came up with this little trick using my loop pedal (a VOX dynamic looper  in this case) that I thought some of you may like trying. Although some may already do this. I plug my guitar straight into my looper and then out from the looper into a circuit on the bread board. This way I can make a loop and then put down the guitar while I madly go about twisting knobs and popping components in and out of the circuit on the bread board. I think it’s much easier to be objective and really hear what effect any changes are making to the sound when I am not actually playing the guitar, but letting the looper do my dirty work. Well I do hope this makes sense and that some of you may find it a useful technique to apply to your tone bending madness. I will now go back to my  mad experiments. Thanks again Joe!

  • joe

    That’s a great idea Roger — one I’m going to steal starting today.  :thumbup:

    Only things to add: Make sure the output level is close to what it would be bypassed (some loopers have a independent gain stage) so you can get an accurate read on the dynamics. And plug in your guitar once in a while just to get a feel for touch response.

  • Mika

    Quick question. I’ve breadboarded the circuit as described (twice now, actually). With either input cap 104/472, I seem to require a LOT of guitar output to get anything out of my amp. Particularly with the 472, I need to hit a big chord really hard to get any noise at all our of my amp – it sounds as if I have a very aggressive noise gate ahead of the circuit. It doesn’t seem right. Any suggestions?



  • Mika

    Oh, nevermind. Problem solved. The multimeter is my friend.

    Great sounding pedal!

  • Mika

    Well, between shopping and dinner it took an entire evening to get it soldered and boxed up. Hardest thing was literally fitting the mess in the box without shorting something. Learned some lessons in wiring, that’s for sure. I will post my own demo sometime tomorrow, great build, Joe!

  • Mika

    So, here’s a quick little demo of the pedal. My wife and I named my one the Rarrmaster 2000. I felt that blending towards the 104 cap added more ‘RARR’, so the name kind of stuck.

    The demo is below. I am running a MIM Stratocaster, bridge and middle pickup to a Line 6 Pod XT Live running a model of a Roland Jazz Chorus 120, no effects, and all settings at 12 o’clock. The cleanest, most neutral tone I could find, so what you’re hearing is 100% pedal.

    I found that unlike ‘modern’ distortions, which you can pluck a not softly and get a smooth tone, you really had to dig in to get the distortion to ‘stick’ in this. This encouraged aggressive playing, which is not at all a bad thing. I really enjoyed the lower gain & 472 setting, just to give the guitar a little character rather than full blown distortion – and of course, the high gain & 104 for the RARR. 

    I had a blast with this! Look forward to more!

    • joe

      Nice looking build, Mika! I’m glad you dig it, and I think you observations are spot-on.

      Unfortunately, the sound cloud link isn’t working for me yet — I get an error message.

      Yeah, the 104 is TOTAL “rarr!”

      rarr tee

        • joe

          Got it! Cool! 

          Man, I love the way soundcloud lets you label section of your audio file. I’d use it throughout the site, except it requires Flash, and is therefore mobile-hostile.

          Now I want to hear it through a darker, tubbier amp simulation, ’cause that faux-Roland can gets real nasty!

          Also, make sure to try this pedal through analog amps. I’ve used the circuit to good effect with simulators, but in this particular case, a lot of the magic has to do with how the pedal interacts with the front end of the amp.

  • Bear

    Question: does the Mammoth kit include the transistor? The description is a little vague.

  • Tonechaser

    Thanks for the build Joe. My playing has been seemingly stagnant for a bit, tried a few OD’s to change things up a  little to no avail but this circiut broke my funk. Mad fun on both ends of the sonic spectrum.

  • piu

    Anyone knows if Mammoth has some international shipping ? Couldn’t find in the site. Really interested in this one.

  • Sam Geese

    Hey Joe

    Say, what’s up with the password protected thing?

  • Sam Geese

    Well, it’s gone now.  
    Under “Recent Posts” there was an entry that, when you clicked on it, you had a box in which you were supposed to type a password.  
    Now it’s not there.

  • I spent 4 hours tonight transferring mine from breadboard to box. and everything works but the tone knob 🙁

    I can turn the knob to any point but all my signal goes through the bassier cap. I’ve checked about 50 times now and I can’t see what I’ve done wrong. Lugs 2 and 3 (left and center as seen from below, as in your photo) are connected to the input and to the 104 cap. Lug one is connected to the 472. That’s what the directions say… The final schematic diagram shows 2 and 3 connected to the 104 and 1 connected to the 104. I would expect that to reverse the behavior, but still work. 

    Wait, does the pot just add one cap value to the other? If so, I can imagine that blending in the big cap on top of the little cap would have a much more noticeable effect than the other way around. Maybe I just need to reverse the caps (which is going to be difficult) to get it to work right.

    • joe

      Yup — flipping the caps should do it. Two pot lugs and the input should connect to the smaller value cap.

      • Cool, that worked. I also got the stereo jack ground terminals mixed up, so I fixed those and now everything works (well, I haven’t tried the AC adapter yet). Now that it’s not a mess of wires that’s going to fall off my desk if I do anything, I’m going to enjoy playing with it. I’ll post some clips when I get a chance.

        • joe

          Yeah, on my first builds, I got ALL those things wrong, usually three or four times. (I remember squinting at wiring diagrams for the big 3PDT footswitches, stumped about the eight connections!) But trust me, those details will become second nature after a few builds. 

          Anyway, glad it worked out, and I hope you dig the way it sounds!

        • joe

          Oh, another thing: I always have trouble deciding which is the best way to arrange that tone control, which is bright/thin on one end of its range, and fat/thick on the other. As you advance the knob clockwise, is it better to have the brighter/thinner tone emerge, as if the pot were a tone control? Or better to have the fat/thick sound emerge, as if it were a gain control? 

          Anyway, if you prefer your control to behave in the opposite manner from how it’s wired, just reverse the connections to lugs 1 and 3 of the tone pot. Use this technique anytime you want to reverse the action of a pot.

          • I like the brighter-as-you-go-clockwise way, personally.

            You should double check your PDF, because the instructions on page 33 say to connect to the 104 when you meant the 472. I’m not upset, though, I had a lot of fun building this and learned a lot from it. I’ve breadboarded a few projects before but this is the first one that I’ve followed through with to completion. Thank you for explaining so many important things in your instructions. I can’t wait to build something else.

  • joe

    Thanks so much for catching that, William! My apologies. I’ve fixed the mistake in v02 of the project file and added an update to the post. :cuss:

  • I had made a mess of that part of the circuit to begin with, and was a bit flustered at how I could fix it. Then I realized I had lots of empty holes in the perfboard, and all it took was moving the input and pot wires and then using a jumper or two to route them to the caps properly.

    I really like this pedal. The tone control gives a really wide range of tones, and I think it’ll be very handy for recording. But if I keep my vox amp just below the overdrive level and turn the tone on the pedal up just enough to get past the muddiest/fuzziest setting, I get a clean and full sound with ridiculously long sustain that breaks up if I dig in more.

  • joe

    I’m so glad you dig it. I think it’s pretty awesome myself. And it’s sort of MADE for Vox amps. Actually, that may be literally true! 

  • Brian Moeller

    Hello. Thanks for all the great info! I was able to really get a feel for using the breadboard.
    However, now on perfboard, Im having some problems: First off I cant figure out the right way to pop in the transistor. Pretty sure the base is center pin, but swapping the top and bottom pins yields two different results. One position gives a pretty transparent tone, the cap switching pot works but other than that there is not much in the way of distortion. The other position yields a sound that is fuzzy but extremely clipped like a bad radio with poor reception, only really low and loud notes would pass signal.
    But, while fiddling with the volume pot, I shorted the leads with my finger and a pretty good tone came out, still the choppy breakup but with a pretty good sustain behind it. I tried a couple configurations of the volume pot with different wiring and jumping the pins with a resistor, and got close to the “finger short” tone but I’m afraid I’m barking up the wrong tree. Suggestions?

  • Mika

    Hey Joe,

    I had a blast building the Fiendmaster and I’m getting really into pedal building. I plan on ordering a bunch of components, and based on what I learned, putting stuff together and seeing what happens. My problem is, I have no idea what to order. Myself, and probably all the other newcomers to this, have no idea which components are commonly used in pedals. I would love if you might compile a list of, say, the 10 most commonly used resistor values, the 10 most commonly used capacitors, most common transistors, pots and anything else you might require. Some of them may even be used multiple times in circuits – you might suggest stocking up on multiples of those.

    You might even put up the kit on mammoth electronics – any beginning pedal builder could buy the part kit and the breadboarding kit and get started!



  • Brian Moeller

    I’m quite a noob… that said I looked at several pedal circuits that looked cool, lots of projects at I made some parts lists of thing to build and bought in bulk bags at
    You can get bags of  200 resistors of like 8 bucks. Everything is real reasonable and if you look at a couple fuzz circuits you can easily see which values keep popping up. Buying in bulk is definitely the way to go, a bag of 200 costs 2$ more than 10…

  • Brian Moeller

    I figured it out, thanks anyways. Sounds pretty good! I cant wait to put it in an enclosure and try it on the AC30… One thing though, I’ve checked – and in some cases resoldered – power and ground bus connections and I am still getting a pretty wicked hum. Could just be the monitoring setup, could be the lack of metal enclosure to ground the thing. Any suggestions?

  • Dave

    Hi I just wanted to this is a great series! Your write-ups are broken down very well for beginners, I wish I had found these sooner. My only complaint is that you stopped including a bill of materials after project #1. I look forward reading more. Thanks again!

  • Rich

    I tried the stock circuit and with the 50K Ohm resistor and AC128 transistor in the kit it had a pretty high level of hiss.   I have it going into a Epiphone Valve Jr head and Celestion Modern Lead 70 12″ speaker.   Driving it with a Gibson SG Special 60’s tribute guitar.

    Went into the old parts drawer and found a RCA 2N388 NPN Ge transistor and a 10K Ohm log pot.  Used the negative ground version of the circuit and it is low noise and very cool sounding!  Basically a Rangemaster with negative ground.   Will be putting this into the Mammoth Electronics kit and red baron box.

    Thanks for the cool projects! :thumbup:      

  • Brent

    I am up to page 17 of the Fiendmaster, Project 4v02. At this point, I am getting no signal from the guitar to amp. If I bypass the circuit, I get my normal guitar tone. Checking the power and ground busses, I do get full 9 volts. I double checked each step up to this point and everything seemed correct. Still no signal. I took the circuit off the breadboard and reassembled it step by step. Still nothing. Do you have any suggestions for troubleshooting at this time in the project?

  • Brent

    I made the tool and began testing the breadboard connections. As soon as the emitter of the transistor is connected to the circuit, there is no guitar signal to be found anywhere except with direct connection.

    • joe

      Do you hear audio on the transistor’s base (middle pin), where the signal enters the transistor? Ideally, that should sound pretty much like your direct symbol, while touching the probe to the collector should be relatively loud and distorted. 

      If you hear tone when touching the base, but not the collector, triple-check all the connection to the transistor. Also, make sure it’s not in backward (i.e., flip it around 180 degrees).  

  • Brent

    When the collector and emitter were connected to the circuit, there was no guitar signal at the collector or emitter (or anywhere else) Switching the collector and emitter had no effect. Is it possible that the base is not the centre connector?

    I just removed the 2 resistors connecting the base to power and ground, and now I have a strong signal.

  • Brent

    What do those resistors do? Is it safe to have them out of the circuit?

  • joe

    Did you buy the Mammoth Electronics kit with the AC-128 transistor? Then it should be as labelled.

    But if you used some other transistor, try the different combinations — there are only six possible arrangements. And I assume you’ve verified that you’re using a PNP-type transistor. The circuit with not work with an NPN. 

  • Brent

    I did buy the mammoth kit with the AC128

  • Brent

    R1 and R2 are out of the circuit right now and I am getting lots of gain and fuzz. I am not sure if it is the “fiendmaster” sound, but something is happening!

  • joe

    Well, if you like it, box it up! You may have invented a new pedal. 🙂

  • Brent

    Thanks for the help. I think I will strip down the breadboard tomorrow and start again from scratch. (I may try replacing R1 and R2 first in case the resistors are defective.)

  • Brent

    I have reassembled the circuit on the breadboard. At first  I still had no result. I moved the transistor to another location on the breadboard and began swapping the hookup to the transistor using jumpers. It turns out the transistor had the opposite pinout with the collector and emitter being swapped. (It was the AC128 from the Mammoth kit) :whatever:  Thanks again for all the help.

  • Brent

    Should page 29 and the last line on page 28 refer to C2? and not C3?

  • Brent

    Should page 33 refer to C5? I am guessing the longer leg of this cap goes to the power bus (+)?

  • Brent

    Since there is no volume control on this one, does the output wire from the perfboard go directly to the top left lug on the footswitch? I connected it there, but I get no sound from the pedal. The LED lights up, but that is it.

  • joe

    Yes, that’s correct. If you want to post a pic, I’ll take a look.

  • Brent

    Here is a shot of the interior and some views of the perfboard. I mirrored the center shot of the perfboard to make it easier to compare to the top shot

  • Brent

    I only meant to mirror the center image of the back of the perf board but I see that I forgot to correct the bottom one.

    Does it matter where in the circuit the D1 (Circuit Protection) and C5 (Noise Reduction) go? I just realized the schematic shows them close to the input while I  put them close to the output. 

  • joe

    Nope, the placement of D1 and C5 should have no bearing on whether it works or how it sounds (unless they’re shorting out something else).

    Try this: Use the continuity function on your multimeter, which beeps when it detects a connection. Touch one terminal to ground, and touch the other to EVERY component that, according to the schematic, connects directly to ground. They should all beep.

    Next, flip over your perfboard and start touching all the parts the should be connected and verify that they beep. Then touch all any clumps of wires that are close together, but are NOT meant to connect, and make sure you DON’T hear a beep. I’m most concerned about the connection at the center of your board, surrounding the transistor, since they look like they could be touching where they shouldn’t. If they are, use a small soldering iron tip to separate them, or scrape a clearing between them using a small screwdriver. 

  • Brent

    I found the problem. There were no shorts, but the center pin of the transistor socket was not connected properly. The solder let go under the mass of wires, but the assembly was so stiff it had seemed solid. I now have sound. I just have to figure out how to shoehorn the whole thing into the box and troubleshoot a loud pop when the footswitch is engaged.

    • joe

      Yeah, those crowded connection around the transistor are always a trouble spot. Glad you figured it out!

      Worst case on the box: Order a larger 125B or 1590BB enclosure, and save the 1590B for another project. 

  • Brent

    The pop I am experiencing seems to be capacitor related as it dissipates after a number of clicks, but comes back again later.

    I may just build a second one of these, this time reversing the tone control so that it growls more as it is turned up. Is it normal for the gain control to go all the way to silence?

  • joe

    R4 should remedy the switch pops.


  • Brent

    Would it hurt to solder another 1M resistor between the input and ground right at the input jack? R4 seems to be correctly connected but I am still getting wicked pops

  • Devin

    Maybe you can help me. I’ve built it, Rebuilt it and rebuilt it again and i still cant get it to work. it just pops cracks and fizzes. kind of like a dying battery. Please help!! I want this to work SOOOO bad ha :cuss:

  • Brent

    Devin: Try reversing the collector and emitter on the transistor. I found the pinout on my transistor was opposite to the instructions.

  • Brent

    I have now built a second Fiendmaster and it has exactly the same issues as the first one. The pinout on the transistor is opposite to the pinout in the project PDF. It also has very loud switch pops. I am going to try adding another resistor to ground after the output capacitor to see if that will eliminate the pops. I will comment again after I try that

  • Brent

    SUCCESS!! I soldered a 1.0M ohm resistor between the output and ground. No more switch pops and the circuit is quieter as well!  :smirk:

    • joe


      Many stompbox schematics include a resistor on the output as well as the input, and many do not. I tend to leave it out — but probably won’t from now on, since you have provided the first empirical evidence that the output resistor actually DOES anything. Thanks! 🙂 

  • Devin

    Brent: I will try it and see how it goes. Keep you guys posted! Thank you!

  • Gavin

    Firstly, many thanks Joe for such a great blog. Your PDF instructions for the DIY pedal projects really make sense to me and have eased the learning curve tremendously. Bloody well done!

    I’ve breadboarded the Rangemaster. Like others have said, the transistor pinout is backwards, so once I got that sorted I was up and running.

    Something I noticed when playing with the circuit is that the resistor from collector to +9V (the one in parallel with the polarised cap) may not be necessary. I replaced it with a jumper – the circuit still sounds the same but has MUCH less hiss.

    Do you know why this happens?

  • Gavin

    OK, finished my build. Had an issue where the pedal only works with a battery, not my One Spot adaptor. Never worked out why…

    Otherwise, worked first time! Awesome!!! :thumbup:

  • Gavin

    Scratch that… had the + battery wire and the wire to the circuit backwards on the DC jack. All good now.

    I should learn to read. :shake:

  • Hi there!

    I just can’t state how inspirational your site is, Joe! You got me hooked on the Broadcaster wiring, and I definitely have the pedal- building bug in me now! It’s like building models you can stomp on later!

    I got the Mammoth electronics kit, put it together, and it worked briefly (after several attempts where no sound would come out…) However, when I closed the box, I’d get no signal when engaged,, although the LED lit up and the bypassed signal was there. On opening my baby, I noticed the battery was VERY hot. Yup, got me scared… I’ve checked and couldn’t find the fault (maybe the connections to the center of the transistor?)

    Anyway, here are some annotated pics of it in case someone can tell. Any ideas? Thanks! 

  • Oh, and a picture of the back of the perfboard, also annotated:

  • Hmm… I’ve been checking things, and it seems that the R1/R2/C1/C4 connection to Q1’s base is the weakest bit. But I already cut the elements’ legs pretty short. Would it be a good idea to braid them and have a wire to the transistor’s base, or would it add noise?

    Thanks a lot!! 

    • joe

      Oh, I braid them all the time — shouldn’t hurt as long as the correct connections are made. And if it’s any consolation, the spot where the signal enters the Q1 base is ALWAYS a bloody mess!

  • Oh, you totally made my day… I thought I’d messed it up irreversibly! And the pics really don’t do justice to the mountain of solder in the base!

    Thanks, Joe! 

  • Meh… I braided them, put a jumper to Q1’s base, even rewired some weak-looking stuff, but no dice! The LED lights up, but no sound when the effect is on. I even tried reversing the transistor in case I had read the pinout wrong. I’m actually thinking of getting replacements for R1, R2, C1 and C4 and try to redo the whole thing.

    Here’s a pic of the perfboard’s back. I don’t see any blatant bad joints (sloppy and ugly, sure, but they look solid and shiny, don’t they?)

    Thanks for all the help!

  • Hi Joe,

    I’m completely lost. I got a multimeter to check all the connections were ok. They all seem to be, and nothing’s shorting either. But I still get no sound, even though the LED lights up and it’s loud and clear with the effect off. I’ve noticed a couple occasional pops with the effect on, though, but no guitar-like sound. 

    Could you please help? Any ideas on how to test this further would be an absolute godsend!!

    Thanks again! 

  • MNMagnus

    Hi Joe,
    I have the circuit setup as shown in the schematic, but I don’t get any output unless I really hammer on the strings. I removed R2 and now I get drive, but I’m guessing that R2 is there for a reason so I put it back in and tried reversing C & E in the AC128, now I have full output, but no drive.  I’ve checked the resistor values for R1, R2, and R3 and they all seem to be correct. Any ideas? Thanks.

    • joe

      It sounds like it may be an issue with one of the transistor connections.

      A couple of suggestions:

      1. Some people found that the transistors included in the kit were oriented in reverse from how they’re illustrated in the project PDF. Try flipping it 180 degrees.

      2. If that doesn’t work, and if you’ve double-checked all the connections using your multimeter’s continuity function, try going through the circuit with a signal probe, which you can make for a few cents. Instructions are here.

      Let me know how it goes! 🙂


      • MNMagnus

        I checked through the circuit, I reversed the collector and emitter and I have output, but it seems like there isn’t very much overdrive compared to your demo video, is it possible that this circuit doesn’t like solid state amps? (My test bench setup is a stock Ibanez RGT42 into a Crate G60XL)

        • joe

          I can’t vouch for how it will SOUND through SS amps, but it should be screaming loud. I’d quadruple-check all the values, check all connections with your multimeter’s continuity function, then whip up an audio probe and sound your way through the circuit component by component. 

  • Bob Reedy

    Hi, Has anyone laid out a circuit board for the final schematic?  Just wondering?  Bob

  • joe

    I have had a lot of fun breadboarding this circuit but I am wondering if anyone else has the same issue i am having.
    With the original value of R3 (3.9k) I get a farting , poppy noise. I have tried up to a 47k with better results.
    I think I have settled on 22k being the best sound so far but I dont think I am getting as much drive as I had hoped.
    I have reversed the transistor but that is not the problem.
    Any idea’s.

    • joe

      Yes, I do have an idea: In any case like this, wire up a pot with a larger value than the indicated resistor, and twist it until it sounds great. Then remove it from the breadboard, measure the resistance, and then install the resistor with the nearest value.

      A pot is really just an adjustable resistor. Solder wires to lugs 3 and 2. In this case, connect the wire from lug 3 to power and the wire from lug 2 to the transistor’s collector. (You don’t need lug 1 in this case.) Theoretically, you could use any value pot, but if it’s too large, it can be tough to dial in smal increments. I’d try a 25K or a 50K.

  • joe

    Thanks for the reply…..
    That is a great idea and I will definitely do that but I am still curious as to why my value at R3 need to be so much larger than listed.
    Dont get me wrong , I am loving the creamy sound I am getting , blows away the silicon fuzz i built last month.
    just curious , thats all.

  • Digital Larry

    R3 sets the DC operating point of the signal on the collector.

    R1 and R2 form a voltage divider from 9 volts, putting the base voltage at 9 * (470/(470 + 68)) or 7.9 volts. The emitter voltage will be about 0.3 volts higher than this (typical Vbe for a forward biased Germanium transistor), or 8.2 volts.

    (9-8.2) volts across 3.9k is 0.2 mA. 2 mA flowing through POT1 at 50k puts the collector voltage at 10 volts. Except, whoops, it can’t actually go any higher than the (emitter voltage – Vce(sat)) – which is the saturation voltage from emitter to collector – Vce just can’t go any lower than this, unless some external thing like a short circuit is making it happen. For a silicon transistor Vce(sat) is about 0.3 volts and (I’m reading) 0.2 volts for germanium.

    So at DC, the transistor is in saturation (aka slammed into the rail) and any signal coming at the input is not going to make the output wiggle until the current decreases enough for POT1 to start pulling it down.

    With R3 at 22k, this changes to:

    Ic (collector current) = 0.8/22k = 36 uA
    collector voltage = 31 uA * 50k = 1.8 volts

    So now the transistor is not saturated at idle and you get some linear range before it starts slamming into the rails again.

    Note that the combination of R3 and C3 cause the AC (signal) gain to increase. By how much depends on the internal resistance of C3 and the emitter resistance of Q1, neither one of which is easy to determine, and will tend to vary from component to component. But the RC time constant creates a low-frequency roll off, at 1/(6.283 * R * C) or 0.3 Hz for 22k at R3, or 2 Hz for 3.9k. Both of these are well below the lowest audible range. You could also do some tone teaking by reducing the size of C3.

  • Digital Larry

    Here’s a fairly geeky explanation of the common-emitter amplifier (which this thing is):

  • Digital Larry

    Here’s another article explaining the RC time constant and its effect on cutoff frequency:

  • joe

    ok , the breadboard sounds amazing, now is the tricky part for me.Trying to figure out the wiring when including the switch and battery connections. My first attempt did not work but that was before I breadboarded the circuit. I just winged it. I will report in day or two.

  • Just ordered a kit, and I’m looking forward to building it when it comes in. I’ve not ordered from Mammoth before, and I’m hugely impressed by their setup. Great ideas all around. Thanks for putting this in motion!

  • Hey Joe, I love your playing in the demo’s!

    I just finished building this up and I am getting low output even with the gain cranked. If I bypass the pedal the volume jumps way up and drops oce I engage it. Could my transistor be shot or maybe its not getting great connection with the sockets? It doesn’t really sound like the distortion/overdrive portion is doing anything. The tone pot works.

    Let me know if you have any ideas. Thanks

    • joe

      Aww, thanks for the kind words!

      Well, the pedal should definitely be loud. Some folks told me that their transistors seem to be wired backward from how I show them in the diagrams. Can you try flipping it around 180 degrees and see if that makes a difference?

      If that doesn’t fix it, start by triple-checking all the solder joints, especially the ones that go to ground. If you have a multimeter, use the continuity function (AKA the beeper) to verify that all connections are good.

      Hope that helps! Let us know how it goes. 🙂

  • I just flipped it around and I get a lot more gain but I get even more hiss/noise. Not the sound of a noisy pedal either. The hiss is twice as loud as the guitar. I think the gain issue would be right now but the noise is crazy. I am thinking my AC128 is DOA. Does that seem reasonable to you? If so any ideas on how to get a new one that works?


  • joe

    If the part is defective, the vendor should exchange it for you. Alternately, you could buy a few different PNP-type transistors and see whether there’s a particular one you like best. (Though when a germanium transistor fails to perform, the symptom is usually low/no gain, not runaway hiss and noise.)

    Here’s the product page at Mammoth:

  • I just swapped the AC128 with a bc560 I had laying around and it worked. It actually sounded kind of cool. So I think the AC128 is confirmed bad. I will try and get a hold of Mammoth. But in case anyone wanted to try the BC560’s work in these pedals.

    • joe

      Cool! In a circuit this simple, there are many transistors that’ll work — and sound good. In my experience, it’s more an art than a science — just pop in different compatible components till something sounds great. Just make sure you’re using a PNP type transistor like an AC187 or AC 127 (both germaniums) or silicon model like the BD560.

      Now, with the silicon transistor, you’re not getting the unique properties of germanium. These include both unique harmonic properties and a relative buttload of noise. But there are definitely a lot of great-sounding non-germanium overdrive options!

  • Craig C


    Awesome project! I just finished building the kit from mammoth, however, I’m getting a lot of static/cracklings. After checking continuity and reflowing all the solder joints, I used a signal probe. The static noises show up at the emitter of the AC128…..sound like a bad transistor to you?

    Seems similar to what Dan D was experiencing, unfortunately I don’t have a another transistor for an A/B…

    Thanks for your help.

    • joe

      Oh, cool! Glad you’re digging the project.

      I guess it’s possible there was a bad batch of transistors — those things happen. The good news is, only germanium transistors are expensive. I’d follow Dan D.’s lead and try a PNP-style silicon transistor such as the BC560. Mouser sells them for ten cents each here:

      …and they’ll arrive at any US address in about two days. If the circuit works fine with that transistor, yes, that would suggest there’s something wrong with your AC128.

      Now, the Rangemaster IS a noisy circuit, by modern standards. You’ll definitely hear a little hiss and noise when you switch it on, even if your guitar volume is all the way down. But if it’s working right, the tone will be so bitching that you won’t mind the noise. But really loud hiss or any sort of scratching/static noises are definitely not part of the plan!

      • Craig C

        Update – Turned out to be a bad AC128. Got a new one and no more static or crackles.

        Haven’t had a chance to really feel it out yet but, so far it sounds fantastic!

        • joe

          Great to hear!

          Anyway, I believe the Mammoth germanium transistors are new-production, which is great, because it means there might be a steady supply of them. I’ve had no problems with the dozens I’ve used, but apparently there are a few bad ones out there. But Mammoth (and every other reputable vendor) will replace bad ones.

  • mwseniff

    The best way to test a transistor is with a curve tracer. You need an Oscope and the curve tracer which can be made with a small low voltage xfrmr. You should be able to find a schematic online for a homebrew curve tracer. You can also test them with a digital VOM by checking resistance between the legs it is a bit trickier and needs practice. Good luck.

  • Maurice

    After a couple weeks of work-related delay, I started breadboarding, and at the first test phase got a blast of noise–not the good kind, either. Tearing it down and going step by step, I found that the 470KΩ resistor was in fact a 470Ω resistor. It measured 470, the code was 470, but the bag was labeled 470K. Oops. I’ll pick up a pack of 470KΩs tomorrow.

    While the blast-o-noise was annoying, it was pretty awesome to figure out the issue by double-checking resistors. (More frustrating was finding out that my little Kalamazoo amp has developed a constant-hum fault.)

    • joe

      Hehe — you figured it out a LOT faster than I would have when I was starting out!

      Though sometimes, mistakes like that lead to cool discoveries. Not this time, though, I guess.

      • Maurice

        I probably wouldn’t have found it other than having the lingering thought of “I wonder if there’s something wrong with one of these component values.” Yeah, it would have been neat to have discovered something, but in this case all that came through the noise was the *click* of capacitance changes of fingers on and off the strings. Maybe I will try a couple different values in there (or maybe a potentiometer?) after I get something working.

  • I got my replacement AC128’s and a few others. I went through 3 AC128’s just to find one that worked and the forth one sounded killer. Better than the other PNP tranistors I tested and the 2 other working AC128’s.

    So buy a few to test them. Overall this pedal sounds fantastic!

    Joe, quick question can I use this with pedal power and a polarity flipping wire? I followed your schematic.


    • joe

      Weird! Either I’ve been real lucky, or some of you have been real unlucky, but all my new Mammoth germanium transistors have worked fine. But yeah, buying a few and picking a fave makes as lot sense.

      Yes, even though it’s a PNP transistor, it should run fine on standard 9v power. NOT REVERSED POLARITY. It’s not a positive-ground circuit that would require reversed polarity. The circuit has been jiggered so that it runs on standard negative ground.

      But if in doubt, just use a battery. I wouldn’t say that for all pedals, but this one has a real low current draw, and should run for many months on a single 9-volt.

  • Agustin

    Hi Joe!

    I’ve been learning about pedal building from your site for a while now, and want to thank you for a building this amazing resource for effects enthusiasts.

    I started out on my first Fiendmaster build yesterday and everything seemed ok, although I felt the output signal to be a tad on the loud side. Then, when i was about to finish perfboarding I realized that my mammoth kit had a 153, .015uF cap, in place of the 103 cap, that connects to the output wire. Being the newb that I am (and with the added fact that I live in Costa Rica and can’t easily buy box capacitors around here), i’m wondering, does this alternate cap value affect the sound of the pedal? Should I send for a 103cap from mammoth just to play it safe? Thanks in advance!

    • joe

      ¿Qué onda, Agustín?

      The output cap (the 103 in this case) filters out lows, though not nearly so dramatically as the input cap. The higher value (and 153 is a LOT higher than 103) won’t hurt anything, though it may let a more bass frequencies through. Try it out and see what you think!

      You’re right — this is a loud pedal. And IMHO, it has to be for the right effect. A compressed-sounding, diode-based distortion like a Tube Screamer works fine with a master volume control. You can lower the output without changing the tone too much. But a minimal germanium circuit like this is all about slamming the front end of a tube amp. While you can always add a master volume control, it’s just not much fun. 🙂

      ¡Buena suerte!

  • Agustin

    Thanks for the quick response Joe!

    I guess I’m kinda married to the 153 now, seeing as it’s already have soldered into the perfboard. I really dig the sound I just kinda felt maybe the loudness was a by-product of that wrong output cap, but i;ll carry on then! Thanks a lot! And how we say here in CR,

    Pura Vida!

  • nate

    Hey Joe,

    Just finished the fiendmaster, and much to my surprise it worked on the first try!

    i’m concerned though, in the above posts, it’s mentioned that this is a LOUD pedal. even when dimed i don’t seem to have a large increase in volume over the signal when the pedal is off. also, there is a LOT of noise when this pedal is cranked. i get that ocean in the background, white noise, high gain sound. no loud buzzes or anything like that.

    from what i read above, this probably shouldn’t be normal. any ideas for trouble shooting? everything looks pretty solid when i went back and checked the circuit and soldering.


    • joe

      Any chance of getting your hands on another transistor or two, and popping them into the circuit to see whether there’s any change? Did you get your parts from Mammoth? I’ve had really good look with the dozens of transistors I’ve got from them, though some readers apparently have received bad ones.

  • Elliot

    i tried this out a while ago when i was looking for an OD and it wasnt enough gain for me though it sounded great, now im hankering for a good boost and thought id give it another spin.
    i had 2 AC128s from Mammoth and both of them worked fine the first time around (once i learned the pinout was backwards), but now both of them sputter terribly either way i hook them up. so i grabbed an AC125 i bought recently and tried it in the pin configuration in the layout, but it also sputtered til i flipped the collecter and emitter… but that means its hooked up backwards..?
    how is this possible?

  • Joe,

    Your diy club docs are the best available online for beginners (easy to read and funny), you are my hero!!

    This fiendmaster really rocks!!

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