R1 and R10 are draining resistors for C1 and C5. When the pedal is disengaged and if input and output are left floating, due to leakage, voltage can build up on C1 and C5 that would lead to loud thumps when pedal gets engaged. R1 and R10 are draining capacitors to help with the thump. Stability That’s it as far as MXR Micro Amp is concerned. On one hand, the circuit looks intimidating compared to the ones using transistors I did before, it definitely has way more components used then the other circuits. On the other hand, with op-amps I can get more consistent results, and it is easier to predict how they are going to behave, even using different op-amps should not be a big deal. The word ‘transparent’ is used to refer to boosts (and overdrives) that do not alter the general frequency content of your sound. Put equal parts treble, bass and midrange into a transparent boost, and expect similar ratios between frequencies out the other end. While a lot of clean boosts are also transparent, some do occasionally offer EQ controls to boost or cut certain frequencies. And some boosts are neither clean nor transparent… C5 there is used for stability at high frequencies. Forming a useful low-pass filter using RV1 and C5 is slightly more difficult than in Micro Amp. RV1 is variable so the frequency response varies depending on the pot position, whereas Micro Amp has fixed R4. Definitely one of the trad-offs. Nonetheless, C5 does not affect frequency response. Reference voltage MXR was bought by Jim Dunlop in 1987 and since then MXR has seen faithful reissues of classic designs as well as continuing to innovate with new designs that uphold the legendary MXR name. They are all built with reliable quality that can be expected from Dunlop products. Today you can find classic and new pedals alongside reliable power supplies, and professional grade instrument cables. Why Should I Choose MXR?

R9 is there to help with stability and help preventing oscillation driving capacitive load (guitar cable may produce about 100pF capacitance per meter). Final thoughts TL072 it is very, very commonly used dual op-amp chip in pedal builds (and all sorts of other audio equipment). It is a dual op-amp and it has a different pin-out so there’s a bit of a difference, it is not a drop in replacement. Other than that, it should be slightly less noisy than TL061 and it uses slightly more current (so maybe battery won’t last as long if you use battery) but other than that, it is pretty much the same for what I’m going to use it for. A secondary function, per the manufacturer, is to slam the front end of a tube amplifier with extra volume to create even more saturated gain sounds than an amp is capable of producing on its own. Again, the M-133 Micro Amp excels at this, too.The second thing you'll see on many of the best boost pedals is some kind of EQ. On some it may be a simple treble cut, while others will go as far as a two or even three-band EQ. Even without an EQ control, a boost will change the EQ profile of your guitar, and the extra gain will add compression. It's mainly this that makes boosted signals sound 'punchier'.

Front end clean channel: incredible amount of volume boost while gradually pushing the preamp tube into clipping. It's fun to find that sweet spot where you have a little bite/grit. Great for RHCP-like cleans. Even at lower gain settings, it adds a sort of fullness to the sound. The most basic boost pedal is just an amplifier stage, so the only variable there would be how much amplification (or gain) it delivers. Most of the time this will be listed as a decibel or dB value, and most dedicated boosts offer around 20dB. One difference here is that I added RF filter (low-pass filter) on the input formed by R1 and C1. Cut-off frequency for it would be around 16MHz, but in reality, because if either there is a guitar directly plugged into the effect, or there is a preceding pedal, they would have their own output resistance added to the equation so the cut-off frequency would be lower. All values I got through simulation and all are approximate. Both pedals look really good in terms of general characteristics. Breadboard Diagram MXR is a New York–based manufacturer of effects pedals from Rochester. The company was co-founded in 1972 by Keith Barr and Terry Sherwood [1] [2] and incorporated as MXR Innovations, Inc. in 1974. The MXR trademark is now owned by Jim Dunlop.

For this, I just go straight from the schematic, I place the breadboard and the most important components first (in this case the op-amp chip). After that, I place all the other components next to the board. I don’t have breadboard diagram for this one, I’ll do it ad-hoc, but lots of it will be similar to what I have for Thunder. Designators MXR/Dunlop initially marketed the Micro Amp as a mere volume boost, and it definitely does a great job as such. As mentioned earlier, activating on the pedal as you play introduces a boost that is as subtle or extreme as you want it to be; as an added bonus, I can attest that I've never noticed any coloration to my guitar tone when using the M-133. Other boost pedals often introduce a midrange "hump" that I, personally, usually don't mind. But it's nice to know I can use the MXR unit to get more of my sound, unadulterated.

Looking at the highlighted part on the breadboard (going from right to left) R9 is connected to R8, connected to positive lead of C6. Then, there’s a jumper wire going to R3. The connection goes underneath R2 and it’s not connected to it. A boost pedal breaks up this length of uninterrupted audio cable and strengthens your signal, without necessarily adding volume in the process. Using a booster as a buffer, rather than a dedicated buffer pedal, also has the added bonus of giving you more control over your signal level. What is a clean boost? I’ll give some effect characteristics, do a breadboarding diagram, then do the actual breadboarding (with bill of material) and finally test both effects out. Characterizing the Effects In this final build, when it comes to simple booster effects, I am going to use Op-Amps. An op-amp is an integrated circuit (a chip) containing several transistors inside of it to achieve a very large gain. But it does so in a way that makes amplifier design very consistent and predictable.I didn’t have 22M resistor, so I used 10M for R1. This won’t make a difference in sound, it will lower the input impedance just a bit, but nothing significant. Trying it out Firstly, a ‘clean’ boost is a boost pedal that doesn’t introduce any sort of limiting to the signal; it responds linearly to its input. With a clean boost, you double the input volume, and the output volume is also doubled. With a limiting boost, that’s not necessarily the case. Reference voltage is achieved by way of a simple voltage divider using R7 and R8, C4 is there to filter out any ripple coming from power supply. This is necessary for single supply op-amp circuit otherwise negative portion of the input signal would be clipped. R7 and R8 have the same value so reference voltage is half of the power supply voltage, so 4.5V. Coupling Capacitors The Series 2000 was a complete rework of the Reference and Commande lines of pedals. They were higher quality pedals, with electronic FET switching and dual LED indicators. They had a contoured, all-metal chassis and an easily removable battery. They had a fully rubberized bottom and were remote-controllable. Most of the pedals had dual outputs with distinctly different sounds.

Jim Dunlop acquired the MXR brand in 1987 and continues the pedal line of original MXR classics, such as the Phase 90 and Dyna Comp, as well as modern pedals like the Carbon Copy and Fullbore Metal. Dunlop has also added a line dedicated to bass effects boxes, MXR Bass Innovations, which has released the Bass Octave Deluxe and Bass Envelope Filter. Both pedals won Editor Awards in Bass Player Magazine and Platinum Awards from Guitar World Magazine. The MXR Custom Shop is responsible for recreations of vintage models such as the hand-wired Phase 45, as well as doing limited runs of pedals such as the Custom Comp.You left out the studio. If, like me, you often like to play solos on a vintage spec strat or tele into a an old-school tube amp with moderate amounts of preamp gain, a clean boost like this is an invaluable tool while recording. I used to be a dyed in the wool TS9 man (and later an 80s SD1 guy), often using them as a colored, dirty boost for solos with fender guitars (like everyone and their mother likes to), but in the 90s I got turned on to clean boosts, treble boosts and even the venerable MXR Dynacomp as ways to add gain and 'cut' (these pedals generally turn your hi-z guitar signal into a fairly low-z affair that drives the cable a lot easier which will add/preserve treble just like a buffer) for a solo sound without sacrificing the bandwidth and signature voice of my guitar. I do this more in the studio than live, believe it or not. Live I tend to dime an AC30 and control everything with my guitar volume knob. Maybe I'll run an always-on boost or buffer if I need a line-driver on a big stage. I used pen and paper before discovering the tool, and that is such a tedious job. With the tool it is really easy to move things around to your liking. I have a different version of the pedal it seems, mine uses LM741. TL061 and LM741 have the same pin-out, so they can be used interchangeably here. That is a great thing with op-amps, as long as you have the correct pinout, almost any will work. Finally – R3, I’m not sure, it’s probably there for stability and/or possibly DC error. The pedal has been around since 70’s, I’m not sure how much the design changed, 741-type op-amp has been around since 60’s. Not sure if it is still needed. Reference Voltage In late 1981, MXR got the resale rights in the US to sell the KIT (M-178), a digital drum machine. In early 1983, MXR released the M-185 [1] MXR Drum Computer, similar to Roger Linn's Linn LM-1 drum machine with individual pads for the instrument sounds and individual volume controls for each sound.