MI Audio
Category Archive: R&D Lab
THE GREATEST 9V PEDAL POWER SUPPLY EVER?
There's always tinkering happening at the MI workshop and this is a fine example of the R&D that happens here.
Before our NAMM trip earlier this year, we were putting together our pedal boards and struggled to find an ultra-low noise, super compact COMPLETELY ISOLATED*** universal 9V power supply. There are some good options out there, but power supplies need not be the size of a lunch box with the right design.
We've been throwing around the idea of making a power supply for some time after making a few for the workshop. But it wasn't until recently that we successfully built a working prototype, shown in all of its naked glory above. With some hand-wound transformers and a very efficient switching transistor, we have come up with a 9V power supply with as many output taps as required, at any current required, and each individual tap is isolated from each other - all able to fit into a standard Crunch Box size pedal.
***ISOLATED GROUND!!! This term gets spouted in the marketing with every power supply on the market and is incorrectly used by a lot. Let's try and clear this up.***
The aim of your amp/guitar/pedal set-up is to have a single ground path between any two ‘points’ in your signal chain. If you’re using a power supply with a common ground between all the outputs, then you can have multiple paths between any two points. An isolated power supply does this by keeping every the ground of every output tap completely electrically isolated, and relies on the ground connection between your devices to maintain the same reference. This prevents your guitar signal ground from connecting to multiple pedals at the power supply. If there is no isolation, ground loops can occur and that's when you get that nasty hum and buzzing destroying that tone you've worked so hard to get. There's nothing worse than playing a gig with a noisy, "dirty" setup. This is more common in "daisy-chain setups" and non-isolated power supplies.
Most offenders of the misuse of the term "isolated ground" will say that the ground of the input is isolated from the ground of the OUTPUTS AS A WHOLE. However, the grounds of these multiple outputs are actually all connected together - you might as well use a daisy-chain/wall-wart set-up as the ideal power supply should have isolated grounds for EACH OF THE OUTPUTS.
The amount of current available at this stage is dependant on the current supplied at the input. For our proto, 2A is supplied across all THE SUM of all eight output taps. That means, if you have five drive pedals taking 10mA each, the remaining three output taps have 1.95A available. This allows a whole pedal board (of eight pedals) to be powered comfortably. This 2A can be increased to 20A if we wanted, but 2A is normally sufficient for most board uses.
We hooked up our prototype power supply with our drive pedals, including the PNP germanium Neo Fuzz with great, super-quiet success. No need for reverse polarity leads - the pedal power supply takes care of that for you.
Now, who wants one???
NEW SUPER BLUES PRO!
This feedback saw the birth of the Super Crunch Box idea (that is still in prototype phase), and now the Super Blues Pro!
The Blues Pro has always delivered in the low/mid gain overdrive tones, and sounds great through any amp or guitar/pickup combination. As the gain goes up, you can get more compression and super-squishy fuzz tone at a flick of a toggle switch. The mid-focused TS sound is a classic found on a lot of blues and rock recordings, and the Blues Pro took that initial design a step further. That is how the Super Blues Pro was tackled - but what could I add to keep the pedal true to its origin, but extend it a bit further?
First, headroom! Like the new Boost 'n' Buff v.3 and soon, the Super Crunch Box, we have added internal voltage multiplying circuitry to boost the operating voltage from a 9V only input, to give the Super Blues Pro 18V supply. This added headroom gives more clarity in the top end and attack and really adds that sparkle for low-gain boosting your amplifier.
Next, I wanted to expand the kinds of overdrive tones that can be dialled in and stand alongside the tone of the original Blues Pro. This has been done with the introduction of the DETAIL, BODY and TRIM controls:
DETAIL - This is essentially like the original tone control on the Blues Pro
BODY - One of the main features of the Blues Pro is a bass/low-mid boost to help get rid of the typical mid-hump of the typical TS type of pedal. The BODY control essentially makes this variable, so you can go for a more mid-focused tone, traditional Blues Pro (with the BODY set to 12 O'clock), or even more low end by cranking the BODY
TRIM - This is essentially a second gain control, which affects the gain in a different part of the circuit. The TRIM and GAIN controls have different frequency responses, so you can achieve a wide variety of tones by adjusting these two controls. The standard Blues Pro sounds can be achieved with the TRIM control set to 2 0'clock.
Finally, I wanted to give users the control of the clipping structure of the overdrive signal - allowing anything from a low-gain, open overdrive tone to the super-compressed, mid-gain fuzz found in the previous version. This is controlled via the two toggle switches, each having three options; Silicon, MOSFET or none.
The interesting thing (which I don't think has been done before,... I'm certainly not aware of any instances) is the ability to choose the clipping device for each side of the waveform individually. The top switch controls the clipping of the top of the waveform, while the bottom switch selects the clipping device for the bottom of the waveform. This means that you can now experiment with say, diode clipping on the top, and MOSFET on the bottom, or No clipping for the top of the waveform, but diode on the bottom etc.
Another thing to point out as well is that the silicon diodes for the top and bottom are in fact different diodes, to add a slight asymmetry to the waveform in Silicon mode. But this also means that you get a slight difference in the tone and feel of the pedal swap switch settings. Also, the MOSFET mode actually uses the clipping characteristics of the MOSFET itself, not the reverse protection diode commonly integrated into the devices.
The range of clipping tones available include the classic TS sounds of the original Blues Pro, or a range of compressed fuzz sounds, all with varying attack dependent on the diodes selected. As the gain increases and bringing in the TRIM control you can opt for a smooth, mid-rich overdrive a la Dumble amplifier tones, or an open, chiming top-end boost.
I'm really excited about the Super Blues Pro, and I'm really looking forward to getting it into the hands of the Blues Pro fans!
-M
GUITAR NOIZE PODCAST FEATURING MICHAEL IBRAHIM FROM MI AUDIO
The very first "The Guitar Noize Podcast" launched this week and I am proud to have been asked to be the very first builder to be featured.
In the discussion with Jon from Guitar Noize, I was asked about all of our new releases planned for 2012 (which there are many!!) and things that are in the pipeline. Have a listen on the link below and stay tuned to the podcast series for more featured Australian builders and musicians.
http://www.guitarnoize.com/the-guitar-noize-podcast-episode-1-mi-audios-michael-ibrahim/
-Mike
NEW PROTOTYPE LO-FI DELAY
Over the years, MI Effects has been known for great overdrive and distortion pedals and always have been asked "When will MI do a delay pedal?" There have been prototypes, and designs and ideas, but for the designs to come to fruition the pedal would have to retail for $1000, and no-one would pay that (would they?).
But as of late, there have been a lot of manufacturers using the PT2399 chip; a digital delay that emulates an analog or tape delay sound. The PT2399 is a great value bundle in one IC, however it does have its limitations and these are apparent if you have played the current pedals in the market. So instead of trying to force this chip to be the replacement for your Echoplex, I decided to embrace these limitations and release a delay pedal that doesn't quite fit into any category - yes it can do those classic modulated delays sounds (and very, very well too) but can be pushed to do so much more, and in turn, hopefully inspire some new sounds and experimentation.
So here it is: the (as-of-yet unnamed) MI Effects Lo-Fi Delay. A lot of careful design has gone into what goes around the PT chip to give modulation like no other pedal. There is control over the filtering of the delay signal that really gives a new perspective with a flick of the switch, and also the input and output of the pedal carefully honed to give you the control of the best signal-to-noise ratio.
The controls are:
- TIME - delay time up to a max of 600ms.
- REPEATS - go from short, slapback to self-oscillation. The LO-PASS/HI-PASS switch also affects how quickly the pedal will self-oscillate.
- RATE and DEPTH - these control the LFO modulation on the repeats. The RATE goes from super slow to throbbingly fast with a smooth taper for all speeds in between. The Depth also goes from zero at minimum for unmodulated delay, to super warble at maximum. There are some cool octave skipping sounds to be had in square wave mode.
- SQUARE/TRIANGLE WAVE - this switch selects the waveform of the LFO modulating the delay signal. Triangle wave at low rate and depth can give you classic chorus sounds, whilst square wave can give choppy, tremolo sounds, even pseudo pitch-shifting effects.
- LO/HI-PASS MODE - this switch controls the filtering of the delay line. The LO-PASS mode gives dark, analog repeats while the HI-PASS gives clarity to the top-end for shimmering modulation and self-oscillation. Using the LO-PASS mode "smears" the repeats together whilst the HI-PASS mode gives more defined repeats. The production will probably have a 3 position switch for three levels of filtering
- TRAILS ON/OFF - the trails switch allows the control of the trails continuing or cutting off once the pedal is turned off. This is extremely useful to not "cut-off" long delay lines allowing them to naturally decay if switched off mid-trail. Using trails on also allows you to play an atmospheric sound or oscillation, switch the pedal off and play over the top of it, acting almost like a short looper.
- LEVEL - this controls the LEVEL of wet, delay signal whilst having the dry signal constant. This is NOT a mix control.
- INPUT - this controls the INPUT gain of the signal hitting the circuit. This is provided to give you the best signal-to-noise ratio depending on what pickup/guitar/boosters you have in line. Start by setting the INPUT until it clips, then slightly back it off. Raise the LEVEL to taste and you have the clearest signal possible with the lowest floor noise. A bonus is that the INPUT gain can be set to max, and distort your delay line and keep the dry signal clean. This is perfect for stacking with other pedals and the overdrive channel of your amp.
Combining all of these features gives every guitarist, and instrumentalist, a whole new palette of sounds with something there for every guitarist. Modulation can go from subtle to extreme, or have pristine, clean repeats to distorted, washy, smeared reverb-like trails. Use the square wave for choppy, rhythmic pulses or triangle wave for classic chorus/vibrato. I encourage you to dig deeper and get inspired with some new sounds.
NEW SUPER CRUNCH BOX
At the MI Workshop, I have always wanted to fully trick-out a Crunch Box to see how many mods and features we could fit into its small enclosure. So one rainy afternoon I did just that, and decided to give three away for our Facebook and Twitter followers.
I was pleasantly surprised with how the Crunch Box sound had evolved with these added features. This, plus the constant feedback from customers wanting this new Crunch Box, led us to prototype the Super Crunch Box.
The Crunch Box has been around for quite a few years now, and has even inspired several clones and knock-offs. So I threw some ideas around the workshop, and came up with a design that expands the flexibility of the original, without an large rise in price.
First Upgrade: 18V Internal Supply
All stock MI drive pedals can be run up to 24V for more headroom, giving more clarity and a tighter bottom end. We know that a lot of our users run our pedals at higher voltage, but are aware of the troubles of running extra adaptors for these pedals. So a feature I am looking to implement in our future designs is the addition of circuitry to double the input voltage of your 9V adaptor/battery to supply 18V to the pedal. This is a great feature that your pedal board will happy with. The pedal sounds bigger, tighter and more responsive at 18V.
Second Upgrade: External Presence Control
The internal presence control was implemented to integrate easier with every user's amp setup. Some amps are brighter or darker than the ones we use to test, so by dialling in the Presence control you can control the shape of your sound through your setup. By placing it as an external control, you can really pull some great sounds that sit well in a mix, or to have more control with a range of guitars/amps you might use. The interaction with the Tone control is important as dialling in more Presence can cut really well, but also the lows won't feel as powerful, so use it with that in mind. This greatly increases the versatility of the Crunch Box, but for those who want to rock it old school, just leave the presence at 50% and proceed as normal!
Third Upgrade: Lo/Hi Gain Switch
This switch adds a great amount of tones that will suit many different playing styles. In Lo Gain Mode, the Crunch Box really cleans up well with the guitar volume knob and has a glassier tone. It still has a lot of gain (it is a Crunch Box after all!) but there is more string definition and top end than Hi Gain Mode. Hi Gain Mode is the stock Crunch Box amount of gain, so you can still get that "hot-rod" sound as with previous versions.
Fourth Upgrade: Clipping Selector
Like the Lo/Hi Gain Switch, this switch aims to tap in to the lower end of the gain spectrum. The switch selects between two different clipping structures, with one still the stock red LEDs as in the original. The other clipping mode provides a softer clipping of the signal, again to provide some flexibility to the overall distorted signal. The softer clipping mode, coupled with the Lo Gain Mode really provides a sparkly, break-up sound that you wouldn't think comes from a Crunch Box.
I'm proud of the layout of this design and how all of these features were able to be incorporated around the core Crunch Box sound. There are a few hitches we are working through, and a few IC/diode combinations we are experimenting with. Once I'm happy with the outcome, a video demo will go up showing all of these new features. We're hoping for a mid-year release on this one and for the price to be $149 all things going well, which I'm super excited about, give all the extra features we're putting in.
Hope you guys like it!
MEGALITH GAMMA AMPLIFIER – PRODUCTION PROTOTYPE
This is the production prototype of the Megalith Gamma, shown sitting above its big brother, the Megalith Beta. The production prototype uses the final PCB layout, silkscreened powdercoated chassis, and all of the parts that would be used in the final production model. It allows us to finalise any last details before starting a large production run. We whipped up a headshell and covered it in camouflage "camo" tolex for a bit of fun. The production model will be in black. It wouldn't be metal if it wasn't in black!
We are really happy with the final prototype and are looking to begin production come mid-year. Below is a quick demo and explanation of some of the features of the Gamma.
NEW BOOST ‘N’ BUFF V.3 COMPLETE!
The new case design for the Boost 'n' Buff v.3 is now in stock. The circuit is finalised and ready to go into production and should hit the street in a month. You can read about the re-design in this previous blog post: http://www.mieffects.com/
MEGALITH GAMMA HIGH GAIN AMPLIFIER
Here's a sneak peek at our new Megalith amplifier, the Megalith Gamma.
The picture above is of our final prototype. We've been working on this design on and off for about two years now. There have been a few variations of the design, but in the end we went for a design which exhibited maximum simplicity, but all the tone of its big brother, the Megalith Beta.
The Gamma is an 80W (conservative) 2*6550 based amp, but can also use KT88's KT90's, KT100's, KT120's. The amp can also run El34's, 6CA7's and KT77's but the bias needs to be run a bit cooler, as the plates run at close to 700V. The screens, which are the usual culprit for valve failures, run at a conservative 400V, which hopefully translates into less tube failures. However, I question the ability of current production EL34s, 6CA7s and KT77s to handle these plate voltages (even though they're meant to).
The controls from left to right are clean and overdrive gain, 3 band shared EQ, clean volume, gain volume and contour (yes,... and MI Amp with only 8 knobs!!!). The switches are clean and overdrive bright switches, clean and overdrive EQ shift switches, channel select, overdrive gain mode (low/mid/high), and FX loop on/off. The amplifier will come with a two button foot-switch to switch channels and to switch on/off the FX loop. The two large switches are power and 3 position standby (40W low power, off and 80W high power)
The picture above gives you an insight into the way we prototype. We get a bare chassis made to spec. This allows us to mod and drill of required, but also allows us to test how the mechanical fit will work. We don't use any 3D CAD software, so sometimes we run into issues translating a 2D assembly plan into the real deal.
First thing to note about the Megalith is that it's a high gain amp. By this, we don't just mean one amongst a series of high gain amps, but rather that it has more gain on tap than any amp we know of. To give you an idea, mid-band frequencies can be amplified by up to a factor of 2,000,000 from input jack to the output of the preamp. Then there's the amplification of the power amp! So one of the main challenges of this compact design (the main chassis is only 50cm wide * 17cm deep * 6.5cm high) is stability. Good component layout, use of ground plane, lead dress and wire type are all imperative for stability. However, going too far in the other direction can lead to a rather 'dead' sounding amp, due to too much high frequency coupling to ground. So one of things we aim for is the minimal use of shielded cabling, as this is often one of the main culprits for killing top end.
So where are the transformers? They are located under those huge square metal boxes. One of the things we do which is quite unique is the use of toroidal transformers for both power and output. We design our own transformers (really!). Our design philosophy is to design the transformers to work comfortably under worst-case conditions. For example, our output transformer is designed to work down to 40Hz even if the power amp is pushed into full distortion, putting out close to 200watts, with no hint of core saturation.
So why toroidals? As a general rule, a toroidal will run a lot cooler and radiate much less magnetic field than an equivalent E-core, which is perfect for high power, high gain applications. For output application, they do have limitations to do with DC core saturation, but as long as this is accounted for in power amp design, they're the perfect choice for this kind of design.
They transformers' lower radiation means that the amp will run quieter, and also that you can stand a lot closer to the amplifier without your guitar picking up mains hum from the power transformer, or feedback from the output transformer. To push things even further, we've designed our toroidals with a layer of mu metal on the outside of the windings, which are grounded in order to reduce the radiation further. The final icing on the cake is the square external metal shields, which cover the transformer and shield AGAIN!
With this iteration of the prototype, we were prototyping two new features. The first of these is independent EQ shift buttons for the clean and overdrive channels. This increased the flexibility of the shared EQ on the Gamma. This worked without any hitches.
The next new feature which didn't go as smoothly was our new buffered FX loop design. The previous Gamma has a simple passive loop (foot-switchable). We decided to turn this into an active loop with send and return controls. The idea was to make the loop usable with any effect, guitar or line level, and with any input or output impedance. For this design, we used high voltage solid state transistors running at 250V, so there's no issue whatsoever with headroom! During the design phase, we made sure that the loop had a neutral frequency response using PSPICE modelling of the circuit. This all went to plan.
However, where we came unstuck was the noise of the return circuit. It worked well, but was too noisy. So after a day of brainstorming, we came up with an design with variable negative feedback for the return transistor, which reduced the noise by a factor of 40db, and actually increased the return impedance, to make the loop even more effective.
Anyway, here's a clip of literally the first time we fired up the prototype. Please excuse the iphone audio!
MEGALITH DELTA HIGH GAIN DISTORTION PEDAL
The Megalith Delta high gain distortion pedal design came from years of R&D of our MI Amplification high gain amplifier, the Megalith Beta. It took some time for me to really understand the variables behind great high gain tones. But by designing the amplifier from the ground up, I was able to really grasp how to make a complex, sophisticated high gain sound that kept all the nuances, huge bottom end and the clarity and character of the top end.
The Megalith Delta pedal is a solid state 'model' of the Beta preamp, using JFETs to simulate the gain stages of the preamp valves. The transfer characteristics of FETs are very tube-like, so it seemed that this was a great place to start.
This, of course, is not something revolutionary. A quick peruse of the pedal market and various DIY sites will reveal various FET renditions of valve circuits. However, digging a little deeper shows somewhat limited implementations of these circuits. Often, it's just the exact same circuit as the 'simulated' amp, but with FETs instead of tubes, adjusted source or drain resistances, and 9V operation. Little or no thought it given to the operating points, dynamic range, scaling of clipping thresholds, output impedances, and intrinsic capacitances due to things like the miller effect etc.
As you can see, making a FET stage behave like a particular tube stage is actually a very complex affair. One thing which differentiates our endeavour from others' is the fact that the amplifier in question is our own. I designed every single aspect of the Megalith Beta, and have insights into its working you can't get by simply looking at the schematic. I know what I wanted every tube stage to do, the logic behind each stage design,... even things like the effect of track and cable capacitance. Because of this, I was able to feed all these parameters into the design, and come up with something which is as close as humanly possible to the original.
Now the controls,...
The GAIN control offers a wide sweep in gain, from low-mid gain rock tones, to serious crunch, to every dark shade of brutal imaginable.
The three-band EQ and EQ SHIFT are taken straight from the amp as well. The EQ SHIFT allows three different voicings by shifting the response of the tone stack.
One of the challenges of doing the Megalith in a pedal format was how to integrate the CONTOUR control into the design. The CONTOUR control, which changes the response of the phase inverter, is what really gives the Megalith amp its flexibility. If you want a loose, fatter, vintage high gain sound - turn up the CONTOUR. If you are after a more modern, tighter and cutting high gain tone - turn down the CONTOUR. So in order to mimic this response, I designed a phase-inverter like stage, and integrated the CONTOUR control into it. The combinations of the EQ section will give an impressive number of high gain sounds, just like the Megalith Beta amplifier.
A BOOST mode was added to the pedal as the amplifier really steps up going from "mid" gain mode to "high" gain mode. I thought by adding this as a foot switch, it gives you the option to really step up the crazy. I also figured that mid to high switching was a lot more useful than low to high, as there are already plenty of great options out there for the lower gain sounds. Lets face it, someone interested in the Megalith isn't going to be too stressed about missing the low gain mode!
A big part of the Megalith Beta amplifier's huge gain sound is the 160 Watts of headroom! Of course, this would always be the limitation in trying to emulate a high gain amplifier to stomp box form. But by adding voltage doubling circuitry in the Megalith Delta pedal, it allows the 9V supplied by battery, or DC adaptor, to be increased to 18V within the pedal's circuitry. This has the advantage of producing the crushing low end without mush, much like the 160W output of the Megalith Beta does at the amp level.
Now, the biggest challenge was working out how to fit it all into a case, and keep it stable. For those of you who haven't strapped yourselves in for a Megalith ride,... let me tell you, it's one seriously high gain amp. It's the only amp I'm aware of that doesn't need to be driven with a pedal to get a super-tight saturated gain tone. So packing all that gain into a modest pedal enclosure is not only challenging in terms of layout (there are 110 components in the circuit), but also in terms of stability. After a few failed attempts, I moved to a 4 layer layout, with top and bottom ground planes for shielding. This also necessitated a few circuit tweaks to take into account the extra capacitance to ground.
Finally, I designed an output section which is designed to 'compensate' for the standard guitar amp's clean channel response, so that when you plug the Megalith pedal into a 'reference' clean amp, you get something close to the feel of the Megalith Beta. Having said that, one of the main aspects of the Megalith Beta's 'presence' is the sheer headroom and output power it has. So no, you probably won't unleash carnage and devastation plugging a Megalith Delta into a 5W lunch-box amp. That's just the physics of it,... a reality more inviolable than the existence of fragile harmonics in a crystal lattice.
I feel that, although it may sound cliché, the Megalith Delta high gain pedal is unlike any high gain pedal out there. It came off the back of a complex amplifier design in the Megalith Beta, that already pushes the standard in metal amplifier tones. By emulating the preamp of the Beta, it truly captures the essence of the amp with response and character retained.
Below is a quick demo of the finalised design. It goes quickly from clean, to crunch, to the heaviest of metal tones in under two minutes.
NEW BOOST ‘N’ BUFF MINI AND NEW BOOST ‘N’ BUFF V.3
A couple of months ago, we started a Facebook discussion on boost pedals. I was looking at re-designing the Boost 'n' Buff and wanted to make THE booster. We got some great feedback on the matter and it became clear that there were two main uses of boost. Some of you prefer the loud, super-clean, super-simple boost, and others preferred boost with some EQ control to add some sparkle to your tone. So, naturally, I decided to design two Boost 'n' Buffs!
Since discontinuing the first version of our Boost 'n' Buff, we have had a lot of people asking for that simple one-knobber to return - and so it has, in the form of the new Boost 'n' Buff Mini. So the same Class A transistor design was packed into the small, finger-size "1590A" sized enclosure with the same feature set; buffer mode in bypass and +40dB boost when engaged. A flat booster for the lower range of the gain control, and treble booster for the higher range. But one added feature gives the Boost 'n' Buff Mini something extra. A voltage doubling circuit has also been added to provide the boost circuitry with 18V. This means that when 9V DC is added by power jack (the small size doesn't allow for battery), the circuit is supplied, internally, with 18V. This gives more headroom and extra top-end sparkle to your signal - all in a tiny enclosure that could fit on any pedal board.
I then wanted to add an EQ feature to the Boost 'n' Buff so that it could have the flexibility to be integrated into any set-up. However, I also wanted to avoid the large knob count my pedals tend to have. So a neat solution involved adding a three-way mini toggle switch to select between three tone-shaping options, whilst still keeping the same VOLUME and GAIN layout from Boost 'n' Buff v.2.
The EQ options are:
- FULL BOOST - This is a full frequency boost regardless of the gain and volume settings. It not only boosts the volume, but seems to really lift your tone as well. It's difficult to explain. You've just got to feel it.
- TREBLE BOOST - I tuned this mode to be a more of a dramatic treble boost than the stock Boost 'n' Buff. I figured that if the full boost option is now available, then it would be possible to make the treble function a bit more prominent.
- MID BOOST - This came about because I quite liked how the treble boost pushed an already overdriven amp, but for some amps, I found that too much top end made the tone too harsh (For others it was fine). So by rolling off some of the highest frequencies, and beefing up the mids, we were able to get the extra gain, cut and richness, but without the ice-pick.
As well as the added EQ feature, I also added a voltage tripling circuit to boost the pedal's operating voltage to ~27V! Unlike the Boost 'n' Buff Mini, v.3 does have room for a 9V battery, and will internally triple the supply voltage of either battery or DC adaptor supply.
Here is a demo we recorded of the prototype Boost 'n' Buff version 3. We tried to show the amount of boost on tap and the different EQ voicings for each of the three modes into the clean and overdrive channel.