Archive: Nov 2013

MI AUDIO MEGALITH GAMMA HIGH GAIN AMPLIFIER RELEASED DECEMBER 2ND

MI Audio will be releasing their newest high-gain amplifier, the Megalith Gamma, on December 2nd available direct from www.miaudio.com and selected retailers. Following on from the award-winning high-gain Megalith Beta amplifier and Megalith Delta distortion pedal, the 80W Megalith Gamma is set to be on the wish list of every metal rocker!

The “Megalith” name is quickly forging a strong following in the high-gain community, with the MI Effects Megalith Delta high-gain distortion pedal making a formidable impact in the stompbox world. The new Megalith Gamma is already met with high anticipation and looks to follow in its big brother’s footsteps.

The Megalith Gamma is a scaled back version of the Megalith Beta, but with a tough voice of its own. The Megalith Gamma has both Low and High (30W/80W) output modes that provide metal destruction from bedroom to stage! Running off two 6550’s the Megalith Gamma can also use other large octal power tubes such as KT88′s KT90′s, KT100′s, KT120′s, and other medium tubes such as EL34’s (with separate biasing). With two large power tubes and intelligent power-amp design, the big bottom end and punch of the Megalith Beta is still present, whilst also retaining the complex and sophisticated high-gain tone that the Megalith line is becoming synonymous with.

The CLEAN channel is a channel is unlike no other in any high-gain amp. Whilst most high-gain amps can deliver a brutal high-gain tone, flicking to the clean channel leaves most metalheads disappointed. Not with the Megalith Gamma! All the top-end is retained, along with the signature fat bottom end to produce a sweet, full clean tone that most amps are envious of!
The DRIVE channel has three gain modes, and has more gain on tap than most metal amps in the market. Tuning of the brutal gain tone is done via the three-band EQ, EQ SHIFT switch (selectable mid-frequency peak) and the ever powerful CONTOUR control. The CONTOUR (affecting only the overdrive channel on the Megalith Gamma) can go from fat, loose and vintage to tight, scooped and modern with a sweep of the dial! Shared EQ provides functional simplicity and a consistency in tone across both channels.

Place your favourite effects into the Megalith Gamma’s active, footswitchable FX LOOP with SEND and RETURN levels allowing for any effects unit or pedalboard to perfectly meld with the molten fury of the high-gain channel or the full-bodied clean channel. This pint-sized pugilist is designed to pack one hell of a punch!

SPECS

A conservative 80W output using 2 x 6550 power tubes (standard)
3 x 12ax7 preamp tubes
Thick 2.4 mm double-sided through-hole PCB’s with 4oz plated tracks
High end audiophile German made WIMA polyester and polypropylene capacitors for the signal path
Amphenol jacks rated at 10A
16 Gauge Galvanised Steel Chassis
Anodised aluminium faceplates
Custom built overspec’d transformers
19mm plywood headshells
Width – 643mm (25.3”)
Depth – 225mm (8.9”)
Height – 250mm (9.8”) (with rubber feet)
Weight – 21.5kg (47lb)
Note all dimension are close approximations

CONTROLS
2 Channels – Clean & Drive with separate Gain controls
Shared EQ – Bass, Middle, Treble.
3 EQ voicings per channel
Contour Control for each channel – unique tone shaping tool
Bright Switch – 3 position – allows more control over the Clean channels sparkle
Attack Switch – 3 position – switch to adjust the tightness and response of the Drive channel.
Mode Switch – 3 position gain switch on the overdrive channel (low, mid and high gain voicing)
Individual Master Volumes for Clean and Drive channels
FX Loop  – Active, line level FX Loop with adjustable Send and Return Levels
2 button Footswitch (Included) – Channel Select, FX Loop on/off.
Ability to accept most large power tubes – KT100, KT90, KT88, KT77, 6550, EL34 and 6CA7
4, 8 and 16 Ohm output

Available direct from www.miaudio.com and these selected retailers:
Deluxe Audio (VIC), Guitars & Things (VIC), Pony Music (VIC), River Music (NSW), Landers Music (NSW), Top-notch Guitar & Bass (QLD), The Guitar Shop (QLD), Derringers Music (SA), Concept Music (WA). More dealer info can be seen at www.miaudio.com/dealers/

Permalink

NEIL BRIONES’ MI DIY VALVE DUAL DRIVE

neil-briones-1
 

A few month's ago, we decided to run an MI DIY challenge on our Facebook page. We asked for amateur DIY-ers to submit some examples of their work so we could select three challengers to be amongst the first to build the MI DIY Dual Drive Kit.

One of the challengers selected was Neil Briones from the Philippines. He currently makes custom pedals under the name Subzero FX and has made some interesting effects that can be seen on his blog. Neil and the other two chosen DIY-ers were asked not only build the kit but to add something special that they could share with the other MI DIY-ers... and Neil met that challenge. Let's hear it in action!

 

Neil built both the overdrive and distortion circuit provided with the MI DIY kit but chose to add two additional circuits to make this pedal his own. The circuits added are two favourites from the DIY community; the Matsumin Valvecaster and the 1/2W Little Gem power-amp. This inspired design is a small amplifier of sorts - it has an initial valve gain stage then uses both MI Dual Drive circuits as preamps running into the 1/2W power amp. This setup makes for one versatile drive box! Below is a circuit flow diagram:
flowchart

The Matsumin Valvecaster is THE DIY valve overdrive circuit that has been made many times over with great success. A YouTube search will show you just how many and the possibilities this simple circuit has for modifications. DIY guru, Aron Nelson, hosts a website with thousands of DIY circuits and modifications - and the Valvecaster is no exception. Neil used a 12AT7 preamp tube and omitted the tone control from the original Valvecaster design. Any 12A_7 tube can be used with each having a unique gain and tonal character.

Important note: Neil is running his pedal off a 12VDC power supply. The tube boost circuit requires a minimum of 12VDC to operate efficiently. However, both the tube boost circuit AND the MI DIY Dual Drive can take up to 18VDC giving a more responsive drive section, less gain but more headroom.

Below is the amended circuit Neil used:

mi diy valve
 

Following the 12AT7 tube boost stage is a 1/2W power amp design based off Runoffgroove's Little Gem which is a variant of another DIY classic - the Smokey Amp. Neil's take on the Little Gem sees the removal of the GAIN pot and MASTER VOLUME, favouring a MASTER VOLUME control at the front end of the circuit. Pins 1 and 8 of the LM386 amplifier have been left open to reduce the output gain. The addition of this small power amplifier circuit means this MI DIY Dual Drive can directly drive a speaker cabinet! Here is the circuit Neil used in his Dual Drive:

mi diy power amp
mi-diy-master-fx

An interesting feature Neil implemented was the addition of a SEND and RETURN [FX LOOP] via the 3.5mm jacks before the power amp circuit. This allows you to use the Dual Drive with your favourite drive/modulation/delay pedals to add some grit, drive and/or boost.

Also, the 1/2W power amp is switchable: When on, it enables the output jack to run directly to speaker or a 4x12 cabinet rated at 16/8 ohms, turning the whole pedal into a 1/2 watt "head". In this mode, the Dual Drive becomes the preamp. The MASTER VOLUME knob is only active in this mode.

 

HOW CAN I ADD THESE CIRCUITS TO MY OWN MI DIY DUAL DRIVE???

-- You will need to get some vero/stripboard or perfboard from any number of electronics suppliers (I have linked to Mammoth Electronics for examples). You could also search eBay too.
-- Vero/perfboard layouts can be found at both Aron Nelson's great DIY gallery, and of course the DIY Stompboxes Forum.
-- The Little Gem power amp circuit can be found at www.runoffgroove.com.
-- Check out these sites for many more DIY circuits for you to experiment with.

Permalink