Jad Freer Sisma Bass Amp

THE GAME CHANGER: A must-have for any gigging musicians

After many years spent building custom amps, SISMA is the first official bass amp release by Jad Freer Audio.

Vintage meets modern: SISMA aims to combine the qualities of a classic tube preamp with the punchy and detailed sound reproduction of a big transistor power section maintaining a portability prerogative, until now, only of class D technology.

Despite its small footprint SISMA is not based on a class D power section, but actually shares the same transistor technology of our CODA power amp, delivering big and authoritative sounds capable to shake the bigger stages without any efforts and headroom to spare.

Build and hand-assembled one by one in Italy, the preamp is based on the iconic B15 sound, modded to our taste.

The tube preamp circuit is fed @ 200v by a proprietary switching power supply capable to deliver high amounts of current, much faster than a traditional transformer-based one. Same technology is used in our proprietary Class G high-performance power-amp module, reducing weight and dimensions a lot with no sound compromise.

The result is the big, open and musical sound of a tube amp with much more responsiveness ad detailed sound reproduction and, of course, a lot more headroom. All this in a small fraction of traditional weight and dimensions, overall making this amp a real game-changer in today’s market offer.

SPECS

• Dimensions: 25 × 28.5 × 6 cm – 9.8”x 11,2”x 2,3” inch
• Weight: 3,9 Kg – 8.5 lbs.
• Power rating: 350W @ 8Ohm / 700W @ 4Ohm / 950w @2Ohm
• 2x Speakon-combo speaker output
• 230/115 VAC selectable power supply: WORLDWIDE USE
• FX Loop
• Headphone out/Aux in
• Hand-made padded bag included
• Rack mount system available as optional

The core of the power section consists in a custom heat dissipation system, a heavily oversized power supply, and many custom components much superior in specs and performances to the corresponding off-the-shelf available ones.

In aid of the proprietary heatsink it has been engineered an intelligent forced ventilations system, that, following the signal dynamics, allows the amp to work flawlessly in safety, never getting hot and performing dead silent at low volumes or studio applications.

Another great benefit of a well filtered and engineered switching power supply is that it doesn’t generate magnetic fields in the audible bandwidth, unlike the old toroidal PSU that suffer a lot of 50 / 60Hz hum. This allows SISMA to perform with no audible interferences with other devices or pickups, even single coil ones.

The classic, passive two band baxandall tone stack is combined with two active semi-parametric eq sections, tailored after classic studio channels eq, to maximize flexibility, while a studio grade D.I., FX loop and Class A transistor headphones amp complete the connection options.

Unlike most amplifiers on the market, preamp and power amp in the SISMA don’t share the same power supply, which means that in remote cases of power amp fails or overheats, the D.I. out will continue to work as usual letting the user to finish the performance through the P.A.

Safety and durability are two aspects that Jad Freer Audio has always a great attention to: SISMA as all other our product has many internal protection systems that isolate any small problem letting you finish your performance flawlessly shutting down the device only before any critical damage will happen eliminating any risk for the connected equipment.

CONTROLS

• High impedance Input: the first stage of the tube has an input impedance of 2,2M Ohm, letting the amp reproduce every little detail of your instrument even with low output piezo pickups

• Bass/High: baxandall, tube driven. These controls are very broad and musical, how they affect the sound is, in our opinion, one of the aspect that make SISMA special in the modern amp market.

• Two band semiparametric eq: active section after the tube stages, with Q and gain tailored differently for each band, in order to guarantee the most effective and musical response both in live and studio applications.

• Gain: it controls the second stage of the tube. We wanted an amplifier with lots of headroom but where the gain has great impact to the overall sound texture. So, depending on the instrument output, the sound will remain clean till 12/13 o’clock, becoming bigger and beefier and gradually more compressed going up. After 13 o’clock the sound starts to break into a very warm, musical and dynamic overdrive resulting in mild distortion territory when the control is dimed.

• Master: despite it’s compact dimensions, SISMA is a very powerful amp. We have set the master in order to be able to play also at low volumes, unlike many amps that at give 90% of their volume before 9 o’clock. The potentiometer has in fact a logarithmic curve, so the volume increase is gradual and continues till the pot is on full.

• LPF: active filter carefully tailored to soften treble response placed at the preamp’s signal chain. Very useful using cabs with tweeters or to achieve a good D.I. sound while cranking the gain of the SISMA or using dirt boxes that sound harsh going straight into the audio interface.

• Deep: active low-end boost after the tube stages that gives you more bottom without mudding your sound or altering your mid presence.

• Mute: mutes both power and D.I. out to allow silent tuning or practice, monitoring your performance through the phones out.

• D.I. out: Pre Master balanced output. It has ground/lift and pad control. We put a lot of effort to have a great D.I. sound: totally noise free, big, punchy and articulate.

• FX Loop: serial effects loop, completely transparent and noise free. Send can be used as an unbalanced output without interrupting the signal. Return can be used to bypass the preamp section and go straight into the SISMA power amp, even with your passive instrument.

• Headphone out/Aux in: we paid a lot of attention for every part of the project, the headphone amplifier is another thing where we wanted to make a difference. This section is a full Class A transistor amplifier so powerful that can drive headphones of any impedance with no effort. All this force and power translate in a very big, punchy and controlled sound experience for the user. An auxiliary input completes the section allowing the user to silent practice or use the headphones for monitoring the performance of the band during a performance or recording session.

• Line Out: it’s an unbalanced copy of the D.I. output signal. It can be used to combine the preamp section with another power amp in case you need it as a slave unit or simply to achieve a different sonic character. It can be used also as an always on tuner out, very convenient using SISMA in a rack mount system.