Jad & Freer Audio SISMA Hybrid Tube & Class-G Bass Amp Head Made in Italy PRE-ORDER

Hybrid tube and Class-G bass amplification

The SISMA combines a B15-inspired tube preamp, operated at 200V, with Jad Freer Audio's Class-G transistor power section. It is hand-assembled in Italy and designed to keep this hybrid format portable.

The preamp combines a passive Baxandall bass/treble tone stack with two active semi-parametric EQ bands. Gain adds tube colour and compression, while the Master controls the speaker level.

Specifications

• Dimensions: 25 × 28.5 × 6 cm – 9.8”x 11,2”x 2,3” inch
• Weight: 3,7 Kg – 8.2 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
  
• Rack mount system available as optional

The power section uses a custom heat-dissipation system, switching power supply and fan cooling. Keep ventilation paths clear; the manual specifies space above a rack-mounted unit.

The preamp and power amp use separate supplies. The DI remains available during the protection conditions described in the manual, including power-amp overheating or failure, so the signal can still be sent to the PA.

Controls and connections

• 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 (LPF will not available on this out). 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: a Class A transistor headphone amplifier and auxiliary input support silent practice and monitoring during live performance or recording.
• 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.