The Jad Freer Audio Sisma is a bass amp head that puts a tube preamp and a Class G power amp in one compact box. Bass Magazine's Jonathan Herrera described it as "a fat, rich, and warm tube preamp coupled with a hugely powerful power amp and just enough EQ to get the job done"1. The design goal, according to the review, was an amp that captures the lush and creamy character of an Ampeg B-15, mated to a modern power amp1.
The preamp and power amp
The Sisma's single 12AX7 does real work rather than acting as a token buffer: it handles the input gain stage and drives the 2-band Baxandall EQ1. A proprietary switchmode power supply provides the juice, including a legit 200 volts to the tube, which the reviewer took as a sign of engineering chops1. Behind the preamp sits a Class G power amp, a topology the review flagged as being of further interest1.
How it responds matters as much as what is inside. Herrera wrote that "Much like the Capo, the Sisma is dynamically sensitive like a proper tube amp," moving smoothly from clean into saturation as you dig in1. He also noted the character of even its cleanest tone: still a bit thick and saucy, not a dry straight-wire-with-gain sound. His advice on that point: "If you prefer a dry, 'straight-wire-with-gain' sound, then it may not be the right amp for you."1
Controls and connections
The EQ section pairs the 2-band Baxandall with two semi-parametric bands that together cover 40Hz to 5kHz, a slightly more modern touch on top of the classic layout1. Beyond the EQ:
On the connection side, there is an aux jack, effects send and return, a DI with ground-lift and pad, a pair of Speakon combo jacks for the speaker, a line out, and a headphone output1. The DI and headphone output make the head usable on a quiet stage or in a practice room without a cabinet.
What reviewers said
Herrera's verdict after gigging the amp was strong: "In practice, on many a gig, the Sisma proved to be one of the most impressive new amp designs I've ever encountered," with seemingly limitless headroom and honest, clean volume1. At just 8.5 pounds, he added, the promise of that tone in a light head "isn't just a fantasy"1.
He did flag one build criticism: chiefly, the size of the mute, lpf, and deep switches and their accompanying indicator LEDs, with a tiny, dim red LED indicating mute1. Players who use those switches on a dark stage may find them hard to locate and read.
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JAD FREER AUDIO
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Jasper Mortier
Questions
Does the Jad Freer Audio Sisma use a tube?
Yes. The Sisma runs a single 12AX7 tube, and it is not a token buffer: the tube handles the input gain stage and drives the 2-band Baxandall EQ. A proprietary switchmode power supply provides the juice, including a legit 200 volts to the tube, which is why the reviewer described it as dynamically sensitive like a proper tube amp.
What does the deep button do on the Sisma?
The deep button adds a subtle low-frequency bump to the sound. It sits alongside a switchable lowpass filter as one of the amp's additional tone-altering features, so you can thicken the bottom end or roll off top end without touching the main EQ.
How much does the Sisma weigh?
The Sisma weighs 8.5 pounds. Bass Magazine's reviewer called it a remarkably dense head, and noted that at just 8.5 pounds the promise of big tube-amp tone in a light package is not just a fantasy.
Does the Sisma have a DI output?
Yes. The Sisma includes a DI with ground-lift and pad, alongside an aux jack, effects send and return, a pair of Speakon combo jacks for the speaker, a line out, and a headphone output.
Can you plug headphones into the Sisma?
Yes. The Sisma has a headphone output among its rear-panel connections, so you can practice quietly with the head without a speaker cabinet connected.
Sources (1)
- Review: Jad Freer Audio Sisma Head & Capo Multi-Preamp Pedal, Bass Magazine, 2024-09-04
