Hands-On Review:Peavey JSX Mini Colossal Amp

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Classy sound for practice, stage or recording

By Daniel Vincennes


Peavey JSX Mini Colossal Amp

The quest for the ideal small amplifier started for guitar virtuoso Joe Satriani when he was laying down tracks for his album Super Colossal. Joe had tried several well-known Class A single-ended amps that were all rated at about five watts. He thought each amplifier did one thing well, but was missing a feature that another had. In the past, Joe had called on Peavey to help him build a guitar amplifier to his specifications. The result was the JSX Guitar Amplifier with 120 watts and three channels: Clean, Crunch, and Ultra. It quickly became one of Joe’s favorite amps. Joe called on Peavey again to ask if they could develop a small tube amp for practice and recording.


Class A all the way


The first, and most important, requirement Joe specified for his dream mini amp was that it employ true Class A tube circuitry with no negative feedback from the power amp. In the last few years, small Class A tube amps have become quite popular for several good reasons, but especially for what is often described as a "sweeter" overdrive—the vintage sound of the Vox AC-30, for example. First, a definition: Class A circuitry output tubes handle the complete 360° cycle of the guitar signal. This is compared to a Class AB amplifier (used by a majority of guitar amps such as Fender and Marshall) in which output tubes trade-off handling part of the 360° cycle. Sharing the load between output tubes means Class AB operates more efficiently, resulting in longer tube life. On the other hand, because Class A operates in a more linear fashion than AB, it emphasizes more of the desirable harmonics in the guitar signal that result in that great vintage sound. Because this Class A amp is only required to pump out five watts at the most, the inefficiency of the design is not as critical.


Sweet spot


Just as they had done in developing the earlier JSX, Peavey sent three or four different prototypes for Joe to try out and offer his feedback and tweaks. Here’s what Peavey and Joe came up with: a single-ended amp with true Class A circuitry. The preamp has one 12AX7 tube and the power amp uses one self-biasing EL84 tube. Both are handmade by JJ/Tesla at their factory in the Slovak Republic. When I tried out the JSX Mini Colossal I was thrilled to bathe in the wash of vintage sound. Like Joe, I love the coloration and full-bodied tone as well as the response. The JSX Mini Colossal provides a smooth transition into overdrive instead of suddenly reaching distortion as do many other Class AB designs. The JSX creates a looser feel better suited for a bluesy, dynamic style of playing. When A/B’d with a small transistor amp, and then a small tube amp, I hear that legendary vintage "sweet" sound from the Mini Colossal, especially in the lower harmonics. Chords become more "musical" and tonally balanced.


Tweaking the dream


Joe was into retro sounds and decided he wanted the tremolo sound he heard on another vintage amp. Peavey offered an old analog tremolo circuit. When he heard it, Joe raved about the deep, rich tremolo from the opto-electronic circuit. The 8" C8R-type speaker (based on the Jensen C Series ) is specially voiced. Peavey engineers tell me it took a little tweaking to get the right speaker sound. Joe was aiming for a tonality between two well-known mini-amps. Peavey took the same C8R 8" speaker used in both mini-amps and re-voiced it to better handle the amplifier’s output stage and not peak out. The re-voiced speaker handles the tonal transition from smooth to "grindy" with a full-bodied, less-airy tonality and tighter bass response.


I used the JSX’s send and return jacks to run a chorus unit through the buffered effects loop. This means the chorus is applied to the signal coming from the preamp before it goes to the power stage, avoiding the noise and loss of tone that that often happens when you run an effect straight from the guitar into the preamp.


With just the one volume and one tone control you can quickly dial in sounds from clean to crunchy to overdriven. The power level attenuator in the back of the amp lets you set the overall output level once you dialed in your tone. I do want to emphasize that this amp gives you back what you put into it. So a guitar with humbuckers has a higher output that brings on crunch and overdrive at lower volume settings. Most single-coil pickup guitars have a lower output, so you can get a cleaner sound with the Mini Colossal set at higher volume.


Not just for guitars, the Mini Colossal makes a terrific harmonica amplifier. I plugged in a Green Bullet mic, whipped out my favorite Bb harp and immediately got the warm brown sound made famous by harp players such as Big Walter Horton. In addition to being a great practice and recording amplifier, the Mini-Colossal has enough output to fill a small club. This is one amp you can crank to the max without the sound breaking up or getting out of control.


Since the album is named Super Colossal, Joe chose the name "Mini Colossal" for the amp. You can hear how Joe used the microphone-simulated XLR direct output of the Mini Colossal to capture the actual sound of the amp when he recorded the song "Just Like Lightnin’" on the Super Colossal album. Dig the way Joe peels off some earthy Beck-ian riffage on this "down-home blues stomp," as Joe calls it—the sound directly from his JSX Mini Colossal.


Features and Specs:

  • Single input
  • 1 x 12AX7 and 1 x EL84 tube
  • Pure Class A operation
  • No negative power amp feedback
  • Preamp volume and tone controls
  • Power Sponge output power level attenuator
  • Buffered Effects Loop Send and Return jacks
  • Classic opto-electronic tremolo circuit
  • Microphone Simulated XLR recording output
  • XLR ground lift switch
  • Specially voiced 8" C8R-type speaker
  • Chrome-plated brass control knobs
  • Rated power: 5W RMS into 4, 8, or 16 ohms (selectable impedance)
  • Power consumption: 30W, 60Hz, 120VAC
  • 14-3/8"H x13-3/4"W x 9-1/4"D
  • Weight: 22 lbs.