Soultone 45ps Amplifier

By Jack Devine


Today we’ll be examining the JTM-45 PS Superplexi (tm) combo amplifier from Soultone Amplification. Over the last few years, Soultone has made quite a splash in the boutique amplifier market. Amps for sale in TGP’s Dealers Emporium with introductory pricing have helped to pique players' curiosity and raise the company’s profile.

Soultone has chosen to focus on perfecting the sonic blueprint established by the classic Marshall amps of the 60’s, 70’s and 80’s. Boasting a plethora of modern features, like Mercury Magnetics transformers, power tube mixing, power scaling, a fat/lead boost, and a buffered FX loop, these amps have been tempting the tone tweakers here to give Soultone a try. Converts claim Soultone has captured the timeless roar and signature voice of a vintage Marshall amp while addressing the volume and tonal needs of today’s guitar player. If that’s the case, then score one for today’s discriminating amp geek… like me.

soultonefrontThe big story behind the JTM-45 PS is volume control. One of the biggest concerns for guitarists today is getting the sound they want at Sound Pressure Levels (SPL) their neighbors, bandmates and soundmen can tolerate - a tricky proposal, especially with a Marshall style amp. Michael Corrieri (TGP screen name Mickey C), the grand poobah of all things Soultone has spent the last 3 years experimenting with, and in the opinion of some, perfecting the implementation of Kevin O’Connor’s power scaling technology into the Marshall platform. I’d read the reviews, looked lustfully at the website, and lurked on the message board, but I’d never heard a Soultone. So when Mickey offered to send one of his power scaled Marshall styled combos to me for a write up, I jumped at the chance. In the end I preferred the sound of the amp without the Power Scaling. I use an Ultimate Attenuator with an integral FX loop to lower my 100 watt NMV Marshalls, and prefer a good attenuator to the power scaling. But it would be foolish to compare them. My attenuator cost nearly half of what this amp sells for! A better way to look at the power scaling is like a master volume. Good for taking the edge off--down to say 20-25 watts, but not for getting to bedroom levels. (BTW the amp sounded great with my attenuator down at bedroom levels!).

Basically, power scaling controls overall volume by varying the voltage to the tubes, rather than a master volume or attenuator between the head and speakers. Power scaling, according to its supporters, achieves its goal by preserving the ratio of voltages within, and between the pre-amp and power amp sections of the amplifier. The idea being that once the ideal tone has been dialed in, if the voltage is raised or lowered proportionately, the tone will stay intact, as will the dynamic response of the amplifier… regardless of level. This is a bold statement, and an interesting solution to the volume issues that come along with this type of amplifier. However, the one part of the Marshall tone recipe that changes via Power Scaling is the amount of output transformer saturation present in the tone, which decreases as the power is reduced (unlike when using an attenuator). Some love the side shifting, swooshy swirl of a transformer being overloaded. Others find the artifacts of an over-taxed output tranny and the ghosting that accompanies them as tonal taboo. I for one missed that stuff, but I see it as being a personal thing…not a better or worse situation at all.

soultonebackThe amp I have is a 2x12 combo based on the venerable Marshall JTM-45. To some this is the “Holy Grail” of Marshall tones. I myself have a tremendous soft spot for these amps and have chased this sound in particular for a long time. Just about every new builder is offering their interpretation/refinement, or in some cases a faithful replica of the JTM-45 tone. The Superplexi (tm) is firmly based in the former category. The combination of its lean, more refined, and potentially more aggressive voice with its modern feature set puts the JTM-45 PS in the 21st century. The starting point is still classic Marshall, but rather than repeating some of the design quirks of the original, Soultone has refined the design. The Superplexi tm is really very well engineered, and as a result, is a bit more polished sounding and versatile amp than an original JTM-45. One particular refinement is the separate DC heaters used in the amp. This makes the amp extremely quiet at idle, something I wish could be said about my vintage Marshalls.

The tube compliment, sonic character and appearance of the amp are still essentially that of a Marshall. Three12AX7 tubes drive the pre amp, a 5AR4/GZ34 tube rectifier and two KT66 tubes (though other tubes can be used or mixed for new tones- I used a pair of EL34) put out a maximum of 32 watts. One has the option of making this amp produce more gain than an original JTM-45 by using its buffered tube FX loop as an extra gain stage, or with the implementation of the “fat boost” function in the pre amp. The feel of the amp can be tightened up via the solid-state rectifier switch, which also gives more headroom if spanky cleans are the tonal objective.

The classic four hole input set-up is straight from the plexi amps of yore, and so is the front panel's metallic gold appearance. Jumping channels and all the old Marshall set up tricks still apply, though the tone controls are a little more powerful/active. So, with the exception of the Power Scaling controls, it’s got the traditional 6 knob set up, with presence, bass, middle, treble, volume I and volume II. Bottom line: you’ll feel right at home if you know your way around an old Marshall.

So how does it sound? You decide!

The first clip is played on a strat. I was shooting for a nice overdriven sound that could clean up via picking pressure and at the same time sounded good with the Fat boost engaged for solos. I used the Normal channel’s high gain input at 8 with and jumped the Bright channel, low gain at 4 on it’s volume. Settings: Presence at 5, Bass at 6, Mid at 9, Treble at 6. No power scaling.

I used my 1986 ‘57 AVRI strat with VV pickups from DiMarzio. The delay is courtesy of my TC 2290 and the reverb is a plugin added in post from my pro tools rig. I recorded the guitar in one take with a single AKG 414 into my chandler Mic preamp.


The second clip is focused on the cleaner side of the amp. Once again my strat handles the majority of the tune. The solo is my 335 with pat sticker pus- I’m using the neck pickup. This time it’s the lo gain input from the Normal channel alone. Volume is up at 4. Tone controls are the same as above…as is the signal chain and mics. The Solo is recorded using the bright channel, high gain input with the Normal channel jumped. Bright Volume is at 5 and the Normal channel is set around 6.


That wraps it up! Next up in this series we’ll take a listen to Sommatone Amplification’s Roaring 40 and their new high gain offering, The Outlaw. Look for upcoming articles featuring Wallace Amps, Morgan Amps, Danocaster Guitars and Bombshell Guitars…all TGP members!

Stay tuned and stay positive.  ~ Jack

Editor's Note:

Here is a thread on the TGP Forums discussing the article:  Thread Link

Builder's Note:

I discussed the Power Scaling with the reviewer, and the main problem was that he found the two knob type power scaling to yield unfavorable results in comparison to the single knob adjustment of the UA. The underlying issue is that the player needs to adjust the Power Scaling Drive level at a slightly different ramp than the Power level, which becomes increasingly imbalanced when scaling below 70%. An improper adjustment will produce awful tones!

I completely agree with this assessment, however I would like to add that there is a flexibility afforded in this design that some players will find desirable, and that with experience the controls can become second nature. Adding an attenuator to your toy collection can give you the best of both worlds, providing complete control of preamp drive levels, power tube clipping, transformer artifacts, and final volume levels!

Kudos to Jack Devine for such exceptional playing and songwriting - if only there were a Grammy for amp clips!

Mickey C.
Soultone Amplification, Inc.