Independent Reviews of The Ultimate Tone Book Series

The following are independent reviews of our The Ultimate Tone series of books by Kevin O’Connor. Our thanks to the reviewers for sharing!

“The Ultimate Tone – A Book Review of the Best DIY Guitar Tube Amplifier Series”

Published March 29, 2010
by Mark Douglas Roberts,

See original review of The Ultimate Tone Series

This article is a book review on a series of six books that is the most comprehensive and lucid explanation of guitar tube amp architecture, circuits, tone, components and construction technique for DIYers I have ever found. The review deals with each book separately and recommends purchasing them in a specific order to grow your knowledge in step with your building experience.

Kevin O’Connor of London Power has created a series of books under the main title of “The Ultimate Tone.” These books are truly unique and carefully tailored for the Do-It-Yourself (DIY) guitar tube amp hobbyist and boutique amplifier builder. The books have a home-made ‘feel’ as well… all the illustrations are done by hand and the books are photocopy-printed on 8.5″x11″ paper and bound with plastic spines and clear plastic covers. There are six books in the series now with the most recent being released in the late spring of 2008.

You may want to buy the entire series all at once and get a modest savings, but I think you should consider buying them one at a time and digest as you go, building projects along the way. A key point though… you don’t necessarily want to buy them in numerical order. I recommend the following sequence:

The Ultimate Tone Volume 3 – Generations of Tone
The Ultimate Tone Volume 5 – Tone Capture
The Ultimate Tone Volume 2 – Systems Approach to Stage Sound Nirvana
The Ultimate Tone Volume 4 – Advanced Techniques for Modern Guitar Amp Design
The Ultimate Tone – Modifying and Custom Building Tube Guitar Amps
The Ultimate Tone Volume 6 – Timeless Tone Built for the Future Today

The Ultimate Tone Volume 3 – Generations of Tone

This is the most important book in the series for the beginning tube amp builder.

Chapters 2 through 4 lay down the foundation of good DIY tube amp construction, filling you in on good electrical connections, grounding technique, lead dress and other wiring techniques, and mechanical layout including assembly methods like terminal strips, turret and eyelet boards.

The subsequent chapters each pick a particular ‘iconic’ amplifier, each iconic amplifier being a prototypical example of amplifiers of its class, and they are examined in detail as to the circuit topology, peculiar tonal characteristics that result and fatal flaws that the product is notorious for.

Kevin provides the original schematics and then shows how you can apply the techniques detailed in the earlier chapters to improve the performance and reliability of the icon without harming the tone. The schematics are redrawn, layouts are provided and mechanical solutions are worked out to make each chapter a complete, self-contained, build-it-yourself amp project.

This process is repeated for several variations of the Champ in chapter 5 (this chapter greatly influenced my own single-ended amp project), then in quick succession: the Bassman, Plexi, 800, Bull Dog, AC-30, Portaflex, SVT, Bass Master, Custom Special, Guitar Mate, Herzog and Laney amplifiers are dealt with.

If you can only buy one book for your DIY guitar amp hobby I’d heartily recommend this one.

The Ultimate Tone Volume 5 – Tone Capture

Volume 5 picks up where Volume 3 left off, with a project-oriented approach and some sophisticated DIY tube amp solutions for guitar and bass.

The book starts off with a chapter overviewing vacuum tube operation called ‘tube tone,’ followed up by a chapter on guitar electronics and pickup characteristics.

The next two chapters are small projects: Sigma for effects switching and Triple-X for amplifier switching.

Chapters 5 & 6 are on transformers… important components but it made me yawn, sorry.

Starting with chapter 7, all the stops are pulled out and you are in project heaven… Major (200W), Soma 84 (EL84 amp), Standard (the London Power Standard Preamp from 1995 coupled to a 50W amp using four power tubes), Doppelsonde (mixing power tube types), AX84 (discussion on the original goal of a very low output power amp), Kelly (50W from 4 6V6s), and several other projects of lesser scope.

One favorite project I did was based on Kevin’s reworking of the HotBox tube preamp pedal from Matchless in chapter 16. I built this pedal in a truly “true point-to-point style” (meaning terminal strips) in a tube pedal enclosure from Doug Hoffman, substituting a Baxandall tone stack and reworking the preamp values to be more Dumble-esqe (non-HRM type).

What would you do to match an amplifier to Yngwie Malmsteen’s style? See chapter 18, ‘Swede.’

The Ultimate Tone Volume 2 – Systems Approach to Stage Sound Nirvana

Volume 2 is not project oriented. The bulk of the book, chapters 2 through 5, deals with power supply tricks and a comprehensive overview of power amplifiers, including tube, solid-state and hybrid power amps. Chapter 3, on tube power amplifiers, has some very practical information on mods and fixes to Marshall and Fender bias circuits.

I like the 1st and last chapters of Volume 2 the best. The first chapter is a short discussion of sound stages and how you might setup your gear on stage for the best audience/band experience. The last, chapter 6, is called “Pillars of Tone” and in this chapter the major contributors tone at the block-level of a guitar tube amplifier system design are discussed one by one and Kevin provides some very valuable insight into tone shaping throughout the preamp/amplifier.

The Ultimate Tone Volume 4 – Advanced Techniques for Modern Guitar Amp Design

This is the book you’ll want to buy if you feel the need to get deeply involved with the power scaling technology that Kevin has developed. Power Scaling, coined and trademarked by Kevin, is the way you can get aspects of power amp distortion (as opposed to preamp distortion) into your tone at bedroom volume levels. Volume 4 is not DIY project oriented but explores the issues, including attenuation, power scaling (both down and up), sag, and power management, tackled by modern guitar tube amp designers.

That said, the second-to-last chapter in Volume 4 might be important for a broader group of enthusiast builders… design philosophy. In this chapter Kevin provides a hierarchical design process that could be used to make key decisions on how you approach your next project.

The Ultimate Tone – Modifying and Custom Building Tube Guitar Amps

There is no volume number in the title of this book, it was the 1st. Personally, I bought it for completeness. I specifically wanted to have the ‘perfect effects loop’ information, although the loop itself is incorporated into a project in Volume 5. TUT also has some excellent material on reverbs and signal switching methods that is not explained in the other volumes. The first half of TUT introduces/overviews tube amp systems, power supplies & grounds then focuses on preamp and power amp modifications to commercial amplifiers (e.g. Marshall / Fender)… if you are totally new to tube electronics you may want to buy this 1st volume at the same time as Volume 3.

The Ultimate Tone Volume 6 – Timeless Tone Built for the Future Today

In many ways, Volume 6 is a continuation and extension of the material in Volume 4, where Power Scaling is introduced. In Volume 6 a new ‘direct control’ version of Powerscaling is featured which was introduced in Vol 4 but flushed out with comprehensive circuits and applied to ‘sag’ and sustain control as well in Vol 6. The new scaling circuits have many advantages for a DIY builder like greater noise immunity and less sensitivity to layout, etc.

I applied the new DC Power Scaling to a Trainwreck clone project and was really impressed with the improvement in ‘playability’ at lower volumes… the unmodified Trainwreck Express circuit is just too loud for domestic use, needing to be cranked to get the sweet tones it is renowned for.

One of the chapters in Volume 6 is dedicated to the Dumble amplifiers… something I was really looking forward to since many of my hobby projects focus on those circuits. I found this short chapter to be a good introduction to the overall architecture of the Dumble amps, written from the point of view of the evolution from the early modified standard amps that Alexander Dumble started out doing, but I felt the chapter fell short in discussing some of the more important subtleties of the later Dumble models.

Volume 6 also has lots of other material in it, including a great tutorial on designing really high output power amplifiers and a great chapter on high gain amplifier designs with real-world circuits referenced and detailed.

In Summary…

Kevin’s books have a very empirical approach. He encourages you to set aside convention in some instances or not be afraid to try combinations of tubes or even pulling tubes and in all cases clearly explains why it is o.k. and points out any reasons why it wouldn’t be o.k. All the examples in the books are very practical and he certainly has the DIYer in mind as he is writing.

Kevin’s body of work is truly encyclopedic in nature, and considering that, one feature sorely lacking from his books is any kind of indexing… this is aggravated by the fact that Kevin constantly refers to previous writings rather than repeat himself in a new volume, and it is very difficult to put your finger on the reference even with the other book in hand. Perhaps search engine technology, like Google’s ability to search protected content, could be put to good use in this case and provide a kind of ‘auto-index’ on the web of all of Kevin’s books without actually giving away the book itself. Or better yet, how about an e-book format of Kevin’s entire collection of TUT books… I think all of the e-book readers include searching capabilities… and Kevin’s hand-drawn schematics would probably scale adequately and be very readable on the e-paper displays these devices feature.

Meanwhile, how do you get Kevin’s books today? The best way to get the books is to directly order them from London Power Press. They now have a shopping cart on


Effects Loop Truths


This is a discussion of effects loops as used in London Power amplifiers, and described in our book The Ultimate Tone (TUT1) – and as understood (or misunderstood) by musicians.

Effects loops have become a source of contention among players.

Some like loops, and some don’t. The original iconic amps did not have loops of any kind, so the amps could be “approached” as single functional blocks. The player cold therefore explore specific textures that would not be fully realized if he or she thought in terms of two blocks – a preamp and a power amp split by the effects loop.

Loops were a fad in the 1980s and early 90s, but many players simply did not use them properly, or at all. They received an undeserved bad reputation. However, many players persevered, and use loops correctly. Thus, such a feature continues to be desirable.

There are three common types of effects loops: inserts, side-chains and mixing loops.

The Insert

The insert is a series make-break connection, usually simply consisting of the jacks themselves.

The wide implementation of this minimal loop gave series loops a bad name. These are best suited to line-level applications or for simply connecting to passive outboard devices, as in London Power’s original STUDIO amp. An improvement on this arrangement is the simple addition of a pure buffer on either side, a form most often found in high-end mixing console channels.

The Side-Chain

Side-chain loops accommodate low-level devices in the loop with gain added only in the return signal path.

This loop type was used in the earlier versions of London Power’s SESSION amp. Passive mixing of the dry and wet signals assures very low-noise operation regardless of what is plugged into the loop.

The Mixing Loop

Mixing loops have feedback-controlled gain for transparent mixing of the return and dry signals.

A simple switch allows the breaking of the dry path for series operation. This type of loop is an industry standard described in TUT (our book, The Ultimate Tone) as ‘The Best All-tube Effects Loop’. It is used verbatim by many amp companies. In all of these loops, the ‘send’ output can be used to slave other power amps or as a line out. This type of loop is used in our SUSTAINOR amp, and in our Best All-Tube Effects Loop Kit (BFX) kit.


In our previous product line-up, the LONDON POWER SORCERER had two fully featured effects loops built without compromise. This is all-tube circuitry the way it was meant to be, configured to give modern performance and convenience. Each section of the SORCERER had separate SEND and RETURN level controls, and a GAIN switch that optimized the return path for instrument-level devices or line-level gear – that’s -20dB or 0dB signal levels in sound-man lingo. So, your pedals could go in here just as easily as that new pro piece you just picked up. This allows one loop to be “early” in the system and the other “late”. Look for a schematic of this product in our upcoming book, The Ultimate Tone – Vol. 7 (TUT7).

The original London Power STUDIO amp models had a series loop between the preamp and power amp. The loop in the 2003 STUDIO amp could be used as a gain boost, just as many mixing loops can be. The STUDIO’s loop did not have a gain switch like the SORCERER; rather, it had sufficient gain within the return path that pedal-level signals could be boosted up to match the dry path level. Inserting a patch cord between the SEND and RETURN jacks let you access this extra gain. To make this foot-switchable, an A-B box could be used in place of the cable. The SERIES switch should be ‘down’ (parallel mode). STUDIO-10 models have a series loop.

SUSTAINOR has a switchable loop that can be operated in series or mixing modes, and can have stereo returns or mono, and has variable SEND and RETURN levels. Stereo effects loops were shown in our book The Ultimate Tone Vol. 2 (TUT2).

AURORA has a series loop with controls for the send and return levels. The RETURN control is actually a variable gain so that signal-to-noise is optimised at all settings. The loop can be used for extra gain without effects plugged in.

The SUPER-STANDARD and MINI-MARSHMALLOW preamps have loops that can operate in mono or stereo, with Send and Return controls and a gain switch for 0dB/-20dB.

Loop History

In the ’70s when people first started using effects loops, the loop was just a pair of jacks with an interrupt contact on the ‘return’ jack. Usually these jacks were inserted into high-impedance circuit points that could not drive the effect inputs very well, so there would be level and tone changes when effects were plugged in.

Techs and amp designers got a little fancier in the ’80s, adding ‘Send’ and ‘Return’ controls. At least you could chop the signal down enough not to overload your pedals anymore, but you still had significant loss. So, some loops had gain added after the loop to make up for the expected loss. This gain was always there, adding noise, boosting whatever noise was coming from the preamp. Some compromise! AND …  some big-name companies are still doing this …. duuumb. (PV 5150-series, Fender Twin, the Dumblater).

In the ’90s, studio techniques were applied to the whole “effects loop fad,” and suddenly loops seemed to have something good to offer. ‘Parallel’ or ‘mixing’ loops became popular – with a lot of help from our book, The Ultimate Tone, which was released in 1995. These allowed the ‘dry’, or uneffected signal to stay inside the amp. The loop now became what sound engineers call a “side chain”. The signal is tapped off, routed through the external effects, then mixed back in with the dry sound. The effected sound is called the ‘wet’ sound – as you might have guessed!

So, what does a mixing loop do that a simple loop can’t?

With a parallel loop, you never have an instant without sound. Many of the effects processors introduced through the ’80s and ’90s would mute the signal for a fraction of a second while patch changes occurred. This meant a drop-out in your sound: a tiny slice of time filled with SILENCE. With a mixing loop, your dry sound is always there, even if your processor takes a little nap.

Still, there are times when you want really “in your face” effects sounds that need a simple series loop like those primitive amps had.

More Magic

You hear those really cool tricks on albums where a delay is being used on a guitar lead and then at the end of the solo, the echoes continue even though the guitar sound has changed back to the rhythm tone. Wow. That must be hard to do outside of the studio, right? Wrong. It’s just the difference between controlling the input or output of the effect in the loop, or ‘Post’ to ‘Pre’ effects muting. Awesome.

In The Ultimate Tone (TUT1), we called this “head” and “tail” switching. Switchable LONDON POWER amp loops all use ‘pre’ switching, where the ‘send’ signal is turned ‘off/on’ allowing the effect sound to fade out naturally like an overdubbed track.

Tube vs. Solid-state Loops

Loops can be built with equal performance using solid-state or tube circuitry. Considered as a functional block, an effects loop should provide unity gain – that is: no gain, no loss of signal – and be transparent. The presence of the FX block should itself not be obvious tonally.

Techs debate whether loops should be fully bypassable, while designers who know what they are doing realize it is best to leave the loop in the signal path at all times. A transparent loop does not change the signal. Any amp builder who tells you this is impossible needs to go back to school.

Modern solid-state loops often use a single dual-section FX mix control to set the send signal level and return gain. With op-amp circuitry this is simple, but it can be applied to tube topologies, too. Semis are about an order of magnitude quieter than tubes, but very respectable noise performance can be eked out of the glowing glass bottles.

Tube loops are more aesthetically pleasing in a tube amp, but they easily corrupt the signal if poorly designed. They are usually designed by the same folks who insist on a bypass. It is very difficult to design a solid-state loop with sonic compromises. There may be signal handling issues if the designer has not anticipated tube preamp output levels as “used by real musicians”. Fortunately, most big manufacturers have competent designers.

Where can I learn more about loops?

Our book The Ultimate Tone (TUT1) illustrates the basic loop concepts of level, send signals, return signals, mixing/series options, noise optimization and dB level references. It takes one full dual-triode tube to make a proper loop. Anything less will be a compromise to your sound, let alone to the ergonomics you might miss out on.

The Ultimate Tone – Vol. 2 (TUT2) shows the basic stereo effects loop layout, and our upcoming book TUT7 will expand on all things loopy.