The Schaffer Replica is a unique instrument effects unit with an equally unique backstory. Spanning four decades, three continents, and involving a world famous rock guitarist, a prolific inventor and an obsessive music fan from Italy, there is an almost cinematic quality in the narrative that traces the steps taken to reintroduce the world to the captivating tone that may have otherwise been lost forever.


Born in Texas, but raised in Rome, Fil “SoloDallas” Olivieri had been obsessed with AC/DC’s Back in Black (the second best-selling album ever with 40 million sales worldwide) since its release in 1980. In a quest to replicate the album’s distinctive guitar tones, Olivieri began purchasing the same equipment used by lead guitarist Angus Young (late ‘60s/early ‘70s Gibson SG guitars, late ‘70s Marshall amplifiers), but as close as he got, it was obvious there was still a key ingredient missing.


Guitar Player Magazine, 1984

Fil "SoloDallas" playing his Gibson SG Guitar, with AC/DC shirt and Star Wars Stormtroopers

Fil “SoloDallas” Olivieri

Eventually, he happened onto a 1984 interview with Angus Young in Guitar Player magazine (“Angus Young: Seriously”, Guitar Player, February 1984). A question was asked about the recording of AC/DC’s iconic Back in Black album: “Do you use any effects?” Young’s reply was “I just have a Schaffer-Vega wireless system.” That next month, in Guitar World Magazine, he elaborated: “Yeah, I use the Schaffer-Vega. I’ve been using that since ’77. On the receiver you’ve got like a monitor switch you can boost the signal and in the transmitter you’ve got the same sort of thing. You can really give a guitar hell with ‘em. I have used the remote in the studio and it worked really good.

Olivieri wondered why anyone would mention a wireless system as an answer to a question regarding effects. Wireless systems help musicians run around on large stages without getting tangled in yards of cables and are not usually thought as functional tone shaping devices. He scoured the globe trying to find one of these elusive 40 year old units. (Only 1000-odd were ever made.). What could be there in a wireless system that would cause Angus Young to use it even in the studio, just feet from his amps? It may sound sort of strange that a wireless system may be worthy of just an audio circuitry replication. The Schaffer-Vega Diversity System was used by many artists of the magic era of the 1970s, even in the studio. It is really the case with Angus, who began using it from 1977 to at least 1984 (documented), in the studio, recording with it all the solos and overdubbing some rhythm parts of Powerage, Highway To Hell, Back in Black, For Those About To Rock and Flick Of The Switch.

What could be there in a wireless system that would have caused Angus Young to use it even in the studio, just feet from his amps?

The Missing Link

Ken Schaffer and Fil "SoloDallas" Olivieri

Ken Schaffer and Fil “SoloDallas” Olivieri

The Schaffer-Vega Diversity System (SVDS) had already succeeded in its raison d’être: revolutionizing rock ‘n roll staging. Less known is the fact that many SVDS users took their units into the studio with them and recorded with it. The Schaffer-Vega system introduced a new twist to a process called “companding.” Angus used the SVDS’ proprietary processing and companding to shape his sound and create his unmistakable signature.

Not without some hesitation, Fil finally reached Ken Schaffer in early 2011 – pleading for Schaffer’s help in getting his hands on one of these magical units. After many heart-to-heart conversations and awestruck by Fil’s 30 year dedication and perseverance, Schaffer felt inspired to give Olivieri his last two functioning units.  Ken’s last two remaining “souvenir” units were on their way from the back of his closet to a “better home,” Fil’s, in Rome.

Olivieri:Finally getting these units was a dream come true for me, as that sound had been haunting me almost all of my life. Indeed, once the Schaffer-Vega was in connected, there, for the first time in 30 years, were those pure tones sought after by everyone. Schaffer’s system was the secret ingredient in creating these sounds.

Moments after Fil plugged one of his numerous Gibson SG’s into the 37 year old SVDS transmitter, ran the receiver into his Plexi… Instant Angus!

It took only a few demos before the 15,000 member SoloDallas blog’s community of tone-hunters began scrambling to get one of these magical units.

Says Olivieri, “I thought that many more people deserve and want that tone. The idea of a one-to-one audio replica of this great system came to be born.”

It was then that Fil asked Schaffer to condone his producing a replica – an audio replica, not a wireless – of the SVDS to be used for those – like himself – in love with that iconic sound. With Schaffer’s blessing, Fil hired a team of electronics experts in Rome and Vienna to reverse engineer the SVDS to re-create it in the form of a non-wireless unit, under the company name SoloDallas. Development and reverse-engineering were slow but steady. It took roughly two years of hard work before the first working prototypes were manufactured in 2013. It was a very low-key endeavour, with very little advertising, destined primarily to the members of the SoloDallas.com blog community. Pre-orders rolled in, certification was completed shortly after, and production of the first 25 units began in Vienna, during the Christmas Holiday season. The Replica was oficially introduced at NAMM and the first pre-ordered units finally shipped in January, 2014  – The Schaffer Replica was born.

Angus Young Gets His Sound Back

The story then comes full circle when The Schaffer Replica Gold Tag SN#001 was delivered personally to Angus Young at the Warehouse Studios in Vancouver, Canada, where AC/DC was recording their 2014 album “Rock or Bust”. The Schaffer Replica was used throughout the entire album – he’d rediscovered the secret to the best tone he’d ever had!

You can read about that incredible meeting directly from Fil.

“Rock or Burst” is AC/DC’s first album since 1983 to employ “the Schaffer Sound”.

Angus got his sound back.

In fact, he liked it so much he has been using it on tour ever since, as seen on Premier Guitar’s AC/DC Rig Rundown.

Angus Young & Ken Schaffer at the NYC Palladium, 24th of August 1977, as the first Schaffer-Vega Diversity System was delivered to AC/DC.

Ladies & Gentlemen… 37 years later, the same two folks doing quite the same thing; AC/DC “Rock or Bust” recording sessions, Vancouver, BC.

Keep in mind that AC/DC’s Back in Black is one of the best-selling albums of all time. Much of the lead guitar tone of Angus Young from that magic era is due to the Schaffer-Vega. The SVDS sported a clean boost, a compressor and an expander (companding), and a optical limiter in its audio circuitry, allowing it to further overdrive the amplifiers and add a unique signature to the sound. As with all guitar effects or sound effects in general in the known universe, some will like it and some won’t. We have tested the original Schaffer-Vega and its Replica extensively for two years and published many videos with it.

Nothing is new…

G93R3394 (1)

…except what has been forgotten.

And the story doesn’t end here.

Scores of the Replicas’ initial users found that both versions of the Replica indeed contributed the SVDS’s legendary character through a wide variety of amplifiers – not only tube, but also cheap solid state – and even emulation software. Its signature tone still makes the difference, being recognizable as that sound: a definitive replication of the audio effect of the original SVDS.

The Schaffer Replica is not just an “AC/DC tone device” anymore – it has gained a life of its own. The Schaffer Replica’s reputation within the music community has grown steadily. Gilby Clarke and Richard Fortus (Guns N’ Roses), Doug Aldrich, Phil X (Bon Jovi), Elliott Randall, Steve Stevens and keyboardist Derek Sherinian are among its current adherents, but its appeal isn’t limited to guitarists/bassists or even rock musicians. Our products were found to work excellently in a number of different musical styles – recording engineer Clint Gibbs (whose credits include Shakira, Miley Cyrus, Nicki Minaj and Wiz Khalifa) is finding new applications for the effect in the studio, mainly with keyboards. Many big names of the music industry added the Schaffer tone to their setup. While it’s not a big surprise since the original Schaffer-Vega Wireles System had to work well with a large range of instruments (bass, guitar, miked strings, brass etc.), it’s still a very rewarding accomplishment.

The overwhelming success prompted us to step up our game to keep up with the demand and the decision was made to move production to the United States of America.

Being true to our isolated obsessive nature (term coined by The Police’s Sting to describe a handful of his friends, notably Ken Schaffer), we couldn’t rest until we made sure that our products captured the very essence of the original SVDS. While our first attempt had been extremely successful, a second reverse-engineering of the Schaffer-Vega was in order now that we truly understood the potential of this forgotten piece of kit. Nothing less than perfection was accepted.

Nevertheless, we continue striving to make our products even better whenever possible.

Thank you for being with us.

What is The Frequency, Ken?

Ken Schaffer in his shop in the late 1970s.

In 1975 American inventor Ken Schaffer created the first dependable, beautiful sounding wireless system for electric guitar and bass. Little did he know he was also creating a circuit that would transform the sound of rock and roll.

The original Schaffer-Vega Diversity System (SVDS) was the first reliably working and beautifully sounding wireless system for musicians or, in general, stage performers. Other wireless microphone systems pre-dated the SVDS, but never became widely adopted because even the best of them lacked reliability (fade-outs, police and taxi dispatch calls!) and their sound was nothing to cherish, especially at high decibel rock n’ roll sound levels. When attending to a Rolling Stones soundcheck, genius inventor Ken Schaffer was baffled by the amount of interference and fade outs that plagued the current-generation wireless units being used by Mick Jagger – he thought he could do better – and he did. Thus, the Schaffer-Vega Diversity System was born.

Ken Schaffer was a New York-based recording engineer-turned publicist who had moved on from the record business in order to focus on being a full-time inventor. The first wireless prototypes saw light in 1976 and in 1977, full production was running. The Schaffer-Vega Diversity System was catching on with some of the big names in rock. One of the early adopters was KISS, whose motivation was one of practicality since guitarist Ace Frehely once had to be revived after having been shocked by a guitar cable connected to an ungrounded amplifier. Within a few years, you couldn’t throw a brick in a room full of household name guitarists and bassists without hitting someone who was using the SVDS in a live setting; Eddie Van Halen, the Rolling Stones, Bootsy Collins, Peter Frampton, Frank Zappa and numerous others were all SVDS users. However, Schaffer designed it to boost low-mid range frequencies usually lost in wireless transmission, as well as to compand (compress then expand) the signal, thus providing the added side effect of enhancing the instrument’s tone. Numerous groups decided that, apart from serving its basic function, the SVDS also sounded good and began using it as an effect in the recording studio – namely Electric Light Orchestra, Pink Floyd (The Wall) and, of course, AC/DC, beginning with 1978’s Powerage.

Says Angus Young, “George [Young, Angus and Malcolm’s older brother and first AC/DC producer] had suggested that I use the SVDS in the studio in 1978, then when Mutt Lange came in [producer of Highway to HellBack in BlackFor Those About to Rock We Salute You], he asked me to use the same stuff that I was using for my stage sound, so we used the SVDS again.”

This unit changed the way Angus Young sounded and played.

This unit changed the way Angus Young sounded and played.

The device was prohibitively expensive for the time ($4.100USD, roughly $20.000 USD in today’s money), but famous performers did not hesitate and bought one (or two! Pink Floyd bought 20!) units because of its quality and reliability. It was probably the only choice for use with live musical instruments in the 1970s. The SVDS was actually used well beyond 1981 (year of cessation of production) by some artists – there are documented pictorial evidences of this (Pink Floyd’s David Gilmour for instance, as pictured here in the mid 80s).

Schaffer’s design incorporated two antennas – as used by the army – so when one antenna would go down, the other one would still pick up the signal (such a setup was called a diversity system), as well as an ingenious pre-processing circuits to preserve the integrity of the wireless signal. Notably, a mirror-image paired compressor and expander increased the radio circuit’s dynamic range to over 100 dB, 35 dB greater than the theoretical maximum that could otherwise previously be achieved within the bandwidth limits covering wireless systems by the US FCC. Schaffer wanted to make sure that the SVDS would be capable of being used with musical instruments such as electric guitar, which, according to Schaffer himself, was a much more difficult task to accomplish because of the guitar’s stronger attack and richer harmonic content.

Beyond the staging freedom afforded by Schaffer’s wireless, many A-list players discovered something unintended: the sonic result was pure magic! The wireless design’s unique preprocessing enriched their signal with copious amounts of harmonic content unlike anything they’d ever heard. News traveled fast. Schaffer’s wireless units became the system of choice for nearly every major artist of the mid-70s to mid-80s.

By 1982, after becoming interested in other endeavors, including intercepting internal Soviet television for the U.S. government in the waning days of the Cold War, Ken Schaffer ceased production of the Schaffer-Vega Diversity System. Soon, new, stricter FCC regulations on wireless specifications prohibited fully-analog wireless systems of its caliber from being used. SVDS artists – including AC/DC – were forced to move on… the legendary “Schaffer Sound” slipped into obscurity.

To listen to more stories directly from Ken Schaffer – listen to this great intervew by the AMPS & AXES SHOW.

AC/DC, Aerosmith, America, Bay City Rollers, Beach Boys, Billy Joel, Black Sabbath, Blondie, Bob Seger, Bob Weir, Bob Welch, Bootsy Collins, Boston, Bruce Springsteen (Clarence Clemons, Steve Van Zandt), Chic (Nile Rodgers), Derringer, Earth Wind & Fire, Electric Light Orchestra, Elvin Bishop, Fleetwood Mac, Foghat, Foreigner, Frank Zappa, Heart, Heatwave, Janis Ian, Johnny Guitar Watson, Kansas, Kiss, L.T.D., Mahogany Rush, Mandre, Nektar, Pat Travers, Peter Frampton, Peter Gabriel, Pink Floyd, Randy Bachman, Rolling Stones, Rufus, Stephen Stills, Steve Miller, Styx, A Taste of Honey, The 5th Dimension, The Grateful Dead, Thin Lizzy, Tom Petty, Todd Rundgren, Van Halen, Yes, ZZ Top.

If one of your heroes is in this list, we recommend checking the period of time going between 1977 and 1981: likely, they were playing with a Schaffer-Vega Diversity System. There were way more than these names, yet only a total of about 1000 units were ever manufactured.

The Schaffer-Vega Diversity System

A Closer Look

Original SVDS - X10 transmitter and  EX63 receiver

Original SVDS – X10 transmitter and EX63 receiver

The Schaffer-Vega Diversity System was a very sophisticated piece of equipment and it was built like a tank – 40 years later it is still working perfectly. The system is basically a radio unit composed of a pair of cream colored transmitters (X10) and a receiver (EX63), pictured above.

“The Schaffer–Vega diversity system used a space diversity method consisting of two independent VHF receivers fed by antennas placed at least one wavelength apart. Use of two full independent receivers, rather than two parallel antennas, made the Schaffer-Vega the first “True Diversity” system. The diversity technique prevented signal degradation due to multi-path cancellation. In the Schaffer-Vega system, a comparator monitored the instantaneous RF signal strength delivered by each antenna to its dedicated receiver, that switched to the other receiver when the currently selected receiver’s signal strength fell below a quieting threshold.”

(Diversity Receivers: Musiclab Glossary of Professional Audio and Music TermsMusiclab, Australia. Retrieved February 10, 2012.)

“The Schaffer-Vega Diversity System also used companding. By compressing signal amplitude 2:1 in the transmitter and then expanding it in the receiver, it was possible for the system to deliver a signal-to-noise ratio and dynamic range of 100 dB.”

(What is Audio Reference Companding?, Shure Brothers, February 20, 2006. Retrieved February 10, 2012.)


The microphone or instrument is  plugged into the transmitter (usually with the gray cable included in the package, as pictured) and the small knob on the upper part of the transmitter controls how much signal (gain) is compressed and sent by radio.

X10 Transmitter

X10 Transmitter

On the other end, the antennas pick up the radio signal and send it to the EX63 receiver, where it’s converted back into something the amplifiers can understand. Here the magic happens – the signal compressed by the transmitter is expanded, getting back the dynamic range that supposedly could not be sent by radio due to the technology limitations of the time.

There are two audio outputs – one on the rear panel, a balanced XLR line level output, and a P10 output on the front, originally conceived for headphone monitoring – with its own amplifier circuit powering it. More often than not, the front output was used as the main signal output instead – and the amplifier circuit actually worked as a pre-amp, boosting the signal that was sent to the amp. This is how an analog radio unit doubled as a very expensive boost pedal.


So How Does it Work on the Replica?

On the Schaffer Replica and Storm, because they are NOT wireless devices, both the transmitter and the receiver are wired together in the same box.

– INPUT/POWER is the X10 transmitter gain circuit.
– OPTICAL LIMITER/SNAP is the opto-isolator found in the X10 transmitter (it was set at a fixed value in the original SVDS).
OUTPUT/STORM is the EX63 receiver monitor amplifier.

The ‘Gold Tag’

The Schaffer Replica

The Schaffer Replica Tower Gold Tag was the first version of the Schaffer Replica to be produced. It was made in Austria and limited to only 100 units. They featured a brass plate with Ken Schaffer’s signature and the serial number. Further 50 units were manufactured later due to demand, but without the tag.

First Gold Tag Batch

First 25 Schaffer Replica Gold Tags made

Constructed with through-hole components, it was the ‘premium’ version of the Replica. The enclosure was inspired by the original SVDS ’63EX’ receiver, with all the LEDs and VU meter.

A few plexiglass prototype Gold Tags were constructed for display purposes before formal production began and some of them ended up being sold, although they are really rare.

The Gold Tag Towers are also easily identifiable by the silver corners on the enclosure, which are bigger than the current generation EX Towers. The tone of those early towers is more midrangy and warmer, something that a lot of players actually still prefer to this day.

There was a manufacturing defect in the first 25 units batch – two components were reversed – and the mistake was not detected until after most of them were shipped. These were known at the time as the “Overpowered” Replicas because they had a stronger output than intended, at the cost of the tonal quality (muddier, less defined sound). Most of the defective units were recalled and repaired, but there might be one or two that were not returned and are still in overpowered condition. SN #001-025 were the only affected.

Note: SN #001 was fixed before delivery to Angus Young.

We offer a special upgrade for the Schaffer Replica Gold Tag – a board with the opto-isolator limiter can be installed to bring it closer to the current generation EX Tower. Please contact us for more details.

The Schaffer Replica Gold Tag was sold</> out very quickly and is currently out of production.

The Schaffer Replica Pedal

The second iteration of the Replica produced was a much more affordable and user friendly unit – the pedal version. Surface mount technology (SMD) allowed for a much more compact product while still retaining the same sound of the Gold Tag edition.

It was a success, seling well over thousands of units and amassing many awards and positive reviews.

The early Pedal and Gold Tag

Early Pedal and Gold Tag

From 2014 until 2015, all pedals were made in Austria, like the Gold Tags. From late 2015 onwards, they are made in the United States.

Current Schaffer Replica TSR4 Pedal

Current generation Schaffer Replica TSR4 Pedal

Early Austrian-made units are identifiable by their inverted jack positions – input/output goes left to right. This was not a manufacturing defect, it was a design choice made back then. US-made Schaffer Replica pedals after 2015 have a more usual right to left input-output jacks. They still require a 12v center-positive power supply.

The Schaffer Replica Pedal is still being manufactured, although with different graphics, in the same enclosure as the first generation TSR pedals. It is now offered as the Schaffer Replica Classic TSR4 Pedal.

Tone-wise, the TSR4 shares the same character as the first generation Gold Tag Tower, although it received a few improvements and revisions over the years. It’s still a very popular product because of its stronger and more present midrange attack.

For people who want the first generation Schaffer Replica Gold Tag sound without tracking down one of the original 150 units for sale, this is the option that gets the closest in our current range.

The EX Tower


Rear panel

Rear panel

The Schaffer Replica® EX Tower was released in 2016 and is the natural successor of the Gold Tag Tower. After a new study of the original Schaffer-Vega Diversity System, the circuit was reworked for a more accurate voicing and several features were added in order to offer maximum audio quality and flexibility.

The most important new feature is a vintage design analog limiter derived from the opto-isolator found in the original TX10 transmitter. Previously overlooked in our first iterations of the Replica, this component delivers incredible dynamics and touch sensitivity.

Crafted in the United States with the highest quality thru-hole components, the EX Tower is housed in an exact reproduction of the original ’63EX’ receiver enclosure, which was 3D scanned, and features the distinctive rounder profile of the rear panel.

The EX Tower has a flatter EQ response when compared with the previous generation Gold Tag Tower (as is the original SVDS) and is more touch sensitive, with a lower noise floor.

It has two options for the VU Meter: classic white or blue.



The SoloDallas Storm® was released in 2016, featuring the same vintage design analog limiter of the EX Tower. It is voiced like its bigger brother, delivering a more accurate SVDS tone than previous generation pedals.

Smaller, powered by standard 9v power supply or battery, the Storm® was designed to suit the practical needs of gigging musicians and bedroom rockers alike and bring the Schaffer tone to pedalboards all over the world without any compromises, fitting in right beside other pedals from any other household brand.

Made in USA.

The circuit that transformed the sound of rock and roll is back to do it all over… Again.

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Please contact us if you have any questions.

Make sure to check our dealers list below to try and buy our products locally!

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30th Street Guitars – New York, NY
Ludlow Guitars – New York, NY
Rudy’s Music Shop – New York, NY
The Amp House – Scottsboro, AL
Kenny’s Music – Dana Point, CA
The Amp Shop – Sherman Oaks, CA
Vision Guitar – San Jose, CA
Music Gear Guys – Denver, CO
Dan’s Guitars – Honolulu, HI
Up Front Guitars – Franklin, MA
Sixx Gun Music – Saugus, MA
Memphis Backline – Memphis, TN
British Audio – Nashville, TN
Carter Vintage Guitars – Nashville, TN
Austin Guitar House – Austin, TX
The Guitar Sanctuary – McKinney, TX


Gosia Guitars – Lommel, Belgium
Diffusion Audio – Québec, Canada
Electric Mojo Guitars – Quebec, Canada
Guitar Guitar – UK
tonetheory.co.uk – UK
Henri Polizzi – France
440hz.it – Italy
Merlin Guitars – Rome, Italy
YourMusic – Rome, Italy
Thomann – Germany
Miyaji Imports – Tokyo, Japan
Ikebe Guitars – Tokyo, Japan