The Chandler Limited RS124 Compressor is a modern recreation of exclusive Abbey Road compressors that use the variable voltage gain characteristics of tubes for smooth compression and character.
Until the rise of independent recording studios in the ’70s, recording equipment was mostly custom made, or made to be sold specifically to the industry. The average musician of the ’50s and ’60s never thought about owning an Altec 436B compressor, let alone be aware of its existence. Things are a little different these days, and thanks to Chandler Limited, audio processors that shaped the sound of popular music from its infancy have become available. Speaking of the Altec 436B, it was a tube compressor found its way into Abbey Road Studios but proved to be insufficient. As such, EMI engineers gave it a thorough going over to bring it up to Abbey Road standards and the RS124 variable tube-gain compressor was born. The sound of the RS124 compressor left its sonic imprint on virtually every Beatles session. If you wanted that sound for your music, your only option was to record at Abbey Road, since the RS124 was not commercially available—that is until Chandler Limited reimagined the RS124 compressor for the modern age.
Chandler Limited RS124 Compressor—Just the Facts:
- Variable transconductance (Mu) compression circuit
- Three favorite historic RS124 compressors in a single unit
- 11 recovery options (six release, five “hold”)
- Hold function presets compression level to prevent abrupt compression onset or level dips
- SuperFuse mode for faster and more aggressive character
Chandler Limited RS124 Compressor—Under the Hood
The RS124 is a variable transconductance compression circuit. Transconductance, otherwise known as variable Mu,* is the ratio of the change in output current to an input voltage as passes through an active device, such as a tube. In essence, output current decreases as input voltage increases. Hence, clockwise adjustment of the RS124’s input control simultaneously raises the incoming signal level, while lowering the compressor’s threshold and increasing the amount of compression applied to the source material. It is this operating principle that’s responsible for the creamy smooth compression of the RS124 and its ability to tame transients without punching holes in the mix.
Along with features found on the original counterparts, the Chandler Limited RS124 Compressor includes modern facilities such as adjustable attack, selectable output impedance, and a special twist, know as SuperFuse.
*(Variable Mu® is a registered trademark of Manley Labs)
Three RS124s in one
Since the original RS124 compressors featured a fixed attack time, i.e. the attack timing was hardwired internally to a set time constant, not all RS124s shared the same values. Each historic RS124 was unique, exhibiting its own character and personality, variances between units were enough so that Abbey Road engineers would request a specific serial numbered unit depending upon the source material it was to be applied to.
Not only does Chandler Limited make the RS124 available for the first time ever, it has three attack settings that harness the sound and personalities of Abbey Road Studios’ favorite historic RS124 Compressors (Ser. No’s 60070B, 60050A, and 61010B) still in use at the famed studio to this day, all in a single unit.
Recovery and Hold functions
The RS124 provides six recovery or release time options with five corresponding Hold positions. Setting the Recovery switch to any of the Hold positions will keep the source signal compressed to the most recently processed peak level.
Historically, the Hold feature was an ingenious way to prime or preset the compression level of the incoming signal as a way to overcome potential processing issues. To prevent abrupt compression onset at the beginning of a track during mastering, Abbey Road engineers would roll tape forward to the highest peak level and set the RS124 to the nearest available Hold position from the desired Recovery setting. With the compression level held or preset, the engineer would rewind the tape and begin from the top of the track, and any artifact of initial compression onset was removed.
Another use of the Hold function was to prevent level in-rush when there was a precipitous drop in level during quiet passages of a track below the compression threshold. Here again, engineers would switch the Recovery control to the nearest Hold position until the quiet passage had passed, before setting it back to the previous release value.
What is Superfuse mode?
While Chandler will not divulge the inner workings of this special feature, all you really need to know is that it changes the normally unflappable British personality of RS124 to become faster and more aggressive overall (or more American, if you will). When activated, the source material may become more lively and appear to jump out of the monitors. Warning: Superfuse is highly addictive.
First designed in 1960 by Abbey Road Head of Technical Bill Livy, Deputy Head Len Page, and seasoned EMI Audio Designer Mike Bachelor, the Abbey Road RS124 compressor is one of the most desired and mysterious pieces of recording gear ever developed.
The RS124's undeniably smooth character and ability to tame transients without muffling the sound at steep compression levels quickly became popular with Abbey Road Studios engineers and widely used throughout the now historic studio, for tracking, bus compression, mixing, and mastering. They were so integral to the recording and mixing process that a pair can be seen in almost every control room photo in Abbey Road Studios during the 60s period.
Through the years, from incomplete information and supposition, some have tried to recreate the holy grail of tube compressors, though never fully capturing the elusive Abbey Road RS124 in all its glory.
Schematics themselves only told part of the story, and access to Abbey Road Studios’ historic units and various handwritten modification notes would prove paramount towards understanding the true nature of the Abbey Road RS124 compressor and variances between units.
Many revisions were carried out since its inception, and as a result, the inner workings of the Abbey Road RS124 valve compressor has remained an enigma wrapped in a mystery for decades—until now.
Along with features traditionally found on the original counterparts, Input control, Output attenuation, ‘Recovery’ (release) control and the unique ‘HOLD’ setting, the Chandler Limited RS124 Compressor includes modern facilities such as adjustable attack, selectable output impedance, and the aforementioned SuperFuse.
Standard units come with variable Input and Output control. Stepped Input and Output controls are available via special request for an additional fee– notify your dealer prior to order.
Bring home the previously unattainable sound of not just one, but three legendary RS124 compressors reimagined for the modern era, thanks to the persistence in the ingenuity of Chandler Limited. For more information, call or chat online with your PAD Studio Specialist today—or order your RS124 now.
- Channels: Mono
- Circuit: Tube (6BC8,6CG7, 6AL5)
- Inputs: XLR (pin 2 hot)
- Output: XLR (pin 2 hot)
- Transformer balanced I/O (custom wound)
- Input Control: Variable (stepped special order)
- Output Attenuator: Variable (stepped special order)
- Attack: Selectable, Stepped (9 settings, including 3 Abbey Road Historic serial numbers)
- Recovery: Selectable, Stepped (6 settings, and HOLD)
- SuperFuse (switchable mode)
- Output Impedance: 200/600 ohms, switchable
- Stereo linkable: Standard 1/4" jack
- Internal power supply