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The AT-1 is a mono limiter closely based on the classic Fairchild 660 using all the original parts specified in original models of the day. The circuits for these units are the same as the 660 models which include the use of the 6386 tubes .


The Fairchild 660 is not one half of the stereo 670 version as it behaves slightly differently in operation to its stereo counter-part. These models have a different tube power supply and different tubes for the AC threshold,  as well as transformers. Standard additions to this limiter include; Bypass, External *Key* input  and a 21 x 1%/div stepped AC threshold as an option. Stereo linking is standard.



What It Does


The AT-1 is a Mono compressor with a stepped and tapered audio attenuator. It provides the user with more gain than the AT-101 and a rich tone. It has bypass, a key input stage, stepped AC threshold and stereo linking ability. All inputs and outputs are transformer balanced. Both AC threshold and gain reduction circuits can be split allowing the user to pass audio only through the tube input stage. The TC settings are the same as the stereo units with the same micro second attack times.


The AT-1 can also be used as an excellent De-esser where the 'Key' insert function is used. Sibilance can be removed effortlessly without any perception of the process bleeding on or around the ''Sibilance" band / frequency leaving your processed program smooth and transparent as before.

Here's how:  When the Sibilance signal is split and run through a band-pass filter to isolate the offending frequency range it is then connected into the side-chain input of the of the AT-1 which only compresses the signal when this frequency is present. It is important to remember that to achieve this careful adjustment of the point where the compressor is triggered is needed as compression will begin at the point where the boosted Sibilance signal is present.

(careful adjustment of the TC settings is also necessary)

An extreme version of this could be 'ducking' 




  • Original tapered 1db per step ‘T’ Attenuators (21 step total)

  • Original complement of tubes

  • Fully transformer balanced audio path

  • Newly developed 6386 Triode tubes– new feature

  • 5 &12 Watt Non-Inductive Wire-Wound resistors throughout Audio Path

  • Original Non-Inductive Pots throughout

  • 40 stepped AC threshold 1% tol pots fitted - new feature

  • Switched bypass control - new feature

  • Switched *key* input - new feature

  • Switched Stereo linking - new feature

  • Original Anode supply

  • Original CVT heater supply

  • High Voltage Polypropylene film capacitors throughout – new feature

  • Silver Mica capacitors – new feature

  • PTFE ‘Point to Point’ wiring throughout – new feature

  • Ceramic Tube sockets throughout – new feature

  • Stereo Link switch fitted – new feature

  • Simpson Electric metering

  • Top panel torque hinges - new feature

  • Original front panel

  • New Chassis Design – new feature

  • Large Knobs

  • XLR Chassis mounting connectors – new feature

  • Specially made Sowter audio transformers throughout - new feature

  • Switched IEC mains socket - new feature

  • US & EUK adjustable - new feature


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