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 211%/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.
Technical
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
21 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
Hovland Musicap 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
De-Essing
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’
