Owners Manual

TECHNICAL NOTES

SWITCHING ON

The power switch is located on the right hand corner of the front panel. Flip the switch up to turn on the

Limiter Compressor and down to turn off .

TUBE LIFE

As with all tubes, their quality degrades with age. This is due to cathode emission, a natural process found in

all tubes. We recommend that you have your unit checked every 4-5 years, depending on usage, usually the

limiter will require re-tubing after this time has elapsed. Furthermore, any adjustments such as meter

calibration should be performed when the unit has sufficiently 'warmed up'.

NOTE

Almost all compressors have only two "gain" controls of a possible three: Input, Threshold and Output. With

all three theoretically one is redundant. Utilizing a Dual Input has confused some "engineers" when it was

needed for two different sounds. Simply find a good compromise position on the Dual Input and use the

Threshold and Output as usual. The Input control is very useful with stereo material - try it - but it is not

meant to be used for stereo "fades". Use it to set up a general level and final tweaking.

The principle of operation of this unit is based around a 5670 variable-mu (variable gain) double

triode operating in a fully balanced or symmetrical circuit.

Because of the need to preserve symmetry, a balance-adjustment pre-set potentiometer is placed

onthe vertical circuit board adjacent to the 5670 variable-mu double triode. This control is set so that the two

individual triodes amplify equally. (See Adjustments Section).

The benefits of utilizing a variable-mu vacuum tube as the 'heart' of the limiting (or compression)

function is that a widely varying range of input signals can be handled in a rapid-acting without introducing

harmonic distortion - unless the operator / engineer wishes to do so for creative reasons.

As with all compressor limiters there will be little change of gain reduction with various settings of

ATTACK and RELEASE controls using a sine wave source. With music there will be changes in the amount

of gain reduction with changes of these controls.

OPERATION

OPTIONS

EARLY VERSIONS

Originally we used 6386's as the variable MU tube. These are now too rare. They will not directly

replace the 5670 in your unit without component changes. The 7044 output tubes are an improvement on the

original 12BH7 - Higher output current and better consistancy being the prime reasons. We also improved the

transformers from the first units made.

Also available: MASTERING VERSION-- with 1/2dB THRESHOLD, and OUTPUT CONTROLS,

5 POSITION INPUT PRESET SWITCH, 12 POSITION ATTACK CONTROL. All built up on Grayhill sealed

gold contact switches for maximum sonic integrity, repeatability, and accuracy within immeasurable

tolerances. The panel has each step marked for precise recall. Retail price is $5,000 USD.

There is also an option to emulate the verticle/lateral switch found on Fairchild 670s. This provides for

some M/S coding/decoding. We provide both input and output switches.

Other possibilities include sidechain inserts, remote metering, etc. Avoid ordering all possible options -

there is only so much we can fit.