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Retro Instruments Sta-Level Matched Pair

Matched pair of Retro Instruments STA-LEVEL that comes with custom a stereo link switch panel.

The Retro Instruments STA-LEVEL is a replica of the legendary 1956 Gates STA-LEVEL. The STA-LEVEL dominated the sound of hit radio in the 1960's. Now these super musical sounding compressors have found their way into today's hits. The Retro Gold Edition celebrates fifty years of the products existence. Each Retro STA-LEVEL is point-to-point hand wired in the normal tradition. We wanted to fully capture the magic of the original sound. We think you'll find it very useful in your studio.

The Scarce 6386 Tube
The STA-LEVEL uses the scarce and coveted 6386 tube in a classic G.E. circuit design. Scarcity is no longer a concern. The Gold Edition STA-LEVEL can use a pair of commonly available 6BJ6 tubes in place of a 6386! The choice is yours and the sound is undeniably true to the original.

The Original 6386 Circuit
The original 6386 compressor developed by G.E., The Unilevel, utilized a novel program controlled release circuit. Several manufacturers began creating compressors using this wonderful sounding 6386 design. Models were made by RCA, Collins, ITA, Metron, CBS Labs, CCA and Gates. The STA-LEVEL implementation creates density and consistency while minimizing typical compressor side-effects at up to 40dB of gain reduction! The program path is push-pull and transformer balanced to cancel control-induced distortion. A 6V6 output stage provides wide voltage swing allowing 40 dB compression and line output of up to +24 dBm. The result is that the STA-LEVEL brings a uniquely familiar intimacy, air and warmth to your tracks.

One Trick Pony
Most all compressors and limiters bring out some noticable detail because of the nature of attack time on peak transients. Compression also pulls up softer sounds which creates useful density. The most critical aspect of a compressor is the musicality in which the gain is changed over time. The STA-LEVEL original attack and release times are very well chosen to minimize the audibility of pumping and distortion while adding the desired density and consistency. The release time is also dependent on the 6386 transconductance so it becomes a non-linear function, releasing faster at higher gain reduction amounts. In dual mode, another constant is added that further creates density and masks the sound of the slower constant acting as AGC or "gain-rider".

The STA-LEVEL adds a pleasing transient distortion manifested as subsonic punch. This subsonic energy is created at gain reduction attack periods and accentuates the natural attack waveform of the audio material. It is referred to as VCA thump by circuit designers and occurs from imbalances in the VCA response to control bias. It is a very characteristic sound of real tube compressors that make them so useful. Subsonic energy present in a live instrument or performance are easily lost in the recording process. The STA-LEVEL brings back the live realism. Furthermore, your recording processes down the line will have new usefulness and meaning. Real vacuum tube compression is the one trick pony you will applaud again and again.

Revisions to the original design include: Tube balance can be instantly aligned on-the-fly without test equipment; Uses 6386 tube or a pair of 6BJ6 tubes; Two or more STA-LEVELs can be coupled together for stereo, surround or sidechain operation; XLR transformer balanced input and output; IEC Power Connector; Hand matched audiophile-grade coupling capacitors; High quality, custom wound transformers used throughout; top AND bottom plates; Internal component safety cover.
The Couple Jack
The coupling jack allows you to couple two or more units gain reduction. A diode can be used to "reference couple" two or more units. This is useful to send a midrange reference control signal to a bass compressor in a multiband configuration or for sidechain subsonic enhancement or ducking purposes.

Faster Recovery
We now build new units standard with a six position recovery selector which allows the Sta-Level to go from the stock slow recovery to medium, fast and very fast in six steps. We also added a three position switch inside that captures three different classic tube compression flavors. Position One is the stock single time constant for attack. Position Two provides very musical dual time constants. Position Three is dual time constant with very fast attack like the famed Fairchild 660 and 670. Let's record!

Balance Nulling
You can check a new STA-LEVEL circuitry balance without test equipment. Listen to the output while holding the BAL. NULL button, adjust the BALANCE control for minimum 60 Hz. You have just balanced the gain of the push-pull circuitry! If the null is at the edge or end of the control range, you likely have a weak tube or bad component. It's easy to check whenever you like.

Custom 6386 Board
The 6386 Board uses a pair of 6AU6-family tubes. The choice of tubes has a significant effect on the sound of your compressor. We always hand-select a pair that performs closest to the original 6386.

We have several 6386 tubes around the shop. They are all unique. Some are noisy. Some are poorly matched. Many times they will not maintain match with varying bias (gain reduction). Fortunately if you have a 6386 that isn't matched well, they can still sound fine in the STA-LEVEL. A decent 6386 performs well in terms of noise and microphonics. If a STA-LEVEL sounds bad, the original coupling capacitors probably need to be replaced!

The 2C51/5670 is a tube that is pin compatible with a 6386. The transfer curve is radically different and will produce an undesirable compression ratio curve. The 2C51/5670 is also very microphonic in the STA-LEVEL application. Don't use it.

The Retro 6386 Board has a rectifier for the filaments, keeping this circuit hum-free when using the following tubes with varying characteristics. Here are most of the tubes that will work in the board. We only recommend a few of them for use in a STA-LEVEL. It's always best to use a matched pair. We check the bias curve, noise and microphonic performance. Many of these tubes were used in TV sets and radios and are plentiful.

6AU6, 6AK6, 6CG8, 6AH6, 6BA6, 6BH6, 6BJ6, 6CF6, 6265, 6136, 5749, 5725

We have these boards available for retrofitting many 6386-based units. Please contact us for information specific to your model.
  • Delivered with custom stereo link switch panel
  • Gain Reduction Threshold: Continuously adjustable from +24dBm to -20dBm
  • Available Gain Reduction: 40dB
  • Total System Gain: 35dB (with standard input and output pads)
  • Distortion: 1 percent or less from 0-30 dB gain reduction
  • Frequency Response: ± .25dB from 20-20,000 Hz
  • Noise: -70dB or better referenced to gain reduction threshold
  • Output Level: Continuously adjustable from -40 dBm to +18 dBm
  • Input Impedance: Accepts low impedance active or transformer balanced 0-600 Ohms
  • Output Impedance: 600 Ohm transformer balanced, terminated and resistive pad coupled
  • Tube Complement: 6386 (or 2-6BJ6), 1-12AT7, 2-6V6GT, 1-6AL5, 1-OB2, 1-5Y3
  • Power Requirements: Three prong IEC 100-125 VAC, 50/60 Hz, 45 Watts
  • Mounting Requirements: 3U metal rack 5.25" high, 19" wide, 8" deep
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    For more information about the Sta-Level Matched Pair, please visit the website of Retro Instruments
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