The SA-609+ features all historic 33609 revisions.

The 33609 used a diode-bridge based topology and spawned several revisions since its inception in the late 60’s making its way into the chain of virtually every studio in the world. Unlike any other 33609 clone on the market the SA-609+ features all these revisions stuffed in into a single unit.

Each unit uses UK-made Carnhill transformers and a Class A/B amplifier with two reversed engineered BA-440 op-amps which should be the only transformers and op-amps used on this circuit. Thanks to a proprietary relay switching matrix we have managed to incorporate the most iconic 33609’s revisions into a single unit including the 33609 “Metal Knob, “C”, J/D and N revision. This means you are getting 4 legendary compressors for the price of 1. The SA-609 MK3 also overcomes the limitation of the original metal knob with the inclusion of a Super Slow attack MOD which makes it perfect from Mixbus duties on heavier music as well as a side chain high pass filter and a Dry/Wet blend control. With UK-made Carnhill transformers, reversed engineers BA-440 cards, Vishay, tantalum and polystyrene capacitors the SA- 609 MK3 retains the same transformers, op-amps and components that made this iconic unit so special making it an identical sounding replica of the vintage, thick and dark Metal Knob , the brighter sounding Rev C, the aggressive and mid forward revision J/D as well the flatter sounding revision N at the twist of a knob.

Metal Knob

Affectionately known as the “Metal Knob”, the first 33609 featured a class A/B amplifier with two BA-440 cards and Marinair transformers. It was a smooth sounding compressor with a dark top end and a huge low end. In an attempt to remain as close and faithful to the original we are using UK-made Carnhill transformers which are direct descendants from the original Marinairs. No other transformers come close, and no other transformers should be used on this circuit. We also carefully reverse engineered the original BA-440 amplifiers on the output section where all the magic happens. This meticulous combination of parts ensures that the metal knob mode on our 609 MK3 sounds exactly the same as an old 33609. Huge, dark and smooth.

Revision C

Revision C as it should have been. This unit was noticeably brighter than the previous metal knob version with a pronounced push above 6kHz and an open top end which was beloved by many engineers but lost the warmth and character of the BA-440 output cards which were replaced by BA640 IC cards which became highly unpopular amongst audio engineers. On the Stam Audio SA-609’s Rev C this has been corrected. It has present mids making any modern mix shine and bringing darker mixes back to life while retaining the warm character of the previous metal knob making it a much more desirable sounding unit. This comes as a result of respecting some critical values on Rev C but maintain the discrete BA 440 op-amps on the output and using the same Carnhill/Marinair transformers used on Rev A and B also known as the metal knob

Revision J/D

Made in the 90’s, rev J/D saw the return of the discrete class A/B amplifier and BA-440 cards per popular demand. It also presented further value changes on the circuitry which resulted in an aggressive and mid forward sound with a pronounced drop after 16kHz. We decided to incorporate these values and obtained the same frequency response making Rev J/D the most aggressive sounding one and an ideal compressor for drums.

Revision N

Based on the most current/modern unit, M revision (which stands for Modern) has an almost flat frequency response with a tight low end and smooth top end. This setting is perfect for any type of genre or instrument allowing the original frequency response to be preserved while adding the character of transformers and tantalum capacitors. The fast attack found on this unit (2ms) has been used on the fast attack setting

Super Slow Attack MOD

The SA-609 MK3 was designed to overcome the original 33609 limitations. By adding some critical new features this unit is far more versatile in the modern studio workflow. A major complaint was it was too fast with a fixed attacked time of 5ms it was excellent on subtle mixbus duties but was never optimal for heavier or modern music, so we added our famous Super Slow MOD with an attack time of 20ms making it ideal for rock, electronic and heavy metal mixbus duties. Another shortcoming was that it was too slow to use on more percussive sources. To overcome this limitation, we added a fast attack time of 2ms to handle loud sources such as snares and kicks which is the same found on the current 33609 “N” revision

Enhanced Functionality

The SA-609+ expands upon the legendary design with a number of modern enhancements while preserving the unmistakable sonic character that made the original a studio favorite.

New Features

Expanded Attack Time Selection (2ms, 5ms and 20ms)

Additional fast (2ms) and super slow attack (20ms) settings provide greater control over transient response

Allows everything from ultra-fast peak control to more open, punchy compression characteristics.

Three-Position Sidechain High-Pass Filter

Prevents low-frequency content from excessively triggering the compressor.

Preserves bass impact while maintaining a stable and musical compression response.

Particularly useful on mix bus, drum bus, and mastering applications.

Mid-Side Processing Mode

Compress the center and stereo information independently.

Greater control over image width, depth, and overall stereo balance.

Powerful mastering tool for enhancing focus and spatial detail.

Transparent Mix Blend Control

Easily dial in parallel compression without external routing.

Retains transient detail while adding density, punch, and glue.

Classic 33609 Performance

Just like the original vintage unit, the SA-609+ delivers exceptionally transparent compression with its gentle 1.5:1 ratio setting, while ratios up to 6:1 provide all the attitude and character required for more aggressive applications.

Its versatility extends far beyond the mix bus. The original unit earned its reputation on drums, vocals, pianos, and a wide variety of acoustic instruments due to its ability to effortlessly control even the most dynamic and complex sources. The SA-609 MK3 faithfully captures this behavior while offering the additional flexibility demanded by modern engineers.

High-quality stepped controls allow for precise adjustments, effortless session recall, and the accuracy required for professional mastering applications. Gain reduction is clearly displayed via the front-panel VU meters, while each compressor channel features independent Threshold, Release, Makeup Gain, and Ratio controls.

The discrete makeup gain circuit can also be used creatively to introduce additional warmth, harmonic richness, and character, even when compression is not being applied.

For peak control, each channel includes a dedicated brick-wall limiter with independent Threshold and Recovery controls positioned after the compression stage. The limiter can be completely bypassed whenever limiting is unnecessary.

For maximum operational flexibility, the SA-609 MK3 can operate in traditional stereo-linked mode, dual mono mode, or Mid-Side mode. Dual mono operation is particularly effective for material with significant dynamic differences between the left and right channels, while Mid-Side mode provides an entirely new level of control for mix bus and mastering applications.

100% satisfaction guarantee – if you don’t love your SA-609+, we’ll refund you

If you’ve used an original metal knob 33609 before, we’re extremely confident the SA-609+ will put a big smile on your face every time you use it. However, if you’ve never touched the original before, as gear-lovers we understand that the only way to really know if this compressor is right for you is to put it through its pace. That’s why the SA-609 comes with a 30-day money-back guarantee. This allows you to get it into your studio and see how it impacts upon your recordings. If you love it (and we think you will!), great…keep the unit and create amazing music with it. If not, no problems. Just send it back to us and we’ll fully refund your purchase.