Field Test: Inward Connections VacRac TSL-3 Limiter

Oct 1, 2007 12:00 PM, By Michael Cooper



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Inward Connections VacRac

In 1995, Steve Firlotte and Steve Barker designed the Inward Connections all-tube VacRac, a modular system that integrated the company's TMP mic preamp, TLM-1 limiter and TEQ equalizer, both with external power supplies, in a 19-inch, rackmountable Lunchbox-type chassis. The TLM-1 mono opto-limiter proved to be the biggest hit of the three modules, and many pros were disappointed when the VacRac was discontinued around the year 2000. Hopes were renewed a couple years ago, however, when Inward Connections resurrected its favored limiter in a stand-alone, dual-channel design made for Vintage King Audio, the company's current distributor. And so the VacRac TSL-3 tube stereo limiter was on the market.

Housed in a well-ventilated, gorgeous, 3U steel chassis sporting large knobs and VU meters, it's the TSL-3's onboard power supply that actually deserves the headline. The high-power (300-volt), tube-regulated supply immaculately preserves audio transients, which factors largely into the TSL-3's beautiful, signature sound.


Like vintage dynamics processors built around opto-electronic gain-control elements, the TSL-3's front panel sports few controls, making the unit's operation exceedingly straightforward and lightning-fast. Each of the two channels have continuously variable reduction controls that feed light-dependent resistors (LDRs) to adjust the depth of compression up to 40 dB. A continuously variable, rotary gain makeup control for each channel supplies up to 14 dB of gain and is active even when its associated channel-bypass button is engaged; this lets you run audio through the unit's all-tube audio path without any dynamics processing. The gain makeup control serves a 12BH7A tube in the output stage and does not feed back into the gain-reduction circuitry. Each channel's input stage features fixed gain from a 6072A tube.

Two large (3×3-inch), backlit VU meters — one for each channel — can be independently switched to show either gain reduction or output level (the latter setting referenced to +4 dBm and zero'ed using recessed trims). A stereo-link button and rocker-style power switch finish off the spacious front panel. All switches are backlit with LEDs when active.

The rear panel features XLR I/O connectors, an IEC receptacle for the detachable AC cord and a voltage selector accommodating either 120- or 240VAC operation. Inputs are transformer balanced and rated to handle levels up to +20 dBm. Outputs are unbalanced (pin 2 is hot, and pins 1 and 3 are ground) and specified to handle up to +20 dBm at 600 ohms or +34 dBm at 10 kilohms. Output transformers are optional, although not a single customer has ordered them. Frequency response is stated to be 20 to 20k Hz, ±0.5 dB.


The TSL-3's action at its “knee” is noticeably firmer than that offered by my Universal Audio LA-2A tube compressor, another opto-compressor. On some sources, such as vocals, compression depth swung from 0 to 10 or 20 dB with fairly small adjustments of the TSL-3's reduction knob and only moderate swings in input level above threshold. Even with such deep compression, however, the unit's sound remained remarkably transparent. The TSL-3 put a firm yet clear lid on triple-tracked, two-part background vocals recorded with a Lawson L251 mic and Millennia HV-3D preamp, preventing a submix pileup and delivering a rich and present tone for the group.

The TSL-3 sounded incredible on strummed acoustic guitar. With swings in gain reduction between 1- and 7 dB, the unit dramatically tightened up the instrument's bottom end while treating the top with kid gloves, creating a leaner and more sparkly track that needed less EQ cut to reduce boominess. Similarly, applying a moderate amount of gain reduction to a kick drum track reduced the amplitude of shell decay to produce a sound that popped more.

Next up was a Strat playing palm-mute diads through a Roland Micro Cube amp miked with a Royer R-122. The TSL-3 transparently controlled the track's level so that it neither dominated nor disappeared into a dense Southern-rock arrangement. Placed on the stereo tracks for overhead drum mics, the TSL-3 gently moderated peaks and shaved off some low end on bleed from the traps. Even with 20 dB of gain reduction on peaks, I couldn't get the TSL-3 to pump; for the bombastic sound of John Bonham-style drums, another limiter would be a better choice. Results on electric bass guitar were also fairly pedestrian, although perfectly usable.

Despite its conservative headroom specs, the TSL-3 handled the 26.5dBu output of my Yamaha 02R mixer's stereo bus outputs without distorting. In a 2-bus application, the TSL-3 lent the mix a more velvety sound and tighter bottom end (not necessarily appropriate for this thumping R&B production). The unit's attack time proved to be too slow to dramatically reduce peaks, leading me to conclude that the TSL-3 is not the best choice for increasing the loudness of a mix.


My only criticism of the TSL-3's build is that the XLR input connectors don't latch. The $4,500 list price is high, but premium-quality tube gear doesn't come cheap. What matters is the sound. The unit's sonic character tends toward modern and pristine rather than vintage and highly colored. Yet the all-tube audio path certainly adds a warm, velvety touch to digital tracks. If you're looking for an ultratransparent tube limiter with a sweet tone, the TSL-3 is worth considering.

Inward Connections, dist. by Vintage King Audio, 248/591-9276,

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