Pedals Guitar Amplification Bass Amplification Microphone Preamps Compressor Reverb Direct Boxes Power Amplifiers Speaker Cabinets
Store Sounds Reviews Artists Dealers Links Gallery Manuals Service About Us Guestbook Contact Us

DEMETER VTCL-2B STEREO TUBE OPTICAL COMPRESSOR/LIMITER REVIEW

Pro Audio Review (January 1996)
By John Diamantis

Equipment Review - Demeter VTCL-2A Compressor/Limiter

Every now and then, a product comes along that goes a step or more beyond what you'd normally expect, and in the highly competitive pro sound arena you can either suppress this knowledge and make it one of your "trade secrets." Or, if you're like me and have a tough time keeping your mouth shut, you tell every breathing life form about your little discovery, in the hope of increasing the awareness of the universal, collective cosmic consciousness, or whatever.

The dual-channel Demeter Vacuum Tube Compressor Limiter, or VTCL-2A for short, is just such an item. If you're looking for a box that will give you effects from clean limiting to crunchy compression, and every point in between, then look no further. This baby does it all!

Features

The audio path is completely tube; no transistors, no ICs. Jensen transformers are an option, if you desire balanced ins and outs. This circuit is comprised of five dual triodes, one 12AX7 and one 12BH7 per channel, one shared 12AU7, and appears to be fairly conventional (no schematic was provided, but my curiosity drove me to tracing out the circuit by hand). The side chain is entirely solid-state, and the gain reduction is accomplished via a photocell opto-isolator, similar to the infamous Teletronix LA-2A. The DC supplies for filaments and high voltage are regulated.

Parts quality is very good,a nd there's a lot of point-to-point wiring between the three circuit boards and the front and rear panels. Construction is mostly very good, but during shipping the rear panel, which is where the power transformer is mounted, was bent. The shipping malady didn't affect the operation of the box.

The VTCL-2A contains the typical attack/release/threshold, etc., front-panel controls. There are also bypass switches for each channel, as well as an input sensitivity control to optimally match your source's output level to the VTCL-2A's operating range. A lighted VU meter for each channel can be selected to display input level, output level, or compression level. A switch allows a 10 dB increase in meter drive sensitivity to better view low-level inputs and/or outputs.

Connections can be made via XLR connector (pin 2 or 3 hot, switch-selectable), tip and ring connector, or miniplug. The power cord is a detachable IEC type.

Although I didn't receive an operator's manual, per se, there was an instruction sheet that described basic operation of the unit. Also included was a chart showing typical attack/release settings to make the VTCL-2A mimic the characteristics of Teletronics LA-2A or the notorious Fairchild 660 series.

In Use

Having a pair of vintage LA-2As on hand, I set them up on my bench for a quick A/B comparison. The Demeter's dynamics could be made to sound close to those of the LA-2A, but VTCL-2A's overall character was cleaner and had more deep low end. And in my opinion, that's a good thing! Would I sell my LA-2As? For nostalgia's sake, I don't think so. But the Demeter VTCL-2A is one flexible piece of gear.

Not having a Fairchild 660 on hand (or $15K to purchase one) I was unable to make a direct comparison to the VTCL-2A. But I have used a 670, and I was able to replicate, to the best of my recollection, the overall flavor and feeling that the Fairchild box imparted to a performance.

A big difference with the Demeter is you don't need to balance variable mu tubes for minimum thump feedthrough or even try to find some matched 6386s to do the job. There are no matching or adjustment requirements, and the VTCL-2A's audio path is definitely cleaner.

I ran a variety of audio through the Demeter VTCL-2A and was struck with how easy it was to get the sound I wanted. Vocals could be cleanly leveled, or run hard and fast without sounding bad. Percussion, always tough to get right, did real well, whether trying to tame a snare drum or trying to level a completed production, without squashing the life out of the dynamics. The "soft knee" or gradual increase in compression ratio with increasing input surely aided in this effect. I found myself using more gain reduction than usual in some cases, as the VTCL-2A's dynamics were clean and controlled.

In fact, by running the release fast, and dialing in 15-20 dB of compression (an extreme amount), I could produce a great sustain effect.

Unlike most other compressors I have tried, the VTCL-2A's attack control feels more like an audio zoom lens, allowing you to get close by slowing the attack and adding punch to the audio, or zoom back by speeding the attack and shrinking the audio peaks. Despite the wide range of control, it was very difficult to get into a dynamic dilemma, even when running the attack and release controls at full tilt fast.

One small complaint: The controls feel very sensitive. The attack control, for instance, is scaled reverse log, and a whole lot of change occurs from full fast at complete clockwise rotation to relatively slow (25 ms) at less than one-quarter turn. It takes practice to line up both channels in this range, if you want to process stereo without linking the channels.

The Demeter VTCL-2A performed very well on my test bench, with no more than 0.05% THD under normal operating conditions. As you increase the input level, and the front-panel green light activates, distortion increases to a still imperceptible 0.1%. Max input level is greater than +20 dBm, and maximum output level is +32 dBm. Frequency response was +0, -1 dB from 7 Hz to 22 kHz, the -3 dB points were 3 Hz and 41 kHz. The extended low-frequency response (especially for a tube unit) added to the great sound of this unit. Square wave response at 5 kHz was excellent, with no ringing and square corners.

When I attempted to measure IMD and noise, I noticed the readings were much higher than they should have been. Troubleshooting turned up 15 mV of 120 Hz hum on the outputs. This was traced to a malfunctioning HV power supply that passed voltage onto the circuitry even though it was no longer properly regulating.

I talked with designer James Demeter, who assured me that failure of the power supply is extremely rare. He suspected shipping damage as the culprit, as evidenced by the rough treatment the unit had received. Demeter products have a reputation for being well-made and reliable with hundreds in the field. So I didn't worry about the hum element being typical. After all, nothing is immune to shipping damage if the handling is rough enough.

Plus

  • Flexible adjustment parameters
  • Cleaner sound, better low end than LA-2A
  • Excellent attack control

Minus

  • Controls a bit sensitive
  • No schematic

The Score

One of the better stereo tube compressors on the market that gives you the character of the old LA-2A, but with cleaner audio.

Summary

I was very impressed with the Demeter VTCL-2A's audio and dynamic performance. Definitely recommended for anyone looking for a great sounding, high-quality and extremely flexible compressor/limiter.

John Diamantis is a freelance writer, chief engineer at WBQB/WFVA in Fredericksburg, VA, and a certified tube fanatic.