Audio Limits Passive Controller

      Date posted: September 12, 2007

Audio Limits Passive “Preamplifier”
Sugg. Retail: $180.00 USD
Manufacturer: Audio Limits Canada, Richmond Hill, ON
Audio Limits Passive Preamp

I discovered this product on eBay a couple of weeks back (late August 07), and was struck by its elegant simplicity. It’s a 4-input switcher, with a high quality potentiometer in a simple box, with long shafts on each rotary control to keep all contacts and point-to-point wiring at the rear near the high quality RCA ins and outs. Internal cabling is done with “24 AWG silver-plated copper wire with Teflon insulation”, according to the web site. This cabling is said to be “stranded wire with 19 strands.” The overall design cleverly simple and efficient. Inputs are marked as Tuner, CD, Aux 1, and Aux 2, the rotary selector at right on the front panel. The high quality pot at left varies the output impedance from 0 to 100 KOhm, and feeds a pair of unbuffered direct outputs to allow bi-amping or tape and amplifier feeds.

The excellent gold-plated connectors can be seen in the photos, as can be the two colour designs, silver and black, both with sleek silver knobs. The neat front and back lettering is on a silver stick-on tape surface, and easy to read on top, so that connections can be made quickly and accurately. What could be simpler?

It was exactly what I’d been looking for, needing just such a device to interface between my matrix and discrete centre and overhead outputs from the Cantares Surround decoder and OPPO 970HD 5-channel universal digital player, respectively, and a newly acquired Bryston 2B amplifier. I already had a 2B LP amp for the surround channels with an outboard switcher box, with surround level attenuation set by this pro version of the 2B’s front panel level controls. This matched them to the front channels, driven by a perfectly tonally matched Bryston 3B SST, and the additional slightly differing efficiency/impedance situation of the Energy Veritas 1.8 and the second set of ads 300s and Cambridge Soundworks passive sub for centre/overhead speakers required similar outboard attenuation to facilitate level-matched master control from the matrix and discrete sources right through the 6 speakers.
Audio Limits Passive Preamp (rear)
This way the Audio Limits/2B and 2B LP gave me complete trim control and powering of these 4 channels, which combined with wireless remote master level control for discrete 5-channel play from the OPPO in a quite short final analog signal-path situation for all channels, with a very short path out of the Audio Limits of less than a foot of RCA cable to the 2B inputs, the passive controller nestled on top of the amp. Similar master levels for stereo and matrix are handled in the separate paths through a Monarchy Class A preamp that drives balanced cables to the Veritas/3B SST and the switched unbalanced cables to the Cantares matrix decoder and surround channels. But my major concern was, having matched these 4 additional channels with virtually identical sounding amplifiers and speakers, how, in particular, would the centre channel work with the left and right tonally?

I had previously been driving centre and overhead (part of the Cantares matrix Ambisonic system) with a sweet-sounding little Luxman L-3 amp that proved to be a not-quite-perfect tonal match, and at 30 wpc, woefully underpowered with any recordings with strong centre energy.

Well, all I can say is that the Audio Limits proved to be the perfect solution to the centre channel problem along with the additional 2B. With the bi-wired centre/sub combination being close to 3 ohms, the little amp that could, would put out something near 120 rms watts when needed at centre, and thus had plenty of oomph on demand, and the clipping of the L-3 became a memory. The tonal match of the front facade of speakers became seamless, so that all my SACD 5-channel orchestral recordings, many of them superb Telarcs (see current and upcoming reviews), came to life to an even greater extent. And the Overhead matrix channel requires relatively little power, thus leaving lots of current room in the twin-mono Bryston power supply for strong centre signals (I’ve made the matrix centre available in discrete play as well if desired with 4-channel SACDs, and the Overhead feature has its own level control on the Cantares ambisonic decoder).

So discrete multichannel pop and jazz benchmarks like James Taylor’s Hourglass, Miles Davis’s Kind Of Blue, and, of course, Pink Floyd’s Dark Side Of The Moon became completely immersive experiences. My wife has started to ask why I keep playing these recordings. Yesterday I was listening to a 5-channel Pentatone Mahler 5th (SACD 5186 004) with Hartmut Haenchen conducting the Netherlands Philharmonic in the Concertgebouw hall in a concert performance, and it was more than ever before, just like being there! Maybe even better…

And the Audio Limits passive preamplifier (an oxymoron, I know) makes its contribution of neutrality and control apparent, or invisible, depending on how (or whether) you think about it. Its level and switching controls have a nice feel, if a little rubbery from the long shaft from knob to pot or switch at back, but they are also very smooth and quiet in operation.

And that’s all I have to say about this neat, effective, and pretty (in either silver or black) little box. It’s Canadian made and available at a very reasonable price, especially considering its exceptional quality. The last time I experienced this combination of functionality and economy in a passive pre was the slightly more expensive FT Audio controller.

Andrew Marshall

Comment & Questions


I have enjoyed your reviews of the FT and Audio Limits passive preamps.

I need a temporary solution to use my Bel Canto REF 1000 monoblocks while I find THE preamp that will be a permanent fix with these powerfull digital amp:

2 quick questions please:

A) Any significant AUDIBLEĀ  differences between these two preamp ?

B) Ever heard the (active and tubed) Sounstage Vacuum 2 preamp? Any comments?

Thank you very much if you can help me out,

Mike (Quebec)

AM Replies:

Hi Mike,

Of the two preamps (or passive switcher/attenuators) I would choose the FT Audio for build quality, but both offer excellent transparent sound quality. That passive preamps crush dynamics is a big myth, as they merely pass the signal without gain, and switch inputs. The FT Audio, however, is about twice the price.

While tubed preamps can be excellent (tube amps less so because of sheer physics), and many great recordings have been made with them, I would not recommend any for reasons of ultimate reliability. They also tend to microphonic behaviour as tubes age, which can cause speaker failure and other problems down the audio chain. One of my writers had his Quads destroyed by an Audio Research tube preamp that went DC on him quite suddenly. A passive device will never do that, and if your amps have the gain, it’s a good match, though you might need an active phono stage. My son, Aaron has reviewed several of these.

cheers, Andrew

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