SL-1 Signature Pre-Amplifier

A masterpiece is completed with the Signature

The SL-1 has been acclaimed by audio purists and music lovers worldwide as the finest preamplifier available since its introduction seven years ago.

Continued refinement of the power supply and components has pushed the sophisticated and innovative pure vacuum tube audio circuitry ever closer to the realization of its fullest potential.

Now with the introduction of the SL-1 Signature, the realization is complete.

The resulting sound is everything the people at Convergent Audio Technology envisioned seven years ago ….

Listen to a masterpiece.


Specs tell little about a component's sound quality, and this is especially true with audio electronics.

Any good engineer can design an amplifier with excellent specs. In fact that is almost always his sole design goal. Good specs can be achieved without improving, and sometimes at the expense of, the sound quality. CAT knows of no standard spec which was established with the use of listening tests to determine just how relevant, that spec really is. Specifications have become a numbers game to play with the consumer.

Despite CAT's disdain of specification as an absolute indicator of sound quality, they believe strongly in using measurements (of numerous and usually non-standard types) as a design tool, coupled with listening tests, to enable them to determine which parameters are important and how to improve them. Fortunately, for the spec lover in all of us, the specifications of the SL-1 all range from excellent to spectacular. Some of these specs could have been even better at the expense of sound quality, but this would be inconsistent with CAT's slogan "Technology Serving Music." 

Gain (@1 kHz) Line 26 dB
Phono 46 dB
Total 72 dB results on IHF phono input sensitivity of 0.12 mv
Gain Tracking Line 0.05 dB
Phone 0.05 dB
Frequency Response Line 0.1 hz to 600 khz = 0, -3dB (rise time 0.6 microsec.)
Phono RIAA +/- 0.1 dB 20 hz to 20 khz
Harmonic Distortion (@ 1 volt) Line less than 0.0005%
Phono less than 0.001%
Slew Rate Line 16 volts/usec
Phono 10 volts/usec
Maximum Output (@ 1 khz) Line 50 volts rms
Phone 50 volts rms
Input Overload Line 100 volts rms
Phono 250 mv rms at 1 khz
Noise Line 90 dba below 1 volt output
Phono 96 dba below 10 mv input
Separation Line greater than 90 dB
Phono greater than 90 dB
Input Impedance Line 50 kohms, 20 pf
Phone 47.5 kohms, 180 pf (user adjustable)
Output Impedance Line 75 ohms
Phone 75 ohms
Maximum Load Line under 4000 pf, over 5000 ohms
Phono under 4000 pf, over 10000 ohms
Dimensions Main chassis - 19.0" x 5.24" x 12.2"
(standard rack mount faceplate)
Power Supply - 12.2" x 4.0" x 6.0"
(connected by fixed cable)
Weight Net 54 lbs
Ship 60 lbs
Power Requirements 120 v, 60 hz, 50 watts
export version available
Power Supply
Separately grounded nickel plated steel external power supply chassis contains the transformer's magnetic field, eliminating it as a source of hum.
Pure DC voltages delivered into the main chassis. Rectification and initial regulation are done in the external power supply.
Isolation Transformer eliminates entry of AC power line noise into the preamp yielding greater benefits than any of the expensive add-on power conditioners.
Three independent fully regulated filament supplies eliminate dynamic compression caused by filament to filament crosstalk.
Slow filament power-up greatly extends vacuum tubes life to several years.
Quadruple cascaded audio power supply with nineteen time compensated zero-feedback MOSFET sub-regulators, one for each stage of each channel, provides unequalled dynamic contrasts and soundstage realism.
Pure vacuum tube audio circuitry produces harmonically natural gain-free music.
Extraordinarily quiet high gain phono amp accommodates both MM and low output MC cartridges without the need for an external step up device.
The fastest tube preamp, faster than the fastest transistor units, and without their edginess.
The lowest openloop distortion of any preamp yields a level of resolution which must be heard to be believed.
Low feedback ratios eliminate the radio frequency resonances, and attendant hardness, of high feedback designs and yet gives excellent channel to channel gain matching.
Matched output impedance snubs reflections from inter-connects yielding exquisitely lucid highs.
Balance and Volume controls are high reliability military grade solid silver contact rotary switches wired with precision resistors providing unprecedented channel gain tracking while eliminating both the highly non-linear resistance element of conventional "pots" and the poor contact on the wiper on the resistance element.
CAT manufactured RIAA capacitors use a unique dielectric with several times lower loss than any other capacitor dielectric including TFE.
The best sounding precision resistors are used everywhere for the best resolution, lowest noise and minimum unit to unit variability.
Premium audio wire used for audio signal to eliminate wiring as a consideration in the sound quality.
Rhodium/Gold jacks provide audibly superior connection over any other jack.
Silver solder used for the best electrical connection.
Custom designed hermetically sealed switches used for best sound quality.
Very heavy steel chassis with anti-RFI plating ensures hum and RF free operating environment for circuits.
Damping material lines chassis to stop mechanical resonances which would otherwise modulate the electric fields, and hence the signal, in the preamp.
Mechanical isolation from floor vibration provided by high loss viscoelastic feet.
Front panel muting switch.
Automatic mute engaged at turn-off and 30 seconds after turn-on.
Front panel LED indicates when unit is operational.
"Record/Normal" front panel switch eliminates the non-linear load of the turned off tape deck when in "Normal" and provides full fidelity taping when in "Record."
Extra set of MAIN OUT jacks useful for special audiophile setups.
"Load" jacks on back allow channeling MC cartridge load resistance plugs (supplied) while playing music.

"What is best? This is always very difficult to answer as nothing is perfect and everything is personal. We have been working with the C.A.T for some years now and it still takes the top place for us even though there are many others that are very good and close on its heels. If you have had a C.A.T. in your system for some considerable time then it is very difficult to live without it. This is because it seems to do one thing better than any others do -- it plays music. Many of its rivals some of which are very, very good like the B.A.T or the Woodside both of which we are very keen on and recommend thoroughly, may in some cases have some attributes that beat the C.A.T on a particular point but for us the C.A.T gives the feeling of total reality especially as far as the sound stage goes and on live music its transparency and uncanny way of bringing life to the music keeps it as our No. 1 choice. The JL1 amplifiers have over the last year or two joined the pre-amp and these too are beginning to enjoy the same reputation. A full C.A.T set up is still a benchmark and one that will hold the candle in your system for many years to come."

CAT Fight
A Review by Marc Mickelson - Soundstage March 1996

I've owned a Convergent Audio Technology SL-1 Signature preamp for about a year, and aside from problems with residual hiss--a byproduct of its high line-stage gain--I love what I hear. The CAT has the unique ability to sound highly transparent and utterly musical at the same time?from my experience, a rare feat. It's also built like no other preamp, 60 pounds of heavy steel with internal damping material and an outboard power supply. I've always felt I've gotten my considerable money's worth with the CAT.

Mr. CAT, Ken Stevens, is another matter: he's priceless, an interesting and opinionated man who is constantly tweaking his wunderkind. This ensures that his preamp will always sound the best it can, but all his work is a problem for those of us who buy a CAT only to find that it's changed a month later. More than any other piece of equipment, the CAT preamp is tied to its serial number. Keep this in mind if you look for a used unit.

Although the CAT preamp is in constant evolution, only recently has its model designation changed, to (big breath) the "SL-1 Signature Mk II." My CAT is one year old; it has the most obvious improvements that have been worked in since the CAT Signature's debut: heavier bottom plate, and a new umbilical from the power supply to the preamp itself. I've recently had the chance to compare a new Mk II with my original unit, and from a purely visual standpoint, the differences are slight. The circuit boards in the power supplies have all the same markings, but the board in the Mk II seems to be made of a different material and is perhaps thicker. In addition, the one bright-blue Phillips capacitor in the power supply has been replaced with an IC cap, the same brand used liberally throughout the preamp. I couldn't spy any obvious differences to the board or components in the preamp itself, but I did notice that the wiring in my older unit is much neater, with less slack and more calculated use of wire ties. This, of course, is due to manufacturing variation--if only sloppy wiring were all it took to make a great piece of equipment.

Sound: very, very close. The CAT Signature Mk II seemed to have marginally more extended bass and was a little quieter, but these differences could be attributable to its new tubes, especially the 12 AU7s in the linestage. These are the most prickly pair in the CAT and can affect the sound in a profound way. Convergent is now using "German RFT" (what Ken Stevens called them) 12AU7s; if you have an older CAT, you should strongly consider popping for a new factory tube set. The last I heard, Convergent was not going to offer the Mk II changes as upgrades to older units, but by buying new tubes, you may be getting the bulk of the Mk II upgrade in the process. Oh, I did forget to mention the most considerable difference between old and new CATs: a $1000 increase in price. Who says that high-end equipment isn't an investment?

Marc Mickelson



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