CATO

Class-A Vacuum Tube Preamplifier

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Our new vacuum tube linestage kit has been designed with affordability in mind yet we haven't cut any corners. Its all class-A operation makes for a very sweet sounding pre-amplifier and its single-ended low impedance mosfet output stage is good for all the bass slam you could ask for!  As is typical with all of our products, CATO is supplied with nothing but top quality components including an ALPS volume control, teflon OFC hookup wire, precision metal film resistors and film & foil caps - all housed in a nicely built hardwood chassis.  You will be hard-pressed to find a better deal for a starting price under $700!

Description:
The CATO design features a differential tube input stage with adjustable gain and a class-A single-ended MOSFET output stage with a very low output impedance providing high current drive capabilities.  MOSFET devices possess electrical characteristics that are similar to vacuum tubes and thus enhance the sonics of the driver stage. One of the more interesting features of our CATO design is its use of the ECC86/6GM8 low voltage tube.  The 6GM8 falls into the car radio tube category from the 1950's and 60's with specifications rated for linear operation provided with anode voltages supplied by a car battery, i.e. 12 volts.  The 6GM8 can be operated at higher voltages and in fact sounds better at these elevated potentials and thus we operate CATO from a + 24V supply.  The 6GM8 is an exceptional tube featuring very low noise and low microphonics, but don't let the 6GM8 tubes scare you, CATO can also run with the ECC88/6DJ8, 6922 and others. You will be amazed at just how good these high voltage tubes sound run at low voltages. 

-  Class-A tube amplification with single-ended (SE) mosfet output stage.
The mosfet output provides a very low impedance signal resulting in exceptional bass performance.  Driving long interconnect cables is not a problem with this design.

-  Servo circuit nulls all DC offset voltage.
This new circuit eliminates all dc offset so large coupling caps on the output (a major source of sonic degradation) aren't necessary.

- 3 selectable gain settings.
A linestage doesn't require much amplification these days so CATO has been optimized to operate between unity and 10dB of gain. A handy switch let's you choose between 3 different gain settings.

- Compact Low Noise Power Supply
CATO's power supply features encapsulated Toroidal transformers, Schottky diodes and AC filaments all mounted on an easy to assemble printed circuit board. 

- Stylish Hardwood Chassis
Tigris hardwood chassis accented with Ebony corners that function as feet.

Detailed Circuit Description:
CATO is a DC-coupled hybrid tube/MOSFET line-level amplifier.  It uses a + 24Vdc anode supply and 6.3V for the heaters.  The 24Vdc supply is provided by onboard voltage regulators.   The tube's filaments are powered-on all of the time with just the dc voltage switched at power on.

Its input stage is a differential amplifier with a constant current diode supplying the cathode current. The two anodes, which produce two out of phase signals, are converted to a single-ended signal, using a current mirror circuit composed of Q1, D2, R3 and R4.  Q2, a 2SJ79 P-channel MOSFET, is used in a common-source mode as a class-A single-ended SE output stage.  Q2's drain resistance has been replaced with a second constant-current source to increase its gain and linearity.  This current source is made up of Q3, a 2SK216 N-channel MOSFET.  U3 and associated components implement the dc nulling servo circuit.

A gain select switch allows you to easily choose the perfect gain setting.  The CATO kit is supplied with 3 gain settings of 0dB, 6dB and 10dB.  Of course these settings can be easily modified by changing a few resistors.

Hi Guys - I just finished assembling the Cato linestage kit and had to tell you I am simply thrilled with the audio quality.  This is a killer preamp for the money!  I'm telling all my friends. - Ralph

Hi Ron - This new linestage is great!  Please let me know when you have the matching phonostage ready and I'll be the first to buy it. - Stan

The CATO kit includes everything required to build a complete and functioning line level preamplifier.

The kit includes Vishay-Dale 1% metal film resistors, Nichicon ultra-low impedance electrolytic capacitors, Wima polypropylene film and foil capacitors and 4-layer silk-screened circuit boards.  A high quality ALPS volume control is supplied along with teflon coated oxygen-free cooper hookup wire and a matched pair of NOS 6GM8 tubes. 

The power supply includes two encapsulated low-noise toroidal transformers, Schottky low-noise diodes, Nichicon ultra-low impedance filter caps and a detachable shielded power cord.

The hardwood chassis is supplied fully assembled but unfinished so pick your favorite oil, lacquer or poly finish to bring out the beauty of the wood.  The CATO shown in our photos was finished with a high gloss Tung oil on the Tigris panels and a beeswax oil on the Ebony corners.  CATO's chassis dimensions are 3.0"(76mm) height  x  12.5"(317mm) width  x  11.0"(280mm) depth

ORDERING INSTRUCTIONS

CATO is available in two configurations:  The version shown in the photos features one set of inputs and one set of outputs.  CATO is also available in a five input version featuring a super high quality Grayhill input selector switch.

The assembly manual includes step-by-step instructions for assembling and testing each circuit board module along with a connection diagram for configuring the inputs and outputs.
 

TUBE UPGRADE OPTIONS

ECC86/6GM8 NOS Tubes

PLEASE NOTE:  At this time, these tubes are ONLY sold to individuals that have purchased a CATO kit.

All tubes are tested, matched using a calibrated tester and warranted for 6 months.

VALVO

Valvo brand - made in Germany  One matched pair.

AMPEREX

Amperex brand - made in Holland  One matched pair.

EH6922- ELECTRO HARMONIX

EH6922 GOLD PIN- ELECTRO HARMONIX

Electro Harmonix with gold pins- made in Russia  One matched pair.

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