Model SE84CS DESIGN NOTES
By Steve Deckert

The Select Zen Triode amplifier, model SE84CS, is a tweaked out version of our original Zen Triode amplifier (model SE84C).

Several years after our original SE84C came out we started seeing lots of tweaks emerge that were claimed to improve the sound or performance of the amp.

The only concern we had regarding these "tweaked" amps is what will happen if too many of them find their way into the used amp market.  Will they represent the Decware sound?  How many of them after having been tweaked will actually sound worse?

In response to this we decided to come out with a new version that was already tweaked but done in a way that doesn't stray from the original Zen concepts of balance and simplicity.

In short, no parts were added, nothing was complicated.  In fact one of the two resistors (the grid stop resistor) in the signal path was actually eliminated.  This was made possible by the incredible stability of the amp and its amazing resistance to oscillations. All of the internal parts were upgraded.

We made the chassis black, updated the binding posts and added a pair of "purist" input jacks to the front of the amplifier located only 1/2 inch away from the input tube and connected directly to it's grid.  It can't get any more direct that this, so the wire purists can enjoy using the amp to evaluate the real differences between interconnects.

NOT FAMILIAR WITH THE ZEN TRIODE AMPLIFIERS ?

Here are a few reasons why (in the real world) it's better than other SET amplifiers:

• It does not need an easy to drive loudspeaker and will have no problems with impedance of 4 ohms or less.
• It uses SV83 output tubes which are faster, more neutral, and better sounding than over-priced 2A3 and 300Bs.
• It has less parts than any amp out there, no circuit boards, and is stoutly overbuilt.

This is why this little amplifier can drive a conventional 90 dB 4 ohm loudspeaker with such clarity and why most others can't.

FUNDAMENTAL DESIGN GOAL

The SE84CS power output is designed to sit in the PEAK of the fidelity vs. power graph . The yellow represents the optimum window.

As amplifiers get bigger to create more power they require more parts and often employ cost-effective compromises to get the efficiency up and keep them stable. Things like class A/B operation, push-pull circuits, negative feedback and so on that make cost effective power a reality but at the price of absolute fidelity. Very few people get to hear anything in this optimum range because up till now you needed BOTH efficient AND easy to drive speakers which are fairly rare and expensive.

The SE84CS is not like most other SET amplifiers that work best with no serious dips in the speaker's impedance. Instead it is designed to LOVE difficult to drive loads and will happily drive almost a dead short without complaining.  This means that the amp will drive regular loudspeakers without suffering in the bass regions and that is in direct contrast to the common conception that SET amps don't have very impressive bass response.

SIGNIFICANCE OF HAND BUILDING

We build these amplifiers with seasoned hands and an infectious passion. No circuit boards used here! Each amplifier is built start to finish by the same master solder slingers that have hand built every one of our popular amps!   The quality is impeccable and the reliability is unmatched by doing things the old school way.

If you're into metaphysical tweaks like magic pens and such you will certainly appreciate the massive amounts of Karma that soak into these amps during assembly!

We believe in Karma. Mass produced amplifiers don't have it. Ours do. We think you'll hear the difference right away.

PERSONALITY  

You'll notice a small toggle switch on the front. This is a significant feature of the SE84CS . Similar to our original Zen Triode, this switch controls the signature (or personality) of the amplifier.

The two possible positions of this switch yield an even-tempered frequency balance or a bodacious signature with lots of low end slam. This ensures that the correct dynamics can be applied to different loudspeakers or just your different moods.

CIRCUIT

Many people who own the original SE84 series amplifiers will bridge them mono and run two.  This is possible without a significant reduction in fidelity because the output transformers float with no reference to ground.  When an SE84CS is bridged, the outputs are wired in series causing both halves of the amplifier to act as one.

A pair of these amps will even drive magnapans with excellent bass response at the reduced listening levels associated with late night listening.

RECOMMENDED SPEAKERS

One of the biggest things people will wonder about is the potential compatibility of their speakers.

An acceptable speaker for these amps would be something at least 90 dB 1w/1m or higher and something 8 ohms or lower. For example 91 dB @ 4 ohms would be nice.  Higher efficiencies allow for greater playback levels.  Simple designs are usually better and less crossover circuitry is often better too. If you are content with only low to modest listening levels then you really don't even have to worry about finding special speakers.  Ideal speakers can be found here.

I would invite you to call me to discuss any questions you might have.

Respectfully,

Steve Deckert

WHAT CHANGED FROM THE SE84CS to the new SE84ZS:

The primary difference between the old and the new can be found in the chassis.

The material has been changed to T6 Aluminum which is of course non-magnetic. At the same time the thickness of the chassis has been increased by 4 times.  The plates are precision lazar cut and finished in a baked on powder coat enamel.  The color is near white with a high gloss to minimize infrared heat absorption from the tubes.  

The size of the original chassis was 6 x 10 inches.  The new chassis are 6.5 x 14 inches and are coupled to a solid walnut base adding another 3/4 inch to the dimensions.  By stretching things out a bit the internal layout was able to be further refined.  The original sacred tube layout and spacing remains unchanged.

Circuit wise there are no significant changes except for the use of a more refined G.E. brand film and foil coupling caps.  The volume control has been moved to the front which improved the signal path.  Direct and variable inputs are both located at the rear.

A larger power transformer is used which meets C.E. ratings and can be wired for all voltages around the world.  It is of course both 50/60 cycle compatible.  It's higher mass acts to further suppress resonance.

Speaker binding posts were also upgraded to a WBT style that fits up to 8AWG wire.

Sonically the new amps have a slight advantage due to the lower overall resonance of the chassis/tubes.  This improves focus, dynamics, and makes for blacker backgrounds.

The hardwood bases have been designed as user replaceable making it possible to have any kind of hardwood, domestic or exotic.