A U D I O... P A P E R


THE IMPROVED SE34I Zen Triode Integrated Amp

Sept 2004 by Steve Deckert

 

The SE34I, after a calendar year of development, went into production in 2001.  It has enjoyed a healthy run without any updates.  It has been our second most popular amp since its release, with only two units returned under the 30 day home trial. Needless to say, this speaks volumes about its quality and sound.  

Frankly when I committed to the task, there were no guarantees I would be able to improve it.  My first attempt implemented changes I've pondered for the last year and while some things certainly were improved, the overall sound was less satisfying than the original.  This is something I anticipated would probably happen, but I remind myself that nothing ever gets better unless one tries and I intended to give it my best shot.  I continue on and you can read about the details of this process in my previous paper, titled "Epiphany's"

There were some very fundamental changes made to this amplifier.  These were motivated from years of observing how the amp was being used.  As you may or may not know, the original SE34I had the option of running 2 or 4 output tubes and a variety of switches that gave the user control over the signature of the amp.  When using all 4 output tubes in it's paralleled configuration the amp gave a healthy six watts per channel into 8 ohms.  However, in it's series configuration using all 4 tubes the power was reduced to around 2.5 watts per channel with tons of headroom.  

The overwhelmingly popular configuration for this amp was the series output configuration running all 4 tubes because it usually sounded better than the parallel configuration. Many owners also enjoyed running the amp with only 2 output tubes (1 per channel). This single tube mode had exactly the same 2.5 watts per channel of output, but offered a degree of clarity only found in single tube designs.

The irony's here are: 1) Most people who purchased the SE34I did so to have more power than our SE84CS amplifier. 2) Almost all of them ran the amp in it's series or single tube configuration which barely qualifies as more power.

Of those who owned both the SE34I and SE84CS, most found the simpler SE84CS to have better transparency.  This comes as no shock because if you closely review the two designs, the simpler SE84CS should have better transparency.  However, the higher resolution of the SE84CS comes with a price in that it will reveal the weaknesses in your source and cables.  If you were to plug a $200.00 CD player into it with cheap interconnects the sound would most likely become unlistenable.

The original SE34I design was inspired by my experiences with the old Macs.  In a word, they were forgiving.  In fact they often made music sound better than it really was - given the limitations of the source components and recordings.  I've always thought this to be an outstanding "real-world" accomplishment.  I've seen so many audiophiles in this business who thought they had good sources that I can't keep track of them anymore.  Of course, they didn't have good sources, only expensive ones which does not always guarantee that they were good sounding.  I've also seen heavy trends in audiophiles to spend most of the money on speakers, amps and cables and have to make compromises on the source components.  The source component is the most important component to get right.  It would be better to hear a $7500.00 CD player on a $750.00 amp than it would be to hear a 750.00 CD player on a $7500.00 amp any day.

Being a realist (and understanding what really happens in the majority of listening rooms) I wanted to offer an amplifier with that magic ability to make what comes out of it sound better than what went into it.  Without getting into how difficult that is, I was successful in achieving a very forgiving nature yet with enough resolution to captivate the serious audiophile.

This was an amplifier that was designed through its signature and flexibility to never come back on 30 day trials.  To continue on this theme, it is also one of the goals of the re-designed model.  The biggest difference between the two being a noticeable step forward in resolution.  When people compare the new version with the popular SE84CS I want them to either like it better, or at least have a very difficult time choosing between the two.  I don't want people buying the SE84CS over the SE34I just because they read on the forums that the SE84CS might sound better.

THE NEW DESIGN CHANGES

Since most people used the SE34I in series mode or single tube mode - both 2.5 watts per channel, I made the new model a single tube per channel amp at 5 watts a side. This opened up two positions on the chassis for tube rectifiers.  (The original amp used solid state rectifiers with an elaborate filter to burry the recovery spike noise of the diodes.)  This also opened up two positions inside the chassis for chokes that when used with tube rectifiers can transform an amplifier into a new state of consciousness!  This combination is the corner stone behind the term "liquidity" in an amplifiers signature and performance.  Of course these chokes cost over 10 times what the resistors they replaced had cost so it better sound better!

During the testing phases with different chokes I found that they all improved some facets of the sound, but it wasn't until I tried a custom scramble wound choke with an air gapped core and open secondary winding that ALL facets of the sound started to improve.  I think most people would have stopped right there once they listened to the result - but I wanted to see what would happen if I exactly matched the design specs of the choke with the output transformer.  Having both with identical cores and windings so the DCR and Henries of each were the same.  The more I thought about it, the more certain I was that there would be a "balance" between the power supply (where the music starts) and the output transformer (where the music ends).  I was right, it was easy to hear the difference.  The amp was cleaner, quieter, more relaxed, had better timbrel accuracy and more depth.  Again, the excitement of this discovery is what motivated the previous paper, "EPIPHANY'S".

To drive the output tubes a new SRPP circuit was employed using the same 6N1P dual triodes as before.  The difference in this circuit is that each triode in the 6N1P is stacked together doubling the voltage swing and eliminating the need for the additional stage used in the original design.   Now that we've eliminated an entire gain stage we have one less tube to deal with and a signal path that changes from 4 resistors and two capacitors to 1 resistor and 1 capacitor!

These changes also opened up a lot of room under the chassis and allowed for a more refined layout that eliminated all the hook-up wire that was previously in the signal path with the exception of the internal interconnects between the input jacks and 1st gain stage.  However, the lengths of these interconnects were cut in half. Because of the shorter lengths we were able to upgrade the Beldon cable previously used with Teflon over Silver wire throughout.

In addition, the ground buss design was vastly improved and simplified, the electrolytic's power supply caps were improved in size and quality and the single coupling capacitor was also upgraded to AURICAPs which proved to be the perfect sounding cap for this circuit.  Since the entire resistor count in the amplifier went from 26 per channel down to 10, all were upgraded with special attention given to those in the signal path.

Features that stayed similar to the original is the cathode bypass switch that alters the linearity of the output tube bias resulting in more or less weight in the bass.  Giving you a choice between a warm rich sound, or a dryer "British" signature with tighter but less overall bass.   The amplifier still retains it's super quiet operation with virtually NO hum on even the most efficient speakers.  It also uses the same power transformers but now each transformer only has to run 1 output tube instead of 2.  Standby switches are still used, as is the super high quality silver selector switch wired to 4 pairs of input jacks.  A 5th pair of input jacks is also available wired direct to the input stage with no selectors or switches - ideal for those wanting to use a preamp.

With the additional power and new circuit design it was possible to lower the input sensitivity just a touch so that regardless of what CD you play on a standard player with 2 volts of output, you simply can't clip it.  The original design would allow you to just start clipping the amp at about 3/4's on the volume knob on CD's with lots of bass. Now it requires a full 3.5 volts to start clipping the amp.  This makes it possible for those who don't use a preamp to wind it all the way up and never hear distortion no matter what they play.  It also makes it possible for people with a preamp to get the amp considerably louder than without one.

In the end you have an amplifier that is far simpler to operate and hook up, not to mention understand.  It's amazing liquidity gives it a signature similar to the original - it still sounds relaxed and more forgiving than the SE84CS, yet it competes aggressively for the title of "most refinement and inner detail - best sound stage and imaging" award. In fact it came out so good, some of the technology is quickly finding it's way into our other amplifiers.

 


Here are the before and after schematics.  A classic example of Less is More.

Schematic of SE34-I
  Schematic of original SE34-I

Schematic of SE34-I-2
Schematic of new SE34I-2

 


Shown above, the new SE34-I.2

The Original SE34-I


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