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


OUTPUT TRANSFORMERS
July 2002
by Steve Deckert

 

The secret behind the Zen Triode output transformers is that they are patterned after the older Peerless iron that was hand-scramble-wound for ultra wide bandwidth and flat response. If you are familiar with the any of the all time great vintage tube amps you already know the Peerless output transformers were a large factor. 

Our transformers are also hand scramble wound using a winding topology that evolved from several prototypes.  The air-gapped cores are made from top grade USA made grain- oriented-silicon-steel - the heart of any transformer.  The better the core the less of it you need and the lower the saturation.  In contrast transformers made in China do not have the same quality steel and suffer as a result.

Add to that the fact that I choose to locate them on a different plane than the power transformer and at the opposite end of the amp where no field is present.  Instead of using end-bells the chassis is used to shield it.

I also choose a single 6 ohm tap because I found the single tap prototypes sounded better than the multi-taps, something about the unused taps.  The primary impedance is 9800 ohms with 2850 winds.  This makes the el84 and SV83 tubes couple more power as the speaker impedance drops.  Max power is at 2 ohms.

If you measure the current and voltage on an SE84C Zen Triode Amp with a 1KHZ sign at 2 volts you will find the current output actually exceeds the voltage.

Many people think transformers have to be huge to be good, but its all in the quality of the steel.

Another rather unique feature of our output transformers is that they float.  They have no reference to ground.  This is difficult to do in all but the most stable amplifier circuits.

Now there is a big fuss is over COBALT transformers

There is no evidence that "cobalt" transformer will sound better than our transformers in a Zen Triode Amp.  What it has going for it is a catchy name, high cost, low availability, and it's the hot topic over in Magnaquest/Bottlehead land.  I'm sure it's good, as is nickel, but after reading all the chit chat about it on the Internet I recognize that it's being largely overblown.  The majority if not all are done without air-gaps necessitating a parafeed design.  We went through all that three years ago and concluded that parafeed does not sound better to our ears.  It does however perform better which brings us down to the brass tacks of building amps that excel in performance (ie. parafeed, constant current, etc.) or simpler "zen" like designs that to our ears sound better (but perform worse).  Take your choice.

The main advantages that nickel has over steel is less saturation.  There are two ways to deal with saturation.  A) use nickel or "cobalt", or B) just size the damn things 3 times bigger than they need to be so they don't saturate.  Our transformers do not saturate until somewhere between 15 and 20 watts.  Now depending on the amp we build, that is between 3 and 10 times oversized.  You can be sure that if someone is using expensive core materials like nickel or cobalt they aren't likely to oversize the transformers.

Many engineers will point out that transformers in general induce distortions and therefore not using one is better than using one.  Output transformerless amps (tube) are often great sounding amplifiers, however they are also finicky about speakers and have many other disadvantages.  We feel the transformer is a major key to why most people think tube amps sound better than solid state.  The transformer couples the output stage to the hostile impedance of the loudspeaker in a synergetic way not possible without one.

The common way of doing things in the high power high-end audio world is to build high power amplifiers with high dampening ratios so that they will better control the speaker and be less effected by the feedback voltage generated by it.  On the other end are speakers with high power ratings, low efficiency and complex crossovers that attempt to show the amp a less hostile impedance curve.  Basically put, amps that are less effected by (can't feel) the speakers, and speakers that are less effected by (can't feel) the amps.  

In a great high fidelity tube system the output transformer makes the speaker aware of the amp, and the amp aware of the speaker.  The two work together, reacting to each other with any given passage of music.  This is call synergy.  It is made possible by output transformers.  The best vintage solid state amps I've heard from the 60's and 70's used output transformers.

Output transformers are not a bad thing.

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