The secret behind the Zen Triode output transformers lies in their design, inspired by the legendary Peerless transformers that were interleaved for ultra-wide bandwidth and flat response. If you're familiar with some of the all-time great vintage tube amps, you likely know that Peerless output transformers played a significant role in their success.

Our transformers are also interleaved using a winding topology that has 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 material you need and the lower the saturation. In contrast, transformers made in China often lack the same quality steel and suffer as a result or have to be made much larger to have the same response.

In addition, I chose to position the transformers on a different plane than the power transformer, placing them at the opposite end of the amp where no electromagnetic field is present. Instead of using end bells, the chassis is used to shield the transformers.

I also opted for a single 6-ohm tap because I found that the single-tap prototypes sounded better than the multi-taps—something about the unused taps seemed to affect the sound quality. The primary impedance is 9,800 ohms with 2,850 windings. This design allows the EL84 and SV83 tubes to couple more power as the speaker impedance drops, with maximum power achieved at 2 ohms.

If you measure the current and voltage on an SE84C Zen Triode Amp with a 1 kHz signal at 2 volts, you'll find that the current output actually exceeds the voltage.

Many people believe that transformers need to be huge to be good, but it's really all about the quality of the steel laminations.

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

There's been a lot of buzz lately about cobalt transformers. However, there's no evidence that a "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 currently the hot topic in the Magnaquest/Bottlehead community. I'm sure cobalt is good, as is nickel, but after reading all the hype online, I recognize that it's largely overblown. The majority, if not all, of these transformers are made without air gaps, necessitating a parafeed design. We explored parafeed designs three years ago and concluded that they don’t sound better to our ears. They do, however, perform better, which brings us to the crux of the matter: building amps that excel in performance (e.g., parafeed, constant current, etc.) versus simpler "Zen-like" designs that, to our ears, sound better (even if they perform worse). The choice is yours.

Nickel has one main advantage over steel: less saturation. There are two ways to deal with saturation: A) use nickel or cobalt, or B) simply size the transformers three times larger than necessary to prevent saturation. Our transformers do not saturate until somewhere between 15 and 20 watts. Depending on the amp we build, that means our transformers are between 3 and 10 times oversized. You can be sure that if someone is using expensive core materials like nickel or cobalt, they're not likely to oversize the transformers.

Many engineers argue that transformers in general induce distortions, so not using one is better. Output transformerless (OTL) tube amps can sound fantastic, but they’re finicky about speakers and come with several disadvantages. We believe that the transformer is a major reason why many people think tube amps sound better than solid-state ones. The transformer couples the output stage to the often hostile impedance of the loudspeaker in a synergistic way that’s not possible without one.

In the high-power, high-end audio world, the common approach is to build high-power amplifiers with high damping factors to better control the speaker and minimize the impact of feedback voltage generated by the speaker. On the other side, there are speakers with high power ratings, low efficiency, and complex crossovers designed to present the amp with a less hostile impedance curve. Essentially, these are amps that are less affected by (can’t "feel") the speakers, and speakers that are less affected by (can’t "feel") the amps.

In a great high-fidelity tube system, the output transformer creates and handshake between the speaker and the amp while blocking back EMF from the voice coil. The two work together, reacting to each other with every passage of music. This is called synergy, and it’s made possible by output transformers. The best vintage solid-state amps from the '60s and '70s used output transformers.

Output transformers are not a bad thing, just expensive.