The Big Combo
Zeus Headphone Amplifier & Grado RS-1 Headphones
Russ Novak
9 December 1999

Phone AmpSpecifications

Fuchs Audio Technology
73 Collins Avenue, Bloomfield, NJ 07003
Phone: 973-893-0225 or

Two channel 1-watt OTL tube headphone amplifier. Tubes: 6-6EM7 tubes. Topology: constant current differential input stage, totem pole type output stage w/separate bias and balance controls. Separate tube regulated power supplies for each channel. Price: $1,595.00.

"The Zeus is designed to drive from 20 ohms and up. I have successfully driven 8 ohm Koss (Radio Shacks too), to impressive volumes, but I suggest 20 as a fair minimum. Grados are 30 ohms and Senheissers are 300 ohms (!). It's output voltage swing increases as impedance goes up (as most OTL's do). Distortion is .5% or less. I don't play the numbers game, since you can't hear the difference between .00001 and .1 % anyway." – Andy Fuchs.

Grado Laboratories, Inc.
4614 7th Ave, Brooklyn, N.Y. 11220
John Grado, President
Phone - 718 435-5340; Fax - 718 633-6941

Grado Reference RS1 Stereo Headphones; transducer type dynamic headphones, open air; frequency response 12 Hz – 30 kHz; SPL at 1mV: 98 dB; nominal impedance 32 ohms; drivers matched to within .05 dB. Vented diaphragm, wooden air chamber, Ultra High Purity, long crystal copper in voice coil and connecting cable. $695.

The Summer of ’63

"…in ’63 it was magical. They gave me wide-band response for just a few dollars. Getting this close to the music was an experience. All the subtleties that passed unnoticed through speakers were present in delicate, nuanced detail. Even today it’s uncommon to find a speaker that does as well as a top pair of headphones."

Headphones. The experience of headphone listening sends my mind rushing back to the balmy summer of 1963 in the Chicago suburbs: quiescent late nights reading, a dawn breeze through the windows, sleeping till noon in summer heat. Sixteen is a time of rapid intellectual growth for a young man; adult tastes are formed. I spent much time in my room reading history, politics, hi fi, sports. At 16 one is primed for discovery. I owned a 20 watt integrated tube amp from Allied Radio (Knight) and two woefully inadequate Allied two-way speakers. The speakers lacked any bass response, not even a nice mid-bass hump, and I had no financial prospect of replacing them.

I spent a lot of time at E.J. Korvettes in the plaza, studying the art work on albums, reading the covers, trying to imagine the sounds of the strange music that promised Nirvana. At $3.49 per record I couldn’t afford to make a mistake. Yet I was invariably disappointed. The sound just wasn’t full enough, didn’t have "presence;" wasn’t "there."

By some means I amassed $20 and bought myself a pair of Superex headphones along with a speaker/headphone switching box (no jack on the amp). Decidedly non-audiophile I assure you. Today we’d find them uncomfortable to wear and we would hear the distortion. But in ’63 it was magical. They gave me wide-band response for just a few dollars. Getting this close to the music was an experience. All the subtleties that passed unnoticed through speakers were present in delicate, nuanced detail. Even today it’s uncommon to find a speaker that does as well as a top pair of headphones.

I discovered Debussy’s piano music, Chico Hamilton, Carmen McRae’s jazz singing, Ravel’s "Daphnis et Chloe", and Faure’s Violin Sonatas. My immediate surroundings were removed from the musical experience. Nothing stood between the performer and me. Sound was immediate and intimate, unlike anything else.

Of course, that illusion known as "soundstage" is missing. The music originates in your head: left, right, center, and one hears ambiance information on the recording, but it is not "layered" in the sense that a perfect room/speaker setup is. That was a result I could live with at the time in exchange for better frequency response.

I put away the headphones in later years as I gained disposable income and concentrated on the main system in a home of my own. But I always remembered what I discovered on those quiet summer nights.

Reborn In ‘97

"John Grado responded again with a pair of his top-of-the-line RS-1s. As wonderful as the SR60’s are, the RS-1’s are masterpieces. The bass is deep and full, even more transparent and tightly controlled than the SR60s."

Robert "Houn’ Dawg" Clark was on the phone panting over a headphone amplifier designer Andy Fuchs and he had just cooked up. "I’m bringing it over. You gotta hear this."

It was slapped together in makeshift fashion with miscellaneous parts. But it sounded great! Instantly apparent was a transparent, sweet sound with deep extension in the bass. Better yet, this was all bought without the opaque tube colorations we hear in some speaker amplifiers. "Houn’ Dawg" was pushing Andy to make it a commercial product and I concurred.

I talked to Andy about building me one and I purchased all premium parts and wire. Andy developed a handsome chassis, further refined the circuit, built both of us pairs, and I hauled it home. These units were the final stage in what would be known as the Zeus Headphone Amplifier.

Of course I couldn’t have heard what I heard were it not for the courtesy extended me by John Grado. He, of Grado Laboratories fame had sent me a pair of the wonderful, inexpensive SR60 dynamic headphones following a visit to his CES room the year before. Working with some of the solid state headphone amplifiers in circulation, I never felt I got as much as these little ‘phones were capable of, but through the Zeus I was floored. I got back to John to urge him to hear this amp, but I couldn’t get the two guys together. Well, the best laid plans…

John Grado responded again with a pair of his top-of-the-line RS-1s. As wonderful as the SR60’s are, the RS-1’s are masterpieces. The bass is deep and full, even more transparent and tightly controlled than the SR60s. The top end is more extended and I noticed a reduction in distortion I wasn’t aware of listening to the SR60s alone. With the RS-1s I was able to hear into the recesses of recordings in a way impossible with speakers.

Zeus History and Design

The Zeus Headphone Amp is a transformerless triode, low feedback headphone tube amplifier with all stops out in design and execution of the signal path. MIT caps, 1% metal film resistors, Teflon coated silver wire, and Wondersolder are used in construction. The unit has a brass top plate seated in an oak base. The tubes sit atop in open air for audiophiles who like to watch the glow. It’s an attractive unit. I have mine sitting on a bookshelf over the computer desk and spend long hours listening to my Zeus/Grado combination while working.

The unit has been available on a direct order basis from it’s designer, but with formal commercial production, it is being offered for $1595 through Audioweb or to get to his web page directly at $1,595 seems a lot of money compared to what we might like to spend on a headphone amp, but this unit brings sound reproduction past the level of refinement of the rest of the system to a sort of realistic bliss.

The history of Zeus follows the typical motivation behavior of audio designers and hobbyists: perceived inadequacy of existing sound quality followed by resolution. Designer Andy Fuchs recalls that he purchased a pair of high quality Grado headphones but was frustrated by the generally low quality of headphone amplifiers available on the market. Headphone jacks on supposedly high quality components were similarly inadequate.

Fuchs began a period of experimentation to achieve better results. He first tried conventional single ended, low power tube amps. However the resolution of modern headphones revealed the shortcomings of this approach. He heard the transformers and a high noise floor. Designing around that problem didn’t produce the results he wanted, so he next built a series of all tube cathode follower circuits. This approach showed promise in that it was quiet and had the resolution he was looking for, but Andy was unsatisfied with the dynamic output limitations of that type of circuit.

Something more akin to a small OTL (output transformerless) circuit seemed the answer. That advantage of headphones is that they present a simple load to the amplifier and do not require much power to drive them to loud levels. Andy’s experience working with New York Audio Labs on the Futterman amplifiers gave him insight into what sort of circuit to design.

Next he began a search for an acceptable output tube among the limited offerings on the market. The 6EM7 tube was discovered by accident. He was looking for a triode tube with the lowest possible plate resistance. The reason was that it would produce the lowest possible output impedance without needing the high feedback that most OTLs require to achieve this (the lower the output impedance the less interaction with the headphone load and less consequent change to the signal).

The 6EM7 is a dual-section tube. One section is a very low plate resistance triode, and the second section is a fairly conventional high gain triode, quite similar to one section of a 12AX7. It’s original uses were for voltage regulators and vertical output tubes in B&W TV sets. While no longer a production tube, there are thousands in stock worldwide.

The Headphone Amp uses three 6EM7’s per channel. One of the prerequisites for low noise was a quiet, regulated power supply. A tube regulator circuit (one per channel) uses the 6EM7 in a textbook regulator circuit, which feeds the audio stage. The raw power supply starts from 500 Volts, and is regulated to 400 volts. The entire audio circuit (input as well as output sections) runs on this regulated source voltage.

The input stage tube sections operate on about 275 volts on their plates, which is a very linear point in the tube curve. The output stage operates the two (stacked tubes) on 400 volts, which puts each tube section at 200 volts, a conservative operating point that assures long tube life.

The audio circuit uses the two high gain triode sections as a constant current differential amplifier. One half takes in the audio signal, and the second half receives the feedback return from the output of the amplifier. The second tube sections operate as a totem pole (single ended push-pull) output stage with separate bias and balance pots for each half. The midpoint of the output stage is the capacitor coupled to the phones. The circuit is stable enough to operate open load (no feedback) although it is somewhat noisy due to the excessive gain. The circuit will also run with 100% feedback (a sign of the circuit’s inherent stability) but sounded "pinched" and sterile. The original prototype used a pot in the feedback loop that allowed Andy to tailor the feedback level to the "sweet spot", where the desired sonic balance was achieved.

The circuit produces about ½ watt maximum output into 8 ohms (no you wouldn’t be happy using it to use it to drive real speakers, nor is it recommended). Since dynamic phones run the gamut from a low of 8 ohms (Koss) to 30 ohms (Grado) and a high of about 300 ohms (Sennheiser), the amp needed to be stable into most any load.

The Grado Reference RS1 Headphones

"This is a true reference product. Craftsmanship is excellent and long-term dependability superb…"

Everyone acclaims these headphones as state-of-the-art. The $695 price amounts to "theft of sound" compared to the cost of speakers with equivalent performance. They’ve been reviewed all over: Jack English and Wes Philips in Stereophile (a Stereophile Recommended Component), Ken Kessler in Hi-Fi News and Record Review, and by Cory Greenberg in Home Theater Magazine. There are several reviews on the web:

Or go to the Grado home page:

So my purpose in this section will not be to re-review them, but to add my affirmation of their quality.

This is a true reference product. Craftsmanship is excellent and long-term dependability superb (I’ve used them over two years). They are comfortable and I’ve worn them for as long as 10 hours at a time without their physical presence diverting my attention from the music. Your ears stay cool due to the open-air design and the ‘phones are ultra light with a soft leather headband that conforms well to the shape of the head. The cups seat well around the ears without excessive pressure. The mahogany ear cups are specially cured and treated to eliminate resonance.

Unlike the classic left/right/center, in-your-head placement of instruments with classic headphones, the RS1 gets the sound outside your head, outside the headphone cups. Ambient information retrieval is huge. One is in the musical environment as opposed to "listening forward" to a stage within a hall or a pair of speakers in a room. I like the effect. It increases my enjoyment through immediacy and intimacy.

The RS1 has an ultra refined treble range, a very necessary trait in a product worn directly on the ears. This refined treble was apparent even with cheaper, solid state amplification, or even the headphone jack on my cassette recorder. Through the Zeus the smoothness, liquidity, and extension are phenomenal. The midrange is rich, neutral, and natural. It has no peaks or dips throughout the range to highlight problems. Bass is warm without bloating or booming and is transparent to the lowest depths. This is the Grado "house sound," a smooth creaminess without opacity and an absence of resonant coloration. You hear it in the $69.99 RS60, and you get it in spades with lower distortion in the RS1.

Now to be fair to John Grado, I need to mention the new head phone amp Grado has developed, the RA-1. I have not heard it and John has not heard the Zeus. The RA-1 is a solid state, battery powered unit that should inherently result in the lowest noise floor, but how this will compare with a tube OTL design is another topic entirely. I just want to tip you to the fact that the RS1/Zeus combination lock into each other like nothing I’ve heard, like no tube or solid state guy could dream of.

Just Some Practicalities

The Big Combo will cost you $2,290. You don’t need to do it all at once. If you already own a pair of high quality headphones, stick with them and pick up the headphone amp. Many people already own Sonys, Sennheisers, etc., and regard them as state of the art. I won’t quarrel. But you owe it to yourself to hear them through the Zeus to learn what they can really do. Are you ‘phoneless at present? Grado offers the universally regarded SR60 headphones at $69.99 and the SR80 for a bit more. That gets the price down substantially.

You can connect the headphone amp to the tape outputs of your preamp or do what I do. Take a few extra seconds to run the interconnect cable directly between the DAC and the Zeus. Why put extra circuitry in the way when you are settling in for an evening of music?

Another strategic consideration is where the headphone amp will be placed in relation to your listening position (which can now be anywhere in the room ‘cause you are freed from speaker placement). You can position the Zeus at your equipment rack and run high quality interconnects – not so expensive because you already own them (and you will hear the differences in cables). But if your listening position is some distance away, you’ll have to run a headphone extension cord. Not ideal in my view. Instead, I place the Zeus at my desk and near my couch where the SR1’s cord can easily reach.

That means using a long interconnect from the equipment rack. If you don’t have the mega-bucks to afford a long run of audiophile grade interconnect, you don’t have to dismiss the idea. I made a 25’ pair of interconnect from Mogami Neglex 2549 microphone cable and find it tonally accurate and very inexpensive. This is a simple multi-strand twisted pair of wires with a braided shield. "Float" (do not connect) the shield to the RCA plugs at the signal source end (the DAC) and "ground" the shield to the negative pin at the receiving end of the signal (the headphone amp end). Break them in and you’ve got a super pair of interconnects. You lose almost nothing for headphone listening.

The Big Combo Sound

"The audiophile is completely freed from the external environment and finds himself 'in' the orchestra, hearing detail and nuance not available with loudspeakers. The audiophile becomes unified with the ambient space."

The Big Combo is simply Drop Dead Gorgeous! I could run a lot of bull, like "palpable" this (which it is) and "detailed" that (which it is also). I could run up and down the audible frequency spectrum praising the highs and lows and the rich midrange. All of that you can take for granted with The Big Combo.

Rather, I find my attention drifting to each recording I play and I am transported to the time, milieu, and message of the music. That is as it should be. But my reaction indicates to you, the reader, that I can get no extra copy from discussing colorations in the equipment. It indicates how truly musical the experience is. It shows how readily one can divorce oneself from equipment concerns when the sound is right.

There are only two additional points I wish to make on the sound. "Liquidity" is a overworked phrase in our lexicon. The Zeus headphone amp has it and the Grado can reproduce it. There is no grain, nor etched quality, but liquidity is more than that. The Zeus and Grado are able to maintain the harmonic integrity of the sound, reproducing all the harmonics present in the recording, such that the instruments appear three-dimensional. I’ve heard tube amp/speaker combinations described as "sweet," when in fact, they are dark, veiled, and sweet. The Zeus/Grado combination is transparent, light, three-dimensional, grainless, and has just a touch of sugar. The sound is "liquid" in a way few audiophiles have heard.

"Intimacy" is the other concept you need to internalize if you don’t have long term experience with headphones. The audiophile is completely freed from the external environment and finds himself "in" the orchestra, hearing detail and nuance not available with loudspeakers. The audiophile becomes unified with the ambient space. Instrumentalists may become tangible extensions of the listener. Mirages appear in your mind. You find yourself reaching for piano keys, bows, the deliverers of our unspoken language. The urge to create flows from the brain, down the arms and to the fingers. Think that is an exaggeration? Try listening to your favorite recordings with The Big Combo and tell me different.

The fact is that the only partnership that may better The Big Combo is the Sennheiser HE60/HEV70 electrostatic headphones through the Orpheus tube amplifier with integrated DAC at $14,900.






















































Luminous Audio