Audiolics Anonymous Chapter 27
Electraprint DRD SET Amplifier, Part 1
Article By Bill Gaw

  This month I have definitely hit audio nirvana. First, the Sound Application CF-XE Line conditioners as discussed in the past two articles have broken in. My system now sounds superb at least 90% of the time and just great for the rest. This unit is the best single improvement I've ever made in my system. Taking one out of the system is painful, as I regress to a much lower level of reality. I have even stopped evaluating other AC filters, unless one of my audio friends highly recommends it.

I have also experimented with using different high end power cords with the CF-XE, including several types of NBS, Electraglide, Distech, vs. standard Belden. While there is an improvement with the high end cables, each still has its own sonic signature, it is not nearly as great as the change in quality over the standard Belden without the unit. If I didn't already have the specialty power cords, I'd probably be able to do without. Thus the $5,000 charge for the twelve outlet unit may actually be a bargain, considering you may be able to do without twelve super high-end power cords at $1,000-$6,000 each.

Now that I have the above unit, evaluation of equipment has become much quicker and easier. Why? Because now my electricity is stable. Whatever was driving my AC crazy has been eliminated. Why is that important? Because if the electricity isn't good, most equipment will not perform to its best. How can one evaluate a product if one is time constrained and can't wait for the day when everything is at its best. Thus, I can't understand how most reviewers can rate products against other product they may have heard hours or days or weeks ago, when the electricity, atmospherics, state of mind, etc., are different.

While I don't believe in ABX testing as the penultimate for reviewing, I must admit the ability to hear the equipment side by side at approximately the same time, does take away some of the discrepancies associated with crappy electricity. Unhappily, it makes reviewing a test, and we all know how testing increases anxiety levels that takes away the joy of our hobby... and stresses the testee out. I used to go to Clark Johnsen's Listening Studio before its demise to the wrecking ball, and several of us would sit for hours and compare various types of equipment. While these sessions were invaluable for teaching me what to listen for, within an hour I would invariably end up with a headache and lose the ability to differentiate between a high end speaker and a transistor radio.

Anyway, for the past two months I have been listening for hours on end, as the sound has been addicting. In twenty years of listening I have never been happy for more than a few days before trying something new. Tweak became my middle name. Well that has changed, which will definitely put a crimp in my further reporting.

Therefore, it was surprising when I found a new piece of equipment that has brought me to a higher level of sound, and which I am happy to say is the very close to the best low wattage tube amp I have had the privilege of evaluating: Jack Elliano's newest single-ended amplifier creation. I'll go over the circuit today and then give a full review of the sound next month.

I first learned about Jack and his Electraprint Audio of Las Vegas (www.electra-print.com) several years ago through Bruce Edgar who was using Jack's original VV-30 amps, which I still own, to demo his horn loudspeakers. Jack is a truly great guy and a straight shooter who tells it like it is. He is one of those true geniuses who can imagine a new circuit design and bring it to fruition. He was originally into electronics through the design of some component of electronic time clocks, for which he still holds several patents, and into high end audio through designing transformers and inductors, for which he is famous in the SET community. He then got into designing and building tube amps for his transformers, but felt there were some deficiencies in music reproduction that couldn't be overcome with the present tube circuits.

While most of us may come up with some great thought or invention once in their lives, and most of the time forget about it before it comes to fruition, Jack has thought up two advances for tube circuitry, the Ultrapath Line Stage, and the Direct Reactance Drive.

Just about every different type of tube circuit, especially the SET ones, were first developed in the 30's, with the last being probably the Williamson push pull circuit from the late 40's. Every tube amp development since has been variations on these prehistoric configurations, just using different configurations and quality of resistors, capacitors, inductors, transformers, etc., to adjust the sound. Each new change is considered an advancement by the maker, but is usually just a variation of a theme. Jack has come up with two new circuits which I believe are true advancements for tubes, both for their utter simplicity and quality of sound reproduction.

What follows is distilled from three articles, which I would suggest that anyone who is interested in Jack's circuits, read, as they are probably much more informative than my discussion. All are from Vacuum Tube Valley, probably the finest tube related paper periodical still available.

The Ultrapath Line Amp, Jack Eliano, Vacuum Tube Valley, Issue 10, pg.. 11-12, 1998

Direct Reactance Drive Amplifier, Jack Eliano, Vacuum Tube Valley, Issue 14, pg. 25-27, 2000

Ultrapath, Parallel Feed and Western Electric, Lynn Olson, Vacuum Tube Valley, Issue 16, pg.. 4-9

As Jack has explained to me, all a tube does is act like a valve on a water circuit, modulating and directing the flow (thus the English term for vacuum tubes). Think of the electrons as packets of water. There is a force (voltage) which drives the electrons through a pipe (circuit). The force is supplied by the power supply which changes AC into DC, filters out as much remaining AC noise as possible, and delivers as steady a supply of current as possible, with the maximum amount of force set by the voltage of the supply. Like with the water system, there is a dam holding back the electrons, the vacuum space between the cathode and anode of the tube. When the positive potential (voltage) of the anode is sufficient to pull the electrons across the space, the electrons flow and can then do work, either at the next dam (tube) or through a machine (speaker). The dam only allows the electrons to flow in one direction. Even if the voltage is reversing (AC), only flow in one direction can occur. Thus a diode tube acts as a rectifier, changing AC to DC.

In order for the system to continue to be charged, there needs to be some way for the electrons to return to their starting point. With water, this occurs as rain. In the tube circuit there is usually a central grounding point through which the electrons can flow back to their place of origin.

As with a dam, the flow can be modulated and controlled by placing a gate in the way. In a tube, these are the screens or grids. They work by having a positive charge on them that repels the electrons, the main gate (triode) modulating the flow across the gap, and the secondary gates (tetrode and pentode) funneling the electrons in the proper direction. As the charge on the screen varies, it causes a modulation of the flat DC voltage to be partially converted into AC, which is the signal carried, much as water waves float across the surface. As long as that modulation voltage is less than the total DC voltage, little distortion occurs. How high that modulated AC must be is determined by how much the next stage of the circuit needs.

In order for the electrons to do any work, there has to be a resistance to the flow, and in order not to damage the next level of control (grid in the next tube, or the loudspeaker) the DC component has to be filtered out, so that only the AC wave will be passed on. This is the job of the capacitor, or transformer, which prevents DC from flowing. Inductors act as both a resistor on the DC, and as a modulator decreasing higher frequency AC. Transformers can act as both a DC blocker, and an adjuster of the relative voltage to current flow.

Up to this point, all of the electrons have had to flow through at least a capacitor and resistor or a transformer to block DC from the next stage, and a power supply cap or two, and the cathode bypass capacitor, to get the electrons back to the cathode, as can be seen in the diagrams of a standard circuit, parafeed, transformer coupled and Western Electric circuits, all of which can be found described in my copy of The Radiotron Designers Handbook from 1953.

If one removes the cathode bypass cap, this disturbs the dynamic resistance of the tube (Rp) which will affect the output transformer. Removing the power cap makes for a noisy power supply with AC ripple, and worsens the impedance, and thus the dynamic abilities of the power supply. Thus one is stuck with the signal going through at least four different components, some possibly of very poor quality.

This presents a problem. No matter how good any of these parts are, PARTS IS PARTS, as the chicken commercial stated, and unhappily, the caps used in power supplies are usually electrolytics. These are usually mylar based, and they have an electrostatic barrier, which causes difficulty in changing very low voltage levels. This leads to smearing of the microdynamics of the audio signal, leading to loss of low level information. To this point, the four different circuits have done little to improve the situation except to improve the parts.

Thus the first of Jack's Eureka moments, the Ultrapath Line Amplifier. What he came up with is a variation on the standard transformer coupled voltage amplifier. What he did was to couple the primary return of the transformer directly to the cathode of the tube through an oil signal capacitor of high quality. Obviously, this can only be done through a transformer loaded circuit rather than the typical R-C type. Thus the signal doesn't traverse the two caps, and the power supply caps only function then is to isolate AC in the power supply from the signal.

This has several advantages. First, the power supply with its cheapo electrolytic capacitors, is no longer in series with the sound, but parallel to it. Second, by using an oil capacitor, which has equal charge and discharge cycles, and has little problem with low voltage changes, there should be decreased distortion of the low level sound cues which are so important in differentiating between live and canned music. Theoretically this should improve our perception of hall space, the air around the instruments and phase differences in the sound.

Jack's second Eureka was his Direct Reactance Drive circuit. In the classical interstage tube circuit, a resistor and capacitor (R-C) circuit, or a transformer, is placed between the driver tube and output tube to block DC and drive the circuit. Both circuits use up power in the transformer and resistor, and the capacitor is directly in the circuit. Jack's Ultrapath circuit puts the cap after the transformer, where it does less harm, and shunts the signal directly back to the cathode. The second idea was to place an inductor between the driver tube anode and the cathode of the output tube. This eliminates the resistor, and replaces it with a parallel reactance, which wastes no energy, and again decreases distortion. It also allows the circuit to act as a constant current device with infinite impedance.

What does this do? It allows the output tube to be driven to higher levels with lowered distortion. Instead of a measly 1.5 watts, he gets three watts from a 2A3, and 13 vs. 8 watts from a 300 B without stressing the tube. Distortion figure measured at the transformer? Less than 0.5%, mostly second harmonic.

Also, all sound components ride together with external voltage variations. Thus, the power supply is seen by the tubes as regulated without the deleterious effects, even though it isn't. The power supply is further isolated from the signal by the combination of the inductor and the Ultrapath cap, thus the components for the power supply are less important for the final sound quality. Jack prefers diodes and an inductive supply, which brings down the cost considerably since Jack winds his own inductors, and diodes are much cheaper than tube rectifiers, and burn less electricity.

I have actually received three amps from Jack: the first a stereo 2A3 based unit and the second and third 300B monoblocks. Jack based the circuit of the first for the Vaic mesh plate 2A3, which he found during construction to not be a true 2A3, needing different operating points from a regular 2A3 to minimize distortion. So all of you tube rollers out there using this tube in place of a standard 2A3 may want to get out a distortion analyzer. Actually, I had originally ordered monoblocks, some miscommunication occurred, and the stereo unit appeared. Happily, it has found a place in my system driving my center speaker, as after a short listening session, I couldn't return it.

Jack, full of apologies for the mix-up, talked me into going with 300B's for the second set. The monoblocks were originally going to be optimized for a Yugoslavian 300B which seems to be in favor now, and is relatively inexpensive, but I found some new Western Electric 300B's on the web for almost half price and shipped them to Jack.

Each amp is hand built in Jack's factory to the individual's specs, with Jack winding all of the transformers and inductors to his specs. The amps are broken in, then the operating points are chosen for each amp's tubes to produce the lowest distortion with the highest output without straining the tubes. As previously stated, with Jack's circuit, he can get almost twice the wattage output without straining or decreasing the tube's lifetime, important when a WE 300B set lists for $900, and only put out 8 watts on average. I don't want to have to replace those babies every few months.

The above circuit diagrams were taken from Jack's previous papers, and through experimentation he has changed some of components for my amps. Driver tube is a 6AN4, a single small triode with very high gain and low Rp, originally used as a UHF gain tube in televisions. Because it transmits signals into the GHz range, Jack has placed a 1 kOhm resistor at the 300 B's screen to lower the Q of the system to prevent oscillations if high frequency information should get into the amp. The oil cap has been dropped to 60 mics, and the inductor to 65 Henry.

What has Jack obtained for sound with these units? Specs of 13 watts output from a 300 B without straining the tube, distortion of 0.5% at 8 watts, mostly second harmonic, and 20Hz to 26kHz bandwidth (+/- 1 dB). That's transistor range. Its sound, you ask. Well, you will have to wait for next month's installment as I want to allow the units to break in further and a couple of friends are going to evaluate them in their systems. I will say though that on first turning them on, I find that he in several aspects they have leapfrogged any other tube or transistor amps I have heard. Hope that wets your appetite for next month's article. Till then... Good Listening.

Electra-Print Audio
4113 Roxanne Drive
Las Vegas, NV 89108

Voice: (702) 396-4909
Fax: (702) 396-4910
Website: www.electra-print.com