Greg Smith

May 1997

Z-Man Audio Signal Enhancer

What don't you like about your audio system? I'm assuming there's something, because otherwise you'd be busy listening to music instead of reading about equipment right now. No matter how satisfied you are, there's always a potential for improvement. Usually, the road to system improvement involves upgrading one or more of the pieces of your system. One commonly echoed sentiment states that adding more links to your audio chain can only degrade the sound quality, and that the simplest configuration is best. While there's some truth to that idea, anyone who has upgraded their system by switching from an integrated amplifier to a separate preamp and power amp or improved their sound by adding a D/A converter knows that there are some circumstances where extra pieces can be of benefit. Fact is, all your components react with the ones they are connected to, and controlling that interaction can radically improve what you hear, even if that means adding something new. One product that claims to improve the interfacing between system components is the Z-Man Audio Signal Enhancer. Utilizing tube circuitry, this compact box is designed for connection to your CD player, eliminating some of the things that people dislike about digital sound in its current form. Instead of bright and sterile, Z-Man CD sound is instead warm and full. That's what the ads say, at least. Since I've got a couple of budget systems that could use some "warm sweet sound from digital", I spent some time checking out how well the Z-Man works in a number of different applications.

One of the reasons that audio components are hard to measure is that they interact with each other. When you hook up a speaker to a power amplifier, the frequency response of the resulting system depends not only on the characteristics of the individual pieces, but also on the way the amplifier output interacts with the speaker. The same thing is true, albeit to lesser extent, when connecting a source component to a preamplifier. For a CD player, the D/A converter output is typically implemented with a few transistors or an op-amp that outputs a modest voltage through the connecting cable into the next piece in line. Factors here include the output impedance of the converter's analog stage, the characteristics of the cable, and the input impedance of the preamp. All of these vary unpredictably, because there's no firm standard for any of them. In professional audio land, this isn't quite as big of a factor--the specifications there for component input and output impedance are followed fairly well (this is one of the main reasons pro gear isn't as sensitive to cable changes as consumer models are). If you go browsing around listings of home audio equipment, the line level interfaces are up for grabs. You'll see input impedances that go anywhere from 10K to 470K ohms, with 47K ohms being the most common value. Output stage designers don't know exactly what to expect for the difficulty of the load. In the same way that driving a 2 ohm speaker with an amplifier that isn't capable of the proper amount of current will produce poor results, you can have problems using a preamp with a 10K or 470K ohm input impedance with a CD player designed to drive a 47K ohm input. Mismatches like these can cause all sorts of unpredictable problems, with excess harshness or brightness being a definite possibility.

Impedance matching is central to the debate over tubes vs. transistors. Tube designs tend to be on the higher side of the input impedance range (over 100K ohms), while solid-state implementations tend to be on the low side (under 50K ohms). Also, tube designs often have a flatter impedance with less reactive components. Since almost all budget equipment is solid-state, you're usually stuck with a low impedance that's harder for the previous component in the chain to drive. One thing that might make your source's life easier is to use a tube preamp. While this is a nice idea, in practice those tend to be far too expensive to use in the context of a budget system. This is where the Z-Man Audio Signal Enhancer comes in. Using input circuitry similar to an expensive tube preamp, your source will have an easy input to work with. You'll get hefty output capability courtesy of the tube's output as well. This is why adding another piece to your system can help; if done right, the degradation of going through an additional component is more than made up for by the improvements in component interaction.

Hard Driving

While it all sounds like a plausible idea, the proof's in the listening. I plugged the ASE in and let it burn in for a week before I connected it. Like everything else, tubes can sound different when warm then cold, so letting things cook for a while seemed a good idea. I connected the ASE to each of the source components with a 0.5M length of Kimber PBJ. That's a good budget interconnect I've reviewed before, and what Z-Man recommends for those wanting a suggestion. In this context, I heard the usual small differences between that and the 1M DH Labs BL-1 I usually use, but stuck with the PBJ because I wasn't using it for anything else, anyway. Z-Man suggests keeping the cable between source and ASE as short as possible, with 0.5M being preferred and 1M being a maximum. Obviously, if you've got a CD player that doesn't output as cleanly as you'd like, using a really long cable can only aggravate that problem. Keeping the cable short minimizes the amount you can lose. If you've got a good cable like the DH Labs, I don't think this is much of a factor.

The first system I tried tied Rotel RCC-955AX to a CAL Gamma DAC with DH Labs digital cable. PBJ went from there to the ASE, which then fed into a Rotel RSP-960AX preamp and Rotel RB-956AX power amp with DH Labs BL-1. Speakers were the Klipsch Forte II, which are a set that will certainly let you know if your system is too bright or harsh. Speaker cable was also DH Labs. This is a system I had become fairly happy with, although the bass was a bit weak compared with what I was getting with some other combinations of components. The treble wasn't too forward as far as I was concerned (swaps to get rid of the harshness I used to have was how I ended up with the wimpier bass).

Hooking the Z-Man ASE into this already tuned-to-death system was a mixed bag. Right off the bat, I noticed that the missing part of the bass was back. Mid-bass was warmed up, becoming a bit more solid without going to far and becoming fat. Deep bass frequencies weren't noticeably different. The soundstage definitely sounded more open and lively. At the mid and upper part of the frequency spectrum, things were more complicated.

A Harsh Lesson

We review types like to throw around words like "harsh" and "bright" a lot, as does the material describing the Z-Man ASE. What do they mean? Well, that's a good question. Subjective reviewing pioneer J. Gordon Holt has a neat book called The Audio Glossary where he attaches definitions to lots of these slippery terms. "Harsh", he says, denotes "gratingly unpleasant to the ear; raucous". That's a certainly a subjective term. "Brightness" is easier to get a handle on; that "relates to the amount of energy content in the 4- to 8-kHz band. It is NOT related to output in the extreme-high-end range.". The results of something being too bright is "a hard, steely edge". If you want to get a good feel for what bright sounds like, get an equalizer or some other high-end-unapproved component (like a receiver) with a treble control that's around 4Khz. Crank up the 4- to 8Khz area and listen to something; that is brightness. Got it? One of the easiest ways to pick up that something's too bright is to listen for sibilance, which is the emphasis on "s" sounds.

We're all especially sensitive to problems with this part of the audio band, because our hearing is best around 3-5Khz. Peaks in that area are more noticeable than ones at any other frequency. For some reason, inexpensive audio equipment tends to be bright. I'm not quite sure why this is, but I suspect it's due to impedance interaction problems. Budget CD players in particular are often too bright. I've got a set of torture test material that is recorded on the edge of sibilance, painfully discovered during the days when my own system had big nasty peaks around 4Khz. The most brutal of which is "Just One Victory", a Todd Rundgren song originally appearing on the album A Wizard, a True Star (I use the better mastered copy from the Anthology collection for testing). In this song, Todd has one lyric that starts "shining still". Let me tell you, on a bright system, those "s" sounds will make your ears bleed.

Sure enough, the emphasis on those sounds was effective sheared off by the Z-Man with every system I tried it in. The only problem is that, in the context of the system I described above, the sound was already fine--on a good setup, that section of song doesn't sound bright. The drop in treble output from using the Z-Man was not an improvement as far as I was concerned. Furthermore, the reduced brightness shifted the tonal balance around enough that some of the higher frequency material, up above 10Khz, sounded too forward now.

After the first round, the ASE was on shaky ground. Sure, it improved the bass, but the upper frequency rebalance wasn't really appreciated. The conclusion I had reached so far is that if your system isn't too bright, adding this Z-Man product could be a counter-productive move. Fair enough.

To find a more appropriate testing area, I borrowed a friend's system for a bit. He's perched right on that mid- fi/high-end border, with a Sony CDP-315 changer connected to budget brand NAD 1600 preamp and 2400THX power amp. The speakers are B&W 602, and all the cabling is inexpensive Monster cable. This proved to be a more fertile ground for the ASE. The bottom end was considerably punchier, and there was quite a bit more top-end detail to everything. Vocals had more presence, and guitars were more realistic. Overall, this was a considerable upgrade for that system.

The $198 Question

Whether it's the best way to spend $198 to upgrade that system is a more debatable point. I got an equally large difference connecting the $299 CAL Gamma to his CD player. I think for a lot of people, it's a tough call as to whether the Z-Man would be a better choice than a DAC upgrade. When I asked the Z-Man himself, company president Gerald Zerfas, about this issue, he made one good point in favor of his product. D/A technology is advancing at a pretty good clip, enough so that every year you can get models that are superior and cheaper than their predecessors. The kinds of improvements the ASE makes are independent and complementary to what you get from a DAC upgrade, and it's not going to be outdated in a year or two. In the current turbulent times, with things like DVD on the horizon, it's not necessarily a bad move to put your audio dollars toward improvements that have a longer potential life span.

One of the things the Z-Man ASE does is act as a buffer between your source components and your amplification ones. There are a number of fruitful applications this suggests. For one, if combined with a passive preamp (perhaps just a potentiometer), you end up with a single input, tube buffered preamp (hint to Z-Man: consider this as a new product). Or, you might use it to drive long interconnects in a system configuration where your power amplifier was located relatively far away from your preamp. Using the ASE ameliorates a nagging problem I've been wrestling with. My computer's sound card has a mini-headphone jack for its output. I've got a converter cable that turns this into two RCA plugs I can actually hook to a traditional audio system. That converter cable itself is enough of a problem; I juggled between four of them before finding one actually sounded decent (the Sony model that came with an old DiscMan sounded a better than the 99 cent generic ones I had been using). Well, that cable isn't long enough to reach the audio system, so I need to clamp a set of extension cable onto it. Adding another meter of cable to what is already a more difficult load than the sound card wants to drive degraded the sound further. Nestling the Z-Man near my computer, plugging the little converter cable into it, then letting it drive the long cable proved to provide much better sound. Since much of the computer sound you hear is compressed to take a minimum of memory, it tends to sound nasty when you hook it up to something that actually lets you hear everything. I don't think your average game designer is concerned with the digital audio artifacts (compression, low sampling rate, you name it) being audible when most of the people are listening with cheesy little "multimedia" speakers. The Z-Man smoothed out some of annoying sonic grunge present in the lo-fi sound effects of many computer titles. I recently found out that Kimber Kable makes a 1M PBJ cable with a stereo mini-jack and RCA plugs that Z-Man sells for $40; you can bet I'll try that out as soon as I can get my hands on one.

I dropped the Z-Man into a number of other system configurations I've had over the last few months, trying to get a feel for the general pattern of what it did (note that I didn't try it out with other tube gear). In every case, there was a reduction of brightness, which was usually a blessing; there were some situations where I didn't feel that was an improvement, because those systems weren't too bright to begin with. Bass always seemed more firm but never too bloated. The top-end was usually more detailed, but background hiss and other noise was attenuated some. It was easier to pick up low-level details in the music. I was never able to put a finger on how much of that was due to improved transient response, and how much was reduced masking of sounds by the drop in brightness. This extra detail was a welcome change in every system I tried, even those that didn't benefit from some of the other enhancements. Often this resulted in a more expansive sonic landscape, where all the music sounded more clearly defined in a larger space. The subtle improvements in detail and soundstage were noticeable with all the budget systems I tried, regardless of how expensive or inexpensive they were. That made me wonder where the upper limit on that effect might be. One way to get an idea what range of price class a component would be compatible with is to check out how well it's constructed, so that's what I looked at next.

A Look Inside the Black Box

While I'm not one to normally take apart all my audio equipment, Z-Man makes a point of discussing the high quality of the parts used to implement their design. Accordingly, I grabbed my tools and disassembled the case to see what's in the box. They don't recommend doing this; after all, there are high voltages involved, and you could get seriously hurt. There's quite a bit of capacitance storing charge inside, so even if it's unplugged, you could still get shocked. If you must open it up, you can minimize your chance of injury by turning the Z-Man off while continuing to run an audio signal through it. You can hear the volume drop as the stored power drops off, discharging the power supply. It plays for around 20 seconds before dropping to minimum volume. It lets a little signal through even with no juice at all, so you can still play through it even after the internal charge is gone and hear something.

Inside you'll find a single circuit board the same size as the case. The power supply is toward the front (left side of the picture) , the tube in the middle, and the input/output at the back (right side of the picture). There are some power supply connections done with point to point wiring and push-on connectors, but all of the actual audio parts are on the neatly laid out board, including the RCA jacks soldered directly there.

The power supply is implemented with a main transformer, a choke, and two diodes. There are two regular 100uF capacitors used to filter the power that runs the tube. You get a few generic resistors and capacitors in this section as well. The tube is run at 260V, a conservative voltage (Z-Man claims it could be bumped up as high as 330V, but the tube wouldn't last as long). There is some potential for parts tweaking here, as there parts here aren't fancy premium ones. This is a sensible design, using less expensive parts for less critical portions of the circuit, so that you can spend more on really good ones in the sections that are more important to the sound quality.

The tube itself is a Sovtek 12AX7WXT+. It should last 2-3 years of normal use, and replacements can be had from places like Audio Advisor (their last catalog lists that particular one at $12.95, with the regular 12AX7WXT at $4.95). Preamp tubes like this one actually have dual triode sections internally, so both parts of a stereo signal are handled at the same time.

The circuitry that's actually in the signal path itself uses all premium parts. Each channel has a 4uF MIT Multicap, a .1uF MIT Multicap, and 5 Holco resistors. Very expensive parts as capacitors and resistors go. Stager Doug Blackburn informs me that you can certainly get a better capacitor from TRT (originally the InfiniCap, now called something else) or Hovland (the MusiCap), but I'm paranoid enough to not be sure who to believe. I won't open up that whole discussion here, but I will point you toward REL for one side of the argument over who and what makes a good capacitor (REL sells it's own brand of MultiCap). Since it's advertising, read accordingly. Make sure to check out the seminal paper by Walt Jung and Richard Marsh they've made available.

If you showed me a bill of material for the Z-Man ASE, I'd guess that it cost at least $500 based on what's inside, given how audio parts are normally marked up. $198 is an excellent price for what you're getting. Z-Man has some choice words to say about the quality of their competition's construction on their home page, and I won't go slagging them myself as I haven't done a direct comparison. Just looking at what you get for your money, though, the ASE is clearly ahead of any under-$200 tube design I've ever seen, especially with regard to its power supply.

Since the Z-Man uses so many expensive components inside already, one logical questions is what's left to tweak inside if you wanted to improve it some. Z-Man says that there is some margin for improvement inside the power supply. It's almost always possible to improve power regulation by throwing more or better pieces at it. In the process, you might also increase the voltage the tube runs at some, which should give slightly better performance at the expense of tube longevity.

If you want an easy but significant way to improve the ASE, the most obvious answer is to upgrade the tube it uses. While the Sovtek model used is well-regarded, it's certainly possible to get better. Z-Man says they've had the best results using vintage tubes from Mullard or Telefunken. Gerald Zerfas states:

I have found that by simply replacing the Sovtek with a Mullard ECC83-CV4004 significantly enhances the unit's performance. There is an immediate gain in musicality, bass response, and detail in the upper frequencies. It provides a much better guarantee that the Z-Man will have a positive impact in almost any audio system that it is used in. In addition, the Mullard will have a much longer life in this circuit (maybe 5-8 years). The only disadvantage of the tube is its cost.

Z-Man recommends Vintage Tube Services at (616) 454-3467 as a supplier of NOS tubes, stating "Andy Bowman of Vintage Tubes played a crucial role in developing the ASE, and has a healthy reputation for his knowledge of tubes (he's almost a walking encyclopedia when it comes to the history of various tubes and their manufactures)." The best net-saavy source I've found for buying those older tubes is Upscale Audio's Kevin Deal (kevin@upscaleaudio.com, 909-931-9686). Kevin lists NOS Mullard tubes for $40- $50 and Telefunken ones for $30-$70. He's also got some used tubes that are suitable if you'd like to try it out without investing as much, although be advised he's got a minimum order amount.

A Question of Balance

The Z-Man Audio Signal Enhancer is certainly effective at reducing some of the more offensive qualities of inexpensive audio gear. Considering that it's inexpensive and well made, it seems an excellent bargain for some listeners. I wouldn't go so far as to make an unqualified recommendation for it. If the reason you're dissatisfied with your current system is that it's too harsh or excessively bright, this is probably the cheapest way to fix the problem. The fact that you may find the playback more refined in addition to being less obnoxious would make it an even better addition.

For me personally, the ASE is an interesting study in enjoyment vs. critical listening. There's no question that using it made most of my listening more fun. Here's the question that keeps popping into my mind: if I add something to my system, and it makes bad recordings or poor component matches less objectionable, should I use it? After all, if I can't pick out bright recordings as well anymore, haven't I lost some measure of resolving power for hearing what's really happening on the recording? By that standard, using the ASE gives a lower fidelity system, regardless of whether it might be more enjoyable to listen to or not. By your standards, that may be irrelevant. Since I'm stuck in reviewer mode a fair amount of the time, I try to avoid anything unique because it makes component matching difficult. If I build a system that includes the ASE, and it sounds good, I can't be assured it will still sound good if I remove it. While this is true no matter what component you add or subtract for your system, the qualities of this piece make it difficult to replace with anything else.

Making the judgment call as to whether the Z-Man Audio Signal Enhancer is right for you is a decision only you can make. The most I can do for you is say that it meets the performance claims, has a number of potential uses, and is a good value for your audio dollar. If it sounds like something that might be a good upgrade for you, there is a 30 day satisfaction guarantee, so your risk is low. It might be just what you need to get you back to enjoying your listening instead of fussing around with your equipment.

.....GS (gsmith@westnet.com)