Excellent preamp. Dead quiet and wonderfully transparent. Can miraculously transform many a bad recording and will correct most of the faults in your system. With some effort can perform some basic room correction functions. Also works as a jitter reducing device. Superb built quality.

This is an amazing unit. I used to own the BAT VK 50SE preamp and originally bought the RDP-1 with the intention of using it only as a very precise equalization tool. It turned out that the Z-Systems as a preamp is just as good as the BAT, perhaps even a touch more transparent. I sold the BAT, got the matching Z-systems AD converter to use with analog sources and couldn''t be happier. The music is so much more enjoyable now. The parametric EQ works wonders with poorly recorded disks and help me get rid some of room induced boominess around 60 Hz. Great unit!

Let me sayfirst that this unit is nothing short of spectacular. Superb sounstage,dead quiet. The music is alive in my room. The ability to adjust tone is amazing, however it can be a bit complicated and the owners manual is a little light in explanation, but they do point out that there is a steep learning curve. It is not all that difficult and worth every minutes work. I argue with my audiophile friends who scoff at this unit (not the sound, but the idea). I point of that changing ones cables for instance is done to alter the sound in some way. Why is it that most audiophiles will wiilingly and at great expense do this yet look down on a marvelous piece of equipment taht can do similar. No it cannot do everything, give it a listen, you'll be amazed.

(1) Getting rid of the analog volume control. This is much cleaner and clearer than the best Penny & Giles pots or Vishay switched attenuators.

(2) Precise enough control over EQ to fix what is wrong with the frequency balance of most recordings with no audible distortion or other downside that I can detect.

(3) Will handle sampling rates up to and including 24/96.

Lack of fine gain adjustments at attenuation levels below -20 dB, but this should only be a problem in systems with very high output DACs or high gain amplifiers.

Slight audible hiss when used with DAC directly feeding a power amplifier which, like mine, has very high gain (mine is +37dB, versus more usual figures in low to mid 20s).

Not compatible with most single-box CD players since the RDP-1 accepts only digital inputs and outputs only a digital signal.

Not compatible in its current form with the 24/192 sampling rates or Sony's DSD process, but I'm sure upgrades will become available to handle these digital formats, if and when manufacturers of such equipment allow access to these high quality digital bitstreams by providing digital outputs on transports and digital inputs on DACs.

It IS difficult to learn how to use the EQ functions properly. This is somewhat the fault of the instruction manual, but mostly the fault of the display. There IS a very steep learning curve, and this for someone with lots of previous experience using multiband EQ devices both with home audio and professional PA equipment. BUT: be patient, you'll "get it" sooner or later and the rewards are definitely worth the effort.

Let's ignore the EQ possibilities for a moment and concentrate first on the ability of this device to free you forever from analog volume controls. I have long suspected how much crud such controls introduced into the sound: now I know.

An example: the sound of my Audio by Van Alstine FET-Valve tuner is much cleaner and clearer now even though the tuner's output is first processed by the companion Z-System's analog to digital converter (about $750 for 2 inputs, unbalanced analog in, unbalanced analog out) and then fed to the RDP-1 for volume control. This means that the combination of the Z-Systems analog-to-digital conversion plus digital volume control is more transparent than the simple volume pot I was using before. My prior volume controller--the $8500 Cello Palette Preamp--was no slouch, having bettered the sound of such prior items as a Mod Squad Deluxe Line Drive, Electronic Visionary Systems Ultimate Attenuators (switched Vishay resistors which plug directly into amp inputs), and the best Penny & Giles pot as used in the Joseph Grado Signature Headphone Amp used as a single-input preamp.

Needless to say, the sound of my Cello-approved digital front end (Marantz Professional CDR-620 used as a transport feeding the Cello Reference DAC via Apogee Wyde-Eye AES/EBU connections) improved greatly as well in terms of clarity.

No, the Z-Systems is not as warm sounding as the Cello Palette Preamp. And the Cello Palette preamp arrangement of six knobs for handling the EQ duties is so intuitively easy to learn. And when positioned on the Cello acrylic cart right by the listening chair, the Palette Preamp is so attractively easy to use (there's no need for a remote control with the knobs right there at your fingertips with their set positions clearly indicated). But ergonomics and visual presentation aside, considering only the sonic results, having lived with both in an otherwise all-Cello system, I can't imagine too many folks would prefer the un-EQed sound of the Cello to the un-EQed sound of the Z-Systems. The relative slight leanness of the Z-Systems is more than compensated for by its clearer, cleaner window on the sound and the rock solid staging you get when the vagaries of analog-controlled channel balance are eliminated.

And the EQ functions? The Cello is much easier to learn and use. Even someone who has never turned a bass or treble control can master it in a few sessions of experimentation. And the Cello EQ does not do much harm to the sound: I could always hear a slight increase in the noise floor when the EQ was switched in when music was not playing and there was the slightest of roughening and defocusing of the sound when A/Bing between flat EQ off and flat EQ in. But when I wasn't testing, and was actually using the Cellow EQ functions, there were many times when the greater naturalness the Cello EQ provided would make me forget that the equalizer was engaged and I would be swept away by the beauty of the music.

BUT, there is absolutely no sonic piper to pay with the Z-Systems EQ, as far as I can hear. Plus, the parametric nature of the Z-Systems EQ allows much more precise control of the EQ than even the best-fit analog EQ Cello has adopted.

For example, I am a great fan of the Mercury Living Presence CDs. I own them all. Some sound magnificent without any EQ at all. By far the majority of them, however, need high frequency EQ to bring down a peak in the high frequency response of the old tube microphones used to record them. It is well known that the microphones used to record the master tapes in the 1950s had an inherent peak of about +9dB at about 11kHz. With some of the Mercury recordings, whether due to original mic placment or post-recording EQ, this peak is not much in evidence. On most others, it is there but somewhat subdued, or there is its full "glory." With the Z-Systems RDP-1, I just set the EQ for 11kHz, with the slope of the EQ curve at one (the broadest band) and turn that frequency down until it sounds right. And you won't believe how right these Mercury recordings can sound with just that simple single adjustment. I'm convinced that those who are not enthralled with the Mercs have systems which already exaggerate this high frequency region (many systems do, or have distortion products in that region) and/or have never tried such equalization.

With the Cello it is much harder to properly EQ the highs in such older recordings since the high frequency adjustments are very broad band and centered at 5kHz and 20kHz. To reduce the 11kHz peak enough to matter, you tend to throw away a bit too much of the extreme highs, and/or dull the presence region a bit if you attack the 11kHz peak by means of turning down both the 5kHz and 20kHz controls.

Obviously, with 4 parametric and 2 shelving controls, you can EQ things much more precisely if needed. While there is not enough flexibility to simultaneously eliminate the effect of low frequency room modes, correct deviations from inherently flat response of the speakers, and EQ particular recordings, I have been able to EQ the room response of the speakers flat (or to any target curve) within + / - 1dB at the listening position, with one parametric and one shelving control left over to fix the worst ills of any particular recording, which is usually sufficient.

Up to 100 different settings of all the EQ controls can be stored in non-volatile memory so that, once the proper EQ for a particular recording is determined, you can save those settings to memory, write the preset number on the recordings liner notes, and recall that setting instantly the next time you listen to it.

Also note that while the manual states that the dithered output mode should be used with most recordings, I am finding that with more recent CDs which are already encoded with Apogee's UV-22, Sony's Super Bitmapping, or HDCD, the undithered settings usually sound better. For recordings mader prior to 1993, you can safely assume that none of these encoding processes were used and that the dithered settings will work best, unless you are using something like my Cello Reference DAC which give you the option of engaging Apogee's UV-22 right in the digital-to-analog decoding process. Some older CDs sound best in my system with the Z-Systems dither, some with UV-22, and some with both engaged.

Despite any shortcomings noted above, this product, to me, represents both extremely high value and absolute performance for what it can do and how well it does it. Cello's much more expensive ($25,000) Audio Palette may be the sonic equal of the Z-Systems both in terms of straight-through sound quality and EQ transparency (I have had only limited listening exposure to that masterpiece of analog preamplification and EQ), but now we are talking 5 times the price of the Z-Systems with still no more EQ flexibility than my Palette Preamp.

Similar Products Used:

Cello Palette Preamp