First, let me clarify an important point: the 'Super Tjoeb' appellation designates a souped-up Njoe Tjoeb 4000 CD player package deal offered by Kevin Deal, Upscale Audio, the US direct distributor. It retail price of $849 includes the Njoe Tjoeb ($699), De Mat disc stabilizer mat ($25), tube dampers ($10), and the AC Direkt power cord ( $79) and Tjoebshoes isolation feet ($69) upgrades. Add the Tjoupsampler upsampling board - a stand alone option ($349) - and you have the ultimate tweak statement from Ah! and the subject of this review.
We start our journey with a retrospective look at the stock Ah! Njoe Tjoeb 4000 CD player. The full review (by yours truly) was published in our May 2001 issue. My conclusion back then was, and I quote: "the Njoe Tjoeb represents a fantastic bargain - a clear 100 on our value for the money scale. Outfitted with the Amperex Bugle Boys, the Njoe Tjoeb remains my reference in the under $1,500 price category. If you're a music lover on a budget, look no further, and treat yourself to this Dutch Bonbon. The old Tjoeb is dead. Long live the Njoe Tjoeb!" OK, the stock Njoe Tube is very good, but just how far up does the Super Tjoeb nudge the sonic bar? Since the cost differential is several hundred dollars, is the return on investment marginal or substantial? This is an important question for anyone on a budget. Well, the answer surprised me. I was expecting the usual subtle improvements, the sort of nuances only audiophiles seem to hear, but instead I heard a night-and-day advance in sound quality. The Super Tjoeb no longer sounded much like the Njoe Tjoeb I remembered; its performance now was definitely prime time.
To my mind, the major factor in this dramatic transformation is the Tjoupsampler 24-Bit/192kHz upsampling board, available separately for $349. There remains residual confusion in the marketplace over the technicalities of oversampling versus upsampling digital filters and the reasons for the sonic improvements that result from a correctly implemented upsampling scheme. Mathematically, the two processes are identical. Both interpolate additional data points along the digital bit stream time line. Some audiophiles naively believe that interpolated data represent newfound detail. That just isn't so, in the same way that a blow-up of a photograph doesn't contain more information about the original event. It is correct to say that the interpolated data add ultrasonic energy to the bit stream. Enter Doug Rife of MLSSA fame. If you haven't done so already, you should check out his white paper on this subject (click here). He defines upsampling as a "poor" oversampled digital reconstruction filter having a slow roll-off rate. As a consequence, some ultrasonic images of the base band spectrum are allowed to appear at the output of the digital filter and this ultrasonic energy is input to the DAC.
I'm going to turn the podium over to Doug Rife, since he has me convinced of the usefulness of ultrasonic dither in linearizing the performance of a DAC. The following are quotations (with permission) from several email exchanges with Doug Rife. His thesis is that "the vast majority of upsampling DACs have slow roll-off anti-imaging filters which permit varying amounts of ultrasonic energy to leak through in the digital domain thus adding desirable ultrasonic dither to linearize the output DAC device. But most manufacturers, at least before my paper appeared, believed that the improvement in sound quality was due to the better time domain behavior of their digital filters. As I said in my paper, when you design a digital filter to reduce time smearing you automatically allow some ultrasonic energy through and it is this and not the reduction in time smearing that is audible. However, many still probably believe that it is the reduced time smearing that is the salient characteristic of their filter designs and not the ultrasonic dither produced by them.
There has been resistance to my unique explanation for the sonic improvements of upsampling. Mostly, it stems from the prior statements made by many DAC manufacturers that the sonic improvements are due to reduced time smearing. Nobody likes to admit they were wrong and some of these digital filter designs are patented, which means that their erroneous explanation of upsampling is permanently filed with the US patent office. The other factor is that upsampling is a great equalizer. You can take a mediocre DAC and make it sound like a super linear but much more expensive DAC. Of course, those making the pricier DACs would rather have people think they must purchase theirs to get the sonic improvements they seek and see my upsampling theory as something that could hurt sales, if widely accepted."
In any case, I found that when two MSB upsamplers are cascaded with both using a slow roll off digital filter, there is a double imaging effect (image of an image) which allows even more ultrasonic energy through, measuring about -55dB. The image energy around 60 kHz comes from signals in the very high treble on the recording. Because many recordings have dither in the high treble this also tends to get imaged up to 60 kHz. This energy corresponds to a significant audible improvement in the sound quality even over the normally very good sound quality of the MSB Platinum DAC. Setting either the Platinum DAC or the upsampler board to the fast roll off filter reduces the sound quality and this corresponds to the 60kHz images falling below the noise floor of my HP analyzer. What's good about this experiment is that it can be reproduced by anyone with the Platinum DAC plus a DVD or CD player with an MSB upsampler installed.
My paper is on my web site for anyone to read. I am not in the DAC business myself so my goal was to use the web to get the word out and stimulate further thought, possibly other papers and perhaps better DAC designs. …Using no oversampling or anti-imaging filter of any kind and doing all of the filtering in the analog domain is feasible. However, it would not provide any ultrasonic dither energy to the DAC where it is needed. You need to increase the sampling rate from 44.1kHz to some multiple in order to add any ultrasonic energy that would linearize the DAC."
Whichever explanation you believe, the sonic benefit of the upsampler is undeniable.
My sample was shipped with two pairs of 6922s , a Russian equivalent type (6H23Pi w/rocket logo) and Philips JAN New Old Stock (NOS). Having assumed that the Russian type was the stock tube, I initially installed and began my listening tests with these tubes. It was immediately obvious, right out of the box, that the player had a lot of heart, but a bright and coarse treble range bothered me. Even after a very extended break-in period the glare did not diminish significantly. Out came the Russian tubes and in went the Phillips NOS. The treble range smoothed out as if by magic. Treble transients were also much easier to resolve from initial attack to complete decay. I also experimented with the Richardson re-branded Bugle Boys. This particular pair was originally manufactured in the USA, and this time out it sounded slightly cleaner but remarkably similar to the Philips NOS. Kevin Deal, the US Distributor, informed me that the Philips 6922s are in fact the stock tubes, so that's good news indeed. He also mentioned that one can use the 7DJ8, and even variable mu tubes like the 6ES8 for cheap thrills, since the tubes do not constitute a gain stage, but rather the player's output buffer stage.
The star attraction, without a doubt, was the midrange. The effect of the upsampling upgrade was to shine a bright light onto the soundstage, reducing veiling and increasing the intimacy of the musical performance. You might wonder why I'm obsessed with the midrange as the cornerstone of musicality. It's really a function of the physics of musical instruments. The average spectrum of the orchestra peaks around 400Hz to 500Hz, and then decreases with increasing frequency. The mean spectral level at 2.5kHz to 3kHz is already about 20dB below the peak. And, of course, the lower midrange is rich in fundamentals and their first overtones. In particular, the range of 262Hz to 330Hz (C4 to E4) is common to all voices. In my book, if a component can't get it right in the midrange, frequency extension, imaging, etc., matter very little. The midrange, to my mind, is literally the heart of the matter.
The Super Tjoeb represents a quantum leap in performance relative to the stock Njoe Tjoeb player and a Godsend for music lovers on a budget. It makes clear the sonic advantage of a properly implemented upsampling digital filter in linearizing the performance of even a good DAC. A super linear DAC translates into less digital artifacts and a smoother, more analog-like sound quality. In a world of high-end Goliaths, this David slays every player I've heard to date in the under $3K price range. At its sub $1K asking price, its price/performance ratio is simply out of this world. The Super Tjoeb gets my vote for digital product of the year.
Dynamic range: 95dB
Channel separation: 85dB
Total harmonic distortion: 0.000063%
Transport mechanism: VAM1201+DSD
D/A conversion: CC DAC
Maximum dimensions in mm: 440 x 87 x 280 (WxHxD in mm)
Weight: 2.9 kgs.
Price: $849 includes the Njoe Tjoeb ($699), De Mat disc stabilizer mat ($25), tube dampers ($10), and the AC Direkt power cord ( $79) and Tjoebshoes isolation feet ($69) upgrades. Add the Tjoupsampler upsampling board - a stand alone option ($349)
Warranty: 1 year