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The R-2R ladder DAC design was the starting point for the Totaldac project. Vincent Brient spent 2 years and 5 PCB revisions to improve upon it and finally opted for  0.01% Vishay series foil resistors and further improvements from the field-programmable gate array. The signal path is actually very short - through the 0.01% resistors into an R-C filter and thence into the output stage.

Again the resistor quality was crucial for the project to come off. Many manufacturers and users of precision electronic equipment often suffer needlessly from unexplained instabilities and drifts due to noise effects. They resign themselves to troubleshooting and constant adjustments. These cannot be avoided and instability is often traced to a few supposedly 'fixed' resistors which really aren’t. If these resistors did retain their original values, there would be no need for costly controls and compensating circuitry which generally reduce overall transparency. In high-end audio equipment careful selection of resistors is one of the best ways to avoid or minimize signal-path noise and distortion. Noise can be considered an unwanted wide-spectrum signal that may superimpose itself on music signal and DC. Like other passive parts resistors to various degrees are sources of noise. This depends upon resistance value, temperature, applied voltage and resistor type. Many experiments have shown why some resistors are ‘noisier’ than others. The ultimate test audio experts and audiophiles agree on is comparing the fidelity level that results when different resistor technologies are tried in actual audio systems.

In this resistor hall of fame Vishay foil resistors occupy the very top. Only very expensive machines use them and to Vincent’s knowledge no other DAC in the consumer high-end audio market uses a 24-bit foil ladder configuration, never mind one with VAR types. The Totaldac currently uses 96 x VSRJ 0.01% foil resistors per channel. They deliver the best sound which to date couldn’t be duplicated by any other resistor of various types and values. To Vincent the Vishay parts represent the ultimate choice in the most demanding and critical of high-end circuits. Presently no other resistor exists which could match all of the requirements Vincent Brient had in place to achieve his goal.

While the Totaldac is a 24-bit network, 0.01% resistors cannot easily exceed 14-bit resolution (1/10.000 versus 1/65.536 for a 16-bit signal). The 24-bit foil ladder is not used at full capacity but guarantees 14-bit resolution for both most significant and less significant bits. The R-2R network is said to deliver superior THD+N and microdynamic performance than modern chip-based designs. Built-in dynamic limitation of large-scale signals is obvious but in reality today’s status of recordings and microphones here is the greater limiting factor. The never-ending race towards higher-resolution converters seems wasted in view of the top accuracy of the rest of the playback chain.

A true 24-bit resolution network used at full scale under most conditions would produce distortion levels well below the thermal self-noise of amplification circuits, never mind room noise. 24 bits then are primarily useful for maintaining good low-level signal resolution. In fact the noise floor shown lower could not be achieved by a simple 14-bit resolution chip.

Each channel uses 96 x 0.01% VFR foil resistors

Once the prototype met his expectations, Vincent Brient contacted VFR Europe to choose the most appropriate foil for his DAC. The following graph shows an extremely low-amplitude signal such as long concert hall reverberations. The noise floor is as low as -131dB. 0dB is the max level. These measurements were generated with a Rohde & Schwarz UPL audio analyzer. With such a low-level signal no distortion or harmonic spuriae are visible.

Spectrum of a 1kHz sine wave at -80dBFs with the power supply and buffer board

Today everyone agrees on the impact of jitter on sound quality. This is mainly related to the digital source and system clock. Because mechanical transports are being progressively replaced by computers, Vincent wanted his DAC to reduce the jitter from various digital sources which the audiophile community might use. An external clock is a common solution but requires a digital source equipped with the necessary clock input. This type of solution is still rare in consumer audio. Since he was after a global rather than ultra-specialized solution, Vincent had to embrace an FPGA whose FIFO memory buffer stores about 0.1 seconds of audio data at the digital source input and outputs a local oscillator stream.

At first Vincent used a low-jitter crystal oscillator. Of course it exhibited slight drift and as a result some noise appeared in the sound after a few hours. Practically the problem was elsewhere however as the FIFO pointer reinitialised between tracks. Vincent identified a kind of metallic sound when using crystal oscillators. That's perhaps not surprising since crystals are microphonic and in fact even used to measure pressure. The problem disappeared when Vincent used an RC oscillator instead. Even so its oscillator frequency wasn't completely stable either after a few hours. Next he added a voltage controller to where the FPGA was able to control the RC oscillator’s frequency. An S/PDIF receiver such as a CS8412 or CS8416 already uses a voltage-controlled oscillator but its command changes very quickly to track the input rhythm and this partially inherits source jitter. These devices must very rapidly track the input signal with just an 80 nanosecond thru-put delay whereas the Totaldac has a 0.1 second thru-put which appears long but is unproblematic for home-audio playback.

Subsequent developments: When the Totaldac arrived at my home, Vincent Brient had already tested it in various high-end installations and mostly enjoyed very encouraging results in comparisons to far costlier gear. I had been listening to the Totaldac for almost two weeks when I called my friend Patrick Cesaratto, founder of Legato Cables Company. I knew Patrick was looking to acquire a high-performance 'organic' DAC and so for a few days he auditioned my affordable Yamamoto YDA-01 but finally wanted more dynamics and better soundstage coherence. He loved the naturalness of my Japanese contender with its intrinsic musicality and recognized its value but simply wanted even higher performance, albeit at a still reasonable sticker.

Here the Totaldac became an interesting proposition. Since the two of us generally see ear to ear, Patrick came over to listen to this newcomer. After just two hours his enthusiasm for the Totaldac was so obvious that he decided to call Vincent and order his own unit. Two weeks after I received a phone call from Patrick. In his opinion there was a small lack in the low midrange and he wished for a bit more overall vividness. That more or less had been my personal conclusion about the stock Totaldac too. Patrick then explained that he had already improved his machine with noticeable results. His overall conclusion was that the conversion board was terrific but room for improvement was left with the power supply and output stage.

Here I must add that Patrick teaches Physics and electronics at the Paris university. Contrary to most audiophiles working in sound engineering Patrick has an exceptional ability to conceptualize sonic results from circuit/parts changes and understands precisely what happens at the technical level. Professor Patrick thus has solid methodology and is perfectly aware of the fragile equilibrium of even the smallest modification in audio designs. Add very good listening discernment and you will have a good notion of Patrick’s abilities. In my opinion he cannot be compared with the general DIYer. He combines scientifically trained rigor with the open mind of the passionate audiophile.

Vincent and Patrick had several exchanges to integrate these mods with ‘my’ original version. Vincent personally tested every one of Patrick’s modifications and agreed on their sonic benefits. Final validation of these changes to the stock platform were done by me and Patrick over two critical listening sessions - the first one at Patrick’s with the bread-boarded add-ons designed by himself, and the second one with Vincent’s upgraded version in my personal system. In both cases the new version had more life, depth, air, clarity and detail in the upper and lower midrange. The main modifications designed by Patrick and already integrated with the commercial version of the Totaldac are as follows:

• The 5V regulator for the R2R DAC is now a shunt-regulated power supply.
• A 6dB-gain buffer in the output stage raised the output level to 3.2Vrms over the original 1.6Vrms which was a bit low for most preamps. The buffer uses Vishay foil 0.01% resistors exclusively and there’s not one capacitor in the signal path to extend frequency response to DC.
• Wire gauge and PCB track width were increased for the R2R ladder power supply. This improvement was clearly visible in the earlier -80dB low-level signal spectrum with zero distortion and zero discrete spurious noise.
• The virtual ground impedance was lowered which benefited dynamics.

The core specs of this version are for a non-oversampling 24-bit R2R 2-channel DAC with a solitary S/PDIF input and sample rate support to 96kHz where frequency response is 0Hz – 45kHz. THD at 1kHz is 0.002%, the max output level is 3.3Vrms. The noise floor is –131dB and output impedance is 75Ω unbalanced. Channel separation is 90dB, max offset 0.005dB and power consumption 7 watts.

Sound: It’s been quite difficult to comprehensively assess this machine’s performance as it had to be compared to expensive gear beyond my personal inventory. My Yamamoto SoundCraft was outclassed on all counts, quite an achievement if you know the Japanese. But in such a comparison any descriptions of the French box would have defaulted to useless superlatives and become little more than just another converter review.

The first overall impression I collected over this process of attending to the Totaldac’s spontaneous evolution was a—for a digital source—very rare and uncommon sensation of naturalness. The Totaldac was highly resolving but with incredible sweetness and analogue feel. In that regard my only references were far more expensive machines like the MSB Tech DAC IV, the Vitus Audio MP-D201 DAC and the Zanden Model 5000.

Most D/A converters to my ears are quite comparable to cartridges where each contributes its own style and coloration most of the time with a slight electronic signature. But with top devices like the Zanden or Totaldac one leaves the additive domain. They only provide the sensation of enhanced transparency, of freedom from artifacts and compensatory voicing tricks even if complete neutrality remains as ever an abstract value only.

I will describe what the Totaldac brought to my own system but also tried to compare it to another ‘still affordable’ high-end reference in the MSB DAC IV Platinum (including the MSB Powerbase and MSB CD Drive). It would have been interesting to compare the Totaldac to recent ESS Sabre 32-bit competitors even though MSB Tech recently declared quite resolutely that there is no way to compare their products with this new delta-sigma generation. It could be useful to schedule a future assessment of the Totaldac by our publisher considering his exposure level to this product category. Having already agreed to it we hope to arrange for a published 2nd opinion in due time