APS audio transformers

This is now included in all our Limited Edition Signature Series + DACs

Existing customers can contact us to discuss upgrade discounts.

Our new type Vocm modification. Much better and much lower impedance across the full frequency spectrum than the old Cap over R6 method. Notice all R5 and R6 resistors are removed. No added Vocm capacitor.

Our measurements indicate that all them 0.01% thin film resistors and the Vocm caps are noisy by about 5 dB more than without them.

This not only tightens up the lower frequencies, it also doesn't add color to the top end. It uses much less power than the stock 123-ohm resistor divider.

This Vocm buffer modification is the next best thing to an actual bipolar power supply, which would have no need for all the noisy resistors and capacitors that color the sound.

This new circuit draws only 4mA. So 24mA less per channel than the old method which at 7V is 0.168W per channel... but considering it is dropped linearly from 12V, that's 0.288W per or about 0.6W total within the chassis.

We totaly redesigned the whole Vocm modification process with this newly designed and built Vocm buffer circuit. 

With this new Vocm modification method, which replaces the older capacitor-based Vocm method, changes that Ted Smith made in the latest Sunlight firmware will take full advantage of these new Vocm buffers. The innovation in this approach has led to a breakthrough in audio performance for this DAC. Users have reported astonishing improvements, with the audio quality reaching levels that surpass previous benchmarks.

With this new modification, APS recommended upgrading to the latest Sunlight firmware for a significant improvement in sound quality over the previously recommended Snowmass 3.05.

This continual research and development by APS demonstrate their commitment to refining and enhancing the DAC experience. While some may feel disappointed at not receiving this new upgrade earlier, the ongoing advancements highlight the brand's dedication to excellence and innovation in digital audio technology.

Why the old Vocm mod is not the best for this application:

The impedance of a 200μF ~(47uf x 4 + 2uf) capacitor forms a V-shaped curve across the frequency spectrum. It is highly resistive to low frequencies, drops to near zero at its self-resonant frequency (SRF), and becomes inductive at high frequencies.

Low-Frequency Region: Capacitive Dominance.
In this range, impedance is inversely proportional to frequency, governed purely by capacitive reactance (\(X_{C}\)):
(X_C = \frac{1}{2 \pi f C}\)
Where:f = Frequency in Hertz (Hz)
C = 200μF (0.0002 Farads)

At higher frequencies in this region, impedance falls rapidly:
At 50 Hz: Z ≈ 15.9 Ω
At 60 Hz: Z ≈ 13.3 Ω
At 1,000 Hz (1 kHz): Z ≈ 0.796 Ω

Self-Resonant Frequency (SRF)

Real-world capacitors have parasitic traits—specifically Equivalent Series Resistance (ESR) and Equivalent Series Inductance (ESL) from internal plates and leads.At the SRF, the capacitive reactance and inductive reactance perfectly cancel each other out. At this exact point, impedance hits its lowest point and is determined almost entirely by its ESR (usually a fraction of an ohm).

As one can see, using capacitors to lower impedance is not ideal for lower frequencies and is far from being linear.

Our new Vocm buffer:
Impedance Across the Frequency Spectrum:
Low Frequencies (DC up to ~100 Hz) Where we need this low impedance stabilization.
Input Impedance (\(Z_{IN}\)): 
Extremely high (typically 10⁶ Ω for bipolars, 10¹² Ω to 10¹³ Ω for JFET/CMOS). It appears as near-infinite to the source.
Output Impedance (\(Z_{OUT}\)): Excellent 
Very low (fractions of an ohm to <10 Ω) because of maximum negative feedback.

Upon conducting our A/B comparison between the old Vocm mod and the new buffer mod, we immediately noticed the incredibly tight bass and absence of capacitor coloration. The soundstage projected by the new buffer Vocm mod is undeniably superior. The speakers disappear even more than before, and the sound is significantly more realistic. In comparison, switching back to the old method is simply disappointing. The old Vocm method sounds dull and lacks dynamics. For the past several years, we have preferred the Snowmass 3.05 firmware with all our DACs. Now, with the new Vocm buffer, the Sunlight firmware sounds far superior.

In conclusion, for audiophiles and enthusiasts, it offers an opportunity to experience unparalleled sound quality that redefines expectations. This DAC continues to be one of the finest sounding devices available, proving that even established standards can be elevated through thoughtful engineering and passionate research.