APS audio transformers

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

Existing customers can contact us to discuss upgrade discounts.

Priced per pair (2) installed.

These are installed here in-house. We may consider selling just the circuit boards to qualified technicians. $278 / pair. Send us a message.

In Stock

Introducing Our Enhanced Vocm Modification:

Superior Performance with Lower Noise and Power Consumption

In the pursuit of audio fidelity and efficiency, we've developed a new Vocm (common-mode voltage) modification that represents a significant leap beyond the traditional Cap over R6 approach. This upgrade ensures much lower impedance across the entire frequency spectrum, delivering a cleaner, more accurate sound without the compromises imposed by the older method.

Unlike the previous design, which relied on a capacitor over resistor R6, our new circuit eliminates both R5 and R6 resistors entirely and does not introduce any extra Vocm capacitors. This streamlined design results from meticulous measurements revealing that the existing thin film resistors (all 0.01%) and the Vocm capacitors contribute around 5 dB of additional noise. By removing these components, we tighten the control over lower frequencies and prevent any color or distortion at the higher end of the audio spectrum.

Practically, this modification behaves almost like having a genuine bipolar power supply, which naturally avoids the noisy resistors and capacitors that often degrade sound quality. Additionally, the new Vocm buffer draws only 4 mA per channel — a substantial 24 mA reduction compared to the old configuration. Considering the typical 7 V drop, this translates to a power saving of approximately 0.168 W per channel, or nearly 0.6 W total inside the chassis when accounting for the linear drop from 12 V. This creates less heat.

Ultimately, this thoughtful and efficient redesign offers audiophiles the best of both worlds: enhanced sonic purity with lower electrical power usage and heat. It stands as a sophisticated solution that refines the tonal balance and dynamic response of audio equipment without the practical complexities of a bipolar supply. As audio technology continues to evolve, such targeted improvements hint at the future of clearer, more natural sound reproduction with smarter energy management.

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

This new Vocm modification approach supersedes the previous capacitor-based Vocm method, allowing the changes made by Ted Smith in the latest Sunlight firmware to fully utilize 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 recommends using the latest Sunlight firmware.  It's 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.

We are presently developing a Vocm buffer for the MK2 DACs. They achieved such a significant enhancement in sound quality for the MK1 that we chose to apply a similar change for the MK2. The MK2 employs only a single resistor divider set compared to the four used in the MK1. We initially believed the MK2 included a Vocm buffer circuit, however we were wrong. The schematics we have omitted this detail.

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.