IOM Metric Stereo

Description

IOM Metric Stereo

The IOM Metric Stereo grew out of a simple question: can we combine the exceptional precision and resolution of the NCx platform with a greater sense of musical involvement?

That question did not come from us alone. Several customers already using NCx500-based amplifiers gave us similar feedback. Technically and in terms of resolution, they were highly satisfied, yet some felt that something harder to capture in specifications was missing: involvement, soul, and the sense of being drawn into the music.

That became the starting point for the development of the IOM Analog Stage.

From Listening to Development

Our aim was not simply to impose a sonic signature on the NCx500. The objective was to preserve its transparency, resolution, and low distortion, while exploring what a different analogue input stage could contribute to the musical presentation.

We therefore built, auditioned, and compared many different analogue circuits, components, and topologies. We explored conventional active stages, several discrete solutions, and more unconventional concepts, including the Korg Nutube.

From those comparisons, the discrete Class-A JFET stage consistently emerged as our preferred solution. The difference is subtle, yet to us clear, significant, and repeatable. In particular, the combination of detail, composure, fluidity, and musicality ultimately tipped the balance.

The JFET stage therefore became not an experiment or an option, but the foundation of the IOM Analog Stage and a defining element of the Metric Series.

IOM Analog Stage

Per channel, the Analog Stage consists of an OPA1656 followed by a discrete Class-A JFET source follower with a JFET current sink. The OPA1656 provides the gain and forms the highly accurate, linear basis of the input stage. It is followed by the unity-gain JFET stage.

In this way, we combine the precision and low distortion of a modern op-amp with the classic Class-A operating point and the characteristic behaviour of JFETs.

JFETs share several electrical characteristics with vacuum tubes and are particularly well suited to traditional, proven Class-A topologies. The JFET topology used here is inspired by the principle behind the Nelson Pass B1. We use matched JFETs, allowing the operating point of the Class-A stage to be set accurately and reproducibly.

We also paid considerable attention to the implementation around the Analog Stage. It is powered through dedicated voltage regulation, decoupling its supply from the rest of the amplifier electronics. At critical positions, we use precision resistors with a very low temperature coefficient, keeping their resistance values highly stable as temperature changes.

Metric Stereo

The IOM Metric Stereo is the first production model to feature this Analog Stage. The power amplifier platform consists of two separate Hypex NCx500 OEM modules powered by a Hypex SMPS1200.

• 2× Hypex NCx500 OEM
• Hypex SMPS1200
• IOM Analog Stage per channel
• OPA1656 for gain
• Matched Class-A JFET stage
• Dedicated voltage regulation for the Analog Stage
• Temperature-stable precision resistors at critical positions
• RCA and XLR inputs
• 12 V trigger
• Weight: 4.85 kg
• All-aluminium Metric enclosure
• 5 and 6 mm aluminium panels that also serve as heatsinks

For us, the Metric is the result of a development process in which measurement and listening are complementary rather than opposing disciplines. The precision of the NCx platform forms the foundation; the IOM Analog Stage is what we consciously chose to add after extensive development, comparison, and listening.

Measured for accuracy. Refined by listening.