Harman Kardon 630

This is the Harman Kardon 630 Twin Power Receiver from 1973–75, probably the most rare of the HK X30 Twin Powered series receivers.
The look of the HK X30 series is unmistakable — green dial face, illuminated dial pointer, dark black panel, and the iconic red power button that sets it apart from other receivers of its era.

Produced for Harman Kardon by Roland, the 630 was marketed with a power specification of 30 watts RMS per channel. However, this rating followed Harman Kardon’s more conservative testing standards. If evaluated using the less stringent methods used by many competitors at the time, its output would likely be closer to 45 watts per channel. This understated rating reflects Harman Kardon’s commitment to engineering integrity over marketing hype.

One distinguishing feature of the HK 630 is its “contour” switch — a term Harman Kardon used instead of the more commonly known “loudness” switch. Functionally, it enhances low- and high-frequency response at lower volume levels, compensating for the ear’s reduced sensitivity to extreme frequencies at lower listening volumes.

In 1973, the X30 series lineup included the 630 and the top-of-the-line 930, rated at 30 and 45 watts per channel, respectively. By 1976, the lineup expanded with the introduction of the 430 and 730 models. The 630 was effectively succeeded by the 730, which retained a similar internal architecture but featured a different layout for heat sinks and output transistors. The 730 offered a modest increase in output at 35 watts per channel and remains a popular choice among vintage audio enthusiasts.

The “Twin Powered” designation on the faceplate of the 630 refers to its dual-mono power supply design — separate power supplies for each channel. This architecture is key to the receiver’s remarkable sonic performance. By isolating the left and right channels electrically, the 630 eliminates the risk of cross-talk and ensures each channel operates with full independence. The result is a cleaner, more transparent soundstage with improved dynamics and stereo separation.

A crucial aspect of any amplifier is its ability to respond swiftly to sudden tone bursts and to sustain power during demanding musical passages. Equally important is the speed at which it can recover from these surges. The Harman Kardon 630 excels in this regard. Its dual power supply architecture allows each channel to respond instantaneously to power demands, delivering consistent, uninterrupted performance even under the most challenging musical conditions.

Beyond the specs, the Harman Kardon 630 is simply a great and beautiful sounding receiver. Its warm, detailed sound, paired with its elegant design, makes it a standout piece for both vintage hi-fi collectors and discerning listeners alike. Built during an era when quality and craftsmanship were paramount, the 630 remains a testament to Harman Kardon’s engineering excellence and enduring legacy in high-fidelity audio.