Harman Kardon 630

The Harman-Kardon 630 was produced for HK by Roland and was introduced in 1973. It produces 30 watts per channel and retailed for $359.95. The vintage Harman-Kardon look is unmistakable with the green dial face contrasting against the dark black top panel and the bright red power button. The fully illuminated dial pointer is also a recognizable feature of the x30 series of receivers. The Harmon Kardon knobs are somewhat unique as well. They are manufactured with gold anodized aluminum and have sharp ridges running the length of the knobs.

In 1973, HK offered both the 630 and the top-of-the-line 930 (45 wpc and a retail price of $479.95). In 1976 they added the 430 and 730 which were built by Shin Shirasuna. The 630 was essentially replaced in the line-up by the 730. They are basically the same unit, but the lay-out is different for the heat sinks and output transistors on the 630 as they are open at the rear – covered by a small mesh screen which aids in cooling the unit. The 630 is rated at 30 wpc while the 730 is rated at 35 wpc. both have “U” jumper connectors on the rear panel for pre-amp out/amp-in which gives them both the ability to be used as separates.

Instead of a “loudness” switch Harman Kardon utilizes a ‘contour’ switch.

You’ll notice the ‘Twin Powered’ tag line under the 630 on the faceplate. This refers to the fact that the 630 has separate power supplies for each channel. Why? Well, with solid-state designs, closely regulated supply voltages pave the way for a cleaner and more transparent sound reproduction. A crucial aspect of any amplifier is its power supply’s ability to respond swiftly to sudden tone bursts in the music and effortlessly drive heavy and sustained passages. Equally important is the power supply’s ability to instantaneously recover from these surges, swiftly restoring its voltage level in preparation for the next peak in loudness. The Harman-Kardon 630 takes these requirements to heart, employing two separate power supplies – one for each channel – to ensure flawless performance, regardless of the amplifier’s power output demands. By providing each channel with its own regulated voltages, the 630 eliminates cross-channel interference, allowing each channel to deliver its full RMS power output without compromise. Furthermore, the recovery time of the 630 is virtually instantaneous, ensuring uninterrupted and dynamic audio reproduction.

The Harman Kardon 630 claims a guaranteed power specification of 30 watts, RMS, per channel when both channels are driven simultaneously into 8-ohm loads. With distortion (THD) guaranteed to be less than 0.5% from 20Hz to 20kHz at full RMS output, the 630 adheres to stringent and conservative measurements, similar to those employed for HK’s legendary Citation amplifier. It’s worth noting that if the 630 were evaluated using the measuring methods employed by its competitors at the time, its power rating would likely be rated at 45 watts per channel.

A speaker’s ability to reproduce the sound of say a full symphony orchestra presents unique challenges. With the dynamic range and orchestral tone bursts found in symphonic compositions, a speaker must swiftly change direction to match the music’s shifts. However, the inertia of the speaker cone resists these rapid changes in direction. This is where the amplifier’s role becomes crucial – it acts as a brake for the speaker cone, enabling quick directional shifts. This characteristic of an amplifier is referred to as its damping factor. While many amplifiers exhibit relatively high speaker damping at 1,000 hertz, the Harman Kardon 630 delivers exceptionally high speaker damping even below 20 hertz. This results in tight, clean bass reproduction that enhances the overall audio experience. Furthermore, the 630’s excellent frequency response and virtually imperceptible distortion contribute to its ability to elevate the performance of any speaker system.

The 630 really looks good in the optional wood cabinet.

The Klipsch community really likes the HK x30 series receivers as they seem to pair very well with Klipsch Heritage series speakers.

• Dimensions: 17″ x 13 3/4″ x 4 3/4″
• Weight: 28 lbs
• Optional CW95 wood cabinet was available for $34.95

One issue with the HK 630 is that the MPX IC can go bad. The original OEM ECG722 IC is no longer obtainable but some have mentioned that it might be replaceable with the more obtainable LM1307 IC.

The 630 is probably the more rare of all the x30 receivers. The earlier 330 versions are pretty common but the 630 and 930 are not.

Specifications / Features:

• RMS power 30 watts per channel into 8 ohms(both channels driven)
• 0.5% harmonic distortion at any frequency 20-20k Hz.
• Overall frequency response 4-70k Hz +/-0.5dB (aux input)
• IHF power bandwidth 10-40k Hz
• Hum and noise -85dB(aux input)
• IM distortion 0.15%
• FM sensitivity 1.9uV(IHF)
• S/N ratio 68dB
• Stereo separation 32dB@ 1k Hz with 0.7% harmonic distortion
• IHF capture ratio 2.5dB
• Independent power supplies for each channel
• Defeatable interstation muting and loudness circuit.
• High frequency filter
• Illuminated function indicators
• Rear panel connectors for external Dolby FM processor
• Rear panel connectors for PRE-OUT and MAIN-IN
• Remote speaker outputs
• Front headphone jack
• Phones/main/remote/both speaker switches

The Harman Kardon 630, with its meticulously regulated power supply, instantaneous recovery, and impressive power output, produces clean and dynamic audio reproduction. Additionally, its high damping factor and broad frequency response further elevate the performance of any speaker system it is paired with. In short, it’s a great receiver. For those seeking a receiver that will exceed expectations and deliver an exceptional listening experience, the Harman Kardon 630 is a great choice.

For a very detailed restoration of a 630 check out the thread on Audiokarma HERE.