Harman Kardon A660 (c. 1981)

The A660 is a Japan-only integrated amplifier from the early 1980s. It was designed around Dr. Matti Otala's dynamic distortion countermeasure theory, the same line of thinking behind the brand's more famous high-current designs of the era. The amplifier uses a proprietary protection circuit that deliberately does not trip on very short-duration low-impedance loads, paired with large-capacity power transistors. Inside are a beefy EI transformer and four rows of black-anodized "sharfin" heatsinks. The chassis is partly copper-plated, which was unique to the A660. The later export version, the PM660, didn't get it.

The A660 came in silver only. Vertical LED dots serve as function indicators, instead of the more conventional illuminated dials or meters. The phono stage was properly isolated. Since this predates CD, the front end offers an MM/MC selector with a four-way capacitance trim acting on both phono inputs. Phono 1 is MM, and phono 2 is switchable between MM and MC. A "main direct" switch bypasses everything but the volume pot and source selector, at the cost of a 7 dB drop. The original Japanese list price was ¥105,000 in 1981. The export version, PM660, followed later. The A660 itself remained Japan-only.

Documentation on this model is thin. The most complete source, thevintageknob.org, describes it as "healthy, reliable and very powerful." The record does not include a clear production run, though a cryptic date string suggests activity between late 1981 and 1985. The Vietnamese sales listings that surface occasionally praise its deep, powerful bass and call it "dinosaur-grade" gear. No independent period reviews have surfaced in the accessible archive.

Known specifications (from the most complete source, though some figures may reflect the PM660's listing):

Power output: 2 × 80W into 8Ω (20 Hz–20 kHz, 0.02% THD); 2 × 90W at 1 kHz
Frequency response: 4 Hz–140 kHz (+0/–3 dB)
Phono inputs: MM (2.2 mV / 47 kΩ) and MC (70 µV / 100 Ω)
Dimensions: 44 × 12.2 × 36 cm; weight: 12.5 kg
Made in Japan; 100V version

A caution on the specs above. They come from a page that covers both the A660 and its export sibling, the PM660, and the two are not always cleanly separated in the record. The construction details - the copper chassis, the EI transformer, the heatsinks - are specifically attributed to the A660. The electrical figures are most likely shared, since the two versions are described as internally identical, but treat them as approximate until a genuine service manual surfaces.