Denon DH-710S

The Denon DH-710S is a late 1970s flagship high-performance stereo reel-to-reel tape recorder, produced approximately 1974–1978 (manufactured in Japan by Nippon Columbia/Denon). It was a top-tier model in Denon's DH series, designed for audiophiles and semi-professional use, with a reputation for exceptional build quality, tape handling, and sound. The DH-710S is often grouped with the DH-710F (the "pro" or studio-oriented variant, sometimes with XLR I/O and slight cosmetic differences), but the S version is typically the integrated single-box or home-oriented configuration. It was praised by figures like Tim de Paravicini as one of his favorite machines for its reliability and audio performance.

This was a 2-track (half-track) stereo recorder with quarter-track playback capability (4-head configuration in many units: half-track record/playback + erase + quarter-track playback head), three-motor direct-drive transport, and a two-capstan system for superior tape stability. The design emphasized professional-grade precision, low wow/flutter, wide bandwidth, and gentle tape handling.

Key Technical Specifications

• Recording/Playback System — 2-track (half-track) stereo recording and playback; 4-track (quarter-track) playback compatibility; 2-channel stereo/mono; sound-on-sound/multiplay overdub facilities; no auto-reverse.

• Tape Speeds — Two professional speeds:7½ ips (19 cm/s)
  15 ips (38 cm/s)
  

• Reel Size — Up to 10.5 inches (26.5 cm or No. 10/Type 26 NAB hubs; professional large reels for extended playtime).

• Frequency Response (approximate, within ±2 dB tolerances; varies by tape/condition):At 15 ips (38 cm/s): 30 Hz – 22,000 Hz (some sources claim up to 30 kHz)
  At 7½ ips (19 cm/s): 30 Hz – 18,000 Hz Excellent extension for the era—hi-fi capable with strong highs.
  

• Wow & Flutter —At 15 ips: ±0.02% WRMS
  At 7½ ips: ±0.025% WRMS Outstanding stability from three-motor direct-drive, two-capstan transport, and electronic tape tension servo.
  

• Signal-to-Noise Ratio — 68 dB at 15 ips (DIN weighted; very high for transistor design with low-noise tape; some sources cite >66 dB max).

• Total Harmonic Distortion — <0.5% at 1 kHz (low saturation in recording amp; excellent with quality tape like Scotch 206).

• Heads — 4 heads (in most configs): half-track record, half-track playback, erase + quarter-track playback (Sendust alloy or hard permalloy for record/playback; ferrite erase; high-quality for longevity and HF performance).

• Drive System — Three motors (1 × 6-pole outer-rotor AC servo capstan motor + 2 × 6-pole AC servo reel motors); two-capstan direct-drive system (main capstan + sub-capstan to block vibrations and ensure stable head contact); electronic AC servo tension control (eliminates start-up load fluctuations; one-way air damper prevents excessive tension); fast wind/rewind (~2 minutes for No. 10 reel with 740 m tape); precise dynamic braking.

• Electronics — Fully transistorized; printed circuit board amplifier; NAB equalization; maximum recording amp output >+30 dB @ 1 kHz (low saturation distortion).

• Inputs —Microphone (low-level).
  Line/radio/phono (standard line level).
  DIN-style connectors (some export versions with RCA/XLR).
  

• Outputs —Line out (~1 V).
  Headphones (monitor).
  External amp/speakers.
  DIN-style.
  

• Features —Twin illuminated VU meters (needle type; active for record/playback).
  Electronic logic transport (smooth push-button).
  Off-tape monitoring (source/tape switch).
  Input mixing.
  Pause function.
  Optional remote control terminal (DIN).
  Vertical/horizontal operation; massive chassis.
  

• Power — AC mains (100 V Japan standard; multi-voltage variants); consumption 120–130 W.

• Build & Dimensions — Massive tabletop case (often wood/teak or metal finish); approx. 450 × 550 × 255 mm (17.7 × 21.7 × 10 inches); weight 28 kg (very heavy and robust).

• Manufacturing — Japan (Denon/Nippon Columbia).

Performance & Legacy Context

The DH-710S/F was a "marvellous" machine in tape handling—thanks to its three-motor direct-drive, two-capstan system, and electronic AC servo tension (smooth start-up, minimal fluctuations, gentle on tapes). It delivered ultra-low wow/flutter (<0.02% WRMS at 15 ips), high S/N (>66–68 dB max), wide frequency response (30 Hz–22 kHz+ at 15 ips), and low distortion—often described as "studio-grade" for home use. The Sendust heads and generous recording amp headroom ensured clean, professional results, with the ability to play both ½-track and ¼-track tapes (like Technics RS-1500 or Otari MX-5050). Tim de Paravicini favored it as his road/travel machine for its reliability and sound.

Common issues today: Belt/idler degradation (goo/melting—kits needed), dried electrolytic capacitors, transistor aging, dirty heads (3-head alignment critical), worn idler tires/clutches, and occasional servo/tension faults. Restorations are rewarding—many units achieve superb performance post-service. Service/user manuals available (HiFi Engine, Audio Database—schematics, alignment).

Compared to siblings:

• DH-610S — Similar flagship (often considered close or variant; some prefer DH-710 for refinements).

• DH-510 — Related but sometimes seen as slightly less advanced.

• DH-710S/F — Balanced high-end with pro specs (15 ips, NAB 10.5" focus, two-capstan).