Crown SX-724

The Crown 724 (most commonly documented and sold as Crown SX-724 or Crown SX724, with occasional references to early/variant forms like SS-724 in collector discussions) is a solid-state open-reel tape recorder from Crown International (Elkhart, Indiana, USA), produced from the late 1960s to early 1970s (peak availability around 1968–1971). It belongs to the Pro 700 series (often called the 700 series), where "SX" denotes the basic/simplified electronics package (fixed circuit boards, 2-speed EQ standard, fewer front-panel adjustments) compared to the deluxe CX variants (e.g., CX-724 with plug-in boards, full 3-speed EQ, front bias/EQ, echo). The "-724" indicates a 2-channel (stereo) configuration with ¼-track (quarter-track/four-track) stereo record/playback.

This was a professional/semi-pro deck aimed at audiophiles, broadcast, small studios, or mastering—renowned for Crown's overbuilt American engineering, exceptionally gentle tape handling (no tension arms; torque-controlled reels), rugged durability, and a warm, dynamic "tape magic" sound (slight high-end contour/bloom for musicality rather than ultra-flat). It is highly regarded in vintage communities (e.g., Tapeheads.net threads praise restored units as "excellent" and "like new" after servicing by specialists like Chuck Ziska). Surviving examples are collectible rarities, often refurbished and selling for $900–$2,000+ (e.g., recent listings note recapped/serviced units with new belts/pinch rollers).

Key Technical Specifications 

• Tape Speeds: 3.75 ips and 7.5 ips (standard; some early or modified units supported 15 ips via belt/pulley change—manual intervention required, e.g., turn off and adjust belt position by hand; not all stock units had full 3-speed EQ).

• Frequency Response (±2 dB typical): 30 Hz–20 kHz (or better) at 7.5 ips; 30 Hz–10 kHz at 3.75 ips (respectable for era; slight high-end contour for warmth/bloom on premium tape like Scotch 202/207).

• Signal-to-Noise Ratio: 55–60 dB (overall/record-play; strong for ¼-track stereo, aided by low-noise design).

• Wow & Flutter (RMS wideband): ~0.09–0.18% at 7.5 ips (excellent stability from massive flywheel, hysteresis capstan, and neoprene belt; meets specs quickly after start).

• Track Configuration: ¼-track stereo (four-track two-channel; bidirectional for extended play/overdubbing/reserve tracks; some variants like SX-724-P4C added 4-channel playback compatibility).

• Heads: 3-head design (erase, record, playback); precision micro-gap permalloy heads with hyperbolic contour, shock-mounted/removable for alignment; off-tape monitoring while recording.

• Reel Sizes: Up to 10.5" NAB professional (HAP adapters standard; supports 2400'+ reels; reel-size switch for proper tension on 10.5" or smaller).

• Motors: 3-motor transport (hysteresis synchronous capstan with large flywheel/belt; separate plug-in torque-controlled reel motors—no tension arms; solenoid-operated pinch roller; electromagnetic DC braking for smooth ~3-sec stops).

• Timing Accuracy / Speed Stability: ~99.8% (minimal drift; fast wind/rewind ~60 sec for 2400').

• Other Features:SX basic electronics: Fixed boards (simpler than CX plug-ins); basic inputs/outputs with level controls; NAB equalization (CCIR available in some); mixing inputs (multiple mic/line per channel, unbalanced standard; balanced optional via accessories); dual VU meters; headphone monitoring; source/tape switching; auto-stop; mechanical pushbutton controls (forward/rewind/stop/operate; no full logic memory).
  THD: <1% at 0 VU (1 kHz); high headroom/low distortion.
  Power: ~140W, 117 VAC 60 Hz (50 Hz available).
  

• Dimensions / Weight: ~19" W x 15–16" H x ~10" D (rack-mountable; detachable transport/electronics); ~43 lbs (sturdy aluminum chassis; some listings note 43–49 lbs depending on config).

• Original Price: ~$1,000–$1,500 range (premium pro positioning; e.g., comparable to SX-722 at ~$1,100–$1,595 in era catalogs).

Design and Build Overview

The SX-724 used the Pro 700 transport: mechanical pushbuttons (no "last button" memory issues; basic but reliable), dual-pulley/belt capstan for speed change (manual adjustment on some early units), torque motor control for precise tension (pantograph-like), and electromagnetic braking for gentle, padless stops. Electronics were solid-state (transistor-based) with simpler fixed boards vs. later modular CX plug-ins—reliable, low-heat, instant-on, but fewer front adjustments (e.g., no built-in echo or full bias/EQ like CX-724).

Built overbuilt for longevity (aluminum chassis, field-replaceable motors/heads/belts), it prioritized professional reliability—broadcast/TV standard, audiophile mastering—with warm, blooming sound (dynamics/headroom from slight contouring). It competed with contemporaries like Ampex AG-440 but was more accessible/serviceable.

Today, these are sought-after by vintage enthusiasts. Common restoration needs: electrolytic recapping (critical), bearings, relays, head relapping/alignment, belt/pinch roller renewal. Manuals cover Pro 700 series (SX/CX). Crown exited tape production ~1977 for amplifiers.