Crown 700 Series

The Crown SX 700 series (often referred to as the Crown Pro 700 or 700 Series with SX electronics) is a line of vintage open-reel tape recorders produced by Crown International (Elkhart, Indiana, USA) from approximately 1967–1970. These were solid-state (all-silicon transistor) professional/prosumer decks emphasizing modular design, excellent tape handling, and high-fidelity performance for home studios, semi-pro, or mastering applications. Crown positioned them as reliable, serviceable machines rivaling contemporaries like Ampex or Berlant Concertone, with patented electromagnetic (non-mechanical) braking, straight-line threading, and field-replaceable parts.

The "SX" designation refers to the electronics package: simplified circuitry on four printed circuit cards, two-speed equalization, rear-panel bias adjustment, and mixing capabilities (bridging or balanced options via accessories). Models used a 700 series transport (simplified from the higher-end 800 series, using relays for switching rather than logic boards). Common variants include stereo/mono configs like SX-722 (2-channel ¼-track), SX-724 (2-channel ¼-track with variations), SX-744 (4-channel ¼-track), and mono models (SX-711 full-track, SX-712 ¼-track). Some had "-P4C" suffixes for play-4-channel compatibility.

These decks supported professional 10.5" NAB reels (via included HAP adapters) and were praised for gentle, accurate tape motion, low wow/flutter, and "wild" or blooming sound character (due to pot tapers and head design). They are rare collectibles today, often restored for their overbuilt quality and audiophile appeal, though they require recapping and bearing service due to age.

Key Technical Specifications 

• Tape Speeds: Standard 3.75 ips and 7.5 ips; optional 15 ips and 7.5 ips ($25 upgrade); rare low-speed additions (1⅞ or 15/16 ips +$50 with speed reducer, no EQ).

• Frequency Response (typical, ±2 dB):At 15 ips: 30–25 kHz (e.g., SX-722 half-track); overall 40–30 kHz; record/play 20–20/25 kHz.
  At 7.5 ips: 20–20/25 kHz record/play (varies by model; some show slight 3–4 dB high-end boost or 50 Hz bump).
  Erase/crosstalk: 20–10/15 kHz.
  

• Signal-to-Noise Ratio: 55–60 dB (overall/record-play; e.g., 60 dB overall, 55 dB record/play on NAB/Scotch 203/207 tape; better with premium tape).

• Wow & Flutter (RMS, wideband): 0.05% at 15 ips; 0.09% at 7.5 ips; 0.18% at 3.75 ips (excellent for the era).

• Track Configuration: Varied by model—¼-track stereo (most common, e.g., SX-722/724/744), half-track stereo (some variants), full-track mono (SX-711), or 4-channel ¼-track (SX-744).

• Heads: 3-head design (erase, record, playback); precision micro-gap permalloy heads; removable assemblies with hardened guides, hyperbolic contour, and shock-mounted for alignment stability.

• Reel Sizes: Up to 10.5" NAB professional (standard HAP adapters included); supports 2400' reels.

• Motors: 3-motor transport (hysteresis synchronous capstan drive with massive flywheel and neoprene belt; separate plug-in reel motors); electromagnetic DC braking (no pads/bands); solenoid pinch roller.

• Timing Accuracy / Speed Stability: 99.8% (or ~1.8 sec drift in 15 min); fast rewind ~60 sec for 2400'.

• Other Features:Modular electronics (SX: simplified PC cards; mixing inputs: 2 per channel mic/line, sensitivity -66 dBm mic/-25 dBm line).
  Outputs: Balanced/unbalanced line (600 ohm, up to 14V max), dual headphone jacks.
  Bias metering/adjust (rear panel on SX), NAB equalization (CCIR optional), automatic stop, remote-controllable play/stop.
  Inputs: 4 mic/line mixing (unbalanced standard; balanced XLR via accessories like SMIT/SBIT transformers).
  THD: <1% at 0 VU (1 kHz); low distortion/high headroom.
  Power: ~140W, 117 VAC 60 Hz (50 Hz available).
  

• Dimensions / Weight: ~19" wide x 15–16.5" high x 8–10" deep (rack-mountable); 35–52 lbs depending on model/config (e.g., transport ~35 lbs, full unit ~42–49 lbs with case).

• Original Price: $1,000–$1,600+ range (e.g., similar 722 SX ~$1,595 in 1966 listings).

Design and Build Overview

The 700 series transport was a cost-optimized version of the pro 800 series: mechanical pushbutton controls (four modes), reel size selector, master power, 2-position speed shift, and no "last button pressed" memory. It used belt-driven capstan, electromagnetic brakes for fast/smooth stops (~3 sec from play at 7.5 ips), and straight-line threading for easy editing. SX electronics prioritized reliability and simplicity over deluxe CX (which added echo, front bias, EQ controls). The build was rugged—aluminum chassis, field-serviceable motors/heads—ideal for semi-pro use with low maintenance.

Today, these are highly regarded for restoration potential and "tape magic" sound, though parts (e.g., motors, heads) are scarce. Service manuals cover 700/800 series (SX/CX electronics). Common issues: aging caps, noisy bearings, relay cleaning.