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Technical Details

Brand: Ampex

Model:MR-70

Category:High Fidelity

Application:Studio

Electronic:Tube

Country of Manufacture:USA

Release dates:1966 - 1969

Tracks:1/2 Rec/PB

Speeds: 7 1/2, 15, 30

Max Reel Size("): 10.5"

Number of heads: 3

Head Composition: Permalloy

Head Configuration: Stereo

# Motors: 4

Auto Reverse?:No

Voltage(s): 110-120v

Frequency Response:(overall): 15 ips NAB ±1 db 50 Hz -15kHz, ±2 db 30 Hz -20kHz 7½ ips NAB ±1 db 50 Hz -12kHz, ±2 db 40 Hz -15kHz 30 ips full-track heads ±1 db 50 Hz -20kHz 30 ips multi-track heads ±2 db 50 Hz -20kHz

Wow and Flutter:Wow and flutter: less than 0.05% rms at 15 & 30 ips. less than 0.08% rms at 7½ ips

Signal-to-Noise Ratio:Tape speed full track ¼" tape 4-track 1" 8-track 1" 15 ips 70dB 69dB 65db 7½ ips 70dB 69dB 65db 30 ips 72dB 71dB 67db

Sound quality rating:9 / 10

Long-term reliability rating: 8 / 10

Additional Details

Description

It is rumoured that the Ampex MR-70 was specially built for Capitol Records so that they could master Beatles recordings from EMI England for the local market. Whether this is true or not, everyone seems to agree that the MR-70 was the best Ampex analogue recorder ever made.
Cost was not an issue when designing this state-of-the-art recorder. In 1966, the year of its release, a standard MR70 quarter-inch two-track cost $4500 and $5456 in console format .
Highly modified Ampex 300 transports were used for the MR-70. Massive die-case frames designed to tight tolerances permitted the heads to be mounted for fixed azimuth. Transport features included a viscous-damped reel idler, varispeed fast wind and constant tension tape supply. Fast, positive starts were enabled by supplying power boost to reel idler and take-up motors during start function.
The electronics utilised military/industrial grade 7587 & 7895 Nuvistor vacuum tubes (only 2 types required which lessened spare parts requirements), the highest quality metal film resistors and film capacitors. Because of feedback loops in the circuitry, ultra-wide bandwidth audio transformers were essential, and these were hand-wound.
Multiple track configurations were available from one track on quarter-inch tape to up to eight tracks on one-inch tape. There were two speed options – 7½ /15 ips or 15/30 ips.
The MR-70 supported settings for NAB, CCIR and AME equalization curves and the ability to switch between them.
Another rumour surrounding this machine is that Willi Studer’s life-long goal was to make a tape recorder better than the MR-70. He tried for two decades. then came to the conclusion that he could equal it but not surpass it!
It is believed that Ampex technicians hand-made only 50 MR-70s, and that each one was in some way custom-built.

Additional Info

The Ampex  MR-70 studio tape recorder was available with many different custom variations.

Specifications: Tape speed: full track ¼” tape / Inputs: 20k ohms unbalanced convertible to balanced with plug-in bridging transformer.

Accepts line levels from -20 to +12 vu. Low impedance mic input by use of accessory plug-in Nuvistor pre-amp

Output: Strappable for 150 or 600 ohms, balanced or unbalanced, +4 or +8 vu

Equalisation: automatic by speed selector, choice of curves at each speed for NAB, CCIR or AME (15 ips only). Adjustable to accommodate other curves in the 17.5 to 100 microsecond range (with or without the 3180 microsecond low frequency pre-and post emphasis

Tube complement: 6 x 7587 Nuvistors, 12 x 7895 Nuvistors (for each channel). 4 of each type for bias / erase oscillator / Bias / erase: Plug-in master oscillator on transport. 150 kHz frequency / Erasure: a mid frequency signal recorded at peak record level will be reduced by at least 68dB when erased / Channel separation: less than 0.5% / Even order distortion: 2nd harmonic distortion of a 500Hz signal recorded at peak record level is less than 0.5% / Start time: tape  within ± 0.2% of nominal speed in 0.5 seconds

Dimensions: transport 19 x 24½ x 12″ deep (484.5 x 622.3 x 304.8 mm) electronics (per channel) 19 x 5¼ x 12″ deep (484.5 x 133.4 x 305mm) console 29 x 29¼ x 62¼” high (737 x 749 x 1581mm)

Weight: transport 130 lbs (59.1 kg) electronics (per channel) 27 lbs (12.3 kg) console (4-channel unit) 180 lbs (81.8 kg) / full-track

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