Category:Super High Fidelity
Country of Manufacture:Germany
Release dates:1968 - 1973
Speeds: 7 1/2, 15, 30
Max Reel Size("): 10.5"
Number of heads: 3
Dimension: 6.3 x 16.1 x 18" (160 x 409 x 458 mm)
Head Composition: Ferrite
Head Configuration: Stereo
# Motors: 3
Voltage(s): 110-120v, 220-240v, Multi
Outputs: XLR Balanced
Frequency Response:( 1.5dB): 40Hz to 20kHz 1.5 dB (100Hz to 16 kHz 1 dB)
Wow and Flutter:0.08% (DIN 45 515 weighted)
Signal-to-Noise Ratio:58 dB RMS.
Sound quality rating:8 / 10
Long-term reliability rating: 8/ 10
Weight: 37.4 lbs (17kg)
Squarely aimed at the ‘professional’ end of town, the Telefunken M28A was a three-motor machine with relay-operated transport control. Illuminated buttons required only fingertip operation and judging by the advertising, this was considered to be quite something back in 1970!
Built from 1968 to 1973 in Konstanz, Germany, the M28 and M12 were the only pro tape recorders made by Telefunken that were relatively portable (M28 about 24kg) and had heads that were oriented in the outside direction.
Interchangeable Glass & Ferrite head assemblies were ground to extreme accuracy and mounted directly on a heavy brass plate, with all the gaps vertical to within one minute of arc so no height adjustment screws were necessary. Tapered guide pins in the Tape path keep the lower edge of the tape always touching lower boundary of the head. the upper path boundary is only directed by the leading guide pin which is useful for deformed tape or a poorly wound reel.
Tape tension guides on both supply and take up reels are electronically controlled. Belt driven with a switched pole motor connected to a large diameter flywheel.
A very impressive signal-to-noise ratio was tested at 68 dB on the M28C
3 motors – 2 reel and 1 capstan motor. Max reel diameter 27 cm (10.6″)
Offered with tape speeds of 3¾ – 7½ ips or 7½ – 15 ips and selling for £600 in the U.K.
Broadcast-studio versions (M 28B and 28C – £495) were provided with tape speeds of 7½ and 15 ips, but no mixing, monitoring or VU-meter amplifier.
3 versions of the 28
28A – mixing console version 2-track, 19/9.5 cm/s or 38/19 cm/s
28B – full track broadcast version, 38/19 cm/s, no mixing console, balanced inputs and outputs
28C – half track broadcast version, 38/19 cm/s, balanced inputs and outputs. No mixing console, microphone amplifiers , VU meters, track switching or A-B switching
Tape speed deviation: 0.7% / Tape tension: 80 gm / Starting time: 200 mS / Erase and bias: 35 u.5 and 70 V-S DIN 45 513 / Equalisation: 85kHz / Rewind speed: three minutes for 1 km LP tape / Line input: 1.55 V 5K bridging, balanced / Line output: 1.55 V 600 ohms, balanced / half-track stereo
The service manual available in German is approx. 100 pages And may be available through the following links
All electrolytic capacitors have to be replaced.
All the Plug-in connectors connectors should be repaired (re-solder from the PCB, open it and put some lube on the movable areas).
Clean all the relay contacts. No replacement relays are available.
A source that may be worth checking for various things