Description

Alpine AL-90 Custom Smokey Silver & Black Trim – Advanced Elevated Serviced With Brand New Heads And Full Caps Replacement

On offer is a highly desirable and collectable cassette deck from Alpine model AL-90 with brand new heads Orange Caps Replaced, and Power Supply fully Upgraded !

A great restoration by
Nak Central AudioLabs including full maintenance and recalibration.

Restored to a very high sonic and cosmetic level and now sounding stunning! In excellent condition and a rare
offering!

Your rare chance to buy an Alpine Al-90 Ultimate in this customised Smokey Silver and Black trim and now in immaculately fully  Serviced condition comes only once in a lifetime!

This model is a multi-voltage 240/220/110/127v @50/60 Hz version!

A unique and rare opportunity to purchase a truly holy grail of cassette deck design and performance!

The recording quality is truly outstanding using Alpine’s proprietary computerised technology (B.L.E.S.) that optimises bias, equalisation
 and level separately then correctly matches the optimum points for all. An additional manual bias calibration pot allows you to further tune your own preferred optimum point. It quite simply calibrates the best possible performance from each cassette tape inserted into the loading bay. You can write the data to memory to retrieve these stored calibration parameters at any time.

As expected at this level of performance, this is a three head, four-track – two channel, three motor, direct drive, dual capstan design.
The drive housing is a zinc-alloy ONE PIECE DIE-CAST DRIVE which includes two pairs of capstan bearings for perfect and forever perfect geometry of the closed-loop dual-capstan and 3-DD motor mechanism.
The Dolby integrated circuits were sourced from Hitachi and the inside hides an ALPS 4-way DIP switch to select high-frequency attenuation.
The heads are -aligned and 3-layer lamination (rec), HIP ferrite (Hip Isostatic Press) with special contouring (play) and sendust/ferrite with asymmetrical dual-gap (erase).

These Alpine AL-90’s are truly high-performance monsters whose playback and the recording quality is on par with some of the finest reel to reel machines ever made!

Serial Number 20910239A

New heads fitted.
Power supply: Fully upgraded, and all electrolytic capacitors replaced.
All voltages adjusted and aligned.
All signal orange capacitors replaced.
All signal bi-polarised capacitors replaced.
 
CALIBRATION, ADJUSTMANTS and ALIGNMENTS

 
Conditions:
MONITOR switch: TAPE
PEAK/VU Left and Right meters: PEAK
TAPE SELECT switch: NORM
DOLBY NR select switch: OFF
DATA STD/CALL switch: STD
PITCH CONTROL: Centre
BIAS FINE control: Centre
MIC level controls: Minimum (L/R)
OUTPUT LEVEL control: Maximum
Other switches: OFF position
DC Voltage check and adjusted
24 V ±1 V
12 V ± 1V
-12 V ± 1V
18 V ± 1V
9 V
6 V ± 1 V
10 V ± 1 V
-10 V ± 1 V
Head Height and Tilt Angle
Measurement Gauge: M-300.
The guide check bar smoothly passes through the tape guide.
The guide check bar stays in parallel with the guide plate or the top of the guide plate bar.
 
Tape Guide of Supply Pinch Roller
Measurement Gauge: M-300.
The guide check bar smoothly passes through the tape guide of supply pinch roller.
 
Head Azimuth
PLAY
Test Tape: MTT-114 (10 kHz)
The Left and Right Outputs are in phase and maximum and equal in Amplitude.
 
Tape Speed
Test Tape: MTT-111 (3,000 Hz)
Adjusted VR1 and obtained output frequency reading of 3,000 Hz
 
DC Balance of playback Equalisation Amplifier
STOP
Disconnected the head cable and adjusted each the left and right channels independently.
Switched the oscilloscope to DC range and adjusted both voltage in CH1 and CH2 to the same value: 0.65 V.
Voltage variations are small.
 
Playback EQ and Peak Point
PLAY
Blank tape loaded.
Feed 200 Hz test signal from AF oscillator and adjusted oscillator output so that 1 V (= 0dB) output is developed at each test point.
Changed the oscillator frequency to 20 Hz and 7 kHz so that output levels are obtained.
Changed the oscillator frequency to 27 kHz and adjusted and found peak level so that a peak level is developed between 26 kHz and 27 kHz.
Checked for -15.5 dB output at 7 kHz.
Checked for -20 dB output at 7 kHz when METAL position is selected.
 
Dolby Level
PLAY
Test Tape: MTT-150 (400 Hz)
Adjusted and obtained 580 mV output at each test point.
 
Dolby Level (EXT NR DECODER OUT)
PLAY
Test Tape: MTT-150 (400 Hz)
Adjusted and obtained 580 mV output at each test point.
 
Dolby Level (A/D Buffer Out)
PLAY
Test Tape: MTT-150 (400 Hz)
Adjusted and obtained 1,000 mV output at each test point.
 
Input Sensitivity Reference Level (Dolby Level)
STOP
MONITOR: SOURCE
AF OSC: 1 kHz, 100 mV (Dolby level) input.
Adjusted and obtained 580 mV output at each test point.
 
Input Sensitivity (EXT NR ENCODER OUT)
STOP
MONITOR: SOURCE
AF OSC: 1 kHz, 100 mV (Dolby level) input.
Adjusted and obtained 580 mV output at each test point.
 
Level Meter Input
STOP
MONITOR: SOURCE
Adjusted each the left and right channels independently.
AF OSC: 1 kHz, 316 mV (Dolby level + 10 dB) input.
Adjusted and obtained 1,000 mV output at each test point.
 
Level Meter 0 dB reading
STOP
MONITOR: SOURCE
AF OSC: 1 kHz, 100 mV (Dolby level) input.
Adjusted for 0 dB reading on Level Meter.
AF OSC: Decreased oscillator output level by 20 dB.
Checked the level meter pointer indicates – 20 dB.
AF OSC: Increased oscillator output level by 10 dB from 100 mV reference level.
Checked the level meter pointer indicates +10 dB.
 
AUTO EQ IC
Internal reference voltage
STOP
MONITOR: SOURCE
Adjusted and obtained 3.0 V DC output at each test point.
Input level
REC/PLAY
Test Tape: Blank Tape
AF OSC: 800 Hz, 100 mV (Dolby Level) Input
Adjusted and obtained 100 mV output at each test point.
Peaking
AF OSC: 30 kHz, 5.6mV (- 25 dB) Input
Adjusted and obtained maximum output at each test point.
 
BIAS
OSC Frequency (Erase)
REC/PAUSE
T. SELECT: METAL
Test Tape: Blank Tape
Adjusted and obtained frequency reading of 105 kHz at the test point, 50 mV (100 mA).
Bias Current
REC/PAUSE
T. SELECT: METAL
Test Tape: Blank Tape
Connected the oscilloscope to Emitter of Q5023 (Q5024), adjusted and obtained maximum amplitude across test points.
Bias Current Temporarily Settings
REC/PLAY
TEST TAPE: Blank Tape
Bias current and voltages obtained:
            METAL:            5.5 mV (2.5 mA),         12 V
            CrO2:               3.1 mV (1.4 mA),         6 V
            FeCr:                3.1 mV (1.4 mA),         5 V
            NORM:            2.6 mV (1.2 mA),         5 V
Bias Trap
REC/PLAY
T. SELECT: METAL
Test Tape: Blank Tape
Adjusted and obtained minimum amplitude of Bias voltage wave form at each test point.
Checked oscillator frequency.
 
Peak Bias
REC/PLAY
LINE OUT
1.      Level: AF OSC.: 400 Hz, 5.6 mV (-25 dB from 100 mV)
Adjusted Level Adjust Volume until record/playback output of 56 mV, which is the same level at that as SOURCE.
2.      Bias: AF OSC: 400 Hz, 100 mV (Dolby Level) Input.
3.      Adjusted Bias Adjust Volume.
 
PB AMP Bias Trap
REC/PLAY
T. SELECT: METAL
AF OSC: 400 Hz, 56 mV (-25 dB from 1 V) Line Out.
 
Record/Playback Frequency Response
REC/PLAY
LINE OUT
AF OSC: 56 mV (- 25 dB from 1 V) Line Out
Adjusted respective trimming resistor so that record/playback frequency response within the limits, referred to 400 Hz is obtained.
 
AUTO EQ TONE OSC LEVEL
STOP
TNOE OSC: 800 Hz
Short circuit all four terminals of TEST CN.
Monitor 800 Hz wave form at test point.
TONE OSC frequency can be varied by changing combinations of terminal connections.
 
A/D CONVERTER GAIN
STOP
TONE OSC: 800 Hz
 
A/D CONVERTER OFF-SET
STOP
TONE OSC: 800 Hz
Adjusted and obtained – 150 mV DC at test point.
Checked the DC output decreases to – 15 mV when the TP is grounded.
 
AUTO EQ TEST OSC SELECTION (Built-in OSC)
STOP
TNOE OSC: 800 Hz
Connected TP to GND.
Adjusted and obtained 5.6 mV at each test point.
 
A/D IN (A/D CONVERTER OFF-SET)
STOP
BLES: ON
TONE OSC: 800 Hz
Set the oscilloscope to EXT TRIGGER mode and adjusted the trigger level so that oscilloscope is triggered by ADST signal when BLES switch is placed in ON position.
 
A/D IN (A/D CONVERTER GAIN)
STOP
BLES: ON
TONE OSC: 800 Hz
Changed sweep time range oscilloscope from 50 us to 1 ms.
Disconnected TP8002 from the GND.
Adjusted so that A/D IN TIME of 5 ms is obtained when BLES switch is placed in ON position.

Transport Section Mechanism Adjusted
o   Record Head and Playback Head Tilt Adjusted
o   Head Base Stroke Checked
o   Erase Head Stroke Adjustment and Tape Guide Height Checked
§  Erase Head Stroke Adjusted
§  Supply Tape Guide Height Adjusted
§  Take-up Tape Guide Height Checked
o   Erase Head Height and Tilt Adjusted
o   Playback Head and Record Head Height Adjusted and Azimuth Aligned
o   Record Head Height Adjusted and Azimuth Aligned
o   Tape Travelling Checked
o   Eject Damper Adjusted
o   Reel Motor Speed Adjustment in Play Mode Checked and Aligned
o   Tape Speed Adjustment Checked and Aligned
o   Lubrification: The Tape Transport is of a lubrification-free type mechanism
§  Cam Motor Pulley
§  Thrust portion on the Capstan Shaft
§  Washer between Reel Hub Ass’y and Back Tension Spring
§  Reel Hub Shaft
§  Capstan Shaft

The tape transport mechanism was completely disassembled, cleaned and oiled.

Audio Alignments

o   Meter Level Calibrated (400 Hz Input)
o   MPX Filter (+10 dB, 19 kHz Input, 50 mV, Dolby NR & MPX Filter ON). Attenuation >30 dB
o   Playback Head Track Aligned (1 kHz Track Alignment)
o   Playback Head Azimuth Aligned (15 kHz Azimuth)
o   Playback Level Calibrated (400 Hz Level Tape)
o   Playback Frequency Response Adjusted (10 kHz, 15 kHz, 20 kHz)
o   Bias Oscillation Frequency and Erase Current Adjustment
o   Bias Trap Adjusted (Record Amplifier)
o   Record Head Height Adjusted (400 Hz @ 0dB)
o   Record Head Azimuth Aligned (15 kHz @ -20dB)
o   Bias Trap Adjusted (Playback Amplifier)
o   Record Level Calibrated
o   Recording Bias Current Adjusted (400 Hz @ 0 dB, 20 kHz @ -20 dB and 10 kHz / 20 kHz @ -20 dB)
o   Overall Frequency Response Adjusted (400 Hz @ 0dB and 20 Hz to 20 kHz @ -20 dB)

Specifications :

Type: 3-head, single compact cassette deck

Weight: 10.1kg