This deck was too dull on Dolby cassettes. Either B or C. Owned by a collecting friend but this one he could not succeed aligning for the life of him. Capacitors renewed, contacts cleaned, mechanism & heads inspected. M300 gauge pass, full track test cassettes pass, the works.
After he went by the SM few times with no positive results, in a final act of desperation he tweaked every trimmer and coil in case he could find a clue by luck. No miracle happened.
He finally brought it to me before written off. I first tried by the book (SM 66A + 66C) to make sure he did not skip or screw some important step but no, still dull as mud.
Then I thought of an alternative scenario to try and it worked. Either I am a lucky unorthodox, or something has drifted badly in the particular unit, or some crucial piece of information is lost between production versions and service manuals revisions available online.
Anyway. Sound with Dolby is now normal against his Nak CR-7, Nak RX-505, Revox B215, and he is happy. On commercial B NR tapes and on recordings back and forth between his different decks with B,C NR.
In case someone stumbles on the same problem with this version deck, but without a better SM conforming solution, my notes are:
R353,R310=470R+470R divide HA12058's output (p24,p25) with VR301=5k to ground i.e. output at the RCA is x0.84 (5k/5.94k)*
The user manual states 420mV output. 1/0.84=1.19
420*1.19=500mV original signal from the Dolby chip
It doesn't compute with 580mV TP in the service man
Wait, Nakamichi smaller decks had 0.5V straight output
Maybe they revised to compete in showrooms with that
Nak test tape is 0.917*ANSI or 1.09 weaker (218/200)
500mV*1.09=545mV is analogous with ANSI level tape
Modified settings:
-Playback level set ~550mV on the output RCAs with an ANSI 400Hz Dolby level test tape, output knob at max
-Peak meter set at 0dB for ~550mV (545) output on 38mVRMS 400Hz input, REC level knobs & Master at max
(the meter trimmers are located under a bottom hatch)
-Internal oscillator set for 55mV bias tones & 550mV rec cal tone at the output RCAs
*This deck is sensitive to output loading, has no buffer circuit at its output. Notes are taken at a high 1MΩ load to be neutral
There could be 0.5 dB difference in optimum output setting due to heavier loading. Down to 520mV probably. Worth exploring
-Adjust RecCal and bias vs Level & FR. Try for alike result when using NR and not using NR
Use neutral response tapes for base bias so the fine trim knob acquires symmetric enough range
After he went by the SM few times with no positive results, in a final act of desperation he tweaked every trimmer and coil in case he could find a clue by luck. No miracle happened.
He finally brought it to me before written off. I first tried by the book (SM 66A + 66C) to make sure he did not skip or screw some important step but no, still dull as mud.
Then I thought of an alternative scenario to try and it worked. Either I am a lucky unorthodox, or something has drifted badly in the particular unit, or some crucial piece of information is lost between production versions and service manuals revisions available online.
Anyway. Sound with Dolby is now normal against his Nak CR-7, Nak RX-505, Revox B215, and he is happy. On commercial B NR tapes and on recordings back and forth between his different decks with B,C NR.
In case someone stumbles on the same problem with this version deck, but without a better SM conforming solution, my notes are:
R353,R310=470R+470R divide HA12058's output (p24,p25) with VR301=5k to ground i.e. output at the RCA is x0.84 (5k/5.94k)*
The user manual states 420mV output. 1/0.84=1.19
420*1.19=500mV original signal from the Dolby chip
It doesn't compute with 580mV TP in the service man
Wait, Nakamichi smaller decks had 0.5V straight output
Maybe they revised to compete in showrooms with that
Nak test tape is 0.917*ANSI or 1.09 weaker (218/200)
500mV*1.09=545mV is analogous with ANSI level tape
Modified settings:
-Playback level set ~550mV on the output RCAs with an ANSI 400Hz Dolby level test tape, output knob at max
-Peak meter set at 0dB for ~550mV (545) output on 38mVRMS 400Hz input, REC level knobs & Master at max
(the meter trimmers are located under a bottom hatch)
-Internal oscillator set for 55mV bias tones & 550mV rec cal tone at the output RCAs
*This deck is sensitive to output loading, has no buffer circuit at its output. Notes are taken at a high 1MΩ load to be neutral
There could be 0.5 dB difference in optimum output setting due to heavier loading. Down to 520mV probably. Worth exploring
-Adjust RecCal and bias vs Level & FR. Try for alike result when using NR and not using NR
Use neutral response tapes for base bias so the fine trim knob acquires symmetric enough range
