A-77 level calibration question

[Willi Studer]

I have 2-track calibration tape from BASF and now I have to calibrate the reference output level but on 4-track A-77. Obviously, I cannot use output level sections on test tape because of track mismatch.
My question is: could I use full-track sections on calibration tape for setting output levels? On calibration tape, there are two full-track sections for bias (1 kHz and 10 kHz, both -10dB). Would it be wrong to use these full track sections which fully cover head tracks and set output level to -10dB below reference level (which is +6dB, therefore -4dB VU)?
Thank you in advance for kind assistance.

 

[barrymagrec]

I don`t know the specific tape you have but every test / calibration tape I have ever used (Ampex, EMI, Agfa, BASF) has been recorded full track so it makes no difference what head format you are trying to set up. It is normally better to set the record side (bias etc) on the type of tape you are intending to use rather than the unrecorded part of the test tape.

Barry

 

[Willi Studer]

Thank you for your answer.

My tape is BASF IEC for two track (full tape width) with following main sections:
1. Reference level - stereo recording with 0,75 mm channel gap
2. Bias coarse - full width recording
3. Bias fine - full width recording

I wanted to use tracks 2 and 3 because they are recorded over the full tape width. Does it seem reasonable?

 

[barrymagrec]

I`m not quite sure what you`re trying to do here. If the reference level section is recorded as you say then 1/4 track heads will still replay as normal. The bias sections are surely for setting up the record head and amplifier / bias. You need to set the replay gain and eq first using the recorded section of the tape. once the replay is correct then you set record bias and eq using your normal recording tape.

Barry

 

[Willi Studer]

Barry, here's what I'm trying to do: I have to calibrate reference level on 4-track head using 2-track reference tape. Will the two channels on 4-track head equally reproduce the 2-track recording? I know entire procedure very well but here in particular I am concerned over 4-track head and 2-track tape mismatch in tracks.
So: one channel on 2-track recording should cover both channels on 4-track head?

 

[barrymagrec]

The 4 track head (actuallly 1/4 track stereo) will reproduce the 2 track (1/2 track stereo) recording exactly as if it was a 1/4 track recording, the head is staggered to allow this, the problem would be trying to replay a 1/4 track recording on a 1/2 track head, at best this would give a 4dB loss of level, if there was a recording in the reverse direction it would replay that as well.

Barry

 

[AuroraB]

Willi..
I think you'd be just fine in doing what you suggest. Just proceed as planned,- you can always redo the cal process if it comes out wrong.
The only thing I canthink of, is if the magnetisation level of that cal tape is correct for the A77......
My own A77 have been collecting dust for over 10 years now, and I don't remember the specs....I take it you do have the service handbook-- the process is duly described, if memory doesn't fail me.....

BTW - you don't happen to have a spare knob for the power switch..???
or know where I can find one....

 

[Willi Studer]

@Barrymagrec: Thank you for your input.

@AuroraB: Reference levels for A77 and B77 are identical. Earlier versions were calibrated at 2V instead of 1,55V for 514nWb but that was not due to electronics but because of tapes which had lower magnetisation capacity. Actually I own a B77, the A77 unit is from a friend, so no spare parts, sorry I cannot help.

 

[ashok]

I think I have a A-77 service manual among my piles of books ! Will check it out and let you know. I sure had one and I have a defective A-77 chassis . The motor started running fast . I never looked at it due to lack of time. Maybe I should try fixing the machine and build a cabinet for it.

 

[barrymagrec]

I saw the circuit for the A77 servo when it first came out. I seem to remember it was clever (at the time ) but didn`t look difficult to fix.

Barry