Tape Trail

RE: Hi freq drop

70.81.160.74

In Reply to: RE: Hi freq drop posted by Marantzguy on October 17, 2007 at 11:21:49

The unit had heads realigned and bias adjusted for 456 (I actually use RMG SM911 which should have 456 bias from what I understand).

I picked up the unit, so mishandling is ruled out.

I guess azymuth makes sense. I was not present when the tech performed adjustment, and perhaps he did this by ear... the man is probably 80 years old and probably lost Hi freq. sensitivity years ago.

Perhaps I should have the unit check by someone else, assuming I can find someone in the Montreal area...

Follow Ups:

RE: Hi freq drop - Inmate51 17:35:26 10/17/07 (2)
So far, you haven't provided any hard data, just supposition and subjective impression.

The first thing you need to do is to test and verify the record/playback curve. A test tape, oscilloscope, and level meter will tell the story.

Only THEN can you tell your tech that his ear isn't what it used to be. :)
- RE: Hi freq drop - tanto 12:56:03 10/18/07 (1)
  hello Inmate51,
  
  Supposition and subjective impression are based on a recording I made using a test tone generator. It might not be the best way to check frequency response, but it seems a good way to tell for sure what's missing.
  
  I will follow Marantzguy advice and ask the tech to check again.
  
  Thanks
  - RE: Hi freq drop - Inmate51 07:21:06 10/19/07 (0)
    If you have another source (tech) for doing a frequency response check, I would do that, unless your current tech is a "known good guy". Otherwise, he might take offense at you suggesting that he didn't do the job correctly, if you don't have any data to discuss with him.
    If you can get your hands on a professional test tape, that would be the best way to verify the playback chain. Then you'll have the ability to talk with the tech and say (for example) that it's off by 6 dB at 10KHz.
    But as long as you've at least done a little testing of your own and it really does indicate a problem, you've got a better case than just saying it doesn't sound right. It could well be any of the things Richard mentioned (azimuth, bias, etc.).
    As a side thought, I would speculate that if the guy did it by ear and he's 80, I would expect the machine to be too bright rather than rolled off. ;)
    Good luck!
    
    Edits: 10/19/07
RE: Hi freq drop - Marantzguy 16:55:40 10/17/07 (0)
Hi, Tanto:

Just for the sake of a little experimentation, I wonder if the record head is properly set and the play head is slightly "off-azimuth" or something like that?

Have you tried playing a reliable pre-recorded tape to see how that might sound in comparison to something which you have recorded yourself to the Ampex 456 reel?

By physically skewing the tape with a Q-tip, past the play head, you might find that your "missing" frequencies come back temporarily.

Otherwise, unless your technician friend was using an alignment tape a signal generator and an o'scope to do his adjustments of the play head, etc, I would not trust doing this work by "ear", particularly if the individual in question is really in his eighties. (No offense, but this really the proper way to adjust a machine!)

Perhaps it might be wise to bring the deck back for a second attempt!

Good Luck
Richard Links
Berkeley, CA

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