Fostex A-4 R2R calibration/check

[Gold]

My Studer A80 preview  decks have thumb screws on the azimuth adjust.  I adjust for every tape I lplay.

 

[abbey road d enfer]

I've observed it myself while monitoring on a scope.

Don't take my word for it, try it on a 2 track and you'll see the azimuth going nuts as you adjust the bias.

Really easy to see on a scope running a Lissajous pattern.

IMO, correct observation, wrong analysis. Bias level modifies the HF recording response, introducing a phase shift; that is what you see. The theory about the "virtual gap" moving with bias level is moot.
That is why Lissajous is not a correct method. Azimuth should be set primarily by finding maximum HF level.

 

[Biasrocks]

That is why Lissajous is not a correct method. Azimuth should be set primarily by finding maximum HF level.

The reason that method was suggested is that it's easy to get the wrong phase alignment (180 degrees out) on a scope when you monitor azimuth using a high frequency tone. Which I concur.

By using wide band white noise for your initial azimuth adjustment, followed by a high frequency tone you avoid this problem entirely.

The test tapes and the record side tones that I use here include wide band white noise for accurate azimuth alignment.

IMO, correct observation, wrong analysis. Bias level modifies the HF recording response, introducing a phase shift; that is what you see. The theory about the "virtual gap" moving with bias level is moot.

Did you check the discussion thread I posted, there's some heavy weights chiming in about the virtual gap phenomenon.

I am far from a heavy weight on the theory of analog recording, but I've attained great results aligning my decks using the method I described.

Am I the only one thinking that this discussion and the original poster would be better served by moving this to a different topic title?

Mark

 

[abbey road d enfer]

That is why Lissajous is not a correct method. Azimuth should be set primarily by finding maximum HF level.

The reason that method was suggested is that it's easy to get the wrong phase alignment (180 degrees out) on a scope when you monitor azimuth using a high frequency tone. Which I concur.

By using wide band white noise for your initial azimuth adjustment, followed by a high frequency tone you avoid this problem entirely.

The test tapes and the record side tones that I use here include wide band white noise for accurate azimuth alignment.

I agree that precise azimuth setting using the phase (Lissajous or dual-trace) method  involves starting with a lower frequency in order to avoid the 2.pi aliasing, but phase measurements are affected by equalization; in contrast, setting at maximum amplitude is totally unambiguous and do not require starting with a lower frequency.
Indeed, the phase method is adequate for preventative maintenance, where one starts with both channels very similar, because the phase effects due to EQ and bias will be pretty identical from channel to channel.
And of course, if the azimuth needs coarse adjustment, it is better done with a lower frequency.

IMO, correct observation, wrong analysis. Bias level modifies the HF recording response, introducing a phase shift; that is what you see. The theory about the "virtual gap" moving with bias level is moot.

Did you check the discussion thread I posted, there's some heavy weights chiming in about the virtual gap phenomenon.

I am far from a heavy weight on the theory of analog recording.  8)

Mark

Yes, I did check Bob Katz's post; I respect him very much when it comes to the essence of his activity, but I think he sometimes wander in terra incognita regarding hard theory.

 

[Biasrocks]

Yes, I did check Bob Katz's post; I respect him very much when it comes to the essence of his activity, but I think he sometimes wander in terra incognita regarding hard theory.

Here's one from Bob Ohlsson and one from John Klett, confirming what Bob asserted

http://repforums.prosoundweb.com/index.php/topic,6193.msg62069.html#msg62069

http://repforums.prosoundweb.com/index.php/topic,6193.msg62203.html#msg62203

Really not  trying to beat a dead horse. 

Mark

 

[abbey road d enfer]

Yes, I did check Bob Katz's post; I respect him very much when it comes to the essence of his activity, but I think he sometimes wander in terra incognita regarding hard theory.

Here's one from Bob Ohlsson and one from John Klett, confirming what Bob asserted

http://repforums.prosoundweb.com/index.php/topic,6193.msg62069.html#msg62069

http://repforums.prosoundweb.com/index.php/topic,6193.msg62203.html#msg62203

Really not  trying to beat a dead horse. 

Mark

Yes, I read the thread.
And again, with all due respect, these people are not physicists.
I was a member of the REP forum for some time but I quit when I saw that faith was more important than facts, particularly when supported by a guru. I'm not a guru, just a scientist; I'm also human, I make mistakes sometimes often. If someone can prove me wrong with sustainable arguments, I'm ready to incline. I don't make it a personal matter (read my sig) but I hate to see hazy theories bandied as gospel.

 

[Biasrocks]

Yes, I read the thread.
And again, with all due respect, these people are not physicists.
I was a member of the REP forum for some time but I quit when I saw that faith was more important than facts, particularly when supported by a guru. I'm not a guru, just a scientist; I'm also human, I make mistakes sometimes often. If someone can prove me wrong with sustainable arguments, I'm ready to incline. I don't make it a personal matter (read my sig) but I hate to see hazy theories bandied as gospel.

Fair enough, thank you for clarifying.

Cheers!

Mark

 

[Gold]

I only play tapes recorded elsewhere. My method for checking azimuth is to look for peak level with the provided calibration tone(s) on the VU meters and then to look at the lissajou on the scope to fine tune.

 

[abbey road d enfer]

I only play tapes recorded elsewhere. My method for checking azimuth is to look for peak level with the provided calibration tone(s) on the VU meters and then to look at the lissajou on the scope to fine tune.

It makes sense since your machine is regularly maintained and aligned, and thus there is no phase deviation in the electronics. This makes perfect sense; looking for peak level is essential in the procedure.

 

[Gold]

This is very much OT but maybe Abby knows? A common complaint about the A80 VU electronics is that there is too much phase shift . The playback circuits look pretty straight forward to me. I'm thinking that the phase shift must be on the record side. I can't make that judgement. Any idea? I could post a schematic.