R/E/P Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: [1]   Go Down

Author Topic: Studer A800 Azimuth Question  (Read 563 times)

leftofthedial

  • Newbie
  • *
  • Online Online
  • Posts: 5
  • Real Full Name: Robert S Stevens
Studer A800 Azimuth Question
« on: August 31, 2019, 02:00:44 pm »

So I finally got around to checking the Azimuth on my A800 MKI that I've had a few years.  Fixing all the things. 

I've set azimuth on dozens of 2 track machines and a couple Fostex 16 tracks, never with much hassle.

However, When I set the azimuth on the A800 as per the manual I find phase shifts all over the place.  For instance If I do as the manual says, and set azimuth using channel 1-2.  Then check 1-3, there is a slight shift.  especially when setting the record azimuth. When I check 1-8, the shift is almost 180 degrees. 

If i do similar starting at channels 11-12 then start working outward (ie. 11-13, 11-14/ 12-10,12-9) the drift starts again, being completely out of phase when I get to 11-24/12-1.

The playback head shows a little drift, but mostly the record azimuth is the one that wanders significantly.

I'm assuming this is not normal?

Any insight would be appreciated.

The heads have been lapped by JRF a few years back (before I got the machine) but they look in great condition.  I could send them off to be redone and at a minimum have them do their laser alignment.  But want to know some thoughts before I let the postal services have a chance to lose my headstack.
Logged

mbrebes

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 55
  • Real Full Name: Michael Brebes
Re: Studer A800 Azimuth Question
« Reply #1 on: September 03, 2019, 04:49:25 pm »

The individual track head gaps on multitrack heads NEVER match up perfectly.  What I usually do is see how far out ALL the heads are then pick two that are very close to each and use that as a guide for azimuth.
Logged

leftofthedial

  • Newbie
  • *
  • Online Online
  • Posts: 5
  • Real Full Name: Robert S Stevens
Re: Studer A800 Azimuth Question
« Reply #2 on: September 04, 2019, 04:36:05 pm »

I think the zenith is off on the record head.  Although the service manual implies that is unlikely :).  Obviously something or someone has messed with the head height screws at some point. The ones service manual says to never touch.
Logged

Fletcher

  • Administrator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 590
Re: Studer A800 Azimuth Question
« Reply #3 on: October 08, 2019, 12:34:03 pm »

A couple of things... first, when you do "azimuth", you it on the two exterior channels... as in 1 & 24.  When 1 & 24 are good... all the ones in the middle are good.  When you do "azimuth" you first do the record head... then you record the tone [I generally recommend 15kHz, but I do know some guys the use 20kHz... you can "rough it in with 10kHz, but use that only as a "rough" alignment].  After you get the record head straight [no pun intended], you record the tone and align the repro head... that way the two are exactly in line.

What scares me a bit is you started by saying "that I've had a few years" -- I hope to hell you recorded 15kHz alignment tones [along with the standard 1kHz, 10kHz, 100kHz (on an 800, I usually run my low frequency tone at 50Hz as there is a bit of a "bump" at 100Hz and I find a "larger" sounding low end when I align 800's with a 50Hz tone... but that's for you to decide].  If you didn't -- your azimuth will be WAY out of whack on ALL the previous reels you've had on the machine!!!

Last, and certainly not least... azimuth should actually be checked [along with the alignment of the electronics 1k, 10k, 50Hz] before EVERY session.  If its a "home studio" kind of thing, maybe every 20-25 hours of use... but this is something that you need to stay on top of 100% of the time if you want a recording that sounds correct.

Peace
Logged
CN Fletcher

mwagener wrote on Sat, 11 September 2004 14:33
We are selling emotions, there are no emotions in a grid


"Recording engineers are an arrogant bunch
If you've spent most of your life with a few thousand dollars worth of musicians in the studio, making a decision every second and a half... and you and  they are going to have to live with it for the rest of your lives, you'll get pretty arrogant too.  It takes a certain amount of balls to do that... something around three"
Malcolm Chisholm

Timtape

  • Full Member
  • ***
  • Online Online
  • Posts: 103
  • Real Full Name: Tim Gillett
Re: Studer A800 Azimuth Question
« Reply #4 on: October 09, 2019, 10:55:59 am »

I think the zenith is off on the record head.  Although the service manual implies that is unlikely :).  Obviously something or someone has messed with the head height screws at some point. The ones service manual says to never touch.


Hi, what makes you think the zenith is out?  If the zenith has been correct for some time, the wear flat will be pretty much the same, with maybe a widening at the extreme ends, top and bottom. Normally if zenith has been out for some time, you'd see a head with a wider wear "flat" at either top or bottom of the head. This  leads to upper or lower tracks wearing out before the others, shortening the life of the head. It also means tape pressure across the head tracks is not even, possibly leading to poor tape to head contact (spacing loss) at the place of weakest tape pressure. Like very wide tires on a car, alignment is critical.

I'm not familiar with that machine. Some have no provision for head zenith adjustment. As the manual says, normally the alignment shouldn't go out but all it takes is one turkey to mistake a screw for the azimuth, start fiddling and things start to go pear shaped. I've serviced many tape machines for decades and usually the cause of head misalignment (at least in quality machines) is a local dude "having a go" but not having a clue what he's doing.

As mentioned, inspect the wear "flat" from top to bottom, if necessary with a magnifier in a strong light. 

 
Logged

RadarDoug2

  • Newbie
  • *
  • Online Online
  • Posts: 3
  • Real Full Name: Doug Jane
Re: Studer A800 Azimuth Question
« Reply #5 on: October 11, 2019, 04:01:29 pm »

A couple of things... first, when you do "azimuth", you it on the two exterior channels... as in 1 & 24.  When 1 & 24 are good... all the ones in the middle are good.  When you do "azimuth" you first do the record head... then you record the tone [I generally recommend 15kHz, but I do know some guys the use 20kHz... you can "rough it in with 10kHz, but use that only as a "rough" alignment].  After you get the record head straight [no pun intended], you record the tone and align the repro head... that way the two are exactly in line.

What scares me a bit is you started by saying "that I've had a few years" -- I hope to hell you recorded 15kHz alignment tones [along with the standard 1kHz, 10kHz, 100kHz (on an 800, I usually run my low frequency tone at 50Hz as there is a bit of a "bump" at 100Hz and I find a "larger" sounding low end when I align 800's with a 50Hz tone... but that's for you to decide].  If you didn't -- your azimuth will be WAY out of whack on ALL the previous reels you've had on the machine!!!

Last, and certainly not least... azimuth should actually be checked [along with the alignment of the electronics 1k, 10k, 50Hz] before EVERY session.  If its a "home studio" kind of thing, maybe every 20-25 hours of use... but this is something that you need to stay on top of 100% of the time if you want a recording that sounds correct.

Peace
WOW! Really bad advice Fletcher. You always do the REPRODUCE head first! Then you do the Record head by observing what comes off the reproduce head. You dont do the record head in sync. Some machines have filters on the record head in that position. Also the actual position of the record head azimuth is affected by bias, and the physical position on tape of the recorded signal depends on the transfer function of recording, so just setting record head azimuth in sync does not allow for where on the head recording happens. A subtle but important difference.
Taking azimuth from tracks 1 and 24 is bound to be bad. Very easy to get cycles out at high frequencies. Start with adjacent tracks in the middle of the head. Then work out observing azimuth as you go. If the azimuth varies drastically, you have a head with a bowed gap.
If you always record stereo pairs on adjacent tracks, then the azimuth error will be minimised. If you are multimikig a band, time delays in the room will cover all the strict phase problems.
Logged

RadarDoug2

  • Newbie
  • *
  • Online Online
  • Posts: 3
  • Real Full Name: Doug Jane
Re: Studer A800 Azimuth Question
« Reply #6 on: October 11, 2019, 04:05:37 pm »

One thing I meant to cover on the original post. Use a two channel scope to do azimuth. Start with the low frequencies, and satisfy your self that you are on the same cycle of waveform on both channels. This is easy at low frequencies, not so easy at high frequencies. Work your way up in frequency, checking for each frequency that you are on the same cycle of audio. Its very easy to just use 10K and get a cycle out. This then has the head on a slight slant, and azimuth is definitely out!
Logged

mbrebes

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 55
  • Real Full Name: Michael Brebes
Re: Studer A800 Azimuth Question
« Reply #7 on: October 12, 2019, 12:01:21 pm »

Most of the tape machines I have worked on rarely have the azimuth go out on a regular basis, at least when they are all in-house tapes.  If the azimuth goes out, even in a 48 hour period, I would suspect something wrong with the head assembly mechanics.  If you are using tapes that are from out of house, yes the azimuth will need to be checked, but it shouldn't go out while you are working with that same tape.
Logged

leftofthedial

  • Newbie
  • *
  • Online Online
  • Posts: 5
  • Real Full Name: Robert S Stevens
Re: Studer A800 Azimuth Question
« Reply #8 on: October 14, 2019, 01:16:55 pm »

Thanks for all the responses.  I've had the machine for 3 years, but have not used it yet in a recording with a client situation.  I have been taking my time recapping things and working out all the electronic and mechanical stuff as time permits.  I generally doubt that my original hypothesis of zenith being off is actually what is going on. FWIW, I also have not touched anything but the azimuth screws on the head adjustments because I know I will only make it worse if I do.
Logged

leftofthedial

  • Newbie
  • *
  • Online Online
  • Posts: 5
  • Real Full Name: Robert S Stevens
Re: Studer A800 Azimuth Question
« Reply #9 on: October 14, 2019, 03:58:34 pm »

Also, FWIW, I see no real reason why setting the record head first would be problematic on a 3 head machine in sync mode.  The A800 has the ability to go as high as 16K in sync mode.  That's not how I have been proceeding, but I'm pretty sure I saw a video of Greg Norman at Electrical do the rec/sync head in sync mode on one of their A820. 
Logged

RadarDoug2

  • Newbie
  • *
  • Online Online
  • Posts: 3
  • Real Full Name: Doug Jane
Re: Studer A800 Azimuth Question
« Reply #10 on: October 14, 2019, 11:32:54 pm »

The thing is, it is not the correct procedure. You ALWAYS start with the repro chain and get that right.
Logged

leftofthedial

  • Newbie
  • *
  • Online Online
  • Posts: 5
  • Real Full Name: Robert S Stevens
Re: Studer A800 Azimuth Question
« Reply #11 on: Today at 04:20:47 pm »

Azimuth has been corrected. I was most likely off a cycle at 1K causing errors at 10K and 16K.''

I put some sharpie on the heads and ran some tape for a while.

Zenith still appears to be a problem on the reproduce head https://drive.google.com/open?id=1ZxbFmqyyFde5nouBp2psHUoyJhwURXbm

But the record head looks fine.https://drive.google.com/open?id=1ninVj2msWotmxt3cI9Yy1aP94w9Aw0_R
Logged
Pages: [1]   Go Up