Fostex A-4 R2R calibration/check

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

weiss

Well-known member
Joined
Jun 16, 2014
Messages
1,436
Location
Germany
Hey guys.

I just became the owner of a Fostex A-4 reel to reel machine (never heard of it before though). It is in excellent shape, tape heads are renewed and the device works great so far. My only question is, are there any typical tests, calibrations (whatever) needed before properly using it in a studio or should i just go for it and see how it does?

thanks
weiss
 
You can probably get the manual from Fostex or find it online.  The calibration points for the semi pro machines are "under the hood".  If you don't have a calibration tape you could start recording tones while monitoring from the playback head. If they come back relatively flat then it may be close enough. If they don't it's time to get the tools or call someone.
 
If you are serious about owning and using a reel to reel tape recorder you need to be prepared to undertake basic maintenance. The first thing you need is a tape head demagnetizer. Before doing any tests or running tape through it you should thoroughly demagnetize the the tape heads and tape path.

The next thing to do is to get a replay alignment tape. You use this to set up/calibrate the replay chain. Once that is done you can set up the record chain. I won't go into detail but this involves first setting up the bias for the tape you are using and then adjusting the record EQ. You can probably use a PC soundcard and suitable software to help with this.

Once all this is done you can start recording!! The machine should remain calibrated for quite a while but you should demagnetise weekly and check the replay alignment monthly. It is a bit like owning a care. With careful tuning and maintenance it will give you years of reliable performance.

Cheers

Ian
 
Gold said:
You can probably get the manual from Fostex or find it online.  The calibration points for the semi pro machines are "under the hood".  If you don't have a calibration tape you could start recording tones while monitoring from the playback head. If they come back relatively flat then it may be close enough. If they don't it's time to get the tools or call someone.

Just found it, thanks! :)

ruffrecords said:
If you are serious about owning and using a reel to reel tape recorder you need to be prepared to undertake basic maintenance. The first thing you need is a tape head demagnetizer. Before doing any tests or running tape through it you should thoroughly demagnetize the the tape heads and tape path.
Yes, i am aware of that. Okay i have a demag, no problem.

ruffrecords said:
The next thing to do is to get a replay alignment tape. You use this to set up/calibrate the replay chain. Once that is done you can set up the record chain. I won't go into detail but this involves first setting up the bias for the tape you are using and then adjusting the record EQ. You can probably use a PC soundcard and suitable software to help with this.
You mean for azimuth alignment?
Oh and i think i found something helpful here: http://analogrules.com/alignprint.pdf

ruffrecords said:
Once all this is done you can start recording!! The machine should remain calibrated for quite a while but you should demagnetise weekly and check the replay alignment monthly. It is a bit like owning a care. With careful tuning and maintenance it will give you years of reliable performance.
great! thank you for your answers, you helped a lot ! ;)

weiss
 
weiss said:
You mean for azimuth alignment?


Primarily for level and EQ but it can be used for azimuth too.  You should have one.  They are a bit expensive  but buy new.  An old shedding  calibration  tape is useless.  In the U.S.  you can order them from  JRF Magnetics.  They will sell you the one you need if you call.  A tape stock supplier will probably  Cary them.








 
As a rule I would avoid altering azimuth unless it is way out. Azimuth tends to stay fairly well fixed.  I use a test tap primarily for replay amp set up.

Cheers

ian
 
Gold said:
weiss said:
You mean for azimuth alignment?
Primarily for level and EQ but it can be used for azimuth too.  You should have one.  They are a bit expensive  but buy new.  An old shedding  calibration  tape is useless.  In the U.S.  you can order them from  JRF Magnetics.  They will sell you the one you need if you call.  A tape stock supplier will probably  Cary them.
ruffrecords said:
As a rule I would avoid altering azimuth unless it is way out. Azimuth tends to stay fairly well fixed.  I use a test tap primarily for replay amp set up.
Thanks for clarifying!
So this should do it, right?

weiss
 
The tape you linked to is 15ips only. Check what speeds the Fostex runs at and get a dual speed tape so you can calibrate two speeds. The semi pro machines like the Fostex can't take a lot of level. 250 nW/M may be okay. See if there is an operating level recommendation in the manual. You may want to go with 200 nW/M or 185 nW/M
 
ruffrecords said:
As a rule I would avoid altering azimuth unless it is way out. Azimuth tends to stay fairly well fixed.

Azimuth will vary with bias levels. So you must tweak at least the record head after re-biasing.

Also I find the azimuth to drift with mechanical heating and cooling cycles as well.

I'll check and touch up play and record azimuth on the Ampex ATR100 every time I do an alignment, which is daily in most cases. It's never far off but can usually benefit from a small tweak.

I'll generally use a MRL with wideband noise to get the azimuth in the ballpark and then tweak with a 16kHz tone.

My JH24 is another story, I'll rarely tweak the playback azimuth as it's physically locked in by the adjustment mechanism after many years of use, you can actually feel where it belongs. The record azimuth gets tweaked using the same method described above.

Prosumer grade decks tend not to have alot of adjustments, so you may be stuck with what the designers decided was best.

Mark
 
weiss said:
Indeed, no settings on my machine ;-)

But what is the alignment good for?

Alignments optimize the machine to the tape your using.

A quick perusal of the users guide indicate that you can set BIAS, EQ and LEVEL.

They recommend using Ampex 357 or Scotch 227 tape which I beleive are 320nwb/m tapes.

Mark
 
Biasrocks said:
ruffrecords said:
As a rule I would avoid altering azimuth unless it is way out. Azimuth tends to stay fairly well fixed.
Azimuth will vary with bias levels.
! ? This is very weird. Azimuth is the mechanical angle between the gap axis and the  tape travel (supposed to be horizontal). I don't understand how the bias setting could move the record head; I have never seen that.
 
Also I find the azimuth to drift with mechanical heating and cooling cycles as well.
That is quite possible, although I've never seen a Studer, Ampex, Otari or 3M machine doing that.
In fact the only reason for azimuth  needing to be tweaked is when it is deliberately altered to receive tapes recorded on another machine.
That happened all the time with vinyl mastering, but not that much on multitrack machines.
 
Bias affects the apparent azimuth of recordings as the bias level affects where the magnetisation takes place relative to the plane of the head gap. It's a small effect but it's there

I think the main reason to mention it is because it's possible to bias two (or more) record channels in such a way as to affect the apparent azimuth

If the recorder is biased correctly then there will be no apparent shift in the azimuth

I think adjusting azimuth every time you align is poor practice as you will be chasing a moving target. I was taught that replay azimuth should be set coarsely using a 1 K tone then accurately using higher frequencies up to 10 K, because if you adjust azimuth at 10 K it's easy to find the "wrong" peak of the tone and set the azimuth incorrectly

Record azimuth might as well be set using the sync head playing back a test tape - it's the same head

The only people I've ever seen adjusting azimuth regularly are cutting engineers - they align it as a matter of course

If azimuth drifts with heating & cooling cycles I'd suggest the machine has a poor mechanical construction

Nick Froome
 
pvision said:
Bias affects the apparent azimuth of recordings as the bias level affects where the magnetisation takes place relative to the plane of the head gap. It's a small effect but it's there.
I've never encountered it in 35 years.
I think adjusting azimuth every time you align is poor practice as you will be chasing a moving target.
Checking azimuth is just part of the normal adjustment. On a stereo machine, it is not necessary to adjust the azimuth to find it's out of whack; switching to mono is enough.
Record azimuth might as well be set using the sync head playing back a test tape - it's the same head
Many machines installed in mastering facilities don't have sync replay facility, though.
 
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.

My procedure is to
set Playback azimuth, level and high eq using the test tape.
Load up your recording tape, set bias using a 20khz for 30ips, 10khz for 15ips,
check and adjust record azimuth utilizing full bandwidth noise,
set level, high, low eq
and then fine tune azimuth with a 16khz signal. 

Mark

abbey road d enfer said:
Azimuth will vary with bias levels.
! ? This is very weird. Azimuth is the mechanical angle between the gap axis and the  tape travel (supposed to be horizontal). I don't understand how the bias setting could move the record head; I have never seen that.
 
Biasrocks said:
My procedure is to
set Playback azimuth, level and high eq using the test tape.
Load up your recording tape, set bias using a 20khz for 30ips, 10khz for 15ips,
check and adjust record azimuth utilizing full bandwidth noise,
set level, high, low eq
and then fine tune azimuth with a 16khz signal. 

I don't understand the logic of changing the azimuth of the head to compensate for an error you've introduced by biasing the machine incorrectly - because that's what it sounds like

I've never seen a change in azimuth due to biasing either, but I've never looked for it. I am parroting information fed to me some time ago, but fed to me by people who knew what they were doing

We're probably well off-topic here but I'd recommend the OP to leave the azimuth well alone, clean the tape path within an inch of its life, and demag thoroughly... with the test tape some distance way at the time!

Nick Froome
 
pvision said:
We're probably well off-topic here but I'd recommend the OP to leave the azimuth well alone, clean the tape path within an inch of its life, and demag thoroughly... with the test tape some distance way at the time!
Seems like a good idea  :D Thank you guys
 
My Studer A80 preview decks for cutting all have thumb screws for azimuth adjustment.  I do it for every tape that comes in.
 
pvision said:
I don't understand the logic of changing the azimuth of the head to compensate for an error you've introduced by biasing the machine incorrectly - because that's what it sounds like

I've never seen a change in azimuth due to biasing either, but I've never looked for it. I am parroting information fed to me some time ago, but fed to me by people who knew what they were doing
Nick Froome

I assure you I'm not biasing the machine incorrectly.

I didn't know about the phenomenon until someone who was much wiser in all things analog, pointed it out.

I did my own experiment and sure enough, there it was.

Record azimuth varies with bias.

As I suggested in my previous post, do the test yourself.

I found a discussion here;
http://repforums.prosoundweb.com/index.php?topic=6193.0

And it gets interesting here with a post by Bob Katz;
http://repforums.prosoundweb.com/index.php/topic,6193.msg62021.html#msg62021

To recap the thread, there's an artificial gap that is created which moves around with bias and that varies the azimuth.

Mark
 

Latest posts

Back
Top