[Robert St-Louis]

Hi all,

Quick question on my Nagra 4.2 and IV-S. When I record a steady 1 kHz
signal at 0 dB on the 4.2 (using line-in socket), the output on
playback is higher than when recording, when the potentiometer is left
at the same place. (I record at 0 dB, and playback is +4 dB). From
what I have read, this is normal and expected given the type of tape I
use, and what the machine is likely calibrated for.

However when I do the same with the IV-S, the output on playback is
much lower (-30 or -40 dB), and I have to increase the level of the
potentiometer considerably to bring the level back to 0 dB. This
happens on either of the two channels (when I record the test signal
on each separately).

It's been a while since I've owned a IV-S so I don't know if this is
normal or not. Is it?

If it isn't, do you have a suggestion about what adjustment needs to
be made? (I have the service manual but am not a tech).

Thanks a lot.

--Robert

[Scott Dorsey]

Robert St-Louis wrote:

Quick question on my Nagra 4.2 and IV-S. When I record a steady 1 kHz
signal at 0 dB on the 4.2 (using line-in socket), the output on
playback is higher than when recording, when the potentiometer is left
at the same place. (I record at 0 dB, and playback is +4 dB). From
what I have read, this is normal and expected given the type of tape I
use, and what the machine is likely calibrated for.

Sort of. It's a sign the machine is miscalibrated.

However when I do the same with the IV-S, the output on playback is
much lower (-30 or -40 dB), and I have to increase the level of the
potentiometer considerably to bring the level back to 0 dB. This
happens on either of the two channels (when I record the test signal
on each separately).

This is a sign the machine is even more miscalibrated.

It's been a while since I've owned a IV-S so I don't know if this is
normal or not. Is it?

If it isn't, do you have a suggestion about what adjustment needs to
be made? (I have the service manual but am not a tech).

Do the full alignment, start with the playback azimuth, the playback level,
the playback EQ. Then put on the exact kind of tape you're going to use,
do the record azimuth, the record bias, the record level, and the record EQ.

You're going to have to keep doing the full alignment on a regular basis,
too, so you might as well get the tools to do it now. You will need a cheap
scope, a signal generator (you can use a computer with a test tone generator
program), and the MRL alignment tape for the machine. The MRL tape is the
most expensive of the set.

The Nagra machines don't drift a lot unless they are really bumped around,
but they still drift some and you still need to touch up the alignment
now and then.

If the machine won't calibrate, THEN you have a problem to look into, but
my suspicion is that these have just drifted and probably weren't set up
for the same tape you're using.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Mike Rivers[_2_]]

However when I do the same with the IV-S, the output on playback is
much lower (-30 or -40 dB),

This is a sign the machine is even more miscalibrated.

Or broken, either recording or playback, 30-40 dB seems way to far out
of whack to be within the calibration range. Play a tape on the 4S that
you recorded on the 4.2. If it plays back at near normal level, then the
4s isn't recording correctly. If it plays back at the low level, then
it's not playing back correctly.

[Robert St-Louis]

Thanks a lot Scott, you're very helpful, as usual!
Both machines have likely not been calibrated in a long while, so
you're probably right about the need to go through them thoroughly at
this point.

I recently purchased a handheld signal generator, and handhelp mini-
scope.
http://www.amazon.com/VELLEMAN-HPG1-.../dp/B006YTWMZW
http://www.amazon.com/VELLEMAN-HPS14...589562-5434648

I also have a set of 250 nWb/m MRL tapes that I got with an Ampex 440,
that may or may not do the trick with the Nagras. Unfortunately, last
time I used it, it seems it has started to shed...

Sounds like this is an opportunity to get familiar with the service
manuals and the alignment procedure on these machines, and increase my
knowledge of tape recorder construction and maintenance.

Thanks again!
--Robert

[PStamler]

Everything Scott says is right, but there's one more thing you need to do before you start the alignment procedu clean the bejasus out of the heads. Encrusted crud on the heads (particularly the playback head) can cause severe losses.

Also, before you put your MRL tape on the IV-S, find somebody with a magnetometer and see if any of your heads are magnetized.

Peace,
Paul

[[email protected]]

On Tuesday, January 8, 2013 6:21:58 PM UTC-5, Mike Rivers wrote:
However when I do the same with the IV-S, the output on playback is

much lower (-30 or -40 dB),



This is a sign the machine is even more miscalibrated.



Or broken, either recording or playback, 30-40 dB seems way to far out

of whack to be within the calibration range. Play a tape on the 4S that

you recorded on the 4.2. If it plays back at near normal level, then the

4s isn't recording correctly. If it plays back at the low level, then

it's not playing back correctly.

Mike, good idea about recording and playing back tapes to and from the 4.2 and IV-S and checking playback levels. I'll do so today and report back. Could in fact be something wrong with the playback circuit on the IV-S. Cheers.

[[email protected]]

On Wednesday, January 9, 2013 2:36:07 AM UTC-5, PStamler wrote:
Everything Scott says is right, but there's one more thing you need to do before you start the alignment procedu clean the bejasus out of the heads. Encrusted crud on the heads (particularly the playback head) can cause severe losses.



Also, before you put your MRL tape on the IV-S, find somebody with a magnetometer and see if any of your heads are magnetized.



Peace,

Paul

Thanks Paul. I've been cleaning the tape path with isopropyl before each test run. But it looks like some of my 966 stock is starting to shed (damn!) so I'll pay particular attention to it. My MRL tape was shedding oxide last time I used it, I'll read into baking it to possibly reverse the trend, if that will preserve the tape.

I also demag the tape path before tests (have a couple of demag'ers). Would that not prevent a head from becoming magnetized?

[Mike Rivers[_2_]]

On 1/9/2013 10:44 AM, wrote:

My MRL tape was
shedding oxide last time I used it, I'll read into baking it to
possibly reverse the trend, if that will preserve the tape.

MRL will give you a discount off a new tape, but go ahead and bake the
one you have first. At this point, its use isn't critical, you just want
to see where you stand. And for personal use, you can afford a half a dB
of loss here and there if that happens. I suggested comparing recordings
made on one recorder with the other because I didn't know (or forgot)
that you had an MRL reference tape.

I also demag the tape path before tests (have a couple of demag'ers).
Would that not prevent a head from becoming magnetized?

There's a paper on the MRL web site http://www.mrltapes.com/ about
demagnetization. The short story (and why Paul recommended checking with
a magnetometer) is that if you don't do it right, you can magnetize the
heads when you're trying to demagnetize them.

I think you asked about calibration tapes and reference levels, unless
that was someone else. There's a paper on the MRL web sit called
something like Choosing and Using a Calibration Tape that has a table of
offsets that let you use a tape made at one reference fluxivity to
calibrate to a different reference fluxivity.

[PStamler]

On Wednesday, January 9, 2013 9:44:39 AM UTC-6, wrote:

I also demag the tape path before tests (have a couple of demag'ers). Would that not prevent a head from becoming magnetized?

Not necessarily. Sometimes the head gets magnetized because there's a defective capacitor connecting it to the amplifier. If that's the case, then the head will get re-magnetized every time you turn the machine on.

Peace,
Paul

[[email protected]]

On Wednesday, January 9, 2013 2:48:11 PM UTC-5, PStamler wrote:
On Wednesday, January 9, 2013 9:44:39 AM UTC-6, wrote:

I also demag the tape path before tests (have a couple of demag'ers). Would that not prevent a head from becoming magnetized?

Not necessarily. Sometimes the head gets magnetized because there's a defective capacitor connecting it to the amplifier. If that's the case, then the head will get re-magnetized every time you turn the machine on.

I see, thanks for that important advice Paul. Too bad Nagra didn't include a troubleshooting chart in their service manual (if "x" happens, then look for possible causes "a", "b", or "c") ;-)

Eventually, the various pieces of this 3-D puzzle will start making sense (maybe...). Cheers.

[PenaL]

On 8.1.2013 23:57, Robert St-Louis wrote:
Hi all,

Quick question on my Nagra 4.2 and IV-S. When I record a steady 1 kHz
signal at 0 dB on the 4.2 (using line-in socket), the output on
playback is higher than when recording, when the potentiometer is left
at the same place. (I record at 0 dB, and playback is +4 dB). From
what I have read, this is normal and expected given the type of tape I
use, and what the machine is likely calibrated for.

However when I do the same with the IV-S, the output on playback is
much lower (-30 or -40 dB), and I have to increase the level of the
potentiometer considerably to bring the level back to 0 dB. This
happens on either of the two channels (when I record the test signal
on each separately).

It's been a while since I've owned a IV-S so I don't know if this is
normal or not. Is it?

If it isn't, do you have a suggestion about what adjustment needs to
be made? (I have the service manual but am not a tech).

Thanks a lot.

--Robert

Maybe some part of chain is out of tune or broken. You should have the
test tape for tuning so you notice is the "fail" recording or payback
amp or somewhere else.
Also the tape you use will affect, so you should tune the recorder
according exactly the the tape you use.

It has gone about two decades while I used the Nagras - a lot on these
times. Really nice and lovely tools... :-)

-Pentti

[Scott Dorsey]

wrote:

I also demag the tape path before tests (have a couple of demag'ers). Woul=
d that not prevent a head from becoming magnetized?

Heads don't normally become magnetized... it's actually a very rare event
and most of the time I have seen residual magnetism it's because of someone
degaussing the heads and being sloppy about it.

If you don't have a magnetometer, you're better off not degaussing at all
than doing it all the time, because without the magnetometer you don't know
if you're making things better or inadvertently making them worse.

Head magnetization is a very rare problem, but it does happen.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[[email protected]]

On Wednesday, January 9, 2013 12:35:41 PM UTC-5, Mike Rivers wrote:
MRL will give you a discount off a new tape, but go ahead and bake the
one you have first. At this point, its use isn't critical, you just want
to see where you stand. And for personal use, you can afford a half a dB
of loss here and there if that happens.
There's a paper on the MRL web sit called
something like Choosing and Using a Calibration Tape that has a table of
offsets that let you use a tape made at one reference fluxivity to
calibrate to a different reference fluxivity.

Thanks Mike. I'll try baking that tape at some point (might as well, since it will only get worse using it as it is, shedding away).
Indeed, some very detailed articles on the MRL website, which I've printed off and will spend some time pondering and trying to assimilate as best I can. There's certainly a lot of science and technical detail that went into manufacturing and maintaining good analogue recorders. It's a bit of a shame really, that this technology, which evolved and improved over decades, is now largely discarded by pros and non-pros alike. since digital recording requires comparatively almost no maintenance (other than ensuring the latest firmware patch download!). Still, tape recording is a great hobby and provides much learning opportunities (even though sometimes I feel a bit like an archaeologist...). It would be great for me to get my hands on some Nagra training material (if something like that existed), to walk through setup and calibration operations described in the service manuals...

[William Sommerwerck]

One way to reduce the chance of magnetizing the playback head is to have the
recorder turned on while demagnetizing.

Start moving the demagnetizer toward the head from a foot or so away while
watching the meter. (You'll peg the meter, but don't worry about that.) Then
watch the meter as you slowly move the demagnetizer away. Make sure the meter
reading declines slowly and evenly.

[Mike Rivers[_2_]]

On 1/11/2013 10:39 PM, Robert St-Louis wrote:

I can see your point. However most of the stuff I've read on
demagnetizers state to power off the recorder before using the gizmo.

Well, the demagnetizer creates a strong AC field, just like the magnetic
domains on tape crossing the head gap only much stronger. Although I've
never heard of anyone "burning out" a tape deck by degaussing the heads
with the power on, it can make a mighty loud hum if the output is
connected to anything that you can hear.

The other thing I've come across is people saying the worse thing that
can happen is for the power to go off in the middle of demagnetizing a
tape deck, as if it's going to leave the deck in some kind of limbo-
state.

You've been spending too much time listening to people. If the power to
the demagnetizer goes off when it's close to the head, that will cause
the magnetic field to collapse suddenly, which can indeed magnetize the
heads. This is why they tell you to move the demagnetizer away from the
headds slowly before turning it off - so its magnetic field decays slowly.

Some folks have said they plug the demagnetizer in a UPS
before starting the job... Mysterious stuff, this demagnetizing!

I think that's going a little bit too far. Who are these folks?

Maybe Scott is right: just don't do it...

If the heads are magnetized, then they should be demagnetized, whether
you do it or you get someone who knows what he's doing to do - and show
you how so you'll know the next time. The thing is that unless the heads
are very badly demagnetized and you notice that highs are getting erased
from every tape you play (which is permanent damage to the recording) or
you have a sensitive enough magnetometer (the one that comes with the
Han-D-Mag isnt, really), then you don't know how magnetized the heads
are. Doesn't that scare the **** out of you?

However, there are enough good reasons why heads that aren't magnetized
won't get magnetized under normal operating conditions. Pros who know
how can, and often do, routinely run a demagnetizer over the heads. But
they know how to do it in a way that it will do no harm.

[William Sommerwerck]

"Robert St-Louis" wrote in message
...
On Jan 10, 1:58 pm, "William Sommerwerck"
wrote:

One way to reduce the chance of magnetizing the playback head is to have
the recorder turned on while demagnetizing.

Start moving the demagnetizer toward the head from a foot or so away while
watching the meter. (You'll peg the meter, but don't worry about that.)
Then
watch the meter as you slowly move the demagnetizer away. Make sure the
meter reading declines slowly and evenly.

I can see your point. However most of the stuff I've read on
demagnetizers state to power off the recorder before using the gizmo.
The other thing I've come across is people saying the worse thing that
can happen is for the power to go off in the middle of demagnetizing a
tape deck, as if it's going to leave the deck in some kind of limbo-
state. Something about that being destructive to the electronics in
some way. Some folks have said they plug the demagnetizer in a UPS
before starting the job... Mysterious stuff, this demagnetizing!
Maybe Scott is right: just don't do it...

I've demagnetized heads with the power on, on both cassette and open-reel
decks, and have not damaged their electronics.

If the demagnetizer is shut off during the demagnetizing process, the field
abruptly collapses, which usually magnetizes the head!

Connecting the demagnetizer to a UPS does little good, because power loss
occurs when your finger slips on the power switch -- not because you suddenly
have a power outage.

There's nothing mysterious whatever about demagnetizing.

Scott is broadly correct -- heads rarely get magnetized, and therefore
probably don't need demagnetization. Regardless... the low output on one of
Nagras is almost certainly not due to a magnetized playback head. Either the
deck is badly miscalibrated, or there's a lot of shmutz on the playback head.
They can get so dirty that you have to scrub them vigorously -- under a bright
light -- to find and get it all off.

[Scott Dorsey]

Robert St-Louis wrote:

I can see your point. However most of the stuff I've read on
demagnetizers state to power off the recorder before using the gizmo.

They're worried about you pegging your VU meters and damaging them,
etc.

The other thing I've come across is people saying the worse thing that
can happen is for the power to go off in the middle of demagnetizing a
tape deck, as if it's going to leave the deck in some kind of limbo-
state. Something about that being destructive to the electronics in
some way.

It's not a limbo state, it's when you turn the thing on or off it creates
a brief static magnetic field. If you unplug the thing while using it
instead of slowly reducing the AC field, you get a big spike that magnetizes
things.

some folks have said they plug the demagnetizer in a UPS
before starting the job... Mysterious stuff, this demagnetizing!

It's not mysterious, it's just a big alternating magnetic field.

Maybe Scott is right: just don't do it...

Or take it to someone who has the complete Han-D-Mag kit with the magnetometer
and the degausser both. Check it, demag it, then check it again. If there is
any mystery, it goes away when you take accurate measurements.

You might be able to find used magnetometers on ebay these days; they used to
be pretty expensive.

Still, degaussing is the least of your worries. Get the equipment and the
skills to do the regular alignment first.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Mike Rivers[_2_]]

On 1/12/2013 8:46 AM, Scott Dorsey wrote:

The other thing I've come across is people saying the worse thing that
can happen is for the power to go off in the middle of demagnetizing a
tape deck, as if it's going to leave the deck in some kind of limbo-
state.

It's not a limbo state, it's when you turn the thing on or off it creates
a brief static magnetic field.

He's probably thinking about the Great Electromagnetic Pulse that's
going to brind down all the satellites, launch all the guided missles,
and cause all the planes in the sky to crash, to say nothing of all the
cell phones that won't access Twitter any more. l)

--
For a good time, call http://mikeriversaudio.wordpress.com