Biasing Techniques

[soupking]

Hi GS,

I have started working with my new used JH24 tape machine. It's really cool. Calibrating, is in my opinion, best done on the buddy system but it's really not as hard as people have made it out to sound, at least so far.

However, I've read a lot on GS about biasing. My tech said to over bias levels by 1.5 db. Sometimes the high EQ will only go down to +1 instead of 0 db which I think is kind of strange.

Anyway, I've been calibrating at 15ips on a 16-track head. So we're going for fat currently. I was wondering if anybody had any input on biasing.

Most precisely, I'm trying to figure out why my high-EQ seems to get limited to the ability to go down further, like what could I be doing wrong? Because it only goes down to 1db makes the noise floor a little higher...I think.

That and is biasing different when running at 30 ips? Or using a 24-track head stack instead?

Thanks in advance for any feedback.

[dbbubba]

Yes, Soupking.... each tape speed requires a different bias level.
The record head gap determines the bias level as well.
I believe that all JH-24s and most MCI decks have a 0.25 mil gap.
This applies to 24 track, 16 track, 8 track, 4 track, 2 track and mono head stacks.

OK.... I just pulled out my handy dandy, laminated 3M "Recommended Bias Settings" card and my JH-24 manual...

The 3M recommendations are:

996 (close to Ampex/Quantegy 499): 4 db over overbias @ 10Khz at 15 ips
250, 226, 227 (close to Ampex 456): 3 db of over bias @ 10Khz at 15 ips

For 30 ips the overbias level is halved.
2 db overbias for 996
1.5 db overbias for 250, 226 and 227

The MCI JH24 manual (all were printed pre 499, GP9 and 499) recommends these settings:

Ampex 456 15 ips: 4.5 db overbias @ 10K 30 ips: 1.75 db overbias @ 10Khz
Scotch 250 15 ips: 4 db overbias @ 10Khz 30 ips: 2.5 db overbias @ 10Khz
Scotch 226 15 ips: 4 db overbias @ 10Khz 30 ips: 1.5 db overbias @ 10Khz
AGFA 468 15 ips: 4 db overbias @ 10Khz 30 ips: 3 db overbias @ 10Khz

If you can't get the meter to go far enough back past the zero mark, then something is not right with the machine's set up.
You should be able to go quite a few dbs PAST the overbias level.

Get out your JH-24 manual do a full calibration starting at the REPRO as a minimum.
If you are brave and smart enough enough to do it correctly you should check the WRAP and AZIMUTH.
In fact, I'd set the TENSION as well.
Tension can greatly effect EQ and can cause many headaches if set wrong.

This stuff is all in the manual and it isn't THAT hard to do.

When you get a tape deck you might as well assume that whoever owned it before you screwed everything up.
At a minimum it isn't going to be calibrated for the set up you are running.
I always start over from the beginning of the calibration process.
In fact, the output of my deck was low by a db.
When it was calibrated properly, a 0db signal only came up to +3db instead of +4db.
I would never have known unless I started at the beginning.
I got my deck from an old friend who I THOUGHT knew how to align a tape machine.
He did lot's of 2" to ProTools transfers, so he may have set it low.
Still, I would have never known had I just trusted the deck's meters.

Let me know if you need any more help.

Hey... I was out in L.A. (Anaheim) from the 29th until the 11th, but I was WAYYYY to busy to visit. Sorry....
I drove up and down the 5 and the 101 to and from Hollywood and Motrose twice.
I thought about you and a few other GS guys.

[soupking]

Hi DB,

That's great info. I think we checked the azimuth. My tech sounded like he wasn't to concerned about by the way it was performing. We haven't discussed tension though, so that's something I'll mention to him as well.

Heh, it looks like that for 16-track 15ips 1.5 db overbias isn't enough. That's probably why I thought the noise floor was a bit high.

The tape we'll be using is either the RMG tape which is supposed to be manufactured along BASF standards, and ATR tape which I don't know anything about. I'm not sure how that would compare to your chart. ?

Also, have you ever run into the situation where the high EQ won't go any lower, even if the bias is re-set? Trying to figure out what that could be.

If any of that behavior rings a bell, I'd be all ears.

Thanks DB!
-soup

Originally Posted by dbbubba

Yes, Soupking.... each tape speed requires a different bias level.
The record head gap determines the bias level as well.
I believe that all JH-24s and most MCI decks have a 0.25 mil gap.
This applies to 24 track, 16 track, 8 track, 4 track, 2 track and mono head stacks.

OK.... I just pulled out my handy dandy, laminated 3M "Recommended Bias Settings" card and my JH-24 manual...

The 3M recommendations are:

996 (close to Ampex/Quantegy 499): 4 db over overbias @ 10Khz at 15 ips
250, 226, 227 (close to Ampex 456): 3 db of over bias @ 10Khz at 15 ips

For 30 ips the overbias level is halved.
2 db overbias for 996
1.5 db overbias for 250, 226 and 227

The MCI JH24 manual (all were printed pre 499, GP9 and 499) recommends these settings:

Ampex 456 15 ips: 4.5 db overbias @ 10K 30 ips: 1.75 db overbias @ 10Khz
Scotch 250 15 ips: 4 db overbias @ 10Khz 30 ips: 2.5 db overbias @ 10Khz
Scotch 226 15 ips: 4 db overbias @ 10Khz 30 ips: 1.5 db overbias @ 10Khz
AGFA 468 15 ips: 4 db overbias @ 10Khz 30 ips: 3 db overbias @ 10Khz

If you can't get the meter to go far enough back past the zero mark, then something is not right with the machine's set up.
You should be able to go quite a few dbs PAST the overbias level.

Get out your JH-24 manual do a full calibration starting at the REPRO as a minimum.
If you are brave and smart enough enough to do it correctly you should check the WRAP and AZIMUTH.
In fact, I'd set the TENSION as well.
Tension can greatly effect EQ and can cause many headaches if set wrong.

This stuff is all in the manual and it isn't THAT hard to do.

When you get a tape deck you might as well assume that whoever owned it before you screwed everything up.
At a minimum it isn't going to be calibrated for the set up you are running.
I always start over from the beginning of the calibration process.
In fact, the output of my deck was low by a db.
When it was calibrated properly, a 0db signal only came up to +3db instead of +4db.
I would never have known unless I started at the beginning.
I got my deck from an old friend who I THOUGHT knew how to align a tape machine.
He did lot's of 2" to ProTools transfers, so he may have set it low.
Still, I would have never known had I just trusted the deck's meters.

Let me know if you need any more help.

Hey... I was out in L.A. (Anaheim) from the 29th until the 11th, but I was WAYYYY to busy to visit. Sorry....
I drove up and down the 5 and the 101 to and from Hollywood and Motrose twice.
I thought about you and a few other GS guys.

[ronzie]

Originally Posted by soupking

Hi GS,

I have started working with my new used JH24 tape machine. It's really cool. Calibrating, is in my opinion, best done on the buddy system but it's really not as hard as people have made it out to sound, at least so far.

However, I've read a lot on GS about biasing. My tech said to over bias levels by 1.5 db. Sometimes the high EQ will only go down to +1 instead of 0 db which I think is kind of strange.

Anyway, I've been calibrating at 15ips on a 16-track head. So we're going for fat currently. I was wondering if anybody had any input on biasing.

Most precisely, I'm trying to figure out why my high-EQ seems to get limited to the ability to go down further, like what could I be doing wrong? Because it only goes down to 1db makes the noise floor a little higher...I think.

That and is biasing different when running at 30 ips? Or using a 24-track head stack instead?

Thanks in advance for any feedback.

Soupy, what kind of condition is the cal tape in?

Danny has it right about the wrap & azimuth. It needs to be checked among other things (depth of erasure etc.) or all bets are off. An open head gap i.e. worn heads can give a machine the problem your speaking of. That's not to say YOUR heads need a relap.

Lastly, every machine has it's own quirks as does every piece of tape and alignment scheme. Trimming the pots so everything is @ unity is only the beginning!

Ron Allaire, Skyline

P.S. If you haven't already, download the treatise on the MRL website. It's filled with gold.

[dbbubba]

I think that RMG would be close to the AGFA settings I mentioned.
You might need to research it.
I am sure that RMG has it somewhere handy.

The ATR tape is like 499 isn't it?
It is the formula of 456, 499 or GP9.
Mike Spitz is an ex Ampex guy, so you can bet that his tape mimics Ampex tape!

You should be able to crank the BIAS pot and get the needle to go WAYYY past -4db.
After a point it starts to saturate the tape and the level quits dropping.
It is increasing actually, but the level falls as the overbias takes effect.

You could check to see that the master bias level is correct.
Setting this requires an extender board, but I've done it without one.
You have to use alligator clips to get to the test points if you don't have one.

HERE'S SOMETHING INTERESTING TO LOOK AT AS WELL...

Notice that when simultaneously recording and reproducing a 10Khz tone there is always some "bounce" or global movement of the meters.
This is due to tension changes and the tape moving up and down on the heads.
If you will notice, the movement settles in as you reach the optimal bias point.
The meters quit moving around as much when the bias increases into overbias land.
I am not sure how noticeable this is at 15 ips (I rarely ran 15 ips on my JH24) but it is quite noticeable at 30 ips.
I learned this from an analog guru named Tony Arnold who is one of Europe's Ampex experts.
He worked at my studio in '86 and I learned so much from him.

[Bob Olhsson]

The manuals and 3M cards will get you in the ballpark but there's really no substitute I've ever found for setting bias with a distortion meter. All tape varies from batch to batch and different record head gaps require pretty different settings.

[soupking]

Hi Ron,

I can't remember if we scoped the azimuth or not, but I'll run that by my tech when I get a chance.

He can fix that stuff, but I'm far untechnical to understand waveform measurements. I pretty much just cal the pots and read the meters.

The heads are in great shape, that is to say, at least cosmetically. a little wear, but they've got a long way to go.

I'll check out the MRL treatise as well.

Thanks!

Originally Posted by ronzie

Soupy, what kind of condition is the cal tape in?

Danny has it right about the wrap & azimuth. It needs to be checked among other things (depth of erasure etc.) or all bets are off. An open head gap i.e. worn heads can give a machine the problem your speaking of. That's not to say YOUR heads need a relap.

Lastly, every machine has it's own quirks as does every piece of tape and alignment scheme. Trimming the pots so everything is @ unity is only the beginning!

Ron Allaire, Skyline

P.S. If you haven't already, download the treatise on the MRL website. It's filled with gold.

[dbbubba]

Originally Posted by Bob Olhsson

The manuals and 3M cards will get you in the ballpark but there's really no substitute I've ever found for setting bias with a distortion meter. All tape varies from batch to batch and different record head gaps require pretty different settings.

Tape batches DO/DID vary quite a bit don't/didn't they?

Still, I never saw them off by more than a db back in the heavy production days of Ampex or 3M.
Yes... a db is "a lot" but month to months batches were usually within a half db in most cases.
I can't recall a case of ever thinking, "Hey! What the hell is wrong here?"
I'd notice it when doing a calibration.

These days... who knows?

How well IS it controlled these days?

[soupking]

Cool, I'll plan on figuring that

RMG = AGFA
ATR = AMPEX

I'll also bring up the master bias. We cal'ed the master oscillator because we were having full erase troubles. It turned out to be the culprit. I'm so lucky to have a tech or would be screwed.

Is the master oscillator what you're talking about or is the master bias another additional tower of some kind?

The BIAS can go way low, it's the high EQ that tends to get stuck around .5 db and won't turn any lower for some reason. Its non-responsive. really strange. I wonder if the fact that I'm BIASing the machine to -15 rather than -4 at 15 ips has anything to do with it's non-responsiveness.

I've got to check that tension thing too.

Originally Posted by dbbubba

I think that RMG would be close to the AGFA settings I mentioned.
You might need to research it.
I am sure that RMG has it somewhere handy.

The ATR tape is like 499 isn't it?
It is the formula of 456, 499 or GP9.
Mike Spitz is an ex Ampex guy, so you can bet that his tape mimics Ampex tape!

You should be able to crank the BIAS pot and get the needle to go WAYYY past -4db.
After a point it starts to saturate the tape and the level quits dropping.
It is increasing actually, but the level falls as the overbias takes effect.

You could check to see that the master bias level is correct.
Setting this requires an extender board, but I've done it without one.
You have to use alligator clips to get to the test points if you don't have one.

HERE'S SOMETHING INTERESTING TO LOOK AT AS WELL...

Notice that when simultaneously recording and reproducing a 10Khz tone there is always some "bounce" or global movement of the meters.
This is due to tension changes and the tape moving up and down on the heads.
If you will notice, the movement settles in as you reach the optimal bias point.
The meters quit moving around as much when the bias increases into overbias land.
I am not sure how noticeable this is at 15 ips (I rarely ran 15 ips on my JH24) but it is quite noticeable at 30 ips.
I learned this from an analog guru named Tony Arnold who is one of Europe's Ampex experts.
He worked at my studio in '86 and I learned so much from him.

[dbbubba]

Maybe you are describing things weird, but something sounds wrong.

The "not getting full erasure" thing scares me a bit.
Why was this?
This rarely needed re-adjusting on any tape machine I have ever encountered.
Follow the manual to set it and it should be OK in the end.

You are overbiasing 15 dbs?

It should be close 4 db of over bias.
It should go up and then fall 4 dbs BELOW 0db.
If you have it set up with 15 db of overbias then God only knows how the HI FREQ. pot will adjust!

If it is overbiased too far then the HI FREQ. adjust will only increase until the saturation point prevents loading the tape with any more signal.
The high end would sound pretty crunchy, fizzy and spitty, too!
This is why you have to set your levels at -10db when calibrating for 7.5 ips.
A 10Khz signal at 0db overloads tape at speeds slower than 15 ips.

You can actually tailor the decks EQ curve with the bias settings.
You can play with the bias and use a sweep generator to get the freq. response quite flat.
It is often at the expense of a slightly higher noise floor.
Theoretically, this is what the manufacturer's recommended settings take into consideration along with THD.
Bias was invented to record flat on tape with as low a THD as possible.

You know... I have seen a lot of decks screwed up by people who were clueless knob twidlers (I'm not referring to you SoupKing.)

You might try "zeroing out" the pots.
You turn them ALL counter-clockwise twenty turns (to assure they are at the end of their travel) and then turn them back 10 turns.
This is the theoretical starting point for the pot's adjustment.
It doesn't take into consideration the aged components in the machine, but it is a close starting point.
You have to re-align the ENTIRE machine after doing this, but it helps to have a starting point.
I have done this when I encountered a deck where someone had screwed everything up beyond anything that made sense.
It is a "let's just start from scratch" thing.

BTW... if you can't get any more level out of the HI FREQ. adjusting pot you are probably at the end of the pot's travel.
You should be able to hear the pot clicking when you turn it up beyond it's limit.
The same applies to full off on the pot as well.

[soupking]

!! Sorry DB, typo.

Meant -1.5 db overbiased.

It wasn't full erasing due to a master oscillator issue. My tech got out the oscilliscope and brought it back to whatever microseconds it was. I forget the number, but now it's erasing just fine.

The 20 full clockwise and then 10 back is a good idea. At least at that point I have a clue where the card is dialed in.

Right now it feels kind of like the high EQ is a crap shoot. Come to think of it, we ran into non-response issues with the TASCAM 48. Except with the 48 it was completely un-responsive. With the JH24, the high-EQ pots responds, it just anchors at 1 db or so and then won't go any lower. We re-set the bias over by -1.5 and it still wouldn't budge. I'm hoping my 3.5 db underbiasing misfire from calibrating at 15 ips is the reason.

Right now the high-end does sound a little crunchy. Great way of explaining it. I was tracking drums thinking, it sounds...good, but for some reason I feel unsatisfied. That could just be my perfectionism and not the machine. Logic would lead to that since I don't think I've overbiased it enough at -1.5, so I'll just have to get the pic out and see what's what. Right now it just seems a little too noisy which would be a symptom of underbiasing, or at least that's my understanding.

Since I just kept turning and turning and turning the high EQ pot without any needle response once it hits 1 db or so, it's hard to say if I'm hitting the balance. I was very careful to notice if it was fully unraveled, but after it just sat there after like half a dozen turns I for the most part just stopped figuring that was as good as it was going to get.

Overall, 16 track 2" recording is really cool, we're really excited to lay down tracks. Once I get over this hill, I think we'll be smooth sailing.

Originally Posted by dbbubba

Maybe you are describing things weird, but something sounds wrong.

-15?

It should be close -4 db of over bias.
If you have it set up with 15 db of overbias then God only knows how the HI FREQ. pot will adjust!

If it is overbiased too far then the HI FREQ. adjust will only increase until the saturation point prevents loading the tape with any more signal.
The high end would sound pretty crunchy, fizzy and spitty, too!
This is why you have to set your levels at -10db when calibrating for 7.5 ips.
A 10Khz signal at 0db overloads tape at speeds slower than 15 ips.

You can actually tailor the decks EQ curve with the bias settings.
You can play with the bias and use a sweep generator to get the freq. response quite flat.
It is often at the expense of a slightly higher noise floor.
Theoretically, this is what the manufacturer's recommended settings take into consideration along with THD.
Bias was invented to record flat on tape with as low a THD as possible.

You know... I have seen a lot of decks screwed up by people who were clueless knob twidlers (I'm not referring to you SoupKing.)

You might try "zeroing out" the pots.
You turn them ALL counter-clockwise twenty turns (to assure they are at the end of their travel) and then turn them back 10 turns.
This is the theoretical starting point for the pot's adjustment.
It doesn't take into consideration the aged components in the machine, but it is a close starting point.
You have to re-align the ENTIRE machine after doing this, but it helps to have a starting point.
I have done this when I encountered a deck where someone had screwed everything up beyond anything that made sense.
It is a "let's just start from scratch" thing.

BTW... if you can't get any more level out of the HI FREQ. adjusting pot you are probably at the end of the pot's travel.
You should be able to hear the pot clicking when you turn it up beyond it's limit.
The same applies to full off on the pot as well.

[dbbubba]

Contact my friend Brian McCurry at Platinum Audio Rentals in Hollywood and see who he recommends as a good tape machine tech.
Have someone set the deck up properly.
I'll bet that it is out of whack somewhere.
I'm sure your tech is decent, but get a second opinon or have him do a calibration/alignment.

Platinum Audio Rentals - Contact Us

[Brent Hahn]

Originally Posted by soupking

<< My tech said to over bias levels by 1.5 db. Sometimes the high EQ will only go down to +1 instead of 0 db which I think is kind of strange.

Just double checking... you know "overbias by 1.5 db" doesn't mean to adjust the bias until your meters read +1.5db, right?

[Beech]

If I could interject here, on behalf of any casual readers - a couple of points that may not have been clear.

When setting the bias it is best to drop the Hi Freq tone back from 0vu at the oscillator, otherwise it will probably saturate the tape, thus giving a false reading. If I remember correctly, I used to use somewhere between -4 and -7vu as a starting point, depending on the machine.

Then, wind the channel bias pot all the way anticlockwise. Now wind it clockwise until it peaks. Then, keep winding clockwise. The meter will start decreasing. Keep going until you find the level you are looking for (in soapking's case, about -4db).

Just wanted to clear that up!

[Brent Hahn]

Originally Posted by Beech

... wind the channel bias pot all the way anticlockwise. Now wind it clockwise until it peaks. Then, keep winding clockwise. The meter will start decreasing. Keep going until you find the level you are looking for ....

... which, in Mr. King's case, is 1.5 db below the highest reading (which most likely will be slightly different on every channel).

[dbbubba]

Yeah... I was assuming that this was obvious stuff.

You know... I have been a 30 ips analog guy over the years and forgot that you can saturate the tape with 10K @ 0db wehen running at 15 ips on some machines and tape formulations.
The JH-24 manual doesn't tell you to set the 10K tone lower than 0 db for 15 ips.
Still, it isn't a bad idea to lower the 10K signal.

I have largely dealt with MCIs, Ampex AG-440s, ATR-102s and 351s running 456 and 499 and they all handle the 10K without saturation.

7.5 ips is another matter.
You definitely need to do you bias and high freq. cal at -10db at 7.5, 3.75 and slower.

[Brent Hahn]

Originally Posted by dbbubba

The JH-24 manual doesn't tell you to set the 10K tone lower than 0 db for 15 ips.

At that time, +3 (250 nW/m) was still considered a hot operating level. Nowadays, in the non-Dolby world, +6 is pretty normal. Hitting the tape that hard, you pretty much have to dial back your 10k oscillator before you bias. If you don't, self-erasure will mess with you. And if you have a self-erasure issue, you also have to crank the high-end record EQ (which, in an MCI machine, is as nasty as the EQ in their consoles) to make up for it. A compound error, in other words.

[dbbubba]

I also didn't make clear that the overbias level should cause the VU meter's needle to fall 4 db from the highest reading when turning clockwise.

Once I find the bias peak setting I generally tweak the freq. generator so that it is at 0db on the VU which makes finding the overbias amount easier.
In other words, the meter will drop however many dbs are called for from zero as the bias pot is cranked.

[dbbubba]

Originally Posted by Brent Hahn

At that time, +3 (250 nW/m) was still considered a hot operating level. Nowadays, in the non-Dolby world, +6 is pretty normal. Hitting the tape that hard, you pretty much have to dial back your 10k oscillator before you bias. If you don't, self-erasure will mess with you. And if you have a self-erasure issue, you also have to crank the high-end record EQ (which, in an MCI machine, is as nasty as the EQ in their consoles) to make up for it. A compound error, in other words.

Are you speaking from experience or hearsay?

I had a brand new JH-24 in '81 and another '83 issue JH-24 from '86 until '93 all had the same verbage in the manual describing bias and EQ settings.
My current JH-24 was manufactured after Sony bought MCI in 1988.
The manual doesn't mention +9 tapes because they were not introduced yet.

456 was introduced in the early part of the '80s and it was a +6 tape (hence the 6 at the end of the number.)
+6 was pretty well becoming the standard operating level by the early '80s except for some applications that required archival and matching with established house standards.

JH-24s came out in '80/'81 and the manuals were up-dated.

456 will handle a 10Khz signal at 0db during calibration.
I have done it for years and I have sat and learned the details of analog tape decks from some of the greats in the biz.

[ITJ]

Originally Posted by Bob Olhsson

The manuals and 3M cards will get you in the ballpark but there's really no substitute I've ever found for setting bias with a distortion meter. All tape varies from batch to batch and different record head gaps require pretty different settings.

Excellent point.

I usually turn down the record eq. Feed a 19Hz tone, while listening over bias for minimum asperity. 19Hz works for 30 IPS. Try 10Hz for 15IPS.

[Paul Hammond]

Originally Posted by ITJ

Excellent point.

I usually turn down the record eq. Feed a 19Hz tone, while listening over bias for minimum asperity. 19Hz works for 30 IPS. Try 10Hz for 15IPS.

I believe you mean 19 khz and 10 khz no? 10hz falls off pretty hard on all my analog decks regardless of speed. I have seen and countered the problems mentioned by soupking. Sounds like not enough overbias at 15 ips and possibly lack of tape tension which def affects the high freq. playback and record eqs. If you do the poor mans tape tension adjust and flange the supply reel with your hand while metering 10khz in record/repro you will see a substantial rise in amplitude if the tension/wrap is off.

I use a Tektronix noise and distortion analyzer to set the bias occasionally. Recently though I've had to use multiple types of tape on a
machine through the course of one session and couldn't recal. Since the machine was set up properly (Studer A827) the differences were negligible. Cheers, PH

[soupking]

Originally Posted by Brent Hahn

Just double checking... you know "overbias by 1.5 db" doesn't mean to adjust the bias until your meters read +1.5db, right?

Yes, correct. It means pushing forward 1.5 db past the peak bias point.

Thanks for double checking though.

[soupking]

Originally Posted by dbbubba

Contact my friend Brian McCurry at Platinum Audio Rentals in Hollywood and see who he recommends as a good tape machine tech.
Have someone set the deck up properly.
I'll bet that it is out of whack somewhere.
I'm sure your tech is decent, but get a second opinon or have him do a calibration/alignment.

Platinum Audio Rentals - Contact Us

Cool, will do if problems persist.

Thanks DB!

[soupking]

Originally Posted by dbbubba

The JH-24 manual doesn't tell you to set the 10K tone lower than 0 db for 15 ips.
Still, it isn't a bad idea to lower the 10K signal.

We've been calibrating everything to 0db, and biasing to -1.5 below peak. It sounds overall like that's the 30 ips standard, but the 15 ips to 16 track might differ a bit. I'll probably try -4 bias with +6 standard input, and do everything to 0db without any further documentation. I haven't had time to check the MRL site yet.

If there's any alternative recommended db levels that anybody would recommend for 15 ips cal, I'm all ears.

Thanks everybody!

[dbbubba]

I have used the same system for years and I was really taught the intricacies of tape deck calibration by Tony Arnold (research his name if you need to.)

I don't even crack a manual and my tapes have been in rooms all over the U.S., every broadcast outlet, dub room and many VERY prestigious mastering houses without as much as a question.
I take that back... I once sent a record (CD) off to a Hollywood mastering house and the mastering engineer pointed out that I didn't have the SHELF ADJ. on one side of my Ampex ATR-102 set like the other side. It was off by about a DB and a half.
I had just got the ATR-102 and didn't have a manual.
THAT guy was sharp!
Great ears!

After doing LOT'S of alignments since 1975 I know how it's done.

[ITJ]

Originally Posted by Paul Hammond

I believe you mean 19 khz and 10 khz no?

19HZ ...... Yes.

[MarkRB]

Originally Posted by Bob Olhsson

The manuals and 3M cards will get you in the ballpark but there's really no substitute I've ever found for setting bias with a distortion meter. All tape varies from batch to batch and different record head gaps require pretty different settings.

Sorry for slight off-topic tangent.

Hi Bob. What is a distortion meter? How does it work?

I've never seen one. I am having to become more tape savvy as all the good tape tech's in this town retire. I'm not bad at calibrating a machine these days but there are a few things I used to leave to the tech guys, in fear of breaking something. (Like zenith adjustments!!).

In the spirit of reciprocation:
Good trick I learnt recently; play back a 10kHz tone and gently push the tape onto the repro head with your finger. If the level raises by more than a 1.5dB then your heads are probably in need of relapping. I presume the same is true of the record head.

[dbbubba]

Originally Posted by MarkRB

:
Good trick I learnt recently; play back a 10kHz tone and gently push the tape onto the repro head with your finger. If the level raises by more than a 1.5dB then your heads are probably in need of relapping. I presume the same is true of the record head.

It could also mean that the WRAP is off.
...or the TENSION is wrong.

[Paul Hammond]

Originally Posted by ITJ

19HZ ...... Yes.

Wow,

Thats one I've never heard of. My Tektronix noise and distortion meter nulls whatever frequency you feed to it and measures the noise floor and distortion regardless. Some of the analog circuitry in question will distort sooner at higher levels at 10hz or 19hz. From all I was taught by old school engineers, the most important bands to consider are in the vocal range, ie: 3-5k. Most transformers in older gear don't pass 10hz very well and you will be dealing with saturation at optimum working levels. That will skew your measurements of actual tape distortions. When I used to use the peak bias method at say 700hz, I would then double check it with the noise and distortion method and find that I was within a tenth of a db of the most optimum bias setting. Getting all tweaky bargained me absolutely nothing in real world terms. But hey, everyones priorities are different. Same goes for every machine I've ever worked on. Good luck with your quest for analog excellence! PH

[Brent Hahn]

Originally Posted by dbbubba

Are you speaking from experience or hearsay?

From '79 to the late '80's I worked in MCI rooms that ran 15 ips +3/Dolby by day (jingles & such) and 30 ips +6/NNR by night, so I spent a fair amount of time both aligning those machines and hearing how they behaved. I always felt that those machines really sounded, for lack of a better word, "stressed" at +6 or higher, especially in the top end. And when used with MCI consoles (which they were), an airy top end was pretty much impossible to achieve.

On the other hand, I freelanced in several Neve/Studer rooms, plus one notable API/Studer room, where none of these issues existed. Full disclosure: as a "guest," I rarely aligned those machines.