Biasing Techniques

[Jim Williams]

Originally Posted by ktf

Simple tension test - While recording 10k, increase tension on the supply reel with your hand while watching the meters. Meters should be stablish.

A tentelometer should be used to set tension, otherwise irregular head wear may result. I had best results with wobbly 10k tones by replacing bearings in the guides and motors with grade 9 aerospace grade bearings. That trick makes the bearing grade 5 MCI sit as stable as a Studer A800.

Jim Williams
Audio Upgrades

[MarkRB]

Originally Posted by Bob Olhsson

What you are really doing with bias is moving the print point to where there is the stablest mechanical spot in the tape path after the record head.

I wish I understood this post!! Please elaborate if you can Bob?

Loads of great stuff on this thread. I guess I'm still a "driver" more than a "mechanic".

I had a quick look at that Audio Precision beast Jon mentioned, possibly out of my league, . Are there any THD analysers that cost less than a car, bearing in mind I've relied on ears previously?

[AnalogBrain]

Hey Mark...

This is the THD analyzer I use. I think I bought it for about $550?

Minilyzer ML1

I am just not sure if I can use it in the way Jim Williams describes.

It is a GREAT tool however.

-Neil

[MarkRB]

That looks really useful. Thanks AB!

[DannyMac]

I feel lazy using my 827 (memory/auto-align)

[Jim Williams]

Those can be frustrating when you want a precise alignment. That Sony APR24 had auto memory as well, it used m-dacs for trim adjustments. It would move in 1/4 db increments. As usual, the AP told me to get in between settings, you can't so it's a compromise. That machine cannot be precisly aligned.

Jim Williams
Audio Upgrades

[dbbubba]

Originally Posted by Bob Olhsson

What you are really doing with bias is moving the print point to where there is the stablest mechanical spot in the tape path after the record head.

Wow!
I never thought about it that way, but I guess that is what it is doing isn't it?

As far as the cards being wrong (and I guess the MCI manual is wrong as well.)
You have to trust something and in today's internet world there is always someone that disputes about every point.
There is always some secret "better way" to do things.
There is a way to mod and "improve" everything.
I don't specifically mean to include you in this statement Jim, so don't get mad.
I question the virtue of striking off on one's own too much.

I just prefer to stay "stock" and follow the manufacturer's specs because of these two reasons:
#1) there was/is a hell of a lot more un-modded equipment out there that is performing just fine for a lot of folks
#2) the manufactures built and invested WAYYY more time that most experimenters

I'm just sayin'

[dbbubba]

Originally Posted by Jim Williams

Those can be frustrating when you want a precise alignment. That Sony APR24 had auto memory as well, it used m-dacs for trim adjustments. It would move in 1/4 db increments. As usual, the AP told me to get in between settings, you can't so it's a compromise. That machine cannot be precisly aligned.

Jim Williams
Audio Upgrades

Don't let Steve Sadler see you post this!

Them's fightin' words!

[Sigma]

Originally Posted by Jim Williams

Those can be frustrating when you want a precise alignment. That Sony APR24 had auto memory as well, it used m-dacs for trim adjustments. It would move in 1/4 db increments. As usual, the AP told me to get in between settings, you can't so it's a compromise. That machine cannot be precisly aligned.

Jim Williams
Audio Upgrades

why did you have to bring up that machine [LOL] i still have nightmares of having to check every punchout because of the slow input to tape switching ..


and the tiny buttons on the remote ...and.......

clients always looked at you like a missed the punch and you had to show them and explain..that machine is on my boat anchor list

[dbbubba]

Originally Posted by Sigma

why did you have to bring up that machine [LOL] i still have nightmares of having to check every punchout because of the slow input to tape switching ..


and the tiny buttons on the remote ...and.......

clients always looked at you like a missed the punch and you had to show them and explain..that machine is on my boat anchor list

Again.... don't let Steve Sadler see this!

[msmith]

So I think Im like 2 pages behind now, but for what its worth... I run an Otari MTR90II and an MTR10 at my main studio. I always do a repro align, then bias, then record. I was taught that it would be pretty silly to align a record setup, then readjust the bias! I have never adjusted bias at O VU. At least not intentionally. As far as I understand it, its fairly arbitrary whether you have it at 0 or -10. In fact, its been much better for me somewhere in the -5 area. That way no matter where the bias peak occurs, I got plenty a needle to figure out my over bias setting.
I always(pretty much) run 2" 16 at 15ips, NAB +6. GP9 or 456. I bias using an external 10k oscillator. I get the entire alignment procedure done in about 15-20 mins, and I dont think about it again. It is my belief that you should re-bias every reel of tape. Even the same formulation.
If you are pegging out a pot somewhere on your machine, 1st probability says you are doing something wrong. 2nd is the machine is futzed up a little. 99% of the time its been me, and Ive been like, "Man, how could I not know that!!!"

[dbbubba]

I used to do full electronic calibration before every session, but once we got really busy back in the late '80s and early '90s there just wasn't time!
The average room doesn't have a tech that can do alignments while the engineer and band sleep the previous night's session off.

I would record tones at the head of every reel and look at things to see if anything was off.
I didn't include tones with every session either.
If you use a deck all day six to seven days a week you know it's condition!

I'll be honest...
I used to get tapes from and even do work in MAJOR rooms where theoretically everything was calibrated and aligned to perfection by a crack team of techs.
It was those rooms that had the most errors!

I once had some friends doing a major label record session at a major L.A. studio where the JH24 was giving them HUGE problems causing them to loose days of work waiting for the deck to be fixed.
The staff techs couldn't fix the deck, but when I flew out to mix a live show I fixed the deck in fifteen minutes.
It was routine MCI transport stuff.

There seemed to be some correlation between the perceived status of the project and the individuals involved.
It was almost as if the back room guys were too lazy because they didn't know who the band was.
They should have been embarrassed.

[ktf]

Originally Posted by Jim Williams

A tentelometer should be used to set tension, otherwise irregular head wear may result. I had best results with wobbly 10k tones by replacing bearings in the guides and motors with grade 9 aerospace grade bearings. That trick makes the bearing grade 5 MCI sit as stable as a Studer A800.

Jim Williams
Audio Upgrades

Of course your right Jim - dragging the supply reel is only for diagnosis.

[Bob Olhsson]

The mechanical tape path (including the tape!) is the biggest single cause of distortion in a tape machine. Until you get tape motion right, every other adjustment is pretty meaningless.

[porkyc]

Jim Williams is right. You couldn't precisely align the machine because it didn't have pots it had electronic steps, and not enough of them. The transport was good, the audio was very quiet but it had this fundamental flaw.

Messing with the wrap on heads on JH24s
The wrap really should only be adjusted when the heads have bee relapped and you are starting from scratch. The wrap is then eyeballed in with a sharpie and a magnifying glass to get the gap in the middle of the scrub pattern caused by the tape against the sharpie mark down the gap.
IF you "peak" the HF by rotating the wrap back and forth you WILL end up with an offset wear pattern. The top end will be very good, but not for long, and you will see a wear pattern that has the gap to the right of the wear which will mean you have to do it all over again, including having your valuable heads relapped more than you need to.

Any tape machine is a delicate multi-faceted alignment procedure; it would take me a day to do a JH24 headlap and full mechanical re-align, AND I've got the tentelometer and parallel head alignment tools.
This is the other thing. How do you know how your heads are sitting in the block array without these basic tools. The head height on an MCI is critical, and you have to *iss with the azimuth and front/back to adjust this. No tools, don't mess with/ Get someone in who does know what they are doing. I think Steve Sadler used to work for MCI as did Glenn Coleman in New York. I did this all over Europe.

[Sigma]

Originally Posted by Bob Olhsson

Until you get tape motion right, every other adjustment is pretty meaningless.

so true