Getting the feet wet with head alignment

[xcortes]

Following a discussion on the prerecorded tapes category I thought I'd start a new thread on head alignment for newbies. I want to get a first grasp of how to align the heads on my RS1500, particularly the 4 track head which is giving me problems with a volume difference of close to 3dB between channels.

Here's what I've learned/understand/think so far:

Azymuth is the most critical of the planes to align on a head. It refers to the alignment of the heads perpendicular to the direction of the tape. If you don't get this one right both tracks will be played out of phase. To adjust azymuth you need three things: an alignment tape with a 16 kHz track, a dual trace oscilloscope to compare the output from both heads using the mentioned track and your deck's service manual to find out what screw/screws to adjust to align the head. The idea here is to get the output from both heads as similar as possible.

If your deck has VU meters you could use both instead of the dual trace oscilloscope to compare levels in case you don't have an oscilloscope (although I'm not sure if the test frequency would be the same). This method being for sure a compromise. Or better yet, you can sum the outputs from both heads creating a mono signal and compare the output level. Since azimuth misalignment will cause cancellation at high frequencies you are aiming to the highest reading.

Zenith is the alignment of the head in the same plane as the tape. If you don't have it right the tape will not contact all of the head but rather will be closer to the top or the bottom part. Here you can use the same test track and you want to maximize output from the heads. Zenith misadjustement should affect both channels equally or in a very similar way if the other planes are aligned.

Wrap  / Head height / Tape-to-head-contact usually don't misalign unless you replace the head so I won't get into them.

When doing adjustments at the tape heads a non magnetic screwdriver is recommended.

Hopefully I'm not oversimplfying things and confusing people here. If I am please forgive me!

Xavier Cortes

[docb]

That's a good capsulation. One very important thing to remember when making adjustments is that adjusting one aspect can alter the others you have already made, i.e. adjusting zenith can mess up your azimuth. So the proper procedure is to go around the adjustment cycle three or four times to get it all optimized. The RS1500 service manual has a good section on head alignment, describing what each of the many screws on the headblock adjusts. The order they suggest is head height, azimuth, tilt (aka zenith), contact and tangency (aka wrap). After those are done one should check phase alignment.

But before doing any of this one should make sure the tape path adjustments are dialed in. On an RS1500 that can require a lot of little shims that aren't readily available, and it helps to have some good measuring sticks. The RS1500 service manual is pretty vague in this regard, and I am developing a bit more standardized procedure than they offer in the manual for our own tape path alignment procedure. Tension adjustments need to be checked as well and tweaked where necessary. This requires tension gauges and a tenselometer.

You guys know that I am all about DIY when it makes sense. But do consider that it will require spending some money on good test gear and a fair amount of time refining techniques. Taking the tape machine to a well versed tech who has a lot of studio tape machine experience and the proper equipment is probably the best way to get a really thorough alignment.

By the way, Mike Spitz gives an alignment clinic. Naturally he uses an ATR to demonstrate the process and offers a lot of tips specifically germain to the idiosyncracies of that machine. But the general process is covered very well and the class would be a great way to learn how to do it "right".

[ironbut]

I don't know if you've seen this site, but there's a great section on alignment.  There's also a lot of other stuff there of interest.analogrules.com

[stellavox]

Good discussion so far.

Let me add that you shouldn't make ANY adjustments to a headblock just for the heck of it.  Take a good look at the wear pattern on each head.  This will give you a good idea about how correct the existing head height, zenith and azimuth adjustments are.  If everything looks good then leave alone. 

Problem is, if something looks amiss, like a trapezoidal (versus rectangular) wear pattern on a head - indicating a potentially bad zenith adjustment, trying to readjust it won't necessarily correct the problem, as "the wear is there".

When installing a new head, correct wrap angle and tilt adjustments enter the picture. Carefully monitor the "new" wear pattern after installation - it will tell you how good a job you've done.   

If you're serious about tape setup, the machine to have is the Sound Technology 1500A.

Charles

[xcortes]

Let me add that you shouldn't make ANY adjustments to a headblock just for the heck of it.  Take a good look at the wear pattern on each head.  This will give you a good idea about how correct the existing head height, zenith and azimuth adjustments are.  If everything looks good then leave alone. 

How can one determine wear visually?

If you're serious about tape setup, the machine to have is the Sound Technology 1500A.

I googled and found these: The Sound Technology 1500A was a microprocessor-controlled audio measurement test system. According to an ad in 1981, the unit was conceived to be the ultimate precision test instrument for tape recorder analysis. It was designed around advanced microprocessor hardware, and showed the user ?the whole story on an integral CRT with adjustment cursor.?

Applications of the system included tape recorder mechanical and electronic performance checks; thorough phono cartridge analysis; one-third octave spectral analysis; acoustical room analysis, including mic and loudspeaker measurements; evaluation of audio quality for VTRs; and research and development for the audio tape manufacturer.

The RS1500 service manual has a good section on head alignment, describing what each of the many screws on the headblock adjusts. The order they suggest is head height, azimuth, tilt (aka zenith), contact and tangency (aka wrap). After those are done one should check phase alignment.

I already purchased my own copy!

But before doing any of this one should make sure the tape path adjustments are dialed in. On an RS1500 that can require a lot of little shims that aren't readily available, and it helps to have some good measuring sticks.

Although I haven't done any measurements my deck seems to be very well in this regard. The tape runs centered on every part of the trail.

Thanks all for your comments. I'm learning a lot and hopefully others will be as well by having access to these threads.

Xavier

[xcortes]

After more than a year of starting this thread I finally put the test tape on the decks and connected the scope:



These are measurements at 1khz, 10khz and 15khz of the following heads: Tascam head 1, Tascam head 2 and Technics using the TP alignment tape running at 15ips and iec eq. In the case of the Tascam machine I'm getting a much higher output level on one channel than the other, not the case on the Technics.

If I understand it right the Technics looks very well with both channels in phase at 1khz and approximately 45hz phase shift at 10khz and 15 khz. The Tascams look right at 1khz with approimately 45 degress shift but I'm not sure how to interpret the other two frequencies.