Home Planar Speaker Asylum

Welcome! Need support, you got it. Or share you ideas and experiences.

RE: Should we send a "representative" to Magnepan?

Well, admittedly, we had sucky quads, the RCA's rather than Ampexes, which were much better machines. You haven't seen fun until you've seen a machine decide to dump a client's master onto the floor. RCA's broadcast division is a great example of a company that died because of poor quality. So for that matter is Ampex, in its later years. The Japanese, Sony, in particular, ended up taking over, even though the American companies had a significant edge in technology.

But, in general, I think that the quads were limited by the technology of the time. Consider that you had a wheel spinning at 14,400 RPM on air bearings with four heads around it. A head would hit 2" magnetic tape moving laterally at 15 IPS and write 1/16 of a field of video. It had to dig into the surface of the tape by a precise amount and when the head rotated off the next head had to start writing the track in precise quadrature, or you'd get "banding" in the image -- it would seem to break into 16 segments (you used to see this sometimes on the air). You could also get minor changes in the phase of color subscarrier at the start of a quad band, called one-line error -- remember how sensitive NTSC color was to phase error? The color time base was corrected electronically but it couldn't correct all errors since its only reference was the brief color burst at the start of a line of video.

The position of the tape and the rotation of the heads were controlled by servo mechanisms, which used a separate control track for course adjustment and then the sync signals in the video signal itself for fine adjustment. A vacuum guide insured that the tape had precisely the right tension around the spinning head wheel. And all of this had to be done to the timing standards of black and white television, despite the fact that you were recording on magnetic tape, a flexible medium that wasn't dimensionally stable. And the tape was open reel, running ideally in a controlled environment equipment area but realistically the environmental control wasn't that good, because the practicalities of a production environment didn't permit it.

What's really amazing is that it worked at all.

The ultimate solution to the cost and reliability issues was basic improvements in the technology. Quad VTR's cost $100,000, were the size of a refrigerator, required an army of technicians, three-phase power, a supply of compressed air, and climate control. Within a few decades, a child could make a high quality digital recording on a cassette the size of a matchbox. But you couldn't have done that when the quad was developed in the 1950's, and all they had was vacuum tubes. The engineers who developed it at Ampex (including a young Ray Dolby of Dolby Labs fame) were doing what had been considered impossible, and what no one else had been able to do, despite significant R&D efforts at RCA. The basic problem was that tape recorders could only record up to 15 kHz or so, but the bandwidth of video was 4.2 mHz! The innovations they came up with to solve the problem were remarkable, everything from the rotating head to FM recording to the nested loop servo system. When they showed the first quad at NAB, there was pandemonium.

Edits: 10/18/11

This post is made possible by the generous support of people like you and our sponsors:
  Signature Sound   [ Signature Sound Lounge ]

Follow Ups Full Thread
Follow Ups
  • RE: Should we send a "representative" to Magnepan? - josh358 06:55:45 10/18/11 (0)


Post a Message!

Forgot Password?
Moniker (Username):
Password (Optional):
  Remember my Moniker & Password  (What's this?)    Eat Me
E-Mail (Optional):
Message:   (Posts are subject to Content Rules)
Optional Link URL:
Optional Link Title:
Optional Image URL:
Upload Image:
E-mail Replies:  Automagically notify you when someone responds.