TP-027, Jerry Garcia / David Grisman wins a Writer's Choice Award from Myles Astor of Positive Feedback Online

Show Posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.


Messages - glimmie

Pages: [1]
1
Reel to Reel Tape Machines / Re: Open reel video
« on: October 08, 2009, 07:07:39 PM »
This is a color 1/2inch industrial VTR. It was the last open reel machine Sony made for the industrial market. (They did make broadcast open reel machines well into the 1990s)

The image quality of these machines is as good, perhaps a tad better than 2hr VHS on a "good" day. Keep in mind the circuitry is AC coupled discrete transistor and lacks the stability of later consumer machines.

The audio is terrible! Something like 80-10K MONO with a mediocre S/N ratio. Hey it was good enough for talking heads!

A full reel of tape (7 inches) held an hour. The linear tape speed is standard 7.5ips.

Here's a really good site for these old industrial VTRs if interested:
http://www.labguysworld.com/

2
Reel to Reel Tape Machines / Re: Let dream about designing a new machine!
« on: October 01, 2009, 03:53:51 PM »
Quote

It was another one that me suggesting anything digital in the thread I linked to.
I want to keep it stricktly analog.

"dolph"

You mean a 1/2 inch cassette analog stationary head format? Just keep in mind there is not much tape length in a VHS cassettte for high linear tape speeds.

My we interest you in an El_Cassette? Remember that format?

3
Reel to Reel Tape Machines / Re: Let dream about designing a new machine!
« on: October 01, 2009, 10:39:28 AM »
Quote
When I refer to a VHS format I'm not saying that the entire audio signal chain be that of VHS format.  I'm thinking more on the lines of the tape cartridge, rotating head and transport layout.  The tape speed could run at a faster than VHS speed perhaps double giving 1 hour tape time per cartridge.  As it would not be concerned with a video signal all of the engineering could be devoted to audio only.  Considering that Hi Fi 1/8" cassettes are fairly capable devices the device I envision should be able to exceed that quite easily.

If you keep the rotating heads you have two choices: FM analog or digital technology. The digital is superior in many ways one of which is the data can be buffered to get around the head switching problem.

Again they basically have made a format on this principal, RDAT. The Sony PCM800 is a good example. Tascam made a compatable unit as well.

4
Reel to Reel Tape Machines / Re: Let dream about designing a new machine!
« on: September 30, 2009, 01:17:06 PM »
Since reel to reel machines exist and one could be retro engineered in order to produce a new one (if such a demand arose) a newly built one off reel to reel while an elegant concept I don't see it as having a practical use.

However this does not rule out the possibility of an entirely new style tape recording device.  Along with my recent reel to reel excursions I've also investigated recording into a hi fi stereo VCR and with excellent results.  Results that perhaps exceed my TEAC A 2300 SD.  I'd like to see a purely audio recording device based on the VHS format but with perhaps 6-8 tracks.  Such a machine with on board effects like a modern digital work station and  a USB  interface for communication with digital sources would be an interesting device.

Keep in mind however that VHS HiFi is not a stationary recording medium. The audio is FM modulated to 1.3mhz (left) and 1.7mhz (right) and applied to the video heads. You aren't going to record 1.3 or 1.7mhz with stationary heads running at 0.5ips such as in VHS EP mode. Also FM recording is not the holy grail. As we know the signal quality is a product of the deviation. In VHS HiFi it is rather narrrow hence they use a DBX type compander to get around that. You have the FM video carrier at roughly 3mhz and the AM chroma at 629khz there as well so intermodulation is a serious issue. But as the frequency responce is still very flat across the audio band being recorded andf played back the companding works much better than with straight analog recording but still pumps. Then we have the achiles heel of FM video recording. The head switching. The tape is only wrapped half way around the head drum so they switch between two heads to maintain continous tape contact. this produces a strong 60hz DC offset in the recovered signal due to tension differences in the tape. So to minimize that there is usally a 60hz notch filter employes.

No, VHS HiFi really isn't HiFi by our standards here.

You know they did come up with a solution to all these issues - it's called RDAT!

5
Reel to Reel Tape Machines / Re: Hot Rodding TEAC RTR?
« on: September 17, 2009, 07:01:58 PM »
It's not that simple. Changing the tape speed will require changes in both the record and playback equalization circuits.

6
Reel to Reel Tape Machines / Magnecord 1024 Electronics - comments?
« on: September 17, 2009, 06:58:34 PM »
I just scored a Magnecord 1024 electronics pack. Any tips on restoration and sound quality for this unit? I am an electronics pro so don't be shy with ideas.

7
There are some Ampex 350s on EBAY right now. They don't get more rugged than this!

8
Reel to Reel Tape Machines / Re: My New R to R Project - Ampex VPR-2B
« on: April 16, 2009, 04:16:26 PM »
"Do you know if they ever experimented with using air pressure instead of a capstan/roller like they did on some main frame computers?
Really fascinating stuff, thanks for sharing."

Absolutly. Ampex was the only company with an all air bearing transport and a vacuum capstan. The VPR-3 which succeded my machine used air guide technology. It had incredible cueing and tape handling performance. Apparently you could grab a reel in fast wind and not damage the tape! I don't think any end user ever dared to try it though.  See one in operation here:

http://www.youtube.com/watch?v=-z7ZAZDgiMg

Before that Ampex built the AVR-1 which used vacuum colums to regulate tape tension. Another defunct company, IVC made the IVC9000 VTR which also was a vacumm colum design.

The old 2in machines very early on went to an air bearing on the video head scanner. In the 2in Quad format the speed of the heads is 14,400rpm. In the early 1960s they did not have digital memory to iron out the jitter as we do today so they had to get the mechanical stability as high as possible. Ball or sleave bearings did not cut it.

9
Reel to Reel Tape Machines / Re: My New R to R Project - Ampex VPR-2B
« on: April 16, 2009, 12:48:51 PM »
Well here is an excellent page on VTR theory and history for anyone interested.

http://www.lionlamb.us/quad/theory.html

As for the "helical scan heads" the video heads are on a spinning drum that writes a slanted (helical) track across the tape. The big 2inch monsters from the 60s and 70s were known as "Quad" as they wrote almost vertical tracks on the tape by alternating four heads. Helical machines were first used in non broadcast applications due to stability issues with the long videotracks. By the late 1970s technology caught up to where a broadcast helical machine could be realized. Even today the high end HDTV broadcast cassette VTRs still use a helical scan system not that far off from consumer VHS mechanics. Just as with audio, open reel video tape is just about extinct.

As audiophiles well know, the faster the tape speed, the more HF we can record. So 15ips have much cleaner and powerful high end than does 7.5ips. Well in video we need to record in the mhz range. Well even 30ips comes up way short of this task. So we need to get the tape speed up. We could run the tape at 300ips or faster and some early VTR attempts tried just that. However Ampex invented the idea of spinning the video heads against a traditional 7.5 or 15ips linear tape speed to "cheat" the realitive tape speed up. Of course you now have a whole new set of problems. The track is no longer a linear endless (for the program duration) track. It has a start and end point. The tape must be positioned so that the video head contacts the track at the proper time. This is where the servo system comes into play.

Another tidbit: Ray Dolby was part of the origional design team at Ampex that built the first VTR in 1956. He was directly responsible for the multivibrator type of FM modulator which greatly simplified and improved the video record chain. And most people thought he was an audio guy!

10
Reel to Reel Tape Machines / My New R to R Project - Ampex VPR-2B
« on: April 15, 2009, 11:47:24 PM »


My new toy. This is a 1982 vintage broadcast video recorder. I know these machines inside and out. I have many concerts and the like copied from edited masters. Some are Dolby A encoded and I have a CAT 363 decoder to go along with it.

This is a four motor transport using brush type DC motors, two reel motors, the capstan, and video head durm. Each motor is under servo control. The tape tension is controlled extremely accurately - it has to be to meet broadcast specs. These servo systems are also interlocked to each other. The capstan is belt driven as direct drive is not as smooth. But Ampex did abandon the belt drive on later models.

Audio performance is quite good, three channels 50-15K but it can go a bit wider. 50-15K was/is NTSC TV proof of performance. A lot of these concerts are mixed down from 16 or 24 track direct to the video master so they are on par with studio audio masters.

However there is a drawback to really good audio. The complex servo and control systems generate all kinds of clocks and other pulses right inside the audio spectrum. The power supplies are also exposed to this junk. So I plan to do an external tube based preamp just like the Tape Project. The internal audio system is good, but an outboard tube preamp should be a welcome improvement.

These machines are "direct color high band" recording. This is leaps and bounds above the home VHS format. The machine captures the entire NTSC spectrum from DC to 4.2mhz at around 48db video S/N. Unlike DVD it is also an uncompressed analog recording. Uncompressed video has a distinct quality difference from DVD just as LPs and analog tape has from CDs. And while most movies are transferred to DVD from film via component video, these live concerts are forever locked into the NTSC composite format. So my tapes will always be superior to a DVD of the same concert as the DVDs are made from the same source but are also compressed video.

For those not familiar with analog video recording, the raw video signal is not simply mixed with a bias and put on the tape as is the audio. That would require a 17 octave spread on tape with the all familiar 6db per octave loss. That means an equalizer with a 106db gain spread - impossible to make! So the video modulates an FM carrier from 7.09mhz to 10mhz. This is now less than an octave spread and can be easily equalized. Of course we still need a head to tape speed of 1000ips to lay down a 10mhz signal on the tape. VHS and Betamax machines used a much lower FM frequency due to the much slower head to tape speed - about 400ips. So in turn the incomming video must be rolled off to less than 3mhz thus substantially reducing image detail. Color must be seperated in VHS as well and recorded at an even lower frequency which creates the poor S/N ratio we had with VHS.


11
Parts are easy. Due to the current interest in tube DIY for both HiFi and guitar there are many sources for tubes and transformers. NOS and current Russian and Chinese manufactured. Also due to state of the art switching power supplies, new well engineered high voltage capacitors are highly available. Plus there is the never ending supply of "botique" capacitors and resistors.

www.tubesandmore.com
www.tubestore.com
www.angela.com
www.triodestore.com

Just to list a few!

12
Here is where I got my 350 schematic/manual. It's compressed into a .rar file which is type of zip file. I used a freeware rar decoder program I found online.

http://www.analogrules.com/350index.html

I looked at the Eros but I need to build a custom chassis to fit in my console. Now if Doc would make schematics available (including his famed Repro) I would surely consider those as well. But I fully understand he is running a business and values his intelllectual property.

13
Given the choice which classic repro amp would you copy. A 350 0r 351. I am leaning towards the 350 as it's all octal tube based. I plan on using MC phono transformers to match my modern SS heads.

Of course any other suggestions for a tube repro amp are also welcome.

I'll post pics of my R to R project in a day or two.

Pages: [1]