Getting a KSS-274A Laser into Ballpark - Page 2 - diyAudio
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Old 16th August 2014, 11:36 PM   #11
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You know, I've never seen laser factory photos, but it's a clear possibility, thinking about it, that the whole fixed pickup thing was based on the probably fixed pickup "player fixtures" that would seem to be required for proper adjustments on the KSS240 & such lasers. Some Sony exec touring the laser shop probably thought to himself, hey, that looks pretty cool, and would be a way to sell something new & high tech looking to put the idea into production players.

The whole perception of professional grade gear being built to a higher standard WAS true up until maybe the late 1960's, but in modern times, ALL it means is that the unit will have rack mounts & xlr connectors, and maybe heavier duty *looking* exterior hardware. NOTHING more than that. Just crack open, e.g., a Denon "pro" cd player, and you'll be clear about this.

I have managed to tweak the pots on KSS240's in pause mode. Very gently. Very rarely needs doing, though, and I have worked on hundreds of 240 based units.
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Old 17th August 2014, 08:39 AM   #12
Salar is offline Salar  Germany
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I agree! Besides looking cool, the "fixed pickup" seems nonsense.
Thevintageknob claims that it was used in the very first professional
player "CDP/CDA-5000" available for studios and radio stations
before the CDP-101 was released.
I guess it was simply easier in 1982 to move a spindle motor
than to move a laser in the size of two cigarette boxes.
Still one question: The pot is connected to the monitor diode
not laser diode. Why?

Last edited by Salar; 17th August 2014 at 08:54 AM.
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Old 17th August 2014, 09:29 AM   #13
Salar is offline Salar  Germany
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Quote:
The whole perception of professional grade gear being built to a higher standard WAS true up until maybe the late 1960'
I donīt agree. It was more or less the late 1990īs because integrated circuitry
advanced so much, that you only needed some parts to build a complete player.

Ever opened a Pro BETACAM SP, camera or player? (late eighties to early nineties)

Quote:
You know, I've never seen laser factory photos
So nobody knows for sure that individual alignment was made...

All the best,
Salar
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Old 17th August 2014, 10:27 AM   #14
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Quote:
The pot is connected to the monitor diode
not laser diode. Why?
There is loop with optical feedback.
Pot is for output power.Loop trays maintain laser output power
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Old 17th August 2014, 10:36 AM   #15
Salar is offline Salar  Germany
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Thank you very much.
So this is why biasing will always only work with a laser power meter
or by monitoring eyepattern... never by measuring the ciurrent, correct?
All the best,
Salar
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Old 17th August 2014, 11:44 AM   #16
Mooly is offline Mooly  United Kingdom
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Laser current is critical. As you increase the current slowly in a laser diode it emits dull red light a bit like a side emitting LED. There is no lasing action. As the current increase there is suddenly a point at which lasing begins and from here, a very small increase in current causes a massive increase in the laser light emitted. Go to high and the facets of the laser diode are damaged and it just turns back into a dull LED.

Monitoring the eye pattern is the next best thing. The amplitude directly relates to laser power, however it doesn't allow for misaligned optics or dirty optics.

The bottom line is that the factory setting should not need altering.
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Old 17th August 2014, 04:01 PM   #17
Salar is offline Salar  Germany
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Thanks. I mention it again: The original laser lasted only some estimated 6-7 years , whereas a KSS-123A lasers is playing for 24 years know.
And focus gain between original KSS-274A and the replacement is not the same.

But the fact that the KSS-123A laser in my Nakamichi OMS-5EII lasts for so long could have another reason: Nakamichi used a light barrier to detect the CD. When the tray is closed and a CD is not inserted, the laser will not be switched on.
But this appliance is missing in in the majority of players...
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Old 17th August 2014, 06:03 PM   #18
Mooly is offline Mooly  United Kingdom
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One or two pickups are not statistically significant and in any case you would need to know the actual failure mechanism.

All players only power the laser when instructed to do so via the system control. The laser is not powered when there is no disc in the tray and /or the disc is present but the player is in stop mode.
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Old 17th August 2014, 08:09 PM   #19
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Sony's pro video gear into the 90's was built very nicely, but so was the consumer level hi8, so not a lot of difference there. But Sony was an exception to the rule. Look at Panasonic or JVC's pro video gear at the time, and you find little more than the same low-end consumer dressed up as pro.
The laser current rating is absolutely useful as a "health indicator", only in conjunction with an optical power meter, as a like-new diode will output the proper optical power very close to that rating. This is actually essential way to measure on players like the first gen OMS5/7, where the NEC laser had to be within a certain current range for servo's to work right, but the laser had a habit of needing quite a lot more than spec to output enough light.
The primary reason, in my view, that lasers like the KSS123 have had such very long lives is that they were a LOT more robust laser diodes. They were designed to ouput 0.24mW, rather than the 0.1-0.15mW of all lasers, from pretty much all makers, from the KSS150 era forward. The photo-interrupter disc detect on the Naks had little to do with it, judging by how very few 123 and similar Sony lasers I've ever needed to replace in lots of other makes/models.
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Old 17th August 2014, 10:08 PM   #20
Salar is offline Salar  Germany
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Quote:
The laser is not powered when there is no disc in the tray and /or the disc is present but the player is in stop mode.
But before that the laser checks whether there is a disc at all
Thanks for the explanations.
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