Classe CDP .3 and CD-R's

[gbyleveldt]

Hi Guys,

I've managed to get my hands on one of these and it works great, except it does not play CD-R's. This is a well known issue with these machines.

Now what Classe did was to use some OEM CDP based on the Sanyo LA9200 ASP feeding some Yamaha DSP. They simply tap off the I2S lines for their use.

In the Nakamichi vs. CDR thread it was shown that - in certain cases - CDP's that don't support CD-R's can be modded to support it. I was wondering if something like that would be possible with this player?

I've managed to get a service manual for the Classe, but there's no info on the OEM CDP used as it's meant to be a 'black box'. Any thoughts on other CDP's that use the LA9200? Maybe there's a player using this chipset that does play CD-R's?

Any thoughts would be appreciated!!

 

[Mooly]

A few thoughts...
CDR's as oposed to CDRW are usually considered compatible with most players.
The problems come in the "quality" of the recovered signal from the CDR.
A commercial pre recorded disc is "stamped" into a reflective aluminium substrate and it's the transitions from these "pits" and "lands" that give rise to the digital ones and noughts as interpreted by the pickup and the reflected light... not as many think that a land = 1 and pit =0.
CDR differs in that a dye based ink is actually burned away during recording... it's a fundamental difference... and the upshot is that the quality of the signal that the pickup reads of the disc is variable to say the least.

What you really need to do I suspect is examine this RF or "eye pattern" on an oscilloscope and see first off if the player is 100% with pre recorded, and secondly what the recovered signal is like of CDR.
The old question... have you tried CDR burned on other PC's and at different speeds. I find that using the highest speed (contrary to what many suggest) actually gives the clearest defined signal.

To the best of my knowledge, the problem is totally optical depending on the CDR recording itself. There may be fiddles and fixes that can be applied to the RF stages for specific models... but I think it will be related to the "analogue" front end stages... yes CD is analogue in many repects

 

[gbyleveldt]

Hi,

Thanks for getting back so quick. I'll tinker a little and put a scope of the RF line to check the eye pattern, although I'll probably not see much as the TOC is not even read. It spins the disk up and then gives up.

I've not remotely tried all possible combinations of disks and recorders. I'm also lead to believe that you may be better off getting hold of the older 650MB disks as opposed to the 700MB disks you get now. I've no idea where to get these anymore and doubt that I would be able to.

Anyway, I'll mess with it a little more.

 

[gbyleveldt]

Just as a matter of interest, which CD burning program is generally considered to be the most suitable? All the Nero and Roxio offerings are now so bloated that you must wonder how suitable they are?

 

[Mooly]

See what the RF is like with a good commercial disc first. Note the amplitude and try and compare with what you see when it attempts to read the TOC.

I've only ever used 700mb discs, and as to burning programs, well that shouldn't affect the quality of the burn in itself. That's determined by the actual CD burner and firmware.
I use Ashampoo which is available free at the moment along with other stuff if you are interested. I used to use N.T.I. CD/DVD maker which came preinstalled on laptop but I did a clean install after a couple of years and that's how I came to use Ashampoo. However there is no difference in quality of RF between those two and even Windows media player... it's all down to the CD/DVD drive.

Your personal Ashampoo® gift

code is ASH-444LW1

and as requested by Ashampoo... pass it to as many folk as you want

 

[gbyleveldt]

Just tried it earlier, there's no eye pattern when reading the TOC on either a pressed or burnt CD. But when comparing the waveforms between the two types when reading the TOC, you can clearly see the pressed CDs waveforms more focused on the scope. So I'm assuming there's too much noise in the signal being read off a burnt disc.

 

[stephensank]

Your problem is that the laser is either misadjusted or is simply the wrong wavelength to read cd-r discs. If the unit indeed uses a Sanyo SF-P1 laser, as listed on the dac/transport list, I believe it should be able to read cd-r is properly adjusted.
The first thing you need to do is make sure the focus & tracking servos are adjusted optimally for cd's. Set the focus bias/offset for maximum height & clarity of eye pattern. Then adjust the focus gain control in the direction that makes the 'hiss' from the laser quieter until the point where you see the eye pattern start to freak out, then turn back the other direction about 10 degrees past where it goes stable again. Do exactly the same with tracking gain. Next, find TE tracking error output test point. Put cd in pause mode, and adjust the EF balance to make the postive & negative going low frequency spikes as equal as you can, and the tracking offset to put the center line at 0 volts.
Once these adjustments are made, if the unit still won't read cd-r's, the remaining adjustment is laser output power, which is the pot on the laser. Assuming you don't have a laser power meter, play a cd & make note of the eye pattern amplitude. Turn laser power trimpot a little bit on one direction. Play again and see if eye pattern is larger or smaller. Adjust to make the ey pattern about 1/5 larger in amplitude. If it still won't read cd-r after this, the laser is either incompatible with cd-r by design, or defective.

 

[Mooly]

That's about the sum of it

Also as it's not been mentioned... is the lens really clean ?

 

[gbyleveldt]

Geesh, those are some brilliant pointers! I'll give them a bash and see if I get any luck.

Thanks again.

 

[gbyleveldt]

Brilliant!! Sorted!

For the most part, the settings were correct, but I had to up the laser power with about 20% (which turns out to be a 1/5th, like you said) and it works perfectly. I must add, the laser was replaced some time ago, before I purchased it. I cannot tell if it played CD-R's before though.

Now the question remains if the laser's life has been drastically shortened? Lucky these lasers are cheap but I don't want to be changing lasers every 6 months.

 

[stephensank]

Without measuring with an optical laser power meter, it's impossible to tell for sure. But, considering that it should have been able, as far as I know about that laser, to play cd-r's in the first place, it's probably within tolerable range of normal output now. So, probably be ok for years.

 

[Mooly]

How does the RF compare with CDR to ordinary CD ? and by how much has the amplitude of the signal increased now you have altered the power ?

As to the laser... hard to say without hard facts.

 

[gbyleveldt]

Well, I was very specific about adjusting the pot. I made sure it's not powered up and made super small incremental adjustents. Based on the amplitude of the RF pattern using the same CD as reference, I can tell I had to increase the laser power by 20%. In this player, the RF amplitude needs to be around 2V minimum for it to work. Looking at the datasheet for the LA9200, I'm wondering if a more wise approach wouldn't be for me to increase the gain fro the RF amplifier? It get's set with two resistors, so should be easy enough just to try.

RF output is less than for normal CDs. I also don't see the same definition of the eye pattern between pressed and CD-R's. I suppose it's to be expected.

 

[Mooly]

The problem with increasing gain is that you increase the noise too... without having the player in front of me I wouldn't like to advise on that.

I'm not familiar with that laser pickup either... in that I don't know whether any adjustments need to be made on the pickup itself following replacement, such as diffraction grating adjustment etc, or any mechanical alignment procedure. That can and does have a huge impact on the quality of the signal recovered.

Edit, post number 9
http://www.diyaudio.com/forums/digital-source/165263-nad-c540-cd-player-no-disc.html#post2306272

is about another player and CDR compatability. If you gathered all the info and circuits maybe you could see what areas of the player were modified and what the changes achieved.

On the laser again... when the laser power is adjusted during manufacture, then that's an optical adjustment using a power meter. As the current is increased the laser operates initially almost like a side emmiting LED, then suddenly at a given current lasing action begins, and a very small increase in current gives a large increase in the laser output... this is why it has to be so carefully controlled with the APC (Auto power circuit).
That pre-set current is then correct to give the required RF output from a CD but only if all the mechanical and electrical alignment is correct. If there is a problem there, then the output will be "low" even though the laser power is actually correct, so turning up the power is "fiddling" the issue.

I'm not saying that's what has happened here, just something to be aware of.

 

[stephensank]

I know those Sanyo lasers well enough to say that there definitely is no post-manufacture adjustment of diffraction grating possible, and they are well locked. I can also say that this one is old enough that it's laser diode was almost certainly the sort to have a spec of 0.24mW output, and will tolerate easily 0.28mW constant without degraded life. But I can also say that, given the servo adjustments all checked out ok, it would definitely play cd-r at rated output, so is almost certainly close enough to that to be fine. Were it a later laser with 0.1-0.15mW constant rating, it would be a different story, depending on model. But the 0.24mW lasers have more range of safe operation, usually.