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Old 27th August 2012, 07:26 PM   #18351
6h5c is offline 6h5c  Netherlands
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No, you are not wasting your time:
Quote:
as long as the noise is less than before the regulator is added, the result is positive.
Just connect the scope to the analog outputs. If it's oscillating you'll see a sine wave of some sort appear >10kHz. It's best to check the power rails as well, some regulators start to oscillate with large caps on the output.

Ray
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Old 30th August 2012, 11:00 PM   #18352
mcd99uk is offline mcd99uk  United Kingdom
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I think I may have an oscillation problem on the power rails. Specifically the 5V one supplied by Q871.

The noise at the inputs to the regulators is approx 10mV. The outputs of the regulators are as follows.

Q801/Q802 is approx 60mV noise with the scope reckoning the frequency is varying between 20Khz and 40Khz. Not sure about the accuracy of that but can see the waveform has a consistent period. The peaks on the wave vary a lot.

Q871 is approx 60mV noise at approx 20Khz. Similar waveform as above.

Q811 is approx 20mV noise at approx 40KHz. Similar waveform as before.

Even the analogue outputs have about 50mV of high frequency (>20KHz) noise on them.

Also, the 5V regulators are getting warm. I don't know if this is normal or not.

What do people reckon? Are the power rails in the CD67 inherently noisey anyway and what I'm seeing is normal?

Another question when the DAC is not processing information are the ouputs still actively changing state or do they go quiet?

This where one has to understand how the player works in greater depth.
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Old 31st August 2012, 03:50 AM   #18353
6h5c is offline 6h5c  Netherlands
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I doubt that all regulators are oscillating, it's very unlikely. I'd rather think something is wrong with the ground that you chose for the scope probe. You are measuring with a probe, right? But it could be possible. What exact type regulators are you using, or are they still original?

The DAC inputs and outputs are always active. If there is no audio, the data to the DAC is simply '00000000' (well, sort of) and the outputs will show a 50% duty cycle square wave.

Ray
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Old 31st August 2012, 08:32 PM   #18354
mcd99uk is offline mcd99uk  United Kingdom
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I was using a scope probe and was grounded to the outsides of the Analogue output connectors. I thought that this would be good reference point as this the point where the CD player is referenced to the amplifier.

The regulators are still the originals. I didn't do the upgrades suggested as I wanted to add my own LM317/LT317 regs at a later date.

PSU rails seem very noisey after the regs. I was seeing peaks of over 100mV. The unregulated rails seemed posiotively quiet compared to the regulated rails. This noise seems to be transferring to the analogue outputs and I reckon that this is what is causing the listening "fatigue".

Is my choice of grounding point sound or is there a better place?
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Old 31st August 2012, 08:41 PM   #18355
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Jumper U217 is GND and closer to the regs. I'm not sure it will do any difference but do try.
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Old 1st September 2012, 08:05 AM   #18356
6h5c is offline 6h5c  Netherlands
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The problem with measuring noise like this is that the scope probe also picks up all the stuff that enters in the loop of the probe ground wire. See it as an inductor with one winding that acts as an antenna for radiated noise.

You can do a little test by connecting the probe ground wire to the outside of the analog connector again, and then connect the probe tip to another ground point, like U217 for example. I bet you will see lots of stuff on the screen already, even though you're measuring between GND's.

If you want to measure the noise only from the regulator, you need to connect the scope probe close to the output and GND pins of the regulator. A probe with a ground-spring is used for that. The spring minimises the loop-area.

I don't think the regulators are oscillating, this generally happens at much higher frequencies and with larger amplitude. You'll notice it easily on the scope screen when you see it.
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Old 3rd September 2012, 05:25 PM   #18357
Puffin is offline Puffin  United Kingdom
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Quote:
Originally Posted by 6h5c View Post
This is the famous Acoustica Clock Hack

The regulator is inserted where the 4.7 ohm safety resistor used to be. You can recognize them on the board: they are mounted 'in the air', at some distance from the board. Most chips have such a resistor in series with the supply-line. So it's very easy to separate parts of the circuit from the main supply: by removing the resistor, the section behind it is cut from the main 5V power. And it creates a perfect insertion-point for a new regulator to be added. This is where the output goes.

The new regulator can be powered from a new external supply, but you can also use the supply from the player. In the CD 63, all 5V comes from Q811, and this regulator is fed from C813. This is the point where you can hook-up the input of the new reg (the positive terminal that is). The GND terminal goes to the board's ground-plane on top.


Ray
Did this mod today and have it running on repeat for a couple of hours before critical listening. Am I right to assume that the 12v is taken from one side of the resistor? I have run a separate feed from the OUT of the 12v reg to the new 5v reg. This may not be necessary?

Am I right in thinking that 5v regs could replace all the 4.7k resistors?

Rob.
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Old 3rd September 2012, 08:01 PM   #18358
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Hi Rob,

Which resistor would that be, the original 4.7 ohm? The regulators are fed from C813, do not use the analog +12V that's present in the player!

Ray
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Old 3rd September 2012, 08:16 PM   #18359
Puffin is offline Puffin  United Kingdom
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Quote:
Originally Posted by 6h5c View Post
Hi Rob,

Which resistor would that be, the original 4.7 ohm? The regulators are fed from C813, do not use the analog +12V that's present in the player!

Ray
Ahh, I seem to remember you told me that.....and I ignored it!

Will change it. What about the other 4.7k resistors?

Rob.
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Old 3rd September 2012, 08:30 PM   #18360
6h5c is offline 6h5c  Netherlands
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Yes, you even quoted it...

Never mind, just use C813 as the supply-point for any 5V reg you want to add. All the 4.7 ohm resistors can be replaced, but the interesting ones are around the DAC, decoder and servo chip. But make sure to check the 5V output voltage is correct before you insert an LM317, to avoid smoked chips...

Oh, and leave R136 in place, it's for the laser!

Ray
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