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Need advise to supply a clean DC line to a Marantz CD-42 crystal
Need advise to supply a clean DC line to a Marantz CD-42 crystal
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Old 2nd November 2018, 12:06 PM   #1
andypap is offline andypap  Greece
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Default Need advise to supply a clean DC line to a Marantz CD-42 crystal

Hi, I know this is old stuf business but I want to experiment with this option.
Where should I connect a direct isolated 2,5V supply line to feed the existing crystal on a Marantz CD-42 player? I've read in another thread that crystals can get a direct, isolated DC supply providing signigficant sonic improvement.
Here below is attached the schematics of the CD-42 showing the original clock circuit. I'm a bit confused of what is the function of Xin & Xout pins on SAA7350 DAC, in terms of voltage supply. I have built an external power supply for this rail. I did some measurments along 3645 - 1K resistor found, 2,25V at the chip side (pin 15) and 2,30V the crystal side. Pin 14 @ 2,20V
Should then needed to remove any part (resisistor) around the crystal circuit? Thanks for your advice
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File Type: png Clock pins SAA7350.png (46.4 KB, 138 views)
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Old 2nd November 2018, 02:37 PM   #2
DF96 is offline DF96  England
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Feeding a DC supply to a crystal will achieve nothing whatsoever, apart perhaps from crystal damage if the DC is too high.

Xin and Xout pins are the input and output pins for the crystal oscillator invertor in the DAC chip. You don't need to worry about what their DC voltage is, unless you are fault-tracing; it will probably be about half the chip supply rail voltage. They are connected to a tuned circuit consisting of the crystal and a couple of capacitors, with a bias resistor too. This is the standard crystal oscillator circuit used in many digital items: invertor, crystal, a couple of caps and some resistors for bias.

Maybe you are getting confused about the difference between a crystal and a crystal oscillator?
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Old 3rd November 2018, 12:44 AM   #3
andypap is offline andypap  Greece
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Quote:
Originally Posted by DF96 View Post
Feeding a DC supply to a crystal will achieve nothing whatsoever, apart perhaps from crystal damage if the DC is too high.


Maybe you are getting confused about the difference between a crystal and a crystal oscillator?
Probably yes. I've checked the operation of crystals that work with a voltage dc or alternate, which resonate them by creating distortion on their plates. When the applied voltage stops (probably due to a feedback operation coming from oscilator), crystal recovers it's shape and as a result this creates a self voltage across it's taps sensing the in of the oscilator
The principle over the clear DC line is based is to isolate the power suppliy from the noise created by the crystal itself , contaminating power lines of DAC and other important chips.
What if I set up a divider in place of 1k , let's say 470+ 470R where at the junction of those resistors to connect the new isolated line (2,30V) and also interupt the loop to pin 15 with a small cap , ie 5pF . This will isolate the DC supply from oscilator to the crystal but would akso allow the AC feedback to flow though the cap to the OSC . Does it make any sense ?
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Old 3rd November 2018, 09:24 AM   #4
Mooly is offline Mooly  United Kingdom
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Need advise to supply a clean DC line to a Marantz CD-42 crystal
It doesn't make any sense to me.

You would probably just stop the oscillator because you have removed its dynamic driving voltage from the chip. The crystal is just placed across what is little more than an invertor to form the basic oscillator. Connecting to a low impedance 2.5 volt supply will shunt the feedback signal completely.
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Old 3rd November 2018, 10:13 AM   #5
lcsaszar is offline lcsaszar  Hungary
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Quote:
Originally Posted by andypap View Post
I've read in another thread that crystals can get a direct, isolated DC supply providing signigficant sonic improvement.
Perhaps it's loose wording, they must have meant an external crystal oscillator. These usually benefit from a clean power supply. If you use an external crystal oscillator, you should remove all components around Xin and Xout, and feed the output of the oscillator to Xin.
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Old 3rd November 2018, 10:17 AM   #6
jean-paul is offline jean-paul  Netherlands
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It must be an XO we are talking about. That needs a clean 5V PSU when the SAA also has 5V supply. Remove all parts except the 1MOhm resistor and connect the output of the XO with a 47 Ohm resistor to the XI pin. I recall having problems when the 1 MOhm resistor is removed (this is the case with certain Philips chips).
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Old 3rd November 2018, 10:42 AM   #7
Mooly is offline Mooly  United Kingdom
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Need advise to supply a clean DC line to a Marantz CD-42 crystal
Quote:
Originally Posted by andypap View Post
I've read in another thread that crystals can get a direct, isolated DC supply providing signigficant sonic improvement....
Can you link to this other thread so that we can see what is being discussed
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Old 3rd November 2018, 11:19 AM   #8
andypap is offline andypap  Greece
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Originally Posted by Mooly View Post
Can you link to this other thread so that we can see what is being discussed
Hi, this is the trhread where it 's been discussed about by Pete (Chivyp) in 1st and 2nd page

Marantz CD42 repair and mods


cheers
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Old 3rd November 2018, 12:43 PM   #9
DF96 is offline DF96  England
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Quote:
Originally Posted by andypap
I've checked the operation of crystals that work with a voltage dc or alternate
No crystal works from DC. All crystal oscillators work from DC. You are confusing the two quite different issues. This may be caused partly by others also being confused or lazy and calling a 'crystal' something which is actually a crystal oscillator. Once you understand the difference you will know why your original suggestion makes no sense at all.
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Old 3rd November 2018, 01:46 PM   #10
Mooly is offline Mooly  United Kingdom
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Need advise to supply a clean DC line to a Marantz CD-42 crystal
Quote:
Originally Posted by andypap View Post
Hi, this is the trhread where it 's been discussed about by Pete (Chivyp) in 1st and 2nd page

Marantz CD42 repair and mods


cheers
Thanks.

So (and this is just my opinion), what I think is happening is that the oscillator still manages to free run on its own (such is nature of CMOS invertor type oscillators), and that having the crystal still connected at the invertors input terminal is sufficient for the oscillator to 'lock' to the crystals frequency.

In other words its working by accident rather than design, and almost certainly in absolute terms, the oscillator signal quality will be inferior to the correct connection method.

It may well sound 'different' because of the added jitter/hash/noise of the modified clock signal and that difference may be interpreted as more pleasing.

At the very least you should use a scope to look at the oscillators output signal and compare it to the normal connection. You should also measure the frequency because it may be off a little as the crystal is pulled away from its primary resonant mode by the non conventional circuit.
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