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Old 12th April 2008, 10:32 PM   #301
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Quote:
Originally posted by Peter Daniel
I also tried separate 5V PS with few different regulator types and single supply sounded better.

So did you tried separating from the BJT regulator ??
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Old 12th April 2008, 10:35 PM   #302
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Yes, I tried additional 5V regulator and went back to single supply with 8V regulator only, as it prooved to be better. I even tried double regulation where LT1129 follows LT1086 (like in ML31.5) That's why you see the black wire on my board as I had the traces cut to separate supplies.

I wrote about it in one of my early posts: http://www.diyaudio.com/forums/showt...36#post1468036

Click the image to open in full size.
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Old 12th April 2008, 10:37 PM   #303
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OK thanks
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Old 12th April 2008, 10:42 PM   #304
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I even tried separate transformers as you see in a picture above. I had a toggle switch installed which allowed me switching between dual or single supply conveniently.

If you consider other regulators, I also tested LM317, LM2937, LT1086, LT1129 and LM7808 was my choice.
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Old 12th April 2008, 10:44 PM   #305
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yes , I am doing that as well . My intention is to try some shunt regulator anyway . But I have the same presumption that single PS will work better .
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Old 12th April 2008, 11:46 PM   #306
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by stefanobilliani


I must say in my tests yesterday I preferred to not have the parallel resistor after the series to ground . Guess why ? becouse the dac has its own 75ohm resistor in parallel at the input . That is at the other side of the cable . After some good listening I am going to choose a value for just series at the output that will vary from a min of 47 ohm to max 100 ohm . Will let you know .

This isn't quite technically correct if you are going to drive a 75 ohm cable, for minimum reflections you need a source impedance of 75 ohms and a termination of 75 ohms. Poor performance using the recommended components is probably an indication of another problem. (bad receiver ic, resistor, cable or connector choices) There is also another issue to consider and that is that most receivers are designed to operate with proper source and load terminations with an input (spdif signal) voltage of around 400 - 500mVpp.. Your approach could deliver as much as 3.5Vpp from a 5V powered source and a potential problem arises if the receiver runs on say 3.3V or less..
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Old 12th April 2008, 11:55 PM   #307
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Quote:
Originally posted by stefanobilliani


There seems to be too much un necessary stuff there .

<snip>

I think I am going to be able to eliminate the audio board, I have figured out that I need to provide +12V continuously to the controller board, and a driver to run a relay to control the 8V supply - and I now believe that I might only need one. (The 8V supply now appears to just power the cd mechanism and electronics - nothing else.) My current thought is one winding will provide unregulated 12V (or maybe regulated 8V) for the micro-controller board, back light power, and the other will run a regulator dedicated to powering the mechanism.

I have already done a great deal of simplification and it does sound quite good. Not quite there yet, but I think identifying all of the capacitors that need to be replaced will go far in that direction.

There is one small advantage to this approach and that is that it removes the noisy micro-controller from the DSP chip on the cd mechanism controller board. This is basically similar in configuration to an actual Shigaraki.

In the end I should end up with just one more board than the RCEZ31 based version. In return for that I get a lot of nice cd player features. One thing I have noticed is the seek time on this thing is faster than blazes - perhaps the fastest of anything I own.
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Old 13th April 2008, 12:00 AM   #308
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One thought to Johnm would be to make sure that the motors are mounted on the carrier plate when you resolder, don't just snuggly solder those motors to the board as it the event that the board is not flat (And given what it is made of it probably isn't) you may end up with cracked smd components down the road.

Bluetack or similar is fine to try damping (hf) vibrations, however mounting as Peter suggested should sink most of the vibration into the large low impedance of the mass the thing is coupled to. The bluetack will not be effective against the vibration typical from an eccentric disk - the vibration frequency is too low.
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Old 13th April 2008, 01:22 AM   #309
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Quote:
Originally posted by kevinkr



This isn't quite technically correct if you are going to drive a 75 ohm cable, for minimum reflections you need a source impedance of 75 ohms and a termination of 75 ohms. Poor performance using the recommended components is probably an indication of another problem. (bad receiver ic, resistor, cable or connector choices) There is also another issue to consider and that is that most receivers are designed to operate with proper source and load terminations with an input (spdif signal) voltage of around 400 - 500mVpp.. Your approach could deliver as much as 3.5Vpp from a 5V powered source and a potential problem arises if the receiver runs on say 3.3V or less..
Thank you I needed that explanation .
Indeed my receiver ( CS8416 ) is working at 3,3 volts . So I better keep the divider . I also will use the 75 ohm cable .
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Old 13th April 2008, 08:14 AM   #310
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Quote:
Originally posted by kevinkr
Hi Peter,
I assuming that the short piece of green ribbon you are using probably provides some level of stray or gimmick capacitance already - have you mounted a crystal directly on the board without some capacitance?

One other question is I noted the thevenin equivalent source impedance of the spdif out with 75//200 is: 55 ohms - are you using 50 ohm coax? I am planning on using 243 and 110 ohm resistors which results in ~75.8 ohm source impedance for my 75 ohm coax. (Of course I do not have 75 ohm bnc.. I keep looking... ) I'm assuming signal in the range of 3.3Vpp on the processor chip spdif output.
Sorry to quote this old post, but I calculated the resistors again.
Theoretically it should be 375 and 93.75 Ohm.
(you still woulld have to subtract the chips output impedance from the 375 Ohm)
That would give a perfect 75 Ohm output impedance, 1Vpp unloaded and 0.5Vpp loaded with 75 Ohm.
Any other value will render the coax into an antenna or ignore s/pdif specs. (and thus the receiver input)

--> calculation based on 5Vpp processor spdif ouput.
--> If it's 3.3Vpp, it should be 247.48 and 107.6 Ohm (If this is the case, Kevin's values are the best option!)

Did someone measure the actual chip output?
(would do it myself but the BB has not yet arrived)
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