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Old 16th April 2012, 07:38 PM   #31
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The voltage regulator is a red herring, it is only used on the phono pre-amp. Using the CD input it is completely out of circuit.
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Old 16th April 2012, 10:14 PM   #32
mjona is offline mjona  New Zealand
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Hi,

Simple tests re phono stages.

Plugged into the mains, the power supplies are always powered up. The power amp rails are connected by the "On" switch but the preamp supply bypasses the switch and is always working.

With the power amp switched off any loading effects on the regulator should still be present and you can test for heat by touching the body with a moistened finger. If needed try the NE devices and 394 to see if any is hot. IC's can go short circuit while caps can short out or cause problems through drying out.


If you don't use phono sources a simple cure for any problems would be cutting the live end of the rectifier leads for the phono section - or desoldering these if surgery is too rough.

The main amplifier switch and/or the snubbing capacitors across these have the job of connecting simultaneously the already charged positive and negative rails noiselessly to the amplifier. These switches have to pass a lot of current and may not be as good as new.

Michael Jonassen
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Old 16th April 2012, 11:44 PM   #33
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Quote:
Originally Posted by mjona View Post
Hi,

.............

If you don't use phono sources a simple cure for any problems would be cutting the live end of the rectifier leads for the phono section - or desoldering these if surgery is too rough.

......

Michael Jonassen
When the Cyrus PSX (outboard power supply) is used and the Cyrus 2 amplifier is disconnected from the mains, the phono stage is completely unpowered.
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Old 17th April 2012, 07:07 AM   #34
mjona is offline mjona  New Zealand
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Hello Martin,

Thanks for clarifying the PSX connection.

The better (and non surgical) way to depower the phono section is to remove the amplifier mains fuse. The mains plug should be reconnected after doing this to preserve the earthing arrangements.

Cheers,

Michael Jonassen
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Old 17th April 2012, 11:40 AM   #35
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just to clarify this noise fault i have on turn on.
i have taken the fusses out and i dont get no boing noise,i then connect psx and its back with the boing noise!!! this shout pin point it a bit more for you clever fellas.
im struggling to sort this stupid load noise on turn on!!!!!!!
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Old 17th April 2012, 11:49 AM   #36
AndrewT is online now AndrewT  Scotland
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Quote:
Originally Posted by Sonusthree View Post
When the Cyrus PSX (outboard power supply) is used and the Cyrus 2 amplifier is disconnected from the mains, the phono stage is completely unpowered
could you rewrite that statement to avoid ambiguity?

I know that the phono section continues to operate when the PSX has been added to the modified amplifier.
The phono section cannot be "completely unpowered".
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Old 17th April 2012, 02:31 PM   #37
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I think that it is possible that the +18 volts it is loading the +rail side causing an unbalance. Both are connected to the transformer but the PSX it is already connected. You need to find out what it is loading the +18 volt to read 7 volts. You already proved that by removing the PSX the problem goes away. Like I said before check the resistance for both +/- 18 volts to ground they should read close. Low resistance in the +18 means that something it is loading it.
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Old 17th April 2012, 03:16 PM   #38
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Maybe I have not read this thread clearly but do you use your Cyrus2 only with PSX? If yes then the ground connection resistor is probably broken. This is a small (10Ohm or 15 as far as I remember) inside the PSX to isolate the ground to avoid ground loops. If the PSX is used seperately for whatever reason this resistor burns and the voltages are floating. This may explain some of the symptoms here.
(I repaired this fault at least once way back in the eighties so please pardon me if my memory fails here.)
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Old 17th April 2012, 03:31 PM   #39
lohk is offline lohk  Europe
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And of course you have not forget to remove the fuses in your Cyrus 2 when connecting the PSX, have you? When used with an PSX the original psu from the amp powers the phono section alone - so of course you can switch off the amp when phono is not in use. But the mains cables must left plugged in.
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Old 18th April 2012, 12:51 AM   #40
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Quote:
Originally Posted by AndrewT View Post
could you rewrite that statement to avoid ambiguity?

I know that the phono section continues to operate when the PSX has been added to the modified amplifier.
The phono section cannot be "completely unpowered".
Hi Andrew, I hope you are well and yes I'll try to clarify.

As I understand it, when the PSX is properly connected to the Cyrus 2, the PSX powers the amplifier and the Cyrus 2's own supply powers the phono stage and power indicator L.E.D.

By properly connected, I mean with the correct fuses removed from the Cyrus 2 as prescribed in the service manual.

The extract below is taken from the service manual:
Quote:
Adjustments for use with the Cyrus PSX
The Cyrus Two can be used with an optional PSX power supply. The PSX supplies DC power directly to the main reservoir capacitors of the Cyrus Two and therefore powers the main amplifier
stages. The power transformer of the Cyrus Two remains active at this time to provide power for the pre-amplifier circuits. This improves both the technical and sonic performance of the Cyrus Two.

To use the Cyrus Two with a PSX it is necessary to remove the DC fuses from the Cyrus Two main pcb (FS 1 and FS2).
Having quoted the service manual, I believe that there is an error in the above text and the PSX does not supply the main reservoir caps in the Cyrus 2. The PSX has it's own main reservoir caps and the Cyrus 2's are used for the phono stage alone when the fuses FS1 and FS2 are removed for PSX operation.
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