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Old 9th December 2014, 02:51 AM   #1
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Default Building a Cyrus PSX

Hi all, I'm looking at trying to make a cyrus psx clone, as far as I can tell its a +/- 38V unregulated supply, and from looking at the innards of my fathers its a 500VA torroid, 4x15,000F slit foils and then dual rectifiers.

So, that all said I was planning on 4x 22,000F slit foils [bit pricey], I need to work out what would be suitable diodes, I cant really tell if there would be any real appreciable difference between getting some ultra-fast soft recovery's and using one/ of these GBPC2504 - FAIRCHILD SEMICONDUCTOR - BRIDGE RECTIFIER, 25A, 400V | CPC

The main question finding a transformer that has the necessary 27v secondaries is a bit of a pain, if I use a trafo with 30v secondaries will the 42v output of the PSX cause issues inside of the Cyrus or do I not need to worry about it too much?

Also anyone care to throw any opinions on the idea of bypassing the large slit foils with smaller value caps?

Thanks!

Edit missed this link, but basically I'm just planning to follow the diagram as show here http://sound.westhost.com/psu-wiring.htm and suit it to my needs.

Last edited by James189; 9th December 2014 at 03:54 AM.
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Old 9th December 2014, 11:14 AM   #2
AndrewT is offline AndrewT  Scotland
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buy a 500VA or 600VA 230:25+25Vac dual secondary transformer.
Measure your mains voltage.
You will end up with a 26+26Vac transformer.

Now if you want you can add two windings around the toroid.
About 5Turns to 10Turns will give plenty of voltage to add on to the two existing windings.

The capacitors are so far away from the amplifier due to the umbilical that HF response of the main smoothing capacitors is in my opinion not important.
Good quality standard commercial capacitors will be good enough. Epcos make small cheap good electros. I have 25V, 35V and 50V versions.

The local decoupling inside the amp chassis and on the amp PCB are far more important to the HF performance of the amplifier.

Do you know how the two extra pins in the umbilical work?
I don't.

Have a look at the TNT site for more and deeper PSU explanations.
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Last edited by AndrewT; 9th December 2014 at 11:16 AM.
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Old 9th December 2014, 05:11 PM   #3
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Thanks for your reply, I've also had a look at the schematic on the TNT website, but some comments ive seen regarding it bring up the issue of there being greater voltage drop on the rails because of using dual rectifiers - what would be the purpose of adding two extra pins to the umbilical cord? If I wanted to i could just replace the mini-xlr on the cyrus and use an appropriate connector for it.
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Old 9th December 2014, 05:29 PM   #4
IanS1 is offline IanS1  United Kingdom
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I'm sure the Cyrus PSX-R is a variable supply. Depending on which Cyrus component it is plugged into, the output voltage from the PSX-R changes accordingly.
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Old 9th December 2014, 06:00 PM   #5
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This is the PSX which came before the PSX-R and wasnt a variable voltage, its basically just a +/-38v power supply
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Old 9th December 2014, 06:34 PM   #6
AndrewT is offline AndrewT  Scotland
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3pin plug or 5pin plug?
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Old 9th December 2014, 06:35 PM   #7
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the standard plus is 3 pin mini-XLR - +38v -38v and ground
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Old 9th December 2014, 06:39 PM   #8
AndrewT is offline AndrewT  Scotland
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OK, you just have ONE dual polarity supply in the umbilical.
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Old 9th December 2014, 07:12 PM   #9
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Yeah, thats all it is, just to cut out out the on-board supply to the poweramp.
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Old 10th December 2014, 02:03 AM   #10
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Interestingly reading the service manual it claims that the PSX routes power through to the two 10,000F capacitors inside of the cyrus 2, so in theory if someone is renovating/ building a PSX they ought to also pay attention to the internal caps as local decoupling - AndrewT would you suggest bypassing those caps with smaller value caps as opposed to the very large ones that would be in a PSX?
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