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Old 12th January 2009, 06:22 PM   #1
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Default Cyrus 2 Repair

Hi, I'm in the process of repairing my Cyrus 2 phono stage which has developed a bit of a buzz and suspect some of the capacitors.


However I have noticed that R110 near the main power switch runs very hot and is discoloured (so that I can read the value). Is this normal, One end has a 50Hz sine wave of +/- 40V, the other end has a half sine wave of -40V to about +0.6V.

I only have the Cyrus 1 PSU schematic and can see no reference of R110. Can any one shed any light on this anddoes anyone have a schematic of the Cyrus 2 PSU. I have full access to scopes and DVMs so can easily take measurememys.

Thanks Andy

P.S. Cyrus 2 Vintage -> plastic case, black push button power with illuminated Cyrus 2 logo, purchased in 1985 from Alternative Audio in Solihul.
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Old 14th January 2009, 09:51 AM   #2
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Ok, Having found the casue of the problem being the electrolytic decoupling capacitors around the 317/337 voltage regulators, I am going to replace all the phono preamp electrolytics since they are 25 years old and must be past their best. Not too bothered by the power amp since all I need is the preamp.

I was probably going to use Panasonic Audio capacitors from UK Farnell.

Anyone got any views they wish to share on this choice and other suppliers of audio grade capacitors in th UK.

AndyG
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Old 14th January 2009, 10:21 AM   #3
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AndyG, if you are not using the power section you may be able to pull the rail fuses so that the transformer is only running the phono stage. I think this is what happened if you connected the PSX but it's just in my memory (so check).

sp
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Old 15th January 2009, 12:39 AM   #4
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Spot on Stoolpigeon. That's how my Cyrus2 and PSX is running at the moment.
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Old 16th January 2009, 12:34 AM   #5
Phil50 is offline Phil50  United Kingdom
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Help
i cannot post as this serch first goes on forever so perhaps you can advise me please?

I have a Cyrus 2 but only a circuit for a cyrus 1. My question is what is the correct rail voltage +v and -v_ for the Power amp section and what should Iexpect from VR1 and Vr2 Regulator s for the Pre amp section. I am getting 17.9v from Vr1 and 18.02 vfrom Vr2. It would be helpful if anyone knows or has a schematic for this amp and its PRX
regards
Phil
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Old 16th January 2009, 09:39 AM   #6
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Hi Phil,
To post a new thread you must tick the box near the top left next to the words 'have you searched?'.

I can't remember exactly what the rail voltages are for a Cyrus 2 but I know that the Cyrus 1 has rail voltages of +/- 30Volts.
The Cyrus PSX, an uprated power supply that can connect directly to the Cyrus 2 power rails, gives out +/- 38V. Therefore, I would *guess*, that the Cyrus 2 has rails of about +/- 35Volts.

If both of the phono pre-amp voltage regs are giving out symmetrical voltage then it's probably fair to say that they are working fine. I know that Anatech often recommends changing some of the electrolytics in the phono stage because they cause harmful oscillations as they dry out.

I know I'm being nosey, but why would you need this information?

All the best,
Martin.
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Old 16th January 2009, 01:56 PM   #7
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Hi there, I have my C2 in bits on my workbench, and those values are correct, They should be +/- 17.9V if you use the calculations from the LM317/337data sheet. The values of the resistors are the came (read from the actual parts) as the C1 preamp supply circuit.

Mine measures +17.8V and -18.1V.

If you've got it apart, I'd replace the 470uF and 22uF caps around the regulators, they're prone to failure. I'm using the Panasonic FC range which can be bought from Farnell (20 order) or from Banzai Music in Germany http://www.banzaieffects.com with 4 p&p.
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Old 16th January 2009, 11:40 PM   #8
Phil50 is offline Phil50  United Kingdom
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Well thanks gents for the info specialy on how to tick the post box!

I am asking as I have half a dozen of these old amps and decided to get around to repairing them. I have fixed plenty of Cyrus 1's as they are quite simple but this one was becoming annoying )))))))) I suspected the voltages were correct as the amp seems to have some kind of problem in the driver stage. It also has quite high crossover distortion in the 5% range.

I must start digging deeper. When I have time I may trace the circuit and draw it out as cyrus are rather like Audiolab and quad as in "totally unco-operative". They just hate others repairing their kit. TOUGH!!!
thansk again for your advice.
regards
Phil
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Old 25th January 2009, 09:55 PM   #9
Phil50 is offline Phil50  United Kingdom
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I have repaired this old Cyrus now. IT was Two output transistors now replaced and two drivers, one O/C and one leaking under load and one resistor gone higher resistance than value it should have been.

All in all a lot of little troubles. Its fine now and the distortion is a more repectable 0.02% both channels at 1Khz. Not a bad amp for its day. On to the next one now.
cheers
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