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Old 13th April 2012, 10:45 PM   #1
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Default cyrus 2 amplifier

Hello all hope I'm placing this in the correct place but I need help!!I have a Cyrus 2 and when I turn on I get a large bong noise out of both speakers!! I have changed a few small caps but nothing! Still sounds fab but obviously not good for speakers on start up as I've had my meter on speaker terminals and dc comes through but then settles to zero after about 15 seconds.

once the amplifer has made this noise you can flick the amp off and back on and no noise but this is because I guess that it already all powered up still inside ? Please help and any suggestions welcome. I have tryed swapping the main caps and still the noise drives me crazy!!! I dont want to use it till i get ir sorted i dont want to damage my speakers!! That would just send me over the edge! I use a psx with this and still does the noise when i use psx!

HHHHHHHHHHHEEEEELLLLLLLPPPPPPPPPP.
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Old 14th April 2012, 12:15 AM   #2
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Assuming it's the Issue 7 version with toggle switch. C43 470uF may be taking too long to charge due to old age. On the other channel I think it's C143.
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Last edited by richie00boy; 14th April 2012 at 12:17 AM.
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Old 14th April 2012, 07:01 AM   #3
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Hi thanks for reply. Yes it's the toggle version,and the caps you are talking about 470uf 6v position c43 and c44 . Yes I have changed these and have also changed c67 c68 and also c53 c54 c55 c56 !! All the obvious has been changed and that's me I'm up against a wall and I don't give up this easy . Any more ideas??? Cheers
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Old 14th April 2012, 10:22 AM   #4
richto is offline richto  United Kingdom
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Check the bias current at the left and right bias test points. It should be 8-20mV. If not then adjust to 8mV.
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Old 14th April 2012, 10:55 AM   #5
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Bias current won't cause pops at turn-on, and there is no way to "adjust" it without swapping resistors.

Check that R51 and R71 are good and connected properly.

Are both channels behaving the same? Did anything happen that may cause it, e.g. you unplugged or plugged a connection?
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Old 14th April 2012, 10:59 AM   #6
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Thanks will check later. The two pins for bias testing are under ribbon cable 2 for each channel I guess? And I just put my multi meter across each set of pins per channel? I assume this is correct. I wil be back with readings later. Don't know how to adjust bias if incorrect!!(but I'm sure someone does) :-)
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Old 14th April 2012, 11:38 AM   #7
richto is offline richto  United Kingdom
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You adjust the bias current using the 2 pots on the board.

If you agree to upload it somewhere and link it to this thread, I have the service manual and schematics for this amplifier. Give me an email if so.
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Old 14th April 2012, 01:22 PM   #8
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Have checked the bias test points. they are readind very high.
Left channel 129mv
right channel 131mv
so they are both very similar.
The cyrus does not have bias pots for adjusment so what to do next??
I assume the noise on start up is the bias is to high then??
Please advice .
I really appreciate your help.
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Old 14th April 2012, 01:46 PM   #9
Did it Himself
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I also have the service manual and have worked on these amps before.

The issue 7 "toggle" version does not have bias pots. It used fixed resistors.
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Old 14th April 2012, 01:52 PM   #10
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I've got them too, it took me three seconds to download them from HiFi Engine | Download Free User/ Service Manuals, Amplifier, Receiver, CD, Tape, Tuner, Video
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