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Old 17th August 2011, 07:58 AM   #1
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Default Cyrus I (issue 07)

Hi all,
I have a problem with my Cyrus I. Since some days I notice a humming sound, increasing when turning up the volume. I listen only with the Phono stage. When listening to records you can hardly hear the "hum", but by just turning the volume knob the strange sound becomes loud. I already switched to another high-level input, e.g. CD, AUX, etc. with the result that there is no "humming" sound. I already replace almost all the capacitors except the orange/pink selma Bi-polar caps (1uf-50V & 2.2uf-50V) and the two main Slit Foil black caps.
As this hum is only in phono section i believe the problem is there....
Anyone can help with some suggestion?
Thanks inadvance
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Old 18th August 2011, 10:23 PM   #2
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This is what the always helpful and always nice anatech (Chris) wrote me in a private message:
Quote:
Your problem is a fairly common one with any older electronic product. The parts that should probably be changed are in the power supply for the phono section. You've likely guessed as much already.

There are two (2) 470 uF filter capacitors that need to be replaced, and another four (4) 22uF capacitors as well. Use 63 VDC capacitors for the 470 uF, rated at 105 C if you can. This is not critical. For the 22 uF capacitors, use a 35 V capacitor at 105 C. Using 85 C capacitors will not cause them to fail, they just won't last quite as long.
Thanks Chris for your help...The thing is that I have already changed those caps. Actually I put some panasonic FC 105 (but the strange thing was that the caps on my amp - the 470uF - were not 63V, but "only" 50V...so I replace it with the 63V).
Quote:
At this point in time, it would be wise to replace the two voltage regulator ICs also. Replace them with the same type in TO-220 metal tab. Last comments. Do not buy higher priced "audio name brand" parts. The normal good industrial parts are more than good enough. Anything over that is a waste of money. Do not convert the regulators to LM317 / LM337 types or anything else. Do not replace the 5534A op amps with anything else either. These parts are well suited to the circuit design.
That's the thing I must do next....but actually the two voltage regulators I have on my board are the LM317 / LM337...so at this point I must ask you what type of regulators I should put instead of LM317 / LM337...my amp is a Cyrus One last version (I think...), so Issue 07.
And there's another strange fact that puzzled me when I replaced the caps. On the part list of the service manual the caps C53-C56 are stated as 100uF 50V. But on my board I found that those caps were 220uF 50V. As I ordered the 100uF, I put those instead....do you think this will cause any problem?
Thanks again for your help
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Old 19th August 2011, 04:31 PM   #3
anatech is offline anatech  Canada
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Hi Andrea,
Quote:
strange thing was that the caps on my amp - the 470uF - were not 63V, but "only" 50V...so I replace it with the 63V).
Leave the 50 V units in there, they are fine. I normally install 63 V units instead, but there is no reason beyond a little extra life. The 105 ones will do that for you. Any good brand of capacitor is fine here. Good as in normal industry good, "audiophile good" doesn't buy you anything extra but a slimmer wallet.

Quote:
but actually the two voltage regulators I have on my board are the LM317 / LM337...so at this point I must ask you what type of regulators I should put instead of LM317 / LM337
My error, those are the originals. My mind was on something else where someone had replaced the 7815 and 7915 with the adjustable versions - trashing the PCB in the process. Your model 1 (one) should have supply voltages lower than the 2 (two). That means those regulators run at a lower temperature which is helpful. They may not have heat sinks in this version. If not, why not install a pair? Cooler parts last longer and do not tend to become noisy over time like hot things do.

Quote:
On the part list of the service manual the caps C53-C56 are stated as 100uF 50V. But on my board I found that those caps were 220uF 50V.
If those are original, it was probably a production change. The manuals do not always match the unit perfectly. Are these the ones that supply the two voltage regulators? If so, install a pair of 470 uF (as the later model 2 uses). I wouldn't go any higher than that though. There are some other caps in the amplifier section, are you talking about those?

-Chris
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Old 19th August 2011, 08:25 PM   #4
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Quote:
Leave the 50 V units in there, they are fine. I normally install 63 V units instead, but there is no reason beyond a little extra life. The 105 ones will do that for you. Any good brand of capacitor is fine here. Good as in normal industry good, "audiophile good" doesn't buy you anything extra but a slimmer wallet.
Hi Chris, well I already put the 63V in my unit...so think I will stay with them and get some extra life

Quote:
My error, those are the originals. My mind was on something else where someone had replaced the 7815 and 7915 with the adjustable versions - trashing the PCB in the process. Your model 1 (one) should have supply voltages lower than the 2 (two). That means those regulators run at a lower temperature which is helpful. They may not have heat sinks in this version. If not, why not install a pair? Cooler parts last longer and do not tend to become noisy over time like hot things do.
Ok so I will put two new regulators same as the originals. I do not know if they have the heat sinks but in a few day I will put a photo of my amp....


Quote:
If those are original, it was probably a production change. The manuals do not always match the unit perfectly. Are these the ones that supply the two voltage regulators? If so, install a pair of 470 uF (as the later model 2 uses). I wouldn't go any higher than that though. There are some other caps in the amplifier section, are you talking about those?
Yes, I think that they were the original Rubycon light blue caps. Actually they are the 4 next to the main transistors nearby the heat dissipator...Their value was 220uF...but I changed them for 100uF as stated in the manual...the amp is working fine, exept for the hum on the phono section...do you think that those 4 caps are the culprits?
Andrea
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Old 24th October 2011, 10:26 PM   #5
anatech is offline anatech  Canada
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Hi Andrea,
No, those four caps shouldn't be a problem. 100 uF will be fine. Besides, older capacitor tolerances were extremely wide, so no worries.

Tell me, is there anything near your amplifier that can generate a magnetic field? The reason I ask is that some early models use a plastic top cover. There is poor shielding around the phono circuit area. You can try using Aluminum foil that is grounded to the chassis to block that area to test. Make sure you allow for air flow. If you find this is the problem, glue the foil to the top cover (inside) leaving "tails" where the rear screws go through for grounding. Make sure you cut the vents holes open.

If you had an electronic fault, I'd expect there to be a large AC component on your supply voltages. That is something I normally check whenever anything is done or suspected with the power supply. First thing to check on the bench really.

Let us know how you make out with this Andrea. You seem to have a good grasp on what can be important.

-Chris
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Old 3rd December 2011, 05:46 PM   #6
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Finally I found some time to work on my Cyrus and to complete the recapping. Changed the 4 caps 100uF (as stated in the user manual..) with 4 220uF (as found inside my Cyrus...), changed both the voltage regulator.....and the ampli now sounds AMAZING!! No noise in the phono input, and the overall sound quality is really TERRIFIC!
I did change also the power cable with one like this The TNT - TTS DIY mains cable which I made myself, and maybe this also helped...who knows...now I'm enjoying my reborn Cyrus listening some Vinyl, with my Canton Quinto 520 ...btw, thanks a lot to anatech for your help and support...
Quote:
Originally Posted by anatech View Post
Hi Andrea,
No, those four caps shouldn't be a problem. 100 uF will be fine. Besides, older capacitor tolerances were extremely wide, so no worries.

Tell me, is there anything near your amplifier that can generate a magnetic field? The reason I ask is that some early models use a plastic top cover. There is poor shielding around the phono circuit area. You can try using Aluminum foil that is grounded to the chassis to block that area to test. Make sure you allow for air flow. If you find this is the problem, glue the foil to the top cover (inside) leaving "tails" where the rear screws go through for grounding. Make sure you cut the vents holes open.

If you had an electronic fault, I'd expect there to be a large AC component on your supply voltages. That is something I normally check whenever anything is done or suspected with the power supply. First thing to check on the bench really.

Let us know how you make out with this Andrea. You seem to have a good grasp on what can be important.

-Chris
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