Power Caps Question

[lbossp29]

I want to replace the power caps in my XAM Mark III integrated amp. The old caps say they are rated 2500UF@25V. I went to radio shack and they only had 2200UF@35V and 2200UF@50V. I purchased both pairs for the heck of it and tried each. The 35V got pretty hot after the amp was on for a minute, so I tried the 50v. One of the 50V caps got hot, so I had switched the direction of one and then they both remained cool. When I hooked up the speakers I had a terrible buzz, but the music was finally CLEAR and not DISTORED as before. So the problem is the caps, but I'm thinking either the mismatched rating or the type of caps I bought is now causing the buzz, which is only coming out of one channel. I don't know much about power caps and the purpose they serve in theory. Can anyone give me a brief education? My XAM is out of service until I can find the right replacement

-Luke

[oldhifiguy]

strictly to keep the DC smooth and ripple free. nothing else. you may have put them in backwards, they are polarized +/-. won't cause buzz in only 1 ch.
60 cycle hum is the sound of weak filters.

[Agellius]

Oldhifiguy: Does "smooth and ripple free" mean anything in terms of the sound that comes out? What effect do the ripples have on the sound, if any? Thanks.

[mech986]

Hi,

If you don't have a good knowledge of power supplies, electrolytic capacitors, and polarity hookup issues, you need to be very careful in replacing things in an amp. The voltages and current that can be let loose with a wrong move or hookup can be potentially dangerous or fatal in the wrong situation.

Either of the two sets of caps can be used since they both exceeded the voltage rating of 25V of the original caps. The capacitance values will be fine - most electrolytic caps are specified +/- 20% or more so the absolute values are not real critical - you do want something though very much in the ballpark.

Since both of the caps are 22000uf they are within 3000uf of the original 25000 uf values or about 15% off - will do for now.

You must pay close attention to the polarity of the caps when replacing them. The + terminals and - terminals and hook up wires must be identified on each cap you are replacing and marked, and the new ones similarly identified and put in place the same way. If a cap heats up quickly, you have it reversed and its very possible the cap was damaged. I wouldn't use that cap again on general principles, think of the cost as a lesson learned. Taking a picture before any work is done is useful so that you don't have to rely on memory for your hookup.

Ripple - This is the fluctuation of the voltage from the power supply around the nominal DC voltage the supply is supposed to put out. The AC voltage coming into the power transformer is then stepped up or down by the transformer. However, it is still fluctuating at the same rate (60 Hz) as the input voltage. By using diodes (rectifiers), this AC voltage is converted to a (usually) + and - close to DC voltage which is now at 120 hz. The DC voltage, without any other components, is still rising and falling somewhat but with smaller peaks and valleys than raw out of the transformer.

The capacitors job is to charge up, store that charge, and release it whenever the voltage goes lower than the highest voltage it sees. The charge current it releases keeps the voltage from dropping as fast, filling in the downward slope in voltage. this series of peaks and small downslopes looks like ripples in a pond, hence the term ripple. The higher the capacitance, to a point, the smoother the ripple is and the lower the fluctuations from the designed DC voltage.

What is important is all the electronics - low level phono, line preamp stages, amp preamp and driver stages, and the amp output stage - all depend on a set of stable DC voltages to work from - they can then do their jobs correctly. If you have ripple or varying DC voltages, then the stages of amplification are getting varying conditions to work in and this can affect the linearity of amplification. Literally like sending a signal down the power supply line.

hope this helps.

Regards,

Bart

[mech986]

Oh, BTW, an incorrectly hooked up electrolyic capacitor can get really hot and vent some very noxious stuff (gas and liquid) or at worst can explode so be very sure, check twice or three times and then have someone else check connections before powering up.


Bart

[oldhifiguy]

60 cycle hummmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm

[lbossp29]

thanks for the input guys. I'm going to replace the cap that got hot just to be sure it isn't bad, because now I have a new problem. With the old caps my EV integrated had the hum oldhifiguy was talking about, plus serious distortion when treble and bass knobs were turned over 12 o clock. With the bass and treble at about 9 0 clock the amp sounded decent, but something was still wrong.

With the new caps I feel like the distortion has been lessened, although it is still present. The hum has been lessened, but now I have a major problem with interference. I live across from a water tower with cell phone trasnmitters on top. Some of my audio gear is affected by this. I have an old RCA stereo that looks like a 1960's boombox and the amplifier in it picks up awful interference, like the sound of the ocean coming and going, but it will increase or decrease if you move the radio around the house. Now the EV integrated amp is picking up the same interference, and all I did was replace the two power caps. It never picked up the intereference with the old caps. Any ideas? Do I have to retire my old gear because of the cell phone transmitters?

-Luke

[Kaffeen]

thanks for the input guys. I'm going to replace the cap that got hot just to be sure it isn't bad, because now I have a new problem. With the old caps my EV integrated had the hum oldhifiguy was talking about, plus serious distortion when treble and bass knobs were turned over 12 o clock. With the bass and treble at about 9 0 clock the amp sounded decent, but something was still wrong.

With the new caps I feel like the distortion has been lessened, although it is still present. The hum has been lessened, but now I have a major problem with interference. I live across from a water tower with cell phone trasnmitters on top. Some of my audio gear is affected by this. I have an old RCA stereo that looks like a 1960's boombox and the amplifier in it picks up awful interference, like the sound of the ocean coming and going, but it will increase or decrease if you move the radio around the house. Now the EV integrated amp is picking up the same interference, and all I did was replace the two power caps. It never picked up the intereference with the old caps. Any ideas? Do I have to retire my old gear because of the cell phone transmitters?

-Luke

My pioneer sx 850 made sounds like you describe when I had one of the caps in backwards and one correct. Here's a link to that thread:
http://www.audiokarma.org/forums/showthread.php?t=154621

Kinda long but it might get you on the right track. Any chance you took notes of how it was wired up before you swapped the caps? Perhaps someone here can send you a pic of the correct wiring setup.

Good luck.

[EchoWars]

Quit buying parts at Radio Shack.

[Agellius]

Bart, that was very enlightening, thanks much.

[avionic]

Quit buying parts at Radio Shack.
Absolutely the worst place to buy parts.I believe there capacitors are cheap Xicon caps that they repackage and charge 10 times as much for...:thumbsdn:

[BrassTeacher]

If you installed a cap backwards, and ran it, and it got hot, YES, replace it! It's done.

Actually, at radio shack, if the cap was an axial type, it was most likely a Nichicon VX (dark blue and silver). Those are not a bad choice for low-voltage power supply duty if you need an axial cap. Available cheaper elsewhere, but not a bad cap.

[lbossp29]

I tried to swap out the 50v cap that got hot with a new 35v cap. The electrical interference is still there, very loud, doesn't change with the volume. It's like buzzing mixed with the sound of radio static, and it will increase slightly or decrease based on where you stand in relationship to the unit.

The big question is, why is it doing this with new caps? The old caps were black, tall, can shaped but not actually metal cans. The old caps were Whale brand, and they mounted in brackets with the circuit board above them. The new caps are much smaller so the sit differently. Could it be the type of cap? Did these old caps have some sort of extra filtering? This is really a night and day difference so I have no idea what to think. The integrated amp does work, and it sounds decent once you get the volume above the constand volume of the interference. This is driving me crazy:thumbsdn:

Echowars, do you think the brand of cap is causing this? They are nichicon brand, look like decent caps....

[nashvillebil]

It's not the brand of cap, something else is wrong. This could be a grounding issue (somewhere a ground isn't connected) or some other issue such as a bad part, etc.

I'd start by looking through the grounding all through the power supply section.

[lbossp29]

I replaced all of the power caps and now the EV is more distorted than when I started. What should I replace next? I see two transistors and a bunch of 15mfd caps in the amp section and pre-amp section, could those be causing the distortion? I think the electrical interference is happening because I am running it with the cover off to test it. On the second floor of my home the unit is closer to the cell phone tower than in my basment, but if I put my arms between the amp and the wall it blocks the signal path and the noise goes away. Maybe I could build some sheilding into the cover before I put it back on...but I have to get the distortion out first, any ideas?

[nashvillebil]

There's lots of places "distortion" could be coming from. A complete recap, while its a good idea strictly because you've got aging & dying electrolytics, *could* solve the problem but it's entirely possible it may not solve it either. Merely replacing parts is called "shotgunning" and most of the time you can replace lots of perfectly good parts trying in vain to find the one bad part.

My point is that there's no substitute for a proper test procedure, using proper test equipment. However, if you don't have access to good test equipment (an oscilloscope would be VERY useful here) then you're sorta shooting in the dark...I'd look very carefully at all solder connections in the power supply. Also check the preamp power supply. There's likely either a zener diode or a regulated power supply that's giving the preamp section its power. Look for larger value caps, not as big as the main 2200 mfd caps but still pretty big, 220 mfd or bigger. Try changing these...again, check all solder connections. Use a magnifying glass to look at each solder joint and wiggle the component, there may be a very fine hairline crack in the solder that won't be seen until the component is wiggled.

Do you hear distortion on all inputs? And how about with headphones?