Amplifier Question

[B&K]

I've noticed a bit of talk about the caps found in power amplifiers. What are the symptoms of caps that are going bad? What do the caps look like and what would I look for during a visual inspection?

[mgrabow]

Re: Amplifier Question

In my experience with them, you may hear buzzing. I work alot on RF amplifiers and that is a surefire sign that they are bad.

They look like beer cans...

[B&K]

Re: Amplifier Question

Thank you for the reply. Can a bad cap cause further damage to a system or is it limited to individual part failure?

[ecline77]

Re: Amplifier Question

Thank you for the reply. Can a bad cap cause further damage to a system or is it limited to individual part failure?

Depending on what cap and how long you let the problem go .... a bad cap can definitely cause further damage.

[Æ]

Re: Amplifier Question

I've noticed a bit of talk about the caps found in power amplifiers. What are the symptoms of caps that are going bad? What do the caps look like and what would I look for during a visual inspection?

Bad caps may show no visual indication of failure. However if you see them leaking - oozing a little bit, or if they have swelled up and look like they are going to burst, that is a sure sign of imminent failure.

Pictures courtesy of WIKIPEDIA

[curt_c]

Re: Amplifier Question

There is not a simple answer to this, as electrolytic caps are used in many different situations which can result in different observed symptoms.

As far as power supply filter caps are concerned, yes they can allow power supply ripple to invade the signal path and cause buzzing, although it may initially only show up as increased distortion at higher signal levels.

The electrolytic paste generally leaks out of the can where it is crimped. It’s brown, smells truly horrible, and almost impossible to get off of you or anything else it is inadvertently ‘applied’ to. Electrolytic caps can fail explosively, spewing the aforementioned electrolytic hither and yon inside the amplifier. An electrolytic cap can also become defective with no apparent leakage, so a clean cap is not necessarily a good cap. Failure modes include lack of capacitance, open, shorted, and temperature sensitivity.

If the capacitor is in the signal path (And many amplifiers will have numerous electrolytic caps in the signal path.) a failing cap can cause all manner of audible issues. -Lack of bass, low signal output or lack of output all together. I’ve even have them ‘pop’ repetitively in the audio until they are warmed up.

C

[Guest]

Re: Amplifier Question

There is not a simple answer to this, as electrolytic caps are used in many different situations which can result in different observed symptoms.

As far as power supply filter caps are concerned, yes they can allow power supply ripple to invade the signal path and cause buzzing, although it may initially only show up as increased distortion at higher signal levels.

The electrolytic paste generally leaks out of the can where it is crimped. It’s brown, smells truly horrible, and almost impossible to get off of you or anything else it is inadvertently ‘applied’ to. Electrolytic caps can fail explosively, spewing the aforementioned electrolytic hither and yon inside the amplifier. An electrolytic cap can also become defective with no apparent leakage, so a clean cap is not necessarily a good cap. Failure modes include lack of capacitance, open, shorted, and temperature sensitivity.

If the capacitor is in the signal path (And many amplifiers will have numerous electrolytic caps in the signal path.) a failing cap can cause all manner of audible issues. -Lack of bass, low signal output or lack of output all together. I’ve even have them ‘pop’ repetitively in the audio until they are warmed up.

C

That's right on-the-money... I've got several vintage amps/preamps, and many have those same problems. Low output, popping/crackling sounds, distortion, etc.
I would never have thought of the caps causing the popping sound in my vintage Sony, but now I know... THANKS Curt!!

[dwigle]

Re: Amplifier Question

I have a 30 year old preamp that appears to work fine. I have heard no degradation of sound quality in, well, 30 years.

Except when I use my new turntable. I now hear popping every few minutes. Could that be a symptom of a bad cap in the phone preamp. would there be caps in that path?

[MSaturn]

Re: Amplifier Question

Yes. Any device with a power supply has capacitors.

[Æ]

Re: Amplifier Question

That's right on-the-money... I've got several vintage amps/preamps, and many have those same problems. Low output, popping/crackling sounds, distortion, etc.
I would never have thought of the caps causing the popping sound in my vintage Sony, but now I know... THANKS Curt!!

Old equipment with occasional clicking and popping sounds is probably because of oxidized/dirty/worn switches and potentiometers.

A capacitor that has failed will generate a constant not intermittent problem.

[Æ]

Re: Amplifier Question

I have a 30 year old preamp that appears to work fine. I have heard no degradation of sound quality in, well, 30 years.

Except when I use my new turntable. I now hear popping every few minutes. Could that be a symptom of a bad cap in the phone preamp. would there be caps in that path?

Static electricity buildup/discharge is a problem with turntables/vinyl.
Once around popping also comes from defects in the record/vinyl.
I might initially suspect the RCA connections/connectors as being dirty/oxidized.

[dwigle]

Re: Amplifier Question

Static electricity buildup/discharge is a problem with turntables/vinyl.
Once around popping also comes from defects in the record/vinyl.
I might initially suspect the RCA connections/connectors as being dirty/oxidized.

I'm thinking you're right about the connections. The line from the rca plug to the cartridge leads to the headshell are all very old and fragile.

[olddude50]

Re: Amplifier Question

Guys, I have been looking at a vintage piece of equipment and thinking that perhaps I could replace the electolytic caps myself. I saw the pictures of the caps posted by AE, but is that how all the electrolytic caps look? In other words, if I take this project on, how will I know the electrolytics from the nonelectrolytics in the system?

[Æ]

Re: Amplifier Question

Guys, I have been looking at a vintage piece of equipment and thinking that perhaps I could replace the electolytic caps myself. I saw the pictures of the caps posted by AE, but is that how all the electrolytic caps look? In other words, if I take this project on, how will I know the electrolytics from the nonelectrolytics in the system?

Electrolytics have polarity and as such polarity markings, usually a negative (-) sign.
If you don't know what you are doing, I wouldn't attempt it, not without a little schooling or the help of a friendly technician/engineer.
We can't teach you how to swim or drive a car by posting suggestions over the internet.

[B&K]

Re: Amplifier Question

I can see that this thread has taken on a small life of it's own. Much appreciation to everyone for your time and input. I was experiencing some popping and buzzing from my power amplifier when I originally posted this thread. After getting into the chasis and blowing out a lot of the dust, it has completely stopped. To my eye, the caps didn't show any signs of problems. Of course, that doesn't mean that they are ok but I am hoping that, as AE suggested, the problem was being caused by the dust.