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What are the signs of caps going in an Amp?

I have been blaming streaming since I am new to streaming, like a couple weeks in, new. I was away for a for while as our home was being built and my gear was inactive. I have a Classe CA-151 amp and Classe SSP25 pre that I only use for 2 channel anymore and they are approaching 20 years old. So I bought a Node 2i and have been enjoying my Qobuz trial. It started intermittently the last few nights where I start hearing static, muffled sound, almost like a radio station going softly in and out of tune. I have been blaming it on streaming and wifi or ethernet connection. Someone pointed out it may be a cap starting to go bad. I checked all the other connections and everything is tight and good. What are the signs of a cap going bad? Is it constant or intermittent? Next time it happens I am going to switch over to CD to rule out streaming. When it happened last night I switched to Tidal to rule out Qobuz, and then switched to my MacBook to rule out the Node and it was still there. I did not have the CD player connected at the time otherwise I would have switched, but that is my next step. 
Thanks!
128x128jmphotography
georgehifi's avatar
georgehifi
10,312 posts
 
What are the signs of caps going in an Amp?
First thing you notice if you open the amp, is that the cap top will start to bulge a little, maybe even the sides, some have an X stamped into the top this is a safety pressure release valve, or you see some wetness around the base on the PCB where the electrolyte has leaked out.

Cheers George
jmphotography's avatar
jmphotography OP
161 posts
 
@georgehifi I took the cover off the amp and everything looks clean, all the large caps look great, almost new. No bulging, no shrinking on the plastic wrap on them, no leaking anywhere. Took the cover off the pre and same. There were only 2 large caps in the Pre and they weren't bulged on top, maybe a slight bit puffy, thats a technical term. But not bulged. 
georgehifi's avatar
georgehifi
10,312 posts
 
maybe a slight bit puffy
Could be the first signs, can you take some pics of the puffy ones and post up, use this image hosting https://imgbb.com/

Classe are usually way over spec’d on their caps voltage, so it not likely. And this is a relatively new’ish model, if it were an old early 1990 one then the caps could be sus. https://img.usaudiomart.com/uploads/large/1717936-classe-ca151-stereo-power-amplifier-150w300w-into-...

Cheers George
jmphotography's avatar
jmphotography OP
161 posts
 
@georgehifi here are 2 pics from the pre. The ones that I thought looked slightly puffy are the 2 larger ones
https://i.imgur.com/YtwPcI1.jpg
https://i.imgur.com/d3vZ9cb.jpg

Here are the ones from the amp
https://i.imgur.com/zV1NdU1.jpg
https://i.imgur.com/1CeeqGm.jpg
https://i.imgur.com/fFrIJaT.jpg
https://i.imgur.com/19hd239.jpg
georgehifi's avatar
georgehifi
10,312 posts
 
They all look fine to me.

Are the heatsinks on both sides of the amp, the same temp after 1hr of being switched on?

Does the hum go up and down with volume up and down?

Try just the amp and speakers connected, see if the hum is still there, if not, connect the preamp then and see.

Cheers George
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