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Muddy Bass Vintage JVC JA-S31 Before and After complete recap

Hey this is for any techs or hobbyists out there. I have a flly functioning JA-S31 that finished a total recap on. I used all Nichicon, audio series for as much as I could and general purpose for the ones that they didn’t have in Audio series. The exception was the power caps which I went with Chemicon 12000uF 80V (up from 10000uF 50V). Overall the sound is improved. Highs are superb. However, the biggest issue that I was having before the recap, as well as after is thick muddy bass. I can trim it down almost all the way on the bass pot or maybe one click from the bottom, which will take the muddiness out, but then I lose a lot of midrange and vocals become tinny. I had heard really good things about the amp and I don’t think that was an issue from the factory.

What avenues should I explore to help narrow down the cause of the muddy bass? Are there any known weaknesses with the electrical design and/ or are there particular components that could fail leading to this issue? Also, are there any mods one can do in general to help attenuate the bass without sacrificing mids? I’m fairly new to this, I’ve recapped 3 amps and thats the extent of my knowledge. BTW the other 2 came out wonderfully.

Any help or advice is sincerely appreciated.
Manual Download available here
https://www.hifiengine.com/hfe_downloads/index.php?jvc/jvc_ja-s31_service.pdf

charnich

Showing 1 response by millercarbon

millercarbon's avatar
millercarbon
12,531 posts
 
With your experience I’m sure you already know the answer, you’ve pretty much answered it yourself, and just need a little confirmation. Because you don’t like the answer. I don’t blame you.

The other two that you recapped came out wonderfully because recapping doesn’t really change the fundamental character of a design, it simply allows that character to be realized more fully and heard more clearly. Recap an amp with dynamic extended highs and the highs will be just as dynamic and extended, maybe even a bit more so, only with less grain and glare. Recap an amp with tight powerful tuneful bass and the bass will be just as tight and powerful and tuneful, maybe even a bit more so.

The problem you’re having is this time you didn’t recap either one of those amps. You recapped the one with too much wooly bass. So now you have even a little bit more wooly bass.

Certainly there are all kinds of workarounds. My experience however is that in situations like this, rather than try and go off balance elsewhere attempting to correct what is off balance here that you are far better off to chalk it up to experience and move on.
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