Technics SU-X502 Amp Crackles

MouthBoy

MouthBoy

MouthBoy

Soldato
Joined
6 Apr 2010
Posts
2,906
Location
Cambridgeshire
Hi All,

Today I bought a few bits from a friend to swap out of some older stuff I had.

The amp however seems to crackle the first time any music is played through it. This can last for a few seconds only or up to about half a minute. I have tried the speaker A and B outputs but same result. I have also changed the input device, the speaker cable, the speakers and taken the EQ out the mix, but it stills does it.

Am I doing something stupid, or is there something I can check to ensure its actually a fault rather than be doing something wrong?

Thanks

Scott
 
No, you're not doing anything wrong. It's an older amp and needs some service work to bring it back up to spec.

Most likely the big power supply capacitors are dried out or swollen. They're usually found in pairs, and they're the biggest ones in the amp. You can see them at 1:12 on this Youtube vid. The two big black cylindrical things next to the black ribbon cable bottom-middle of the frame. In RL they'll be about the size of C cell batteries.

The fix is to replace them, if they're what's at fault. Not hugely expensive to do unless that parts are scarce. My guess is they're 56V 4700uF (microFarad) caps, but you'd need to check by looking at the part directly.

With caps, stick to the same voltage - that's important - but you can go up in capacity if the exact match for the original part isn't available. A couple of 56V 8200uF would be fine.

Next, it's the temperature rating. There's 85 degree and 105 degree. The higher temp rating is better but more expensive. After that it's the brand and whether the caps are Low ESR for audio applications. Elna and Nichicon brand caps are suitable.

Parts cost will be somewhere between £15 and £30 depending on brand and spec. It's not a guaranteed fix though. You might tip these an and then find there's still a fault somewhere else on the board. The question is whether you're prepared (and skilled enough) to take the gamble versus the value of the amp? A lot of fan boys like Technics, so it's over-valued for what it is. In this case it's the amp from an 80's stack system that was a bit underspec'ed so they had to fit it with a cooling fan. Although the amp is technically a separate, all that means in this case is it came from the higher end of Technic's stack system range. It's not a stand-alone separate amp like those from the SU-V series.
 
Thanks for the advice. I have talked to my friend and he has said to pass it back to him and he will give my money back.
 
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