I recently found a 1993 Now Hear This! SW2Pi 10" sub and the accompanying amplifier, the 200w SA-2 from Craig's List. It had a problem, according to its previous owner. It basically had an 'unmusical' sound when connected via its RCA inputs. This makes it a great deal if I can fix it and integrate it into my system, so I called the owner and checked it out.
It's owner even demonstrated the issue. My thought was a bad pot, possibly bad caps. Either way, I'd have a perfectly good sub in an almost-mint container (sans front screen) to play with, so I bought it.
When I got it home, I proceeded to diagnose the cause of the output issue. A -> W and B -> W on the volume pot were both compromised. The volume knob no longer controlled the volume. It jumped from dead to full force in a millimeter.
I went back to the previous configuration until the pot came in. It arrived today. I also ordered a Weller soldering station from Amazon, along with a Helping Hands tool.
Using my new soldering station is a dream. You set it and forget about it cooling off. It's amazingly precise.
Swapping the new part in for the old took about 10 minutes. I was surprised how easy it was. With a 25 watt iron I had to wait 2 minutes between solder joints.
I had to guess on which a50k to get, so the shaft was a bit short, though the original knob still works with it.
I took it into the living room to give it a quick run, and it was perfect, wiping from a to b without issue. Well, one issue. The sub component rattles glass. Very precisely.
After re-assembling it and testing it out in the system, I have to say it makes an amazing improvement when hooked up via low-level loop-back. It crosses into full range speakers and provides a pretty smooth shift between sub and all else.
What caused the mechanical failure of the pot? If I had to guess, I'd say it's marketing-induced.
Almost all of the marketing material for the sub and amp shows the amplifier sitting right on top of the sub! Brilliant!
Time + Pots + Vibration = Failure
I suppose that means that all plate amplifiers are essentially going to be dead in a few years for the same reason. Or it's the reason for so many RMAs occur for them within the first month.
I did notice an issue with one of the SA-2's RCA inputs. It probably just needs to be either re-flowed or re-soldered. For now, a chopstick between plugs fixes things well enough. Adds a Timber Timbre to the sound. :] (the second's pronounced tam-bər, btw.)
I also need to fix my Rotel RB-850's speaker posts. It should be really easy, except for pulling the boards out to work on them.
If I sent the SA-2 to a local repair shop, it would have cost me at least $90. I'll probably be able to save more money on repairing the other two issues myself as well.
So I have a few tools which are assets, and I improved something I bought, which provided me with both skills and sweat equity in resale value.
I want to try my hand at a Nelson Pass design. It would be cool to have one of those $5000 Class-A beasts at a fraction of the cost.