Electronics project notes/Audio notes - amps and speakers

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(note: some content is gone as I'm reorganizing it elsewhere. It'll be back. Probably.)

Design side

Weather-resistant speakers

For example for

• Terrace (deals with moisture, not necessarily rain)
• Marine (deals with water in general)
• Sauna (deals with moisture, some heat)

The heat is not that much trouble if you place them low -- it won't be much hotter there than e.g. the average car on a sunny day)

Those three terms should help start your search.

These tend to have plastic cones, and generally be made of plastic, and maybe have metal contacts coated.

Getting great sound is a little more complex, mostly because there is much less choice / competition.

Repair

Speaker foam surrounds

Surrounds are the soft rings that connect the (classically often paper) cone to the (often metal) frames.

Its function is mainly just to keep the edge from flapping, without limiting the cone's movement much. As such, they are thin, and light.

A thin foam is a cheap and efficient choice, but over a decade or two will go brittle and wear out. (there are other materials that will work as well, or better. Some applications may also see heavier materials, like rubber in subwoofers, which if there are only minor tears may have less invasive fixes)

It's an easy-enough and satisfying fix, given a new ring, some glue, and some patience.

Perparation:

• get some new surrounds

buying foam surrounds of the right size is cheap and easy enough

if you find them too expensive, you can DIY it from a thin fabric or so (fabric surrounds will often last longer, though are also a little more work, and a little bit of considering which fabric works well)

• get some glue

the ebay-style kits will typically contain some.

When you have paper cones, look for acid-free glues (to not damage that paper)

Your basic wood glue seems a decent option, and they seem to often be wood glues (verify) though possibly avoiding certain variants/additives(verify)

there are further glues sold as speaker repair glues (verify)

you could use other glues (like superglue, certain polyurethanes), but it's suggested that something that stays slightly flexible will last longer(verify)

Steps are roughly:

• optional: take the speaker out of its cabinet.

usually not necessary, but often easier to work on

If you disconnect the wires, remember the polarity.

• There is typically something laid inside the frame's metal edge that holds down the foam, the trim ring

This may be a solid cardboard or thick foam, and may well be reusable

if it's foam and has also disintegrated, or when you can't remove the ring without destroying it, make some new ones. Its only function is to hold the surround down, and arguably only during gluing, and telling you afterwards whether all of it is attached. In which case you can make it out of whatever you have handy. I cut one out of generic cardboard box.

• Clean anything that seems to want to come off, or does not look like a good surface to glue on

if there's some foamy muck on the cone, friction may be enough to take that off

be careful scraping things off the cone, because twisting it or pulling it with large forces could damage it. You may find it easier to scrape with a sharp knife

If the foam comes off in a cloud of tiny particles, moistening it with something like rubbing alcohol may make things a little easier

This works on the cone too (and rubbing alcohol won't hurt the paper).

• Plan the gluing step (mostly because the glue doesn't dry very quickly)

You can glue surround-to-cone and surround-to-frame at the same time, but on your first repair you may wish to do them separately, to get a feel for the things to pay attention to

Lay the surround on the speaker to get an idea of positioning, and which parts need glue later

• surround-to-cone gluing notes:

it's easier to apply glue to the foam surround's inside edge (than the cone, because it's easier to tell how far in to cover with glue)

put the two parts together, and for the first few minutes make sure they are in contact (so all the surface takes - after that you can assume the it won't let go). I've made cardboard and foam rings to put even pressure on, but paying attention is about as good.

Amplifier repair

✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.

On protect mode

Most amplifiers have a protect mode that will cause it disable high-power parts (mostly the power amp) whenever it sees more current than sensible. Some also monitors temperature.

This protects amp parts against breaking/burning, and also the speakers, particularly when you do something silly.

Some amps have a light showing protect state, most do not.

Reasons for protect mode to trigger:

• shorted speaker wire (e.g. in cars)

check: if it always goes into protect mode if speakers are connected, and never without

• transistors are broken (often mean it does this at startup - never comes out of the mute delay)

You can check transistors with a multimeters diode test. That is, you can see if there are shorts between pairs.

• noisy (dirty/worn) pots can trigger it -- though only if the protect mechanism is highly sensitive or the pots dirty enough to effectively send spikes

check: if it generally only happens when changing volume knobs, regardless of level

(or always at the same place on the pot)

• thermal protection can trigger

in the sun, near a radiator, if something designed to vent is completely covered

if overdriven too long (where possible)