Difference between revisions of "Electronics project notes/Audio notes - amps and speakers"

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* noisy mains (rare, though, since power supplies tend to filter at least a bit)
* noisy mains (rare, though, since power supplies tend to filter at least a bit)
===Guitar amplifier repair===
Specialized field, because there's a lot of them with tubes either for coloring int he pre-amp,
or even still for the power amplification, and tubes come with some oldschool design choices,
...such as an audio output transformer, because while tubes' output impedance is too high to drive directly into speakers, solid state amplification (transistors) can do it directly.

Revision as of 13:16, 1 April 2020

This is for beginners and very much by a beginner.

It's intended to get an intuitive overview for hobbyist needs. It may get you started, but to be able to do anything remotely clever, follow a proper course or read a good book.

Some basics and reference: Volts, amps, energy, power · Ground · batteries · resistors · changing voltage · transistors · fuses · diodes · varistors · capacitors · inductors · transformers · baluns · amplifier notes · frequency generation · skin effect

And some more applied stuff:

IO: Input and output pins · wired local IO wired local-ish IO · · · · Shorter-range wireless (IR, ISM RF, RFID) · bluetooth · 802.15 (including zigbee) · 802.11 (WiFi) · cell phone

Sensors: General sensor notes, voltage and current sensing · Knobs and dials · Pressure sensing · Temperature sensing · humidity sensing · Light sensing · Movement sensing · Capacitive sensing · Touch screen notes

Actuators: General actuator notes, circuit protection · Motors and servos · Solenoids

Some stuff I've messed with: Avrusb500v2 · GPS · Hilo GPRS · JY-MCU · DMX · Thermal printer

Audio notes: basic audio hacks · microphones · amps and speakers · device voltage and impedance, audio and otherwise ·

Less sorted: Common terms, useful basics, soldering · Microcontroller and computer platforms · Arduino and AVR notes · ESP series notes · Electronics notes/Phase Locked Loop notes · mounts, chip carriers, packages, connectors · signal reflection · pulse modulation · electricity and humans · Unsorted stuff

See also Category:Electronics.

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

Design side

Weather-resistant speakers

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

For example for

  • Terrace (deals with moisture, not necessarily rain)
  • Marine (deals with water in general)
  • Sauna (deals with moisture.
The heat is not that much trouble if you place them low -- it won't be much hotter 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.

Use side


Speaker repair

Foam surrounds

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

Surrounds are the soft rings that connect the (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 ideally thin, and light.

Which is why they're often foam, which makes them one of the first things to go brittle and wear out after a decade or two.

And easy to fix, given a new ring, some glue, and some patience.


  • get some new surrounds
buying foam surrounds of the right size is cheap and often easy to find.
if you find them too expensive, you can DIY it from fabric or so (fabric surrounds will often last longer, though are also a little more work)
  • get some glue
the ebay-style kits will typically contain some.
When you have paper cones, look for acid-free glues. Your basic wood glue seems a decent option(verify)

Procedure is roughly:

  • optional: take the speaker out of its cabinet.
not necessary, but often easier to work on.
If you disconnect it, remember the polarity.
  • Remove the trim ring - the thing inside the outer part's metal edge that holds down the foam.
This is often 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 solidly hold the surround, arguably just to help be part of the glue process, so you could make it from whatever you have handy. I did one out of generic cardboard.
  • Clean anything that seems to want to come off, or otherwise does not look like a good glue surface
if there's such muck on the cone, friction may be enough. Sometimes you may prefer a sharp knife to avoid large forces on the cone.
avoid twisting the cone. Patience is good here.
If the foam comes off in lots and lots of tiny particles, moistening it with something like rubbing alcohol may help if you wish.
This works on the cone too (and rubbing alcohol won't hurt the paper).
  • Plan the gluing step
You can glue inside and outside at once, 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.
Laying the surround upside down can help remind you of which parts need to get glue later
  • apply glue to the foam surround's inside edge (it's easier to tell how far to go than it is on the cone)
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)
you may e.g. like to make some rings that gently hold all parts down while gluing.

Amplifier repair

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

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 (and sometimes also monitors temperature)

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

Your amp may have a LED showing protect state, most do not. If it does, consider that it may, or may not, show during the regular startup mute delay.

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)

Guitar amplifier repair