I am currently looking at this schematic and I'm clueless about the part on pin 5 where the ground on the capacitor should be connected into something that is labeled "To Large Signal GND". What does it mean? (Chip: LA4597)
Electronic – “To Large Signal GND”
schematics
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First of all, this is a nonstandard and unhelpful way of calling out component values. Don't do this on schematics you draw! (In normal practice, "R220" means "resistor number 220" and the value is shown separately.)
But somebody with experience might be able to figure it what's going on. Let's see how I do...
C180 must mean 18 pF. Those are crystal load capacitors, which are commonly in the 10 pF - 20 pF range.
C105 means 1 uF. These are bypass capacitors and 1 uF is a common value and the datasheet-recommended value.
R220 probably means 22 ohms, from the example circuits in the 32u2 datasheet.
I found this drawing in the datasheet:
Also notice the supply connections. The micro has its own internal regulator, so the Vcc doesn't need to be connected to anything else (except its bypass capacitor.)
None of the components are super critical. 10% tolerance should be fine.
Once again, don't use this as example of how to draw schematics.
(edited to revise 0.1uF guess to 1 uF.)
I agree with what Steven said, but want to add a few things.
Ceramic resonators look electrically very similar to crystals. The main differences are:
- Resonators are cheaper than crystals. This is the primary reason they are used over crystals, especially in high volume applications. For one offs, the difference is small and therefore irrelevant to hobbyists and anyone doing small scale builds.
- Crystals are more accurate, which is the primary reason they are used over resonators. Resonators may be accurate to 1% or 1/2%, but that's still way more slop than the 50 ppm even a cheap crystal can do. Note that 1/2% is 5000 ppm. Crystals good to 20 ppm are readily available and not much more cost than 50 ppm. 10 ppm is available, usually at a premium. Temperature controlled crystals can be good to around 1 ppm.
- Resonators are mechanically more robust. They can take more shock and vibration than a crystal can. Resonators are preferred in automotive applications, for example, for this reason.
- Resonators usually require a little higher drive to operate than a crystal. Either is still well within what CMOS circuits can do, so this is not a reason to chose one over the other except in very low power applications. But, it is something to consider when using a resonator. Some microcontrollers, for example, have several different drive levels the crystal circuit can be set to. A resonator may need one level higher than a crystal of the same frequency.
Added:
I meant to say this before but got distracted. The schematic above is missing the bypass capacitor. This may seem unimportant, but it's not. You should solder a 100nF to 1µF ceramic cap accross the power and ground pins of the chip right under the socket. The loop from chip thru cap and back to chip should be as small as possible. Various flaky things may happen without this capacitor, even if it appears to be working.
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Best Answer
That chip is an 11 W audio amplifier. It takes low-level signals (< 1 V) and amplifies them in voltage and current. The output current at peak volume will be several amps. Several amps flowing through the PCB traces will cause a slight rise in voltage along the trace and if this alters the ground voltage at the inputs distortion and instability may result.
Note that the capacitor is on the amplifier power circuit. I imagine that this cautionary note is to minimise the risk of an audible "thump" when the amplifier is switched in and out of standby.
simulate this circuit – Schematic created using CircuitLab
Figure 1. A very crude representation of an audio amplifier using two different ground symbols for the small-signal and large signal grounds. Both are connected at only one point - often referred to as the "star" point and usually located close to the power supply. The red arrows signify the large current paths and the green the small-signal paths.
The solution is to separate the small-signal and large-signal grounds. For you this means that all the left side capacitors will be connected to the small-signal ground.
I had a look but, unfortunately, can't find a recommended PCB layout.
From the comments:
Figure 2. Schematic from the datasheet.
I would take this diagram in conjunction with the one you posted to show that all the small-signals are on the left.
Note that my Figure 2 shows the amplifier used in bridged mode where two amplifiers running in anti-phase are driving opposite ends of the speaker. This allows double the voltage swing on the speaker compared with the arrangement shown in your schematic.
Update 2:
There are two things going on here.
The hiss is probably background noise from your phone. I suspect that you are finding the amplifier good and loud so that you are turning the phone down to achieve the right volume level in your speakers. The problem is that the phone's volume control is before its output amplifier so you are turning down the signal but not the unavoidable noise that is generated by the phone. This means that your signal to noise ratio is poor. You will notice this in quiet or silent passages of your music.
The solution to this is to wire a volume control on the input to your amplifier.
simulate this circuit
Figure 3. Amplifier input volume control. Use a log (audio-taper) pot so that the perceived volume increases linearly with pot rotation.
With this modification connect everything up, turn the input volume to minimum and the phone volume to maximum or close to. Hit play and turn up the input volume to the same audio level you had before. No stop the music. The his should be significantly reduced or even inaudible. The switch-off thump should be reduced also. If this works you have increased the signal to noise ratio. The idea here is to maintain the signal level close to nominal or "normal" or "line-level" all the way through the audio chain and then attenuate as close to the end as possible.
The audio click is caused by the phone's output amplifier switching off. If you consider this to be similar to my Figure 1 then the output of OA1 will be at 6 V when quiet. (This allows the output voltage to swing upwards towards +12 V and downwards towards zero to mimic the positive and negative variations in sound pressure originally picked up by the microphones. C2 blocks the 6 V DC getting to the speaker. When OA1 is powered down, however, the output drops suddenly from 6 V to 0 and the voltage on the speaker gets a brief -6 V "kick" which you hear as a thump. There's not much you can do about this unless you can find an app to keep the phone's amplifier powered on.
Update 3:
The first table in the datasheet gives the recommended heatsink dimensions. There is no mention of whether the metal tab on the package is connected internally to any of the pins so I assume that it is not. You can confirm this with a continuity test between the tab and each pin. Grounding wouldn't matter but shouldn't hurt either.
Update 4:
Yes. If the amplifier is to be able to reproduce low volume source material at normal volume then excess gain is required in the amplifier. This means that a strong signal at full volume may overload the amplifier or the speakers - whichever limit is reached first.
simulate this circuit
Figure 4. Input attenuator.
Yes. Adding R2, a variable or fixed resistor, will attenuate the input and allow you to set a maximum gain.
Your amplifier already uses negative feedback to set its internal gain. You don't need to mess with this. If you progress in your learning you will come across it in op-amp circuits. The basic rules of it are not too difficult.