I looked at an Apple universal dock to connect i-pod classic to hi-fi.

If only it were that simple!

Line Out refers to a fixed volume output (or level) from a device. Usually (or rather, in the old days) line out was just that - fixed. The volume control on the device would not affect the Line Out level. But Line Out from the universal dock is controlled by the volume on the iPod (and - as you appear to have discovered, the remote control). If you turn down the volume on your iPod, the volume out through the universal dock's Line Out will go down. So technically, it is not a true Line Out.

However, if you turn the volume control on the iPod up to maximum, then you will have Line Out Level from the Line Out on the universal dock (in other words, the output will be at the Line Out volume).

So if what you are trying to achieve is line out level from the iPod so that you can connect it to an external amplifier, and have it loud enough, then my recommendation is to use the Line Out from the universal dock but turn the volume on the iPod up to maximum.

BUT - you will ask (go on, ask... 😉 )

1. Why not simply use the headphone socket and just turn the volume up to maximum? Answer: because until recently iPods sold within the European Union (i.e. mine) had a lower maximum volume from the headphone socket than non-European Union iPods, and that lower level could not be changed. This would mean that I would not get a loud enough output from the headphone socket for my old amplifier.
2. Surely, if I have the Volume Limit (on my iPod) configured to give a lower volume, then I will have a lower level output from the Line Out socket on the universal dock? Answer: no, because when an iPod Classic is plugged into the universal dock, the Volume Limit is disabled and the Line Out is at Line Out Level when the iPod's volume control is at maximum.
3. My iPod is sitting on the universal dock, but I cannot find the Volume Limit in Settings on my iPod. Answer: when the iPod is sitting on the universal dock, the Volume Limit is removed from the menu. Take the iPod off the dock and the Volume Limit re-appears.

So you can use the universal dock's Line Out to connect to a Hi-Fi system. However, any music on your iPod at 128Kbps may sound thin on a powerful Hi-Fi. Even music at a higher Bit Rate (256/320Kbps) may not sound quite as good as playing from CD. Without being too technical, to fit so much music onto that tiny iPod, some bits of the music have been removed (or at least, minimised), to reduce storage space. The removal process is know as compression - that is, the music is compressed. On an iPod, even with modern high quality headphones, this is usually not a problem. But playing those same digital music files through a powerful Hi-Fi amplifier can reveal that something has been "lost" (removed) during the compression stage. A lack of bass is one.

If you hear an iPod, played through a powerful public sound system (mobile disco etc.), it can sound awful.

• It is possible to compensate for this to a degree, by using an equaliser to boost the frequencies that are lacking. How happy you are with the result will be a matter of your own judgement.
• Alternatively, music stored on an iPod in .wav format might sound better as that is not compressed. Be aware though, that wav files are the same size as music on a commercial CD - very large (about ten times more space is used).