My handy guide -
Regards to the ways of connecting an ipod directly to an amp:
- LOD or line out dock. A connector goes into the port at the base of the ipod and a cable runs to either a mini jack or phonos, which then plug into the amp. This connection usually bypasses the ipods own amplifier, but not its DAC. The volume is then controlled by the amplifier. The ipod is not charged through the LOD. Examples of LODs are the GQ-24 from Russ Andrews and the iBasso CB03. Both sound excellent.
- Dock. The dock connects through the ipod's port, but it also charges the ipod and does not always bypass the ipods amp, so the connection is different. Many docks then connect by minijack to minijack or to phono cables. Examples are from Cambridge, Apple and Arcam. See What Hifi reviews as many docks are not great.
- Minijack. A minijack cable from the headphone output at the top of the ipod to minijack or phono. The headphone out is the least effective way of connecting an ipod to anything. There are loads of such cables on Amazon and ebay, most for under a tenner and that cheapness reflects the lower standard of connection.
- a digital dock. This bypasses the ipod's amp and sends a digital signal to a DAC. Phono cables are then used to connect the DAC to the amp. There are two, the Wadia itransport which is expensive and reviewed by What Hifi. There is a cheaper alternative from Onkyo now, the ND-S1, but it has fewer connection options. Either are the only way to link an ipod directly to a DAC. You have to bypass the ipods DAC, or else you are trying to send an analogue signal to a DAC. A DAC needs a digital signal.
The alternative to the above is not to use an ipod at all. A PC with itunes connects to the amp via a DAC. Some amps have their own internal DAC. The PC usually connects to such an amp with a USB cable. Otherwise the DAC sits between PC and amp. The connection by PC to DAC is either USB, optical or digital cable. The DAC then connects to amp by phono cables.
There are other variations, but the above are the most common