Thank you both for the helpful replies. I an now aware that "audio-in" is not the same as "microphone-in". I also turned up the volume in Sound input in System Preferences. This helps but I would like a fuller sound quality.
My Sony mic (ECM-MS907) uses a small AA battery which gives enough power when recording to a minidisk player. I can then save and burn the tracks as pure WAV files to a CD. I wondered if I could also record straight to the Powerbook as WAV files.
I looked at the Griffin iMic and PowerWave on the Griffin website and both seem impressive.
One reviewer says that the iMic will improve recorded volume and quality when using this Sony mic. Some reviews seen to imply (indirectly) that the sound is good but could be better (not of professional quality but good enough)?
The PowerWave acts as an external soundcard and amplifier so it seems to be an excellent product. Incidentally, I just tried a USB creative SoundBlaster suitable for laptops which I have been using on my PC and it gave a better input volume when recording to the Powerbook. If the Powerwave can add more gain or an even better sound than this, it will be worth getting. (It also powers Apple-pro speakers but I just bought an iFire for this purpose.)
I sent an email to the Griffin support to see which one they recommend.
Thanks again.
JB