Range small, not large – pick! (8)
I believe the answer is:
spectrum
'range' is the definition.
(a spectrum is a range or variety)
'small not large pick' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'not' is a deletion indicator.
'large' becomes 'L' (eg in clothes sizes).
'pick' becomes 'plectrum' (a guitar pick).
'plectrum' with 'l' taken out is 'pectrum'.
's'+'pectrum'='SPECTRUM'
(Other definitions for spectrum that I've seen before include "Crumpets (anag)" , "'Broad range, scope (8)'" , "All the bands of colour seen in a rainbow" , "Band of refracted colours" , "The bands of colur as seen in rainbow" .)