You generally have to stick with British preamps, and Quad is of course a perfect match to Quad. The issue is that Quad amps were desisgned with input sensitivity of 0.5v to drive to full power. Most American preamps have input sensitivity in the 1.5v - 2.5v range. So American preamps will typically overdrive the 303 beyond very little rotation of the volume control, with normal sources. Conversely, a Quad preamp used with most American power amps will not be able to drive them to full power out.
There are many British preamps that were built to the assumption of a 0.5 - 0.75v input sensitivity. I have a beautiful-sounding Audion tube preamp that works perfectly with a 303, but it was unusable with a pair of Audiopax 88 monoblocks I once owned.
You can widen the range of usable preamps with the 303 if you use in-line attenuators, like the Rothwell RCA - RCA units with 10db reduction in gain.
On the other hand, if you have a disc player with volume control, you can directly drive the 303 with no gain deficiency.
Phil
There are many British preamps that were built to the assumption of a 0.5 - 0.75v input sensitivity. I have a beautiful-sounding Audion tube preamp that works perfectly with a 303, but it was unusable with a pair of Audiopax 88 monoblocks I once owned.
You can widen the range of usable preamps with the 303 if you use in-line attenuators, like the Rothwell RCA - RCA units with 10db reduction in gain.
On the other hand, if you have a disc player with volume control, you can directly drive the 303 with no gain deficiency.
Phil