nad preamps 1130 1155 1240

[rmgvs]

I have a 2nd hand NAD preamp 1240 which I have modified slightly and am very surprised about the real good quality of its sound on both vinyl and cd. The circuit is a general one for both vinyl and line: a differential input pair (bjt) and a push-pull output pair (bjt) where the line-stage also can feed all kinds of headphones. In between is a tone control circuit around 1 opamp for 2 channels.

Now I have seen a 1155 preamp from the inside. The outsides are almost exactly as 1130 and 1240 and I suspected identical circuitry. As I can see it quickly though, the 1155 has a complete different vinyl stage (total of 15 transistors per channel, including fets), another line-stage and the same tone-control circuitry. The 1130 I don't know.

Does anybody know more about 1130 and 1155 preamp circuitry, differences and similarities, impressions of sound quality. First impression of listening to 1155 shows a sound quality that is way behind my 1240.

All preamps seem to come from same years (around 1987-1990). Is this right?