The VMPQuadPlus is very similar to the VMP-4000e in the sense that it is a four channel valve microphone preamplifier with the majority of the circuit being almost identical.The differences account for a slightly broader frequency response, a few db of extra gain and a lower reaching bottom but in most recording contexts the differences may be barely perceivable.
The omission of the 'deep' circuitry accounts for the extra db in gain and allows for the inclusion of the pad/gain control to further push the limits and fine tune valve colouration. This adjusts the level in between the two stages of the triode/valve leaving the normal/+12db toggle to adjust the degree of negative feedback around the first stage similar to the 4000e toggle.
In the 'normal' position a slight amount of negative feedback linearizes the first stage and makes it run more transparently whereas in the +12db position the circuit runs in 'open loop' with a pleasing coloured texture.
This allows for a very wide gain range and means the VMPQuadPlus can handle everything from hot Condensers to lightweight Ribbon signals without the use of external pads or lifters.
Other differences include the addition of a front panel face plate that improves shielding and provides some protecton to the toggle switches and a signal LED on each channel to indicate channel activity.
If your recording requirements extend beyond recording drum kits and other rock styled instrumentation and you desire more control over valve colour then the VMPQuadPlus may be suited to your needs.