Original Website © Amplabs 2009 This new site created February 2024
Quad 303 Full Component Replacement & Output Upgrade (Q303FCR)
Amplabs
The main advantage of going for this modification is increased reliability and longevity as all the components, bar the
transformer ,are replaced with modern high performance parts. Many of the parts on a vintage 3O3 are several-
decades old and electronics parts start to break down. This is why even after a proper service parts can and do fail.
What we do to your 303:
The old set of three PCBs are discarded and we fit Amplabs replacement boards. The four smoothing/output caps
are replaced using our capacitor PCB modification, which includes L & R rail fuses for added protection. The full array
of transistors including those on the heat sink are replaced with modern ‘ON’ devices. All small signal resistors are
high stability 1% types. The key resistors that are susceptible to overheating under fault conditions are replaced with
flame proof types. All semiconductors used in the high voltage stages have higher breakdown voltages and increased
current capability. The output transistors in particular are ON 250W devices compared to the original 117W types.
As an option, the output stage can be modified from 'quasi complimentary' format to a 'fully complimentary' format.
This was not possible when the Quad 303 was first launched. Complimentary high power transistors (NPN/PNP) were
not readily available then.
If you are looking for an improvement in sound quality and are convinced your existing 303 is as good as it can get,
then you may prefer to go for our 303 new circuit option with our SUFI board upgrades. (Q303HPUG)
Full component replacement and new front panel
For ure listening pleasure
