tony sayer wrote:


I think your a bit of a QUAD fan Phil, was arguing with someone the
other day that such as upping the power and LS caps in a 303 from 2200
to 4700 uF was making it something else which it wasn't originally like
modifying the input LM301A chip of the 405 ..

comments?....


** From reading published interviews, I know Peter Walker liked to get a product *right* before selling them to anyone.

From studying some of Quads famous amplifiers ( Quad II, 303, 405 & 306 ) the choice and usage of each part appears carefully considered as to suitability, necessity and reliability.

The large electros in the 303 are adequate for their job. The amp has no hum since the PSU is regulated while the output coupling electros have low enough impedance at 40Hz (ie 0.25 ohms) to effectively damp cone resonance in any 8 ohm woofer likely to be used.

Unless the electros appear to be deteriorating ( ESR heading North )I would leave them be.

The 301A op-amp in early 405s is a sore point with many enthusiasts who *feel* it is obsolete and inferior. It provides 15 times voltage gain to drive the Current Dumping power stage, which has a voltage gain of only 3.8 times.
Cleverly used in the inverting mode, it does that job very well and also provides the sub sonic filter function.

The possible replacements require some circuit modifications and do almost nothing to improve the amplifier's specs.



..... Phil