WDPHONO3 3.18uS

[Richard]

Originally Posted by pre65

From a kit builders perspective Richards solution would seem better as very few of us have the skill, or equipment to adjust the pot properly.

If I remember from my Phono 3s build instructions, the advice was to set the pot in the central position.

That's right and it would make nominally 180pF + 25pF = 205pF which falls between what I checked as 190pF for ECC83 and 220pF for 5751. Leaving it there gives a slight dullness to ECC83 and a slight lift against the RIAA to 5751. Hence, as John says, you'll get folk reporting different sound with different valves. You get this anyway of course across brands but here there is a definite reason which checks empirically and by calculation and is due to the output impedances of the 2 types. Even specifying just ECC83 there is little point having the trimmer if a user doesn't have a sig gen, inverse RIAA filter and scope etc to set it optimally. This is further complicated by those nominally 0-50pF trimmers checking in at around 0-70pF or greater, so even the mid point really is guesswork unless it's checked with a meter before installation. Overall I'd build with fixed caps.

Whether to have the 3.18 is easy. Firstly, the cutter will have been rolled off, if only by non deliberate means or to a non-standard, so it does make sense to have at least some correction in the replay. Secondly, Phono3 will not check poorly against a test RIAA signal of either 3.18 or non 3.18 shape as it rolls off anyway and shows a steady decline after 20KHz with both. Having the 3.18 does help flatten the response around 10KHz upwards and maintains the response a little further after 20KHz. I don't doubt Noel for one minute with other phono stages but would urge you to make your own checks first Dave before dumping 3.18 on this amp. It's also very interesting to check a few older phonos and see how tailored they were. Lest it be thought by anyone reading that this all sounds a bit hit and miss I can assue them that Phono3 really is very good indeed.