Choosing suitable amplifiers for restoration

[ostripper]

Anyways for some reason the 555 seems to have a sort of hype around it, hiking prices up on epay.

The 555 would be outperformed by the 545. Perhaps the perceived durability of the big metal can outputs (TO-3).
Yes , the Honey Badger IPS is a much more refined design. Very accurate , minus the EF-3 ... about the same as the Wolverine.
The 545 is the "baseline" design of this topology (LIN) dating back to the 1960's.
OS

 

[Phloodpants]

Some of the best (wired) aren't bad at .003% , like some well made "Leach" amps. But a PCB leach is typically 1/10 that - 2-3PPM.
You most likely Couldn't tell the difference. I don't mind a good .02% amp , as long as it is dead quiet.

That's a really interesting point, and I have some experimental evidence to back it up. When I restore Adcom GFA-555's, which have lots of long internal wiring, I get about 0.02% THD+N at 2.8V. I get the same result with the 400Hz high-pass enabled on the distortion meter, so it's not just hum.
But on my board testing jig I get 0.005%! Close to the limit of my HP 8903B. The jig contains an exact replica of the 555 output stage, except with just one pair of output transistors. It is compact and has ground plane pour throughout. I suppose the improvement is due to the tightly constrained EM fields. There are return paths available in close proximity. The actual amp has giant loops and acts like a patch-antenna!

 

[ostripper]

Thats why the wolverine is PPM , NO loop of currents. TOP/Bottom of PCB is the rails and semis are P/N/P/N -
alternating genders. Grounds are separate star for current returns and small signal returns.
I've seen most OEM's suck at layout except Pass/Curl audiophile stuff.
OS