What did you do with the Pioneer - was it a refresh, or upgrades?
Long answer to a short question coming up... hopefully answering most of the more likely "matters arising" on the subject
Firstly it is important that folks realise that the processes used etc are the same for all amplifiers, give or take the odd idiosyncrasy... one of the most annoying questions I hear is "have you worked on one of these before?".... It makes no difference to a good engineer whether they have or haven't other than it can be quicker if one is really familiar with a particular piece of kit
The Pioneer was not modified but came in for a re-cap and general service so we could call that a refresh yes. The electrolytic caps were all replaced, but with better than original ones, so I guess that could be called an upgrade of sorts, and all things like bias current, regulated PSU voltages etc etc were checked and adjusted as necessary, all boards inspected for dry joints etc, switches, pots, connectors and fuses etc cleaned with contact cleaner and anything that seemed like it could do with some attention was sorted out. Same as with the Sugden featured here really.
I can carry out all sorts of upgrades to virtually any amp as well of course, the older and cruder it is the more upgrades are applicable/possible and the bigger the improvement generally. I.E. a modern, expensive and well designed and built amp may have many of the things I could do as upgrades on an older/cheaper/less well engineered amp fitted as standard anyway. I can do things like add regulated supplies, build better regulated supplies where already present, fit bigger and/or better caps, fit better signal caps, better op-amps, switched attenuator instead of vol pot if there's room etc etc.
I've gone as far as fitting extra output mosfet's to MF amps and fitting regulated front end supplies to Exposure amps in the past but much depends on the topology of the amp and whether there is the room to fit the prospective upgrades...
What is
not possible is to say beforehand what
exactly will be the nature of the subjective improvements and how much of an improvement each potential upgrade will give! Generally though we are talking greater openness, transparency, neutrality, improved separation between instruments (especially when there's lots going on) and less muddiness and confusion, tighter bass, more detail and better sound staging.
What you won't generally get is more "warmth and lushness" as these are
often due to the amp being basically not very good and having lots of even order distortion and/or a rolled off top end... it's acting as a "tone control" or "nice colouration machine"! Some folk like this sort of thing and may find that by making it into a "better" amp it loses
some of the "rose tinted specs" colouration that they like. I've not had a dissatisfied customer yet but could imagine that if someone's bought an amp that
most of us would consider coloured and/or "wrong" sounding, and specifically because these aspects appealed to them, then they could consider the improvements a downgrade!