I can't answer your question, but I will say that the Caddock resistor upgrade was worthwhile. It resulted in a less aggressive, more natural sound.
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Grateful, I can't speak to the upgrade on an MA-1. However, I did have this upgrade done to an early production MA-2 MkII to bring it up to current MkIII production status. Ralph replaced the big blue filter capacitors for the power supply with the even larger "built for the MA-2" capacitors and he updated the power supply with the new regulated power supply. There were other updates done to my MA-2 at the same time, so I can't completely isolate the impact of the filter cap and regulated power supply upgrade. Nevertheless, the updated MA-2 clearly had noticeably improved control and authority in the bass, which is what Ralph told me to expect from the larger filter caps. And, the entire amp was smoother and more refined (with lower distortion) throughout the frequency range, which is what Ralph told me to expect from the new regulated power supply. I would expect the update to an MA-1 would have similar results.
If you have not already talked with Ralph about what to expect from this upgrade, I recommend you do so. My experience with Ralph is that he is absolutely straight in his comments about what to expect, and I've always found his description to match what I hear.
OK... I've had the MA1s back for a few weeks now, and WOW!!!
The biggest difference is in the low end response -- bass and drums sound truly realistic (depth, tone, decay, impact). There is more air around instruments and more natural tone overall. Sax is especially sweeeeeettttt (I don't mean overly lush but the tone is just spot on). Piano sounds more like the percussive instrument it is -- really uncanny, the improvement, I thought I had a good piano presentation before, but now its amazing.
Now, I did have the amps brought from mkii to mkiii also with full V-Caps -- so there is alot going on here -- my uneducated guess is; the lower end response improvements were reflective of the Power Cap upgrade.
Yes, the Power Cap upgrade is expensive, but the extension in bass I hear now along with the improved impact is very noticeable -- literally, its like I added a sub element to my Quad 988's.