I’ll add to Caddy’s reply, ... because I’m enjoying coffee and The Moody Blues on a Saturday and why not?
True, most caps etc. are going to be fine even slightly outside of their range however: The unit was designed and tested within the original tolerances, bets are off on performance outside of tolerance. Most things will not be a problem, in fact most power supply capacitors can drift quite a bit with only a degradation in their ability to filter noise or store power, which would likely take a lot of drift before it’s noticeable unless it’s causing more heat.
When I was designing, industry-standard 20% resistors (for example) were used when deviations from the designed values had little or no effect, and of course we’d drop to 10%, 5%, 2%, Precision where it really did matter. So in most cases these standard tolerance devices could drift without detrimental effect. Good to have it checked and have all drifted components replaced at this point in its life however.
Regarding electrolytic capacitors: This is highly misunderstood, capacitor replacement is a huge profit center and a great way for people to claim added value and performance. There was (is?) a guy in Ann Arbor, Michigan for example who would take vintage Marantz receivers, add a bunch of extra capacitors wherever they would fit to the power supply main caps, then claim “re-rated to xxx watts”. Sure, Marantz Engineers didn’t think of that when they were trying to get the best power rating out of their design (rolling eyes here as a former Design Engineer).
So what capacitors should you replace, and with what?
First question, any that are out of spec, or could go out of spec before the next time you plan to have it in for service. They are cheap (except a couple of big ones or multi-caps) and testing them properly will cost about as much as just having them all on-hand to replace when you’re in there, which is why most of us will have all EL caps on the part list on-hand before removing covers, just rip them all out and replace (well, de-solder carefully). Leaky ones in the right spots will draw power and make it run warm.
Second question is a bit harder to answer but the easy one is with exactly what the original Design Engineers have in there from the factory! For me this part is easy. For most circuits there is a hierarchy. There are cheap electrolytic caps, more expensive non-polar electrolytic caps, small-value ceramic etc., and yes the film types are usually larger and more expensive.
For many/most needs the electrolytic caps suffice. There was no reason nor advantage to installing a film cap so the standard-tolerance electrolytic cap was designed in and installed. When there is a sonic or other performance advantage or other reason to install a different technology capacitor such as a film cap, it’s already in there from the factory. If a film cap is in there, or a precision value, put one back in. If it’s an electrolytic, replace it with an electrolytic. It is what was designed in, tested extensively, and created the sound and performance that McIntosh provided and it wasn’t about saving a nickel because that wasn’t Engineering’s job.
Will certain boutique caps improve the sound? Likely not. Again, there were plenty of high-end caps around when your amp was built, if it made a difference McIntosh Engineers would have considered it. However designing an amplifier is not a bunch of little parts, it’s the entire amplifier. Replacing a handful of capacitors with goofy $30 caps doesn’t make the amplifier any better any more than replacing my toenails with those from a star quarterback’s makes me a star quarterback. There are many “Technicians” out there, some trained some self-taught, but few if any with EE degrees, and even fewer of those who designed audio amplifiers, and the number who worked on the design of your amplifier lowers this to zero.
Why does this matter? Just the ramblings of an old Engineer who’s a pompous crank? Maybe.
The reason is because when we designed a circuit, it went through iterations that started with a concept, then a specification, then designs and prototype builds, then tons of testing and breaking stuff, then more prototypes, them more pushing beyond limits to find the weak point, then pre-production builds, then the next revision, and eventually production. Once a few thousand went out there would be some tolerance stackup that causes a problem in the field or in validation testing / burn-in, and another revision is made (I did point out five changes to values in the MC2255’s production run that I know of) to improve the stability and/or performance. The real world doesn’t operate in a faraday cage, nor on laboratory AC power, it has people accidentally trip over a speaker wire and pull it out, etc.
Now a “Technician” goes in and replaces transistors with faster ones, capacitors with larger ones (or faster ones), etc. and who is doing all of the testing to ensure that 1) the SQ is as good or better, 2) the amplifier will be as stable if values drift, 3) he is not putting something dangerously close to oscillation or another failure (which might already have been found in the lab and might be the reason for the particular value), and 4) this magic component actually adds value?
Nobody. The Technician doesn’t understand more than basic design and theory at best, and wasn’t around to understand the reasons for the many component choices that the original Designers made. Ever heard “it works on paper”? An old Engineering joke, theory only gets you so far, experience and trials gets you the rest of the way.
So if you want, Nichicon Fine Gold are fine, really just pretty shrink-wrap on industry-standard caps from most testing and evaluation I’ve read but tends to increase the value of the finished job at minor cost, but I don’t drink the $30 capacitor Kool-Aid. Can an electrolytic to film-cap swap change the sound? In many places no, in some parts of the signal path maybe. Will it be better, or just different? I vote different, again film caps were around when your equipment was built, and they’re already used in the appropriate places.
Wow, coffee’s empty and time to become productive around here, sorry for the long rant but I’m sure that if you were able to ask the designer of your amplifier and preamp, they will tell you that they did a fine job and it lasted 40 years without a hiccup, hard to beat that.
