Console Recap Value Questions

[stayingetdown]

Sorry if this has been done to death here but I have to ask before I order parts, just to make sure. I'm new to recapping but I've been reading and searching and have come across many threads that talk about upping the size of capacitor values when doing a recap. I'm looking to do two channels, the power supply, and the master section of a Yamaha PM1000 to start before I jump into the rest of the console. I've read that for power supplies, going with bigger values is generally ok and can even be much better. As far as the channel strips are concerned, I've read that replacing the 47uF/50v, 33uF/25v, and 47uF/25v caps, of which there are quite a few, with something like 56uF/50V Nichicon HE caps would be good.

I guess my question is how much bigger should I go for both the uF values and the voltage values? Is shooting for somewhere in the neighborhood of double both values a good idea for both the power supply and the channel strips like in the above example?
Or will changing values not matter that much? Should I get replacement parts that match the original values but have a higher temperature rating? Just looking for a good general rule that can be used. Thank you very much for your thoughts and guidance.

[The Scum]

I'm afraid there is no good general rule...simplifying this to a single guideline borders on bad advice. Any design has parameters that it was designed to meet. It can be hard to second guess designers when you don't actually know those parameters...however, often parameter #1 was cost, and they may have erred on the side of saving money by using caps that are too small for a given task.

To do a really thorough job, you need to identify how the caps are being used, and make a case by case decision.

Coupling (aka DC blocking) caps in the signal path can usually be bumped up in value with little ill effect. They'll lower the Fc of the highpass filter at each stage, resulting in better low end - lower cutoff frequency, and less in-band phase shift.

Realistically, it's best to analyze the circuit a little, to see what the designed cutoff frequency is. If it's already 2 Hz, you're probably throwing money away to double up caps to drop it to 1 Hz. That said, the couping cap on the fader in the PM1000 is notoriously small.

Power supply decoupling caps, on the other hand, can cause other issues if they get much larger. When the system power up, all of the caps are empty, and must be charged...and they draw a lot of current in that process. Googling "inrush current" will probably tell you a lot more. If you get too many thirsty caps at start up, you may start blowing fuses, or the supply may never properly come up. It depends a lot on the margins that the power supply can support...some supplies will deal with the temporary overcurrent situation more gracefully than others.

I've worked on industrial systems that had a lot of supply decoupling caps distributed, that represented a really frightful load at startup. To deal with it, some low value (100-ish Ohms) power resistors were inserted in series with the supply to limit the inrush. Time-delay relays were deployed to short those resistors after the system came up and the inrush subsided, giving everything a hard connect back to the supply.

I don't know of any good reason to significantly change the voltage rating. A small change (ie: 50V up to 63V) might not do much harm. But electrolytic caps are designed to operate at or near their rating, and their capacitance may stray from the stated value if they're not reasonably biased. You'll also pay more for the higher rated caps, for no particularly good reason.

As for temperature grade, a high-temp cap should have a longer lifespan than the equivalent low-temp cap, installed in the same position.

[stayingetdown]

Thank you very much for the reply. I'm going to sit down with the schematics this week and take a better look. At this point, I'm probably leaning more toward just replacing everything with the same values except getting higher temperature ratings. I do think I'll alter the EQ caps the way I've seen people doing it here. Again, thank you for your time and information. I greatly appreciate it.