Highly valuable information for the audiophile into vintage equipment.

The question is regularly asked whether or when to “ReCap” vintage gear. There are many answers, and there is a lot of “it depends” involved.

To understand whether you should recap, the benefits and risks, it makes sense that you should understand what a capacitor does.

Most people here focus on replacing the electrolytic capacitors, and to a lesser degree tantalum. Both can degrade over time, heat will speed the degradation.

An electrolytic capacitor is largely a small tuned battery, it can charge and discharge quickly. It is also the opposite of a rectifier diode, it will pass AC but block DC.

What will be covered:

1. Why capacitors age
2. What are the risks presented by old caps
3. Which capacitors we need to replace
4. When we need to replace them

1. Why capacitors age: this question can have a long answer and I will try to keep it short and simple. As our main interest and also the fact that these are mostly first to fail, I will discuss the electrolytic caps.  Electrolytics use a liquid to impregnate the dielectric layers, this liquid either dries or tries to escape.  There are a lot of factors that contribute to capacitor ageing, temperature, working voltage, leakage currents and the quality of the capacitor. A power supply cap has the role to charge and release energy when there are short and high spikes of a load. A good example will be a bass passage, every time the bass kicks, the high energy drain is sustained by the main filter caps. The small value caps in the sound path will dry up, having already small capacity, they will lose all properties, and the main purpose is to block DC current between stages in the sound path.
2. Risks: This is also a complex technical discussion that I will simplify. There are roughly two situations: a weak cap in an amplifier power supply will give you weak bass, a dry cap might give you HUM and a faulty/shorted one will probably kill the bridge rectifier and blow some fuses.  In a digital circuit, a weak cap will make a processor go crazy with erratic behaviour, a shorted one will probably kill a voltage stabilizer. One bad cap in a bias/feedback circuit can blow a whole channel. A bad cap in the sound path will sound bad or not sound at all and in the worst situation will let DC component pass and toast your tweeters. Second situation: this is worst in my opinion, also the most common. The equipment works ok and you like the warm and soft vintage sound. Caps are 30-40 years old, none failed but all are long gone out of specs. The unit sound is changed drastically, not energetic and sharp but mellow and you can easily say this is how it sounds, its old tech. Fortunately, that is wrong and a recap can bring the life back in them. Bonus risk: leakage, the electrolyte inside caps is highly corrosive and will attack traces, pins and create a lot of problems.
3. Which caps we need to replace: a quick reminder, we are covering only electrolytics. Simple answer: ALL. The complex answer: for the cheap ones or the people that can’t afford a whole recap: it depends on the device and the circuit. In an amplifier, your most interest is in the power supply, big cans and the smaller ones for the preamp stage. Next step is the sound path and everything that passes sound. A trained eye might spot a cap that is part of something that could use a new cap but a simple power and sound path refresh will bring a new chance for an old amplifier.  In a CD player, the power supply caps have little stress compared to an amp and many times they might be in a decent condition, instead you can put some decoupling on them. In a player, a big impact in sound will be done by the output stage, in there you only go with quality stuff (a good example is in the older 80’s players as most have Nichicon M.U.S.E as output caps). The second important thing in a player is the DAC power supply caps, either if on a separate supply circuit or not, the DAC will have caps close to it. Also, a good place to add some decoupling capacitors.
4. When we need to replace them: it again depends on the budget, if you can afford it, everything over 20 years old could use a refresh. On tighter budgets up to 30, and I consider that the 40-year-old unserviced equipment a fire hazard. Yes, yes, they still work, until they go pop and take half the device down with them, old caps can fail at any time with no warning.