Hot Rod deluxe signal when clean volume off

[Enzo]

A filter cap, a decoupling cap, is from a power supply node to ground. If the cap is leaky, the problem is not that signal leaks to ground, it is that the cap fails to hold the node steady, and signal can become impressed on the supply rail. Paralleling another cap there will hold up the node.

[Mars Amp Repair]

HMM, I always thought of the term 'Leaky' to mean it had leakage resistance as in an ESR issue...in which case you would of course need to replace the cap. Perhaps it's just a matter of semantics...glen

[52 Bill]

HMM, I always thought of the term 'Leaky' to mean it had leakage resistance as in an ESR issue...in which case you would of course need to replace the cap. Perhaps it's just a matter of semantics...glen

I thought that ESR was just the opposite, as if a resistor was added in series with the cap making it less effective.

[Enzo]

There are many failure modes. In the case of a filter cap, leaky means it can't hold a charge as well as it should. In the case of a coupling cap, it means it can;t block the DC as it should.


ESR is a series resistance - as suggested by the letters - while leakage is a parallel resistance.

[Mars Amp Repair]

Hey Enzo,
Yeah I guess I see that now...I'm guessing ESR would be equivalent AC series resistance & possibly change with the frequency being applied as opposed to a straight DC series resistance. I work with some 'younger' guys now that swear by the ESR checker. I think for circuits such as SMPS & higher freq uses the tested would be effective, but I'm just not sold on using it as though it's the last word.

So as not to be 'the older guy who won't change his ways' I tried it just for grins & replaced a handful of smaller alumalytic surface mount caps to resolve a weird issue to no avail even though the tester indicated these caps clearly failed the test. Like any piece of test equipment, you have to apply your experience & logic to the results you derive from it in order to make it an effective tool.

I just have an issue with those with lesser experience thinking ANY piece of test equipment will tell you what's wrong with the amp without the tech thinking a bit deeper into the circuit at hand. I'm slowly imparting that 'wisdom of experience'. It's actually pretty gratifying. glen

[Enzo]

In my experience, an ESR meter is best for confirming what I already know, much moreso than telling me something I didn;t know.

[Mars Amp Repair]

Well put...g