Capacitor/amp question

[JerryF504]

I just bought an amp for my truck, hooked it up and everything is fine until I turn it off, then, there is this loud pop through the woofers. I double checked all of my connections and everything is fine so I contacted the person I bought it from and he says "i got that thump as well...i TOTALLY forgot to mention that (kinda forgot) im sorry about that...i heard you can add a relay or solder something to help with that". So I go looking around online to see what he was talking about and I found this. Basically, it says to replace these caps:

with these caps:

Now, my question to the electronics experts is do you think 1000uF 25V caps left over from the pre-MMM era would work in place of the 100uF 25V caps?

[BrianG]

I would replace with the same capacitance and voltage. You can use one rated for higher voltage, but it will be bigger. Caps have a few purposes: oscillators, filtering, and (de)coupling. If it's just a filter cap, bigger is usually better. But, if it's tuned to a certain frequency, or used for (de)coupling, you should stick to the same value. They probably are not low-ESR, so you should be able to find a direct replacement at RadioShack.

Usually, a bad cap has a puffed or rounded top. So look for that kind of problem first. But, just because they aren't puffed doesn't mean they aren't bad (the electrolyte could have leaked or something).

To eliminate the pop coming from the turn on lead, make a temporary jumper from your battery lead (on the amp) to simulate the control signal (remove the existing turn-on lead first). If the pop goes away, you can use a relay to create a new turn-on lead.

[JerryF504]

Originally Posted by BrianG

I would replace with the same capacitance and voltage. You can use one rated for higher voltage, but it will be bigger. Caps have a few purposes: oscillators, filtering, and (de)coupling. If it's just a filter cap, bigger is usually better. But, if it's tuned to a certain frequency, or used for (de)coupling, you should stick to the same value. They probably are not low-ESR, so you should be able to find a direct replacement at RadioShack.

Usually, a bad cap has a puffed or rounded top. So look for that kind of problem first. But, just because they aren't puffed doesn't mean they aren't bad (the electrolyte could have leaked or something).

To eliminate the pop coming from the turn on lead, make a temporary jumper from your battery lead (on the amp) to simulate the control signal (remove the existing turn-on lead first). If the pop goes away, you can use a relay to create a new turn-on lead.

Well, the caps aren't actually bad. This amp is kinda like a MMMv1. After a few were shipped they found out that there were a few bugs, one of which being the loud thump at turn off. The fix is supposed to be to replace the 10uF 16V caps with 100uF 25V caps so I guess that would mean they are for filtering, right? Also, if they are not low-ESR caps it wouldn't hurt to put low-ESR caps in their place would it?

I did check the turn on before I found out it was a problem with the amp. I even tried with the RCAs disconnected to make sure it wasn't coming from the head unit.

[BrianG]

Well then, I would start by using 100uF caps. Caps can also be used for timing. Higher capacitance means longer time (refers to speed of charge/discharge). The caps could be keeping the amp active long enough for the mute circuit to do its job. And no, using low-ESR caps won't hurt. Probably won't help (only really useful in high current apps), and will probably be physically larger.

[JerryF504]

Thanks, that's what I needed to know!