MMATs 3000.1

[jeanious2011]

You know what you may be right because now the freaking amp is playing at 22v and is pretty loud. What I did was left it at a 20hz low volume for 30min then did a sweep from 20hz to 200hz back and foward on my sinewave generator and now it seems to be louder.

Maybe it was just sitting in someones closet for tooo long???

[m4ick]

Ok, I installed a new HIP4080AIP, installed new B4710s. The amp oscillates and plays nice and loud but it produces quiet hum through the sub woofers that is only audible at low volumes. It makes the hum without the car engine running.

I have 0v to ground on the RCA shields and .11v DC across the speaker terminals.

Here's the kicker, no other amp I have does this but when it is plugged into the RCA out from the highs amp the hum is very noticeable, when plugged directly into the RCAs from the HU it is A LOT quieter but can still be felt on the sub cones.

If I plug only one RCA into the amp it hums extremely loudly, doesn't matter which RCA cable or which RCA jack is used. When both RCAs are plugged in it quiets down, even if the second RCA's shield doesn't make contact, just the center lead, it quiets down.

If I use a Y connector and split the RCAs to the highs and sub amp, I get ground noise on the highs so I'm guessing that ground noise (engine running) is being produced out of the MMATS input jacks.

Any ideas?

[Perry Babin]

Are the RCA shields on the head unit intact?

Is it a hum like a 60Hz hum you'd get from having a battery charger (or something similar) connected to the vehicle?

[m4ick]

Yes, very much like a 60Hz hum even without the engine running.

The shields on the HU are intact. When I run the highs amp by itself or feed the MMATs from the output jacks on the highs amp there is no ground noise (engine running).

[Perry Babin]

That's strange because there's nothing operating at or near 60Hz in the amps. Have you looked that the power supply FET drains to see if the oscillation is constant or is pulsing on and off (30kHz on/off a regular intervals - something near 60Hz)?

[m4ick]

I didn't think there was anything operating anywhere near this frequency either.

It only happens when the RCAs are plugged in so I wouldn't assume the hum is generated by oscillation within the amp but just isn't being filtered out at the input.

Like I said before, if I plug the RCAs directly from the HU into the MMATS the hum is all but completely gone but since there is no output RCAs on the MMATS I used Y splitters to connect the highs. In this configuration I get ground noise on the highs.

It's as if I have a choice, ground noise on the highs with no hum on the subs (using Y splitter) or hum on the subs with no ground noise on the highs (using highs amp RCA out). The previous sub amp did not have these symptoms.

[jeanious2011]

Have you made sure the RCA pins are solder properly on the amplifier (over time they do tend to break or crack solder joints from pushing and pulling force). Just a thought.

[m4ick]

Not likely, the RCAs are held to the side panel with nuts.

One thing about this amp though is that there is no grounding circuit connected to the heat sink and no screws holding the PCB to the heat sink. The only way the chassis is grounded is because the RCA shields are bolted to the side panel.

I'll see what happens if I ground the sink to negative battery.

[m4ick]

Well, now with no RCAs connected the subs pop 3 times when the amp is powered on. There's definitely something going on inside the amp.

Grounding the chassis made no difference at all.

[jeanious2011]

Originally Posted by m4ick

Not likely, the RCAs are held to the side panel with nuts.

One thing about this amp though is that there is no grounding circuit connected to the heat sink and no screws holding the PCB to the heat sink. The only way the chassis is grounded is because the RCA shields are bolted to the side panel.

I'll see what happens if I ground the sink to negative battery.

Not neccesarry because there are plastic insulators around the RCA's, but I did notice on mine that the heatsink is grounded to the ground terminal which are grouned with the transistors (dont know if thats how it suppost to be or if something on mine went wrong).