[GGA]

I have three original Maestro subs. Two of them turn on with very soft thumps, hardly noticeable. The third turns on and off with a very loud thump. My friend said that it is DC offset. Anything I can do about it?

Also when the room is quiet I always hear a very low level hum coming from the subs. I have 106dB sensitive horns and they are dead quiet. I tried reseating the transformers but that did not help. The hum is surprising to me since the Maestros are two prong. Is the hum inherent to the Maestro amps?

That said, the sound from the subs is exceptional and I certainly would not like to part with them.

[Mike Dzurko]

Are all three humming or just the one that makes the louder turn on thump?  Have we had any of these in to check out?

[GGA]

The two amps for the left/right subs in the front of the room both hum. The hum can only be heard if the room is quiet, so it is a faint hum but clearly audible. If this was a dedicated listening room the hum would really bother me. As a living room it is only annoying from time to time. It surprises me because the amps are solid state and have two prong chords. My tube amps and my Crown K2 are dead quiet.

My whole system is powered by a dedicated 3kVA Equitech 240/120V stepdown transformer. Each component, including the subs, has a dedicated line and each dedicated line is very close to being equal in length.

The third amp is in the back of the room and I cannot tell if it hums or not. I can bring to the front of the room for testing if you want me to.

You have not had any in for checking and I bought them at three different times.

[Mike Dzurko]

Hmmm, this is somewhat puzzling. Have you tried plugging the sub amps directly into the wall? I'll PM you with my cell #. and times I'll be available. Give me a call and we'll figure this out. 

[Lkdog]

Have had dual ACI subs (Titans) and now have dual ACI  LFM's and the two prong connectors do not stop certain types of grounding issues.
I am sure you have considered this, but if you have any type of cable TV or satellite connection anywhere connected to your system components in the circuit this can cause a ground loop hum. You can test this by simply disconnecting the coax feed into your system to see if the hum remains. I am guessing with three Maestros you have an AV setup of some type. Satellite requires different interventions than cable if this the case.
You might also wish to check if the coax is grounded correctly outside your house. The cable or satellite company is required to ground and will do it for free usually.

Other than that, it could be some grounding interaction issue with the components, or the way the dedicated lines were grounded or installed.

Hopefully it is something simple.

Have you tried other subs?
Hard to believe that both would have the same thing wrong with them that causes the same hum.

[GGA]

Thanks Mike. I will be happy to give you a call.

Lkdog, thanks for the suggestions. No cable but I do have a Direct TV sat receiver. The incoming cable does have an earth ground. When I unplug the sat receiver there is no change in the hum level. In fact I can shut off all my digital and video equipment with one breaker and when I do there is no change in hum level.

I had REL Stadium IIIs before the Maestros and they did not hum.

 

Hard to believe that both would have the same thing wrong with them that causes the same hum.

Exactly. The only thing I can think of is that the two-prong Maestros do not like balanced power. I will try plugging them directly into the wall and report back.

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I always have a hard time remembering what I can and can't do safely in testing amps. Are the following ok?

1) Disconnect interconnect and speaker cables. Turn amp on. This would tell me if the amp itself is humming or the subwoofer.

2) Disconnect interconnect, connect speaker cable.

3) Connect interconnect, disconnect speaker cable.

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Anything I can do about that loud on/off thump on the one sub?

[Mike Dzurko]

Thanks Mike. I will be happy to give you a call.


I always have a hard time remembering what I can and can't do safely in testing amps. Are the following ok?

1) Disconnect interconnect and speaker cables. Turn amp on. This would tell me if the amp itself is humming or the subwoofer.

2) Disconnect interconnect, connect speaker cable.

3) Connect interconnect, disconnect speaker cable.

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Anything I can do about that loud on/off thump on the one sub?

George:

You can do any of these as long as the amp is switched off and given about 30 seconds before swapping wires, etc.  As far as the turn on, these, like most sub amps are really meant to be left on 24/7.  The only time I advise turning off is if you're going to be away for an extended period. Frankly,turning off and on puts a lot more "age" on these and many amps than leaving them run . . .

[GGA]

Thanks. I'll test the various combinations and report back.

I actually try to leave the amps on 24/7, but we have about 20-30 power failures a year. Plus, as in this testing situation, there are times where I have to turn on/off the amp several times in a short period.

It is a loud pop, and maybe it is irrational, but it bugs me. Why does just the one amp thump?

[Mike Dzurko]

Thanks. I'll test the various combinations and report back.

I actually try to leave the amps on 24/7, but we have about 20-30 power failures a year. Plus, as in this testing situation, there are times where I have to turn on/off the amp several times in a short period.

It is a loud pop, and maybe it is irrational, but it bugs me. Why does just the one amp thump?

I see that in March of this year we replaced (at no charge) a fried circuit board in one of your amps that had been damaged by some liquid getting in. Is this the one with the louder thump? You can tell me more about it when we talk if you want.   

[jimmy b]

I had a hum in my system and after fooling with most everything I found it was my 3 prong plug on my Pioneer plasma tv casuign this. i swapped in a 2 prong connector and whammo no more hum.

So try unplugging one component at  a time and see if this helps.

[Lkdog]

George-

I have Direct TV also and had to fool around a bit with getting rid of a ground loop when it got installed this fall as the digital signal is different than the regular cable, but it sounds like you have eliminated that as a problem.

Maybe you are onto something with looking into the balanced power.

I have one sub plugged into a power strip on my dedicated circuit, but the other sub plugged into the wall. Tracking down a hum can be tricky.
Seems like the better our systems-the more little oddities occur with power and grounding.

Hang in there. Mike will get you squared away. He is the best mfr. for customer service I have ever dealt with in this crazy hobby.