Noise when daisy chaining/bridging/strapping 2 atomic 3k's

[mendon mafia 10+ year member]

hi everyone. a long while ago i had a problem with incredible noise coming from my subwoofer when i strapped my atomic 3k's to it. i did some testing yesterday and neither amp has bad noise when hooked up individually.

when strapped there is a very high pitched and quite loud sound coming from the subwoofer (think its engine noise). i tried using both amps as the master and slave but the sound persists. whats also intresting is when i use an RCA barrel connector to extend the length of my strapping RCA the noise is worse (i need the barrel connector so that the rca will reach both amps when they are both mounted in the vehicle but it will reach without for my tests with one amp unmounted)

I did a repair to the one amp by resoldering the rca connectors (strap and input channels) to the board since they were broken when i bought the amp used and i had to do it ghetto since the rca connector did not have long enough leads to reach the pcb. I think this may be the issue but im not sure how to check it and im not sure why it gets worse when extending my strapping cable. and im also not sure why there is no noise when running either amp solo.

i would also like to add that when strapped (with either as master or slave) there is sound output so they do work strapped but its just noisy.

any insight would be helpful. just want to see if this is common or if i should try to resolder the rca connector or if there is a way i can test where the problem is coming from.

Thanks.

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[hispls 5,000+ posts]

How is the wire you connect both amp's - speaker outs? It must be big and as short as possible. Also the RCA between the two should be good quality and shielded. You can try taking a piece of big wire and touching it to the heatsink of both amps.

Just a few things that have effected noisy strapped pairs for me.

 

[VWBobby 10+ year member]

Sounds like a ground loop issue. The clue is how the RCA's are affecting the issue. Every time I have a noise problem, microphone type effect when handling RCA cables, whine, etc....it traces back to a ground loop. This means one amp is using the other amp's ground or ground through the HU/source. If you ground the chassis of the amp to the car body or ground the RCA's and the noise goes away, then you know it was picking up ground from one of the other units - making noise.

I had a poor ground on a new Kenwood HU that was causing all the problems listed above, grounding the black wire better made it all go away.

 

[audiobaun 5,000+ posts]

Try groung both amps seperate locations, and good quality/Zero Niose Monster(Example) cables short as possible, and as stated,Larger wiring to subs/and amp ground may work for you..shorten the rca up, and use good ones,and a Soild Ground with larger Ground wire at different locations, but short as possible

 

[mendon mafia 10+ year member]

I would also like to add that the noise persists even if the engine is off.

How is the wire you connect both amp's - speaker outs? It must be big and as short as possible. Also the RCA between the two should be good quality and shielded. You can try taking a piece of big wire and touching it to the heatsink of both amps.
Just a few things that have effected noisy strapped pairs for me.

I am using 2 runs of 8 gauge (100% OFC) linking the amps speaker outputs and there about 4-5 foot long each and then dual 8 gauge into the sub from each amp. the speaker outputs are completely full of wire on both amps, i dont think this is the issue.

The RCA is knuconcepts klarity and 1 meter long unless i use the barrel then its 2 meters long but still knu klarity.

For the big wire touching the heat sinks, do you mean link the heat sinks together or ground them to something?

Sounds like a ground loop issue. The clue is how the RCA's are affecting the issue. Every time I have a noise problem, microphone type effect when handling RCA cables, whine, etc....it traces back to a ground loop. This means one amp is using the other amp's ground or ground through the HU/source. If you ground the chassis of the amp to the car body or ground the RCA's and the noise goes away, then you know it was picking up ground from one of the other units - making noise.
I had a poor ground on a new Kenwood HU that was causing all the problems listed above, grounding the black wire better made it all go away.

I thought that was the problem a while back with my HU ground so i added a ground (also have the stock ground hooked up) from the HU to the nearest bit of metal with 3' of 8 ga. Im not convinced this is a great ground but wouldnt I have noise even when not strapped if it was the problem?

I will try to ground the chassis of the amps to something but isint the negative terminal hooked to the amp chassis already?

Try groung both amps seperate locations, and good quality/Zero Niose Monster(Example) cables short as possible, and as stated,Larger wiring to subs/and amp ground may work for you..shorten the rca up, and use good ones,and a Soild Ground with larger Ground wire at different locations, but short as possible

both the amps are grounded directly to my battery bank in the trunk (just one for now but i have 3 usually) and i have 2 runs for + and 2 runs for - from front to back one set is off the front battery the other is direct from the alternator, big 3 (4 in reality) has been done. All the power wire is 1/0ga 100% OFC. My car has ~100' of 1/0 just for the charging system. The ground wires are about 6' long for each amp but if that was the issue wouldn't i have noise when not strapped? Do you really think grounding one of the amps to a place other than directly to my rear bank will help? seems to me that the bank is my best bet with my copper buss bars and all. The bank itself is also grounded to the body of the car in the trunk with 1/0 ofc in addition to the dual 1/0 grounds from front to rear.

 

[mendon mafia 10+ year member]

not sure if this is the issue or not (my guess is it is) but on the repaired amp it appears there is a slight short in the "Bridge out" RCA between the positive and the negative contacts of about 8960ohms. This means the "bridge out" positive it is also shorted to the "bridge in" and both RCA input grounds since all the grounds are common. the resistance between the + and - for the Bridge in is infinity as with both RCA inputs.

It appears that all the grounds for all channels (bridge and input) are common, Im not sure if this is supposed to be like this but Im going to test my other amp and see if it has a 9000 ohm short between the bridge out positive and the RCA grounds.

for clarification im referring the grounds in this case as the outer terminals of the RCA connectors.

 

[mendon mafia 10+ year member]

ok so i got both amps out of the car and i was mistaken before. on the repaired amp AND the non-repaired (at least not repaired be me) there is indeed a slight short between the positive and ground on BOTH bridge channels.

On the amp I repaired, the "bridge in" to ground resistance is 9960ohm and the "bridge out" to ground resistance is 8980ohm. the resistance between the "bridge in" positive and "bridge out" positive is 18900ohm

on the other amp, the "bridge in" to ground resistance is 9930ohms and the "bridge out" to ground resistance is 9110ohm. The resistance between the "bridge in" positive and "bridge out" positive is 19040ohm

On both amps all the grounds (inputs and bridge channels) are common (zero resistance).

On both amps there is infinite resistance between input positive's and ground as well as infinite resistance between the input positive left and input positive right.

hope this helps.

 

[VWBobby 10+ year member]

Definitely helps, thanks for taking the measurements. The "Bridge Out" and "Bridge In" are usually POST pre-amp section, Usually. That means one amp's preamp is feeding the other amp's final amp (master and slave). The input comes from your HU, goes through Amp 1's preamp and the signal is sent to the 2nd amp's power amp section. Then both amp's power amp (final) sections are fed to the subwoofers.

It basically comes down to one amp feeding the 2nd amp BS signal that is loaded with noise. Did you check for a possible short between the repaired amp's RCAs and the chassis? Its possible there there is a small short between the positive and ground. It doesn't look like it from the measurements you took however. Both sets of measurements are very close to each other so I wouldn't say one amp is definitely bad. It is normal for there to be resistance between the ground and positive on the RCA's so I don't see any obvious shorts from your measurements.