My friend bought two new earthquake ph5000w amps to run four subs at 2ohm per amp. They sound great but a few days after the install one amp started making a faint low frequency constant thump regardless of source output. I tried swapping the rca inputs to the amps and also swapping amps to eachothers' locations with no success, the noise is still there. Since they were supposedly still in warranty, he sent the amp to Earthquake and they charged about $75 to check it out... they sent it back "no problem found". He tried contacting them but with no success. I've read their customer service pretty much sucks and I can believe it.
From what I've found I believe it is a noise coming from the input stage. You can make it get louder or quieter by turning the gain up or down. The amp performs flawlessly otherwise, it just sucks when the volume is turned down because you can hear two of the subs making a constant thumping, sounds like around 5hz. There are many tiny sm components but still a lot of normal sized ics and capacitors. I can't see any visual damage but something could have been damaged when he was installing, although he is very meticulous.
I was hoping to avoid him having to send it to another repair company, he's definitely not sending it back to earthquake. Kind of sucks because he had high hopes for the amps and wants to run them for spl competitions.
Any helpful suggestions appreciated
From what I've found I believe it is a noise coming from the input stage. You can make it get louder or quieter by turning the gain up or down. The amp performs flawlessly otherwise, it just sucks when the volume is turned down because you can hear two of the subs making a constant thumping, sounds like around 5hz. There are many tiny sm components but still a lot of normal sized ics and capacitors. I can't see any visual damage but something could have been damaged when he was installing, although he is very meticulous.
I was hoping to avoid him having to send it to another repair company, he's definitely not sending it back to earthquake. Kind of sucks because he had high hopes for the amps and wants to run them for spl competitions.
Any helpful suggestions appreciated
With no RCAs plugged in, is there any DC on the RCA shields?
With no RCAs plugged in, does the amp make any noise?
Can you see any changes in the power supply drive circuit as the amp pulses (no speakers connected)?
With no RCAs plugged in, does the amp make any noise?
Can you see any changes in the power supply drive circuit as the amp pulses (no speakers connected)?
I believe it makes the noise plugged in or not. I can also ground the rca shields and it is still there. I will check for DC with them unplugged and try to check the drive circuit. I still haven't bought an oscilloscope, Perry.
The noise is WAY louder with the RCA jacks unplugged, so the issue must be in the preamp side. Maybe its the input caps? If I short the inputs it gets super quiet. I will check for DC there like you mentioned, Perry.
EDIT--- there is about 30mV Dc at the inputs, measured from power ground, about 24mV measured from the RCA shield
Also, if I change the turn on switch from "remote on" to "auto on" the noise goes away ??????
I bought a cheaper digital scope to see if it would detect the pulses. I'm not sure where to probe and what to use for the ground but thinking of using power ground and then probing the inputs to the power supply fet gates, although I'm worried that might cause them to freak out if the impedance of the scope is too low.
I'm also not sure where to check in the preamp circuit so now searching for pinouts of the IC's in that area.
Now I just have to figure out how to use this scope "properly"
EDIT--- there is about 30mV Dc at the inputs, measured from power ground, about 24mV measured from the RCA shield
Also, if I change the turn on switch from "remote on" to "auto on" the noise goes away ??????
I bought a cheaper digital scope to see if it would detect the pulses. I'm not sure where to probe and what to use for the ground but thinking of using power ground and then probing the inputs to the power supply fet gates, although I'm worried that might cause them to freak out if the impedance of the scope is too low.
I'm also not sure where to check in the preamp circuit so now searching for pinouts of the IC's in that area.
Now I just have to figure out how to use this scope "properly"
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This was the issue!! An unintentional solder bridge at the auto/rem switch. 🙂 You can see the six pins near the top of the picture with the two lower left jumped, they are directly shorted. I reassembled and tested after cutting the bridge.
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Also another tip to pay mind is the fact that there are little fuses on the RCA grounds themselves inside a head-unit.
Ive seen these blow and produce all sorts of engine and digital noise in the audio.
Ive seen these blow and produce all sorts of engine and digital noise in the audio.
He is running an audiocontrol processor and there are no bad ground sides on any of its outputs. The other ph5000 didn't have the problem, we isolated it down to this amp only. Yeah, I'm aware of amps killing deck rca grounds because of the amps losing their main ground connection at the chassis and robbing it through the rca cables or amps just killing the deck rca grounds with stray voltage. I repaired MANY decks over the several years I was with Circuit City, saved a lot of people a lot of money and educated some on how important the amplifiers' chassis ground connections were. So many people just use a crappy single self tapping screw that doesn't have the leverage or surface area to keep the huge ground cables tight and most don't even clean the paint from the surface. You can't expect everyone to understand critical details like this though, that's no problem because we all can specialize in something to help each other.
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