Hi folks,
I've recently completed a 4 channel amplifier based on Anthony' NXLSP400se modules. They work nicely but I've got troublesome noise issues that I'd like rid of. Unfortunately my knowledge only extent to soldering, drilling a few holes and wiring it all up in some fashion so hopefully you can help me out here.
Here's the problem:
This photo highlights the subjective amount of noise with no input and just the same loudspeaker connected in turn to each output. Number 1 is absolutely silent and I need to put my ear right up to the driver, number 2 is likewise nearly as quiet, number 3 is showing audible but quiet hum and number 4 is worst of all with a clearly audible hum from across the room.
With inputs connected the ranking is the same but on number 3 and 4, where hum was noted with no inputs, this disappears with inputs connected. However all channels have quite elevated noise levels in comparison to how very quiet number 1 was without input.
The circle in the photo shows where the chassis ground is.
These additional photo's show the wiring and general layout:
What I've tried so far:
Disconnecting the chassis ground from one of the PSU's and putting a ground link between it and the second PSU. This made no difference to the noise.
Thanks
Ant
I've recently completed a 4 channel amplifier based on Anthony' NXLSP400se modules. They work nicely but I've got troublesome noise issues that I'd like rid of. Unfortunately my knowledge only extent to soldering, drilling a few holes and wiring it all up in some fashion so hopefully you can help me out here.
Here's the problem:
An externally hosted image should be here but it was not working when we last tested it.
This photo highlights the subjective amount of noise with no input and just the same loudspeaker connected in turn to each output. Number 1 is absolutely silent and I need to put my ear right up to the driver, number 2 is likewise nearly as quiet, number 3 is showing audible but quiet hum and number 4 is worst of all with a clearly audible hum from across the room.
With inputs connected the ranking is the same but on number 3 and 4, where hum was noted with no inputs, this disappears with inputs connected. However all channels have quite elevated noise levels in comparison to how very quiet number 1 was without input.
The circle in the photo shows where the chassis ground is.
These additional photo's show the wiring and general layout:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
What I've tried so far:
Disconnecting the chassis ground from one of the PSU's and putting a ground link between it and the second PSU. This made no difference to the noise.
Thanks
Ant
Hi Ant,
I don't know how these amp modules are made, but in a multichannel unit like this, you need to ensure that the input grounds are isolated from the common ground. I use a 10 ohm resistor.
Also, you want to make sure none of the input leads are close to high power leads, AC especially.
I'll attach this drawing a made a while back to show how I do it. I'm not sure how helpful this will be for you, but I don't have any noise or hum with this.
I don't know how these amp modules are made, but in a multichannel unit like this, you need to ensure that the input grounds are isolated from the common ground. I use a 10 ohm resistor.
Also, you want to make sure none of the input leads are close to high power leads, AC especially.
I'll attach this drawing a made a while back to show how I do it. I'm not sure how helpful this will be for you, but I don't have any noise or hum with this.
Attachments
Thanks John, I'm not sure about the input ground isolation either. These module have IP so no schematic and because I'm dumber than a bag of hammers I couldn't work it out from looking.
I'll ask the designer about the point you raised.
Good point about the main input, it is close to the input of one amp. I'll try jury rigging some wiring so I can take it well out of the case and away from modules. This'll let me check for any improvements that makes.
BTW I notice you've got 100ohm resistors inline with your chassis ground. Does this help with noise?
I'll ask the designer about the point you raised.
Good point about the main input, it is close to the input of one amp. I'll try jury rigging some wiring so I can take it well out of the case and away from modules. This'll let me check for any improvements that makes.
BTW I notice you've got 100ohm resistors inline with your chassis ground. Does this help with noise?
ShinOBIWAN said:
That is to isolate the chassis safety earth ground from the common star ground. In this scheme the chassis is connected directly to the safety earth on the IEC connector, and the common ground "floats" above it, separated by that 100 ohm resistor. The resistor I use is a 10 watt cement and for extra safety, it is paralleled with opposing 1N4007 diodes (just in case a large current develops across this resistor).
The 10 ohm resistor for the signal ground has the same thing - opposed diodes in parallel. A couple of these resistors have burned, so my lesson is learned.
Hope this helps.
Ok, the inputs at the rear of the case are RCA's? If so, did you isolate the ground part from the case. See here:
These do not touch the metal case, but go directly back, individually, to each amp module.
EDIT: looked at your pics, they are XLRs. Are you using balanced input?
An externally hosted image should be here but it was not working when we last tested it.
These do not touch the metal case, but go directly back, individually, to each amp module.
EDIT: looked at your pics, they are XLRs. Are you using balanced input?
MJL21193 said:
I'm not sure what you mean. There's 3 terminals and a shield.
Pins 1-3 are hot, cold, ground and finally there's the shield.
I've only connected the pins and ignored the shield as I wasn't sure if it was needed nor where it should go.
Each input is as you've said, isolated and goes to its own amp.
I played around with mains wiring as the noise I'm hearing appears to hum related.
Here's what I tried and discovered:
- With mains wiring in the case but with only one toroid, PSU3 and two modules running(the best noise performance one and the worst) I noted identical performance compared to all electronics running. This includes performance with or without input - no change for either.
- With exactly the same conditions as above but with the mains harness(from IEC mounted on rear panel to primary winding) lengthened so that it didn't pass directly through the case from front to rear. No change again.
- The next experiment was as shown in the photo below. I bypassed that rear IEC and simply wired directly to the mains. This meant the mains input came in through the front of the case instead of rear. I also omitted chassis ground as I was getting desperate, this is only a temporary measure. I noted that noise on the worse effected module was significantly reduced. Instead of being able to hear the hum from at the listening position you needed to get around a foot from the driver.
Any thoughts?
Here's what I tried and discovered:
- With mains wiring in the case but with only one toroid, PSU3 and two modules running(the best noise performance one and the worst) I noted identical performance compared to all electronics running. This includes performance with or without input - no change for either.
- With exactly the same conditions as above but with the mains harness(from IEC mounted on rear panel to primary winding) lengthened so that it didn't pass directly through the case from front to rear. No change again.
- The next experiment was as shown in the photo below. I bypassed that rear IEC and simply wired directly to the mains. This meant the mains input came in through the front of the case instead of rear. I also omitted chassis ground as I was getting desperate, this is only a temporary measure. I noted that noise on the worse effected module was significantly reduced. Instead of being able to hear the hum from at the listening position you needed to get around a foot from the driver.
Any thoughts?
An externally hosted image should be here but it was not working when we last tested it.
Hi Ant,
It can be really tricky to eliminate all sources of noise/hum, but you should be ahead of the game with balanced inputs. Even so, your internal wiring may pick up some garbage, therefore it's always a good idea to plan ahead of time to try and minimize some of the potential problems.
I found out the hard way on my first multichannel build that it's pays to lay everything out so as to avoid trouble. I took that further with this new one, where I have been conscious from the beginning about what needs to be done.
See in the pic the amps are shielded from the centre (where the toriod and power supplies are) with the solid sheet of aluminum. This joins with the shelf where the modules are attached to shield the bottom also. Notice the aluminum wire chase around the heatsink that carries the shielded input leads to each amp module. The power leads are twisted and neatly attached to the shield.
The RCA inputs will be shielded also with a wrap around cover. As it sits, there is complete silence - no hum, no noise (other than a faint "tick tick" from the DCX2496).
This may seem extreme, but it is worth the effort IMO.
It can be really tricky to eliminate all sources of noise/hum, but you should be ahead of the game with balanced inputs. Even so, your internal wiring may pick up some garbage, therefore it's always a good idea to plan ahead of time to try and minimize some of the potential problems.
I found out the hard way on my first multichannel build that it's pays to lay everything out so as to avoid trouble. I took that further with this new one, where I have been conscious from the beginning about what needs to be done.
See in the pic the amps are shielded from the centre (where the toriod and power supplies are) with the solid sheet of aluminum. This joins with the shelf where the modules are attached to shield the bottom also. Notice the aluminum wire chase around the heatsink that carries the shielded input leads to each amp module. The power leads are twisted and neatly attached to the shield.
The RCA inputs will be shielded also with a wrap around cover. As it sits, there is complete silence - no hum, no noise (other than a faint "tick tick" from the DCX2496).
This may seem extreme, but it is worth the effort IMO.
Your shields in a ballanced line should be connected to ground at one end only to prevent ground loops. The XLR pins are +,- (hot, cold) and ground and theres usually a ground lug thats not used (usually the same as the pin ground) If your hum is there with the inputs shorted (+, -) the hum is generated internally.
cbdb said:
Hi cbdb
Would running a link, at the chassis connector, from shield to ground achieve anything? Since they're mounted on perspex plastic with no direct connection to the chassis then I think the shield isn't needed.
Happy to proved wrong since it will be something else for me try.
cbdb said:
The modules are Aussieamps NXLSP400se which allow for a native balanced input.
cbdb said:
Its bolted down good but could try moving since its only bolted down.
Me and the amp designer, Anthony Holton have been talking in emails and we've discovered the source of most of the noise.
The large input film capacitors. These seem to suck up AC like crazy and then feed into the amps. If you notice there's four of these for two modules close to the IEC inlet. I moved my wiring out the way and the amps got a lot quieter regarding hum.
I cut the caps out the signal chain for one module and then shorted signal + and -. The result was complete silence and this is the module closest to the toroids.
I'm now in the process of rewiring the amp almost completely.
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