My signal entry point is the CAT6 female receptacle as you see in the image. I also noticed that when I hook the CAT6 signal cable to the amp's female receptacle, the noise is ten fold (and it's not even hooked up to a source yet).
To do list:
1- Hook speaker ground to ground of DC supply directly
2- Hook input signal ground to common star ground.
3- Will redirect AC supply line away from rectifier board.
4- Ground DC supply to chassis??
1,2 and 4 are the same aren't they?? ..seems to me they share a common ground.
No fuse components at the moment.. running without. Will integrate a 12V triggered relay as power switch later.
To do list:
1- Hook speaker ground to ground of DC supply directly
2- Hook input signal ground to common star ground.
3- Will redirect AC supply line away from rectifier board.
4- Ground DC supply to chassis??
1,2 and 4 are the same aren't they?? ..seems to me they share a common ground.
No fuse components at the moment.. running without. Will integrate a 12V triggered relay as power switch later.
Number two is probably the one generating hum.
You currently have input grounds connected all over the show. This is probably the ground loop / hum generator.
Worry about the AC line redirecting last.
You currently have input grounds connected all over the show. This is probably the ground loop / hum generator.
Worry about the AC line redirecting last.
the signal ground is part of the signal circuit.
The Signal Flow and Signal Return must be a twisted pair starting at the input CAT6 socket and ending at the Power amplifier inputs. For three channels you need 3 of these twisted pairs. These already exist - do not change them.
The Safety Earth needs to be shortened and made permanent. It never comes off.
There are power leads are all over the place.
Remove them all. Start again.
Connect the middle (Zero Volts) of the PSU to chassis. Do not remove the Safety Earth Nut to connect this. You can use a different bolt&nut or add on a second and third nut.
Look at your Power Zero Volts to Audio Ground and then from Audio Ground to each PCB Power Ground. Imagine a 4way star connecting the PSU and the 3 amp PCBs. Where is the midpoint to locate that 4way star? We need to create a floating (in mid air) Star next to the three power amp PCBs.
This has to be converted into a twisted triplet that changes from a single triplet on the first part of the route to three triplets for the final part of the route. The +ve and -ve are twisted with the Zero Volts upto the Audio Ground. Then create two power stars, one for +ve and one for -ve. From these power stars and the Audio Ground create your three twisted triplets to the amp PCBs. This 4way triplet is a bulky and awkward cable set to make up.
I suggest you do this first. When it is complete dress it to it's final locations and tie it in securely.
Take all audio type grounds to this floating ground. Call it Star Ground or Audio Ground or Main Ground or Central Ground.
Take three leads from Audio Ground, one to each Speaker Return.
Take three leads from Audio Ground, one to each CAT6 socket Signal Return.
Take three leads from Audio Ground, one to each PCB Zobel/decoupling Ground.
Take a lead from Audio Ground to PSU Zero Volts.
Take a lead from each dirty auxiliary (relays, soft start, etc) to chassis.
Now the difficult bit. Fit in the few remaining cables such that signal & high currents & mains AC do not pass parallel and close to each other.
This arrangement has copied Self's diagram almost exactly, particularly his other diagram in the book showing the twisted power leads going to the amp PCBs.
Leach also suggests the Signal Return at the input be connected to the Audio Ground. I find this more resistant to interference than doing it on the amp PCB
However for this "external" Signal Ground to Audio Ground link to work, there must not be a direct zero ohms signal to power ground connection in any of the amp PCBs.
One final bit of advice.
use a nut and bolt as your floating Audio Ground. The Grounds that meet here should all be terminated with ringlets. The currents coming down to these ringlets are very different in magnitude. Temporarily bolt them together. You will find that swapping the order of the ringlets on the bolt changes the noise measured at the speakers terminals. I tend to put zero volts first, amp PCB Power Ground next, Speaker Returns next, Signal Ground last. This seems to impose the least dirty voltage on the Signal Grounds.
The Signal Flow and Signal Return must be a twisted pair starting at the input CAT6 socket and ending at the Power amplifier inputs. For three channels you need 3 of these twisted pairs. These already exist - do not change them.
The Safety Earth needs to be shortened and made permanent. It never comes off.
There are power leads are all over the place.
Remove them all. Start again.
Connect the middle (Zero Volts) of the PSU to chassis. Do not remove the Safety Earth Nut to connect this. You can use a different bolt&nut or add on a second and third nut.
Look at your Power Zero Volts to Audio Ground and then from Audio Ground to each PCB Power Ground. Imagine a 4way star connecting the PSU and the 3 amp PCBs. Where is the midpoint to locate that 4way star? We need to create a floating (in mid air) Star next to the three power amp PCBs.
This has to be converted into a twisted triplet that changes from a single triplet on the first part of the route to three triplets for the final part of the route. The +ve and -ve are twisted with the Zero Volts upto the Audio Ground. Then create two power stars, one for +ve and one for -ve. From these power stars and the Audio Ground create your three twisted triplets to the amp PCBs. This 4way triplet is a bulky and awkward cable set to make up.
I suggest you do this first. When it is complete dress it to it's final locations and tie it in securely.
Take all audio type grounds to this floating ground. Call it Star Ground or Audio Ground or Main Ground or Central Ground.
Take three leads from Audio Ground, one to each Speaker Return.
Take three leads from Audio Ground, one to each CAT6 socket Signal Return.
Take three leads from Audio Ground, one to each PCB Zobel/decoupling Ground.
Take a lead from Audio Ground to PSU Zero Volts.
Take a lead from each dirty auxiliary (relays, soft start, etc) to chassis.
Now the difficult bit. Fit in the few remaining cables such that signal & high currents & mains AC do not pass parallel and close to each other.
This arrangement has copied Self's diagram almost exactly, particularly his other diagram in the book showing the twisted power leads going to the amp PCBs.
Leach also suggests the Signal Return at the input be connected to the Audio Ground. I find this more resistant to interference than doing it on the amp PCB
However for this "external" Signal Ground to Audio Ground link to work, there must not be a direct zero ohms signal to power ground connection in any of the amp PCBs.
One final bit of advice.
use a nut and bolt as your floating Audio Ground. The Grounds that meet here should all be terminated with ringlets. The currents coming down to these ringlets are very different in magnitude. Temporarily bolt them together. You will find that swapping the order of the ringlets on the bolt changes the noise measured at the speakers terminals. I tend to put zero volts first, amp PCB Power Ground next, Speaker Returns next, Signal Ground last. This seems to impose the least dirty voltage on the Signal Grounds.
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If there is no noise with the RCA cable, there is probably no grounding problem.
If you use CAT6, use it completely. If you only use wire pairs removed from the cable, you lose the shield. The RCA has a shield. That could be the decisive difference.
Thanks
Thank you gentlemen. Especially Andrew for that detailed step by step post. Much appreciated!
I'll have to re-read it a few times since I'm having some difficulty with "converted into a twisted triplet that changes from a single triplet on the first part of the route to three triplets for the final part of the route."
Kind of lost me on that "route" if you will.. I'll figure it out.
When you wrote "Audio Ground" later in your post.. and when I reference your first entry "Signal Ground" ? They are the same, am I correct?
Thank you gentlemen. Especially Andrew for that detailed step by step post. Much appreciated!
I'll have to re-read it a few times since I'm having some difficulty with "converted into a twisted triplet that changes from a single triplet on the first part of the route to three triplets for the final part of the route."
Kind of lost me on that "route" if you will.. I'll figure it out.
When you wrote "Audio Ground" later in your post.. and when I reference your first entry "Signal Ground" ? They are the same, am I correct?
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Hi,
a schematic has lot's of grounds.
These are usually assumed to be at Zero Volts.
But each Ground has a specific duty.
Treat each Ground as the Return of the complementary Flow.
A Signal Ground and a Signal Flow are part of the same circuit that comes from the Source into the receiver and back to the source. The voltage that the amplifier sees between Signal Ground and Signal Flow is multiplied and sent to the Speakers.
The Audio Ground is the Returns for all the big current Flows for all three amps.
These circuits have nothing in common with the Signal circuit. Do not mix some high current nor current pulses in the Audio Ground with the Signal circuit.
The 4way starred triplet.
You have 3amplifiers and one PSU.
That is four items that need to be connected for Power.
each has a 3way connector consisting of +ve, -ve, Power Return. These mak up a twisted triplet.
From a Central location run a triplet to each PCB. i.e. a 4way triplet from the Audio Ground running to the 4PCBs.
Finally,
the amplifier amplifies a difference of the Signal Pair and sends that as a difference (power) signal to the Speaker. Because the source and receiver and speaker are not connected with balanced lines, they use a common voltage to keep the Signals in step with each other. This is Ground coming back in. All the signals are with respect to Ground (referenced to Ground). The Speaker Return and the PSU and the amplifier are all connected directly to the Audio Ground. They are all referenced to each other.
Now you need to reference the Signal Return to this same Audio Ground.
You can do this with a direct wire connection or you can do it with a low value resistor. You can even parallel the low value resistor with a low value capacitor.
Now choices. Earlier I said each of the three Signal Grounds/Returns have their own reference to Audio ground. You can use a single wire connecting all three Signal Returns together and then direct or resistor connect them to the Audio Ground. A further alternative is you tie in (reference) the Signal Return on the amp PCB to the Audio Ground. That is about 6ways to reference the Signal Return to the common (reference) voltage.
This is much easier to learn in a monoblock that is not in a chassis than in a multi-channel inside a fully wired chassis. Get yourself up to speed by reading that link on our home page.
a schematic has lot's of grounds.
These are usually assumed to be at Zero Volts.
But each Ground has a specific duty.
Treat each Ground as the Return of the complementary Flow.
A Signal Ground and a Signal Flow are part of the same circuit that comes from the Source into the receiver and back to the source. The voltage that the amplifier sees between Signal Ground and Signal Flow is multiplied and sent to the Speakers.
The Audio Ground is the Returns for all the big current Flows for all three amps.
These circuits have nothing in common with the Signal circuit. Do not mix some high current nor current pulses in the Audio Ground with the Signal circuit.
The 4way starred triplet.
You have 3amplifiers and one PSU.
That is four items that need to be connected for Power.
each has a 3way connector consisting of +ve, -ve, Power Return. These mak up a twisted triplet.
From a Central location run a triplet to each PCB. i.e. a 4way triplet from the Audio Ground running to the 4PCBs.
Finally,
the amplifier amplifies a difference of the Signal Pair and sends that as a difference (power) signal to the Speaker. Because the source and receiver and speaker are not connected with balanced lines, they use a common voltage to keep the Signals in step with each other. This is Ground coming back in. All the signals are with respect to Ground (referenced to Ground). The Speaker Return and the PSU and the amplifier are all connected directly to the Audio Ground. They are all referenced to each other.
Now you need to reference the Signal Return to this same Audio Ground.
You can do this with a direct wire connection or you can do it with a low value resistor. You can even parallel the low value resistor with a low value capacitor.
Now choices. Earlier I said each of the three Signal Grounds/Returns have their own reference to Audio ground. You can use a single wire connecting all three Signal Returns together and then direct or resistor connect them to the Audio Ground. A further alternative is you tie in (reference) the Signal Return on the amp PCB to the Audio Ground. That is about 6ways to reference the Signal Return to the common (reference) voltage.
This is much easier to learn in a monoblock that is not in a chassis than in a multi-channel inside a fully wired chassis. Get yourself up to speed by reading that link on our home page.
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Thanks for the follow up Andrew. I've done what you've suggested but I'm still getting a fair amount of noise from the CAT6 inputs. Less than before but almost audible from the seating position. Only one CAT6 pair = no noise (grounded to the chassis) but as soon as I connect the other two pairs, Buuuuzz. What I'll do is go through the process of elimination by moving the ground around till I get the least amount of noise. Also, I've connected the signal wires to a balanced connector to #1 and #2 prongs (It's what the Behringer 2496 accepts). Should I now bridge the signal return to #3 as well? Would that improve grounding between this unit and the amp?
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I built a 5.1 LM3886 amplifier for my car for my 5.1 decoder/DSP.
I was able to get my heat sinks custom-cut from an eBay seller who was selling custom cut lengths of the aluminum material.
I can tell you by experience not to worry about more esoteric things (inverted vs. non-inverted, "audiophile" parts topics, magic power cables, etc.) and focus on getting the amplifier working well, and dealing with things like ground loop noise, etc.
Otherwise, I think you'll find the LM3xxx chip amps to be quite pleasing to the ear even for the basic designs!
Good luck. 🙂
I was able to get my heat sinks custom-cut from an eBay seller who was selling custom cut lengths of the aluminum material.
I can tell you by experience not to worry about more esoteric things (inverted vs. non-inverted, "audiophile" parts topics, magic power cables, etc.) and focus on getting the amplifier working well, and dealing with things like ground loop noise, etc.
Otherwise, I think you'll find the LM3xxx chip amps to be quite pleasing to the ear even for the basic designs!
Good luck. 🙂
Has anyone SUCCESSFULLY done a multi channel (3 or more) with CAT6 as signal cabling from source?? ..and be quiet too. If so, have they posted any info of their amp project?
I think your problem may be that you're using the Cat6 cable as unbalanced cable. Its not designed to be used that way - using balanced cables needs balanced inputs. You appear from your pics to be using one side of the Cat6 as a ground.
Yes cat6 is designed for balanced signal transfer. You can put as much garbage on the line as you like for 500ft and still be find because the garbage is injected equally on both lines so its rejected at the destination.
Whoever came up with this idea to use cat cable needs to be shot. We even have people in the car audio world thinking its better, even with the noise graphs to prove its garbage.
You need to have a shielded cable for a single ended signal plain and simple. The least i would do is Svga cable from mono price. Its got at least 3 coax shielded cables inside if not 5 or 6, and its got shielding around the jacket too. Without shielding that cat6 is gonna pick up every emf from the florescent bulbs to the micro wave to the sat box to god knows what.
Whoever came up with this idea to use cat cable needs to be shot. We even have people in the car audio world thinking its better, even with the noise graphs to prove its garbage.
You need to have a shielded cable for a single ended signal plain and simple. The least i would do is Svga cable from mono price. Its got at least 3 coax shielded cables inside if not 5 or 6, and its got shielding around the jacket too. Without shielding that cat6 is gonna pick up every emf from the florescent bulbs to the micro wave to the sat box to god knows what.
A twisted pair for an unbalanced signal is good for audio signals.
If you want more resistance to interference then go to star Quad using 4 cores of the CAT5/6 wiring.
You do not need a shield if the loop area of the input wires is near zero.
My findings and conclusion agrees with Nightanole. The fact that as soon as I connect CAT6 cable to the amp's input (be it a foot long or 30) adds hiss and hum instantaneously. Mind you, CAT6 over 30 feet into a gainclone sounds very nice ...if it weren't for the damn noise. It's DEAD quiet without the cable plugged in.
Now the difficult part... finding a low cost solution! I really don't feel like re-fishing new cables through walls and ceiling . That's my last solution.
Andrew, can you elaborate on your Star Quad suggestion?
Now the difficult part... finding a low cost solution! I really don't feel like re-fishing new cables through walls and ceiling . That's my last solution.
Andrew, can you elaborate on your Star Quad suggestion?
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Loop area only matters for inductive pick up. There's another kind of pick up - electrostatic - and this doesn't care about loop area at all. Shields are to protect against electrostatic influence and have almost zero effect on inductive.
The lowest cost solution is to use the Cat6 cable in the way its designed to be used - as balanced. Whilst you don't need balanced voltage drive on your outputs you most certainly do require balanced inputs (and preferably balanced impedance drive on the outputs).
I just did a quick test with a CAT5 with shield that I got from work 😉 I connected to the amp then grounded the shield to the Audio ground - presto - no audible noise.
"Quad" means for use all four pairs in the cat-5/6 cable. The cable was a total of 8 conductors or four twisted pair. Use them in parallel to reduce rsistance.
As for the noise, I came here late so you may be doing this already but to use Cat-5 "correctly" you need a balanced signal in the cable and most consumer-audio boxes use single ended RCA terminated interconnects. So the "right way" is to have a transformer at each end of the cable. You can make them or buy them. The transformer matches the single ended audio signal to the 100 ohm impedance twisted pair. Like everything else the best of these are expensive and have Jensen transformers inside. Some are active devices that us op amps on each end to do about the same job, op amps being so much cheaper than transformers.
You said the cables added "hiss" and this is exactly what I'd expect
Believe me it is best to hire and electrician and have him pull wire and terminate it in a wall plate. They can do that for about $100 per wall plate. What I would do is have him put in a conduit and then later you can decide what kind of cable goes inside
Wireless links can work too. Either a wireless network or a simple UHF analog link like a stage performer might use with a headset mic. But again electricians are cheaper. Becuase this is low voltage he does not need to be licensed. The ones who do this kind of work make far less than "real" electricians, about $25 per hour and in 8 hours that can do a lot of work for you.
Does anyone know how much noise does a pot adds to the signal when used? Should I stay away!? I'm thinking that I might have to attenuate 2 of the 3 amps and my options a limited.
Thanks!
Thanks!
you could:
get a 50k pot. get your levels right. Then measure the pot and replace it with resistors. That would be the least noise.
get a 50k pot. get your levels right. Then measure the pot and replace it with resistors. That would be the least noise.
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