Looks like the DC amp part of the circuit isn't adding any noise. I removed the 47K and diode and the measurements are no different
Am I reading the relay spec correctly that holding the switch closed requires 550mw of power to stay connected ?
Okay looks like this circuit does induce some noise so possibly the reason in the BPSP 500 they powered using a separate tap. Green is with the power to the relay circuit removed and a link to provide the output, red is with the circuit in place
Looking at this diagram I can see connections to the low signal components R1,C2,R3,and C3 being shown as connected to a nominal internal ground and not to real Earth.
Looking at the diagram, this looks very elaborate. so where do these separate ground returns meet.
If the aim is to ensure output power ground return currents do not flow through those for signal ground returns, then separation could be including a small value resistor between the two paths. I don't see any such resistor in the diagram
No resistor on the GND, I have mapped the GND in dotted green. Perhaps cut and try a resistor top right
a suggestion:
you have those nice mosfets, mains transformer, psu caps ....... why not build another amp instead?
you have those nice mosfets, mains transformer, psu caps ....... why not build another amp instead?
Ctrix, hi
A fair point but I'm not talented enough to design a circuit and in this case removing the transformer and locating at a distance is not help. The revised GND ing has helped and I agree a redesign of the layout would probably help. Ive ordered a couple of small transformers to power the 7812 and not use the 60V drop from the + ve power rail. Ive not given up yet !
I wonder which parts are the most sensitive to noise
A fair point but I'm not talented enough to design a circuit and in this case removing the transformer and locating at a distance is not help. The revised GND ing has helped and I agree a redesign of the layout would probably help. Ive ordered a couple of small transformers to power the 7812 and not use the 60V drop from the + ve power rail. Ive not given up yet !
I wonder which parts are the most sensitive to noise
I agree with Jean-Paul emphatically. More modifications are variables that will confuse diagnosis. Zoom out.
Revert, simplify, reappraise.
The repair mans mantra is "process of elimination". That is an important focus for these kind of frustrations, as well as steering clear of the drink.
Then get into Noise reduction observations, e.g. Output caps very important on those noisy 78xx/79xx regs- .33uF on the input. 1μf to 10μf to 100μf low esr on the output. Those values would be fine for amps.
The two things I have not seen mentioned are:
Is star earthing implemented? In the amp. Perhaps more importantly, throughout your mains supply system that powers all your audio?. It's best to draw from one mains spur. Multiple spurs create earth loops ( between everything that's connected across spurs; interconnect, mains cables, everything!), that's the most common cause of 50Hz buzz .
(as an aside, SMPS need filtering. To stop the hash going back into the mains, and to stop the list of potential mains interferences affecting the SMPS and the sensitive IC's it's suppling).
Looking at the above quote. Did you try a 'back to back' zener diode arrangement as a potential solution?
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BTW any reason not to increase the capacitance of the band resistor more as well. I am running a 22nF so in theory the high frequency roll off is in theory 1.5KHz so I could raise this to 100nF or more getting it to roll off earlier. The subs are used up to 50Hz max anyway ?
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I hear you and don't disagree, I have been evolving the second amp more piecemeal. I think the drink helps 🙂
I have removed the whole circuit here just to see how much impact this circuit has. It is enough for me to bite the bullet and fit a separate supply to this circuit (this is the case in my BPSP 500 amps). I have added a 0.47uf. I will try a higher Lower ESR cap on the output too (I have a few suitable Panasonic low ESR, FR caps). So when complete it will have a separate LPS and added capacitance
I draw from one ring main for the audio in that room. All the other items are on a seperate ring main. All the mains leads are 2m in length as well and the sockets are on a run. If the house wasn't listed I would have reinstated with an individual matched spur to each unit. As I have 23 individual items powered up to watch one film a single spur wouldn't make sense
The only SMPS in the whole set up is in the lap top that uploads the settings to the DSP, I have tried turning this off to see, no difference it's also on the non audio circuit. I run the projector which has a switch mode from a separate spur -it's been off in all the testing
Interestingly the set up is quiet with 5 existing sub amps (BK BPSP 500), 9 mono power amps (naim 135's), 4 pre amps and supply (naim 32.5 x 4 with Supercap), Panasonic 9000 with LPS, 10x10 MiniDSP with LPS, Lumagen with LPS
Not tried that please explain
It's time to look at the supply rails etc with an oscilloscope.
It would also be useful to know if this noise is common in this model of amp, or whether this particular example is unusual.
I think someone mentioned up the thread that the problem could be demodulation of RF noise, this is worth looking into.
Many audio amps are wide open to RF signals which can be demodulated by any part of the circuit and manifest in the audio spectrum.
Also, mentioning SMPS, that mains powered fan is probably a brushless motor?
It would also be useful to know if this noise is common in this model of amp, or whether this particular example is unusual.
I think someone mentioned up the thread that the problem could be demodulation of RF noise, this is worth looking into.
Many audio amps are wide open to RF signals which can be demodulated by any part of the circuit and manifest in the audio spectrum.
Also, mentioning SMPS, that mains powered fan is probably a brushless motor?
Boom, there you have it. In recording studios or listening rooms, that is a culprit. If you haven't already-
In sequence you require:
1. A good earth, if you can get less than 0.5Ω awesome (very specialised meters required), driving copper rods ( 3 interconnected rods are the IEEE standard for a mains supply) will not always get you there, depending on the conductivity of your available earth, dryness, for example is rarely good, As short as possible over engineered cable helps weather the elements as well as keeps the Resistance down.
2. A dedicated mains spur from the fuse/ breaker box.
3. Then to star earthing inter equipment to prevent loops that pick up interference, like RF , 50Hz buzz, etc.etc.
4. Yes, sequencing power up is a 'thing' in all larger systems. if you can't alter this spur arrangement, and long runs of cables are involved, there is the compromise of Input and Output transformers on the interconnect, like Mixing Console to Stage and D.I. boxes.
Like all Electrics and Electronics each one of these has the potential to be a rabbit hole of research. Zoom out after each session!
If your explorations are to be assisted, defining what, where and types is helpful. May I hesitantly suggest reading back to yourself what you write, asking your self does this mean what I'm trying to say? Does it allow others to 'get your drift'? I use the preview function, it helps.
Where? Input or output of the LMxx? it's easy enough to download the PDF and start with the manufacturers recommendations. In my experience, increasing low ESR caps values on the outputs decreases general noise.
Going beyond the manufacturers recommendations on the input doesn't make much difference, but using a cap there will help keep the output as clean as possible.
Pointless.
Think of all the time and money you could be saving by putting in a 4mm² or 6mm² 'Twin and earth' supply. Not to mention headaches. Not recommended unless you have real experience in mains electricity, but not expensive.
Not A 4mm ø cable.
2.3mm ø copper is 4mm²
6mm² is 2.8mm ø
CURRENT CARRYING CAPACITY (AMPS) | ||||||
Conductor Cross Sectional Area | Enclosed in an insulated wall | Enclosed in conduit on a wall or in trunking etc... | Clipped direct | |||
1.0mm² | 11A | 10A | 13A | 11.5A | 15A | 13.5A |
1.5mm² | 14A | 13A | 16.5A | 15A | 19.5A | 17.5A |
2.5mm² | 18.5A | 17.5A | 23A | 20A | 27A | 24A |
4.0mm² | 25A | 23A | 30A | 27A | 36A | 32A |
6.0mm² | 32A | 29A | 38A | 34A | 46A | 41A |
10.0mm² | 43A | 39A | 52A | 46A | 63A | 57A |
16.0mm² | 57A | 52A | 69A | 62A | 85A | 76A |
This is a good circuit type for mains filtration for SMPSs:
Note the capacitors from both lines to earth AFTER the double choke/ compensating inductor, very important, then the inductor to E
Supply is left. Load is right.
The 'back to back' zener diode arrangement may be an interesting isolated experiment... Using the above diagram, where the single capacitor to earth is, after the transformer/ inductor, as it were, except it would be to chassis in your earlier context.
It's a very long time since I've used that and i'm struggling to find a reference in my files,
but I think it serves as a dissipative function in some earthing situations.
It's best to eliminate fundamental problems first, like your spur loops. At least then you know what is what.
hope that helps.
Thanks
PS when I did utilise a dedicated mains CU , it was wired with an individual 100A fuse from the incomer, then 10A lines of equal length for each socket outlet. Much to the dismay of the electrician
PS when I did utilise a dedicated mains CU , it was wired with an individual 100A fuse from the incomer, then 10A lines of equal length for each socket outlet. Much to the dismay of the electrician
First of all I see there are many imbalances in the overall headroom considerations
For 12 Mosfets you have just 4 x 10000uF cap and that too for subwoofer application is very low capacitance you need hefty capacitance as ripple current demand will be quite high. Afaik you need atleast 60,000uF/Rail and those puny capacitors will not be able to handle the ripple and they would get puntured in bad load conditions as most of the subs run in 4ohm load.
Bridge rectifier is open air cooled they need to be heatsinked as they get quite hot once you are playing at high power subwoofers.
Get the speaker return which is - of the speaker to point to the junction of the capacitor in between +/- terminal of the mains power capacitor
For 12 Mosfets you have just 4 x 10000uF cap and that too for subwoofer application is very low capacitance you need hefty capacitance as ripple current demand will be quite high. Afaik you need atleast 60,000uF/Rail and those puny capacitors will not be able to handle the ripple and they would get puntured in bad load conditions as most of the subs run in 4ohm load.
Bridge rectifier is open air cooled they need to be heatsinked as they get quite hot once you are playing at high power subwoofers.
Get the speaker return which is - of the speaker to point to the junction of the capacitor in between +/- terminal of the mains power capacitor
The Ground Loops presentation (near the back) talks about making sure all pieces of gear come off the same mains outlet if the gear utilises a safety ground. If you are powering gear in a system off separate ring mains you have a huge loop area for mag field pickup and therefore noise.