Building a lm3886 with no / little hum is very possible and a good way to learn about star grounding
http://www.passdiy.com/pdf/articles/ground-loops.pdf
^informative article from the passlabs site
starting with the disconnecting network you are fixing a problem that doesn't exist (at least not yet)
best to make the amp, then when/if hunting ground loops use the disconnecting network as a tool to help solve the issue. Just my opinion
On a seperate note, is the classI/II regs international or just a european thing ?
Andrew you should NOT attack the man (me) just their idea's.
There are another ways to solve ground loops (if you have it) rather than the mains end. The answer is posted above it's easy. As also stated, there are legal questions with lifting a safety ground period, if you do something else other than directly bonding earth to chassis then you are on your own.
There are another ways to solve ground loops (if you have it) rather than the mains end. The answer is posted above it's easy. As also stated, there are legal questions with lifting a safety ground period, if you do something else other than directly bonding earth to chassis then you are on your own.
Hi Inf,
it's not an attack.
I genuinely believe that you and the others, including me, seem to see the Safety Earth connection differently.
I can only explain this difference in stance by saying you do not understand what we are posting about. Would "appear not to understand" sound any better?
it's not an attack.
I genuinely believe that you and the others, including me, seem to see the Safety Earth connection differently.
I can only explain this difference in stance by saying you do not understand what we are posting about. Would "appear not to understand" sound any better?
That's is where you do not understand our posts.infinia said:
We keep repeating that the third wire (PE) of the mains incoming cable must be permanently connected to chassis. That stance of ours has never changed.
Why do you suggest that we are advising otherwise?
I and I think I speak for the others have never said that a Ground Lift Switch should "break" the Safety Earth connection to the other exposed parts nor can it be allowed to "break" the chassis to mains PE connection.
The Ground Lift Switch that is being described is in parallel to the Disconnecting Network. Opening or closing this switch does not interfere with the Audio Ground to Safety Earth capability to pass fault current.
There seems to be a fundamental misunderstanding in what we are posting and how you interpret what you read.
How else can I put that?
What part of directly don't YOU understand. Prove that wonky network is an approved PE scheme by a safety agency. A ground loop can be minimized in the most susceptable part of a ground loop ie the signal ground shield.
I have guided several of my designs thru UL certification and even one through UL listing which is the most rigorous.
My current speciality is RF systems susceptibility and I have been part of tiger teams to solve grounding and noise issues in complex analog/digital systems.
I suggest you review the mechanisms of audio ground loops and their solutions.
I have guided several of my designs thru UL certification and even one through UL listing which is the most rigorous.
My current speciality is RF systems susceptibility and I have been part of tiger teams to solve grounding and noise issues in complex analog/digital systems.
I suggest you review the mechanisms of audio ground loops and their solutions.
Bryston amplifiers have that network in all schematics I have seen so far from them. Bryston is a Canadian company, so it is very likely that they have UL or ULC certification. If you have achieved certification with one of your products, you will get or already have a list with all certified products from UL, where you can look up, if my assumption is correct.
I'm starting to question my own understanding of the schematic.
If we ignore the disconnecting network entirely, the Safety Earth is clearly shown with a direct and dedicated connection to the earth from the power inlet module. This provides a route to earth for any fault which happens to result in the chassis becoming live.
Is this not directly bonding earth to the chassis? Am I misunderstanding this part of the schematic?
If we ignore the disconnecting network entirely, the Safety Earth is clearly shown with a direct and dedicated connection to the earth from the power inlet module. This provides a route to earth for any fault which happens to result in the chassis becoming live.
Is this not directly bonding earth to the chassis? Am I misunderstanding this part of the schematic?
Is that product listed by the UL, I don't think it is. That is your claim not mine. The burdon proof is still in your court if you still maintain that is an accepted and approved safety standard. BTW it isn't. It's possible that you can get an exception, but it is a lot of unecessary work and controls will be put upon you the manufacturer to be even considered. But why go that route in the first place. There are more effective solutions to be had.
I'm less interested in the disconnecting network and more interested in establishing whether I have the direct bonding between the chassis and earth.
Can someone confirm my understanding of the schematic?
My practical implementation will be to run a wire from the earth connector on the power inlet module and and bolt it directly to the chassis. This bolt will service no other connection other than to accomodate this wire.
Should I assume that this is the correct approach?
Can someone confirm my understanding of the schematic?
My practical implementation will be to run a wire from the earth connector on the power inlet module and and bolt it directly to the chassis. This bolt will service no other connection other than to accomodate this wire.
Should I assume that this is the correct approach?
OK Redshift187. Thanks. At least I can be certain that whatever I do with regard to the disconnecting network, I can be confident that the safety earth is in place.
But I am going the implement the disconnecting network and want to allow for the addition of this circuit when laying out the components in the case. Last night I did this and marked up where I need to drill my holes. Things aren't as roomy as I expected mainly due to the large heatsink. Still it does all fit.
I do need to buy some more metal, to subdivide the case internally and create a spacer for the tranformer, which I hope to do today. I'm also going to get a flat brass bar to attach the chip to the heatsink.
But I am going the implement the disconnecting network and want to allow for the addition of this circuit when laying out the components in the case. Last night I did this and marked up where I need to drill my holes. Things aren't as roomy as I expected mainly due to the large heatsink. Still it does all fit.
I do need to buy some more metal, to subdivide the case internally and create a spacer for the tranformer, which I hope to do today. I'm also going to get a flat brass bar to attach the chip to the heatsink.
There are a number of outstanding issues to be resolved in my own mind until I am confident that I have all the circuitry I need.
The first of these is a soft start. Do I need one of these? What's the consequence of not having one? Is it a bit of a pop when I turn the amps on or is it a constant blowing of fuses?
The other two relate to filters and were mentioned by Andrew right at the start of this thread, namely high and low pass filtering.
I'm assuming the high pass (DC) filter needs to be applied to the signal coming in from the RCA socket. I believe I placed two whacking great caps on the signal path to counter this when making my Tangent variant of the CMoy headphone amp. However, I have subsequency read a number of posts (here and elsewhere) saying that caps in the signal path are to be avoided. So what's the best way of addressing DC offset?
In terms of low pass filtering, I have gone some way to address RF by buying a power inlet module which incorporates a filter. However, as was pointed out earlier in this thread, there are other sources of RF (RCAs and speakers?). What's the recommended way of intercepting these sources of RF?
The first of these is a soft start. Do I need one of these? What's the consequence of not having one? Is it a bit of a pop when I turn the amps on or is it a constant blowing of fuses?
The other two relate to filters and were mentioned by Andrew right at the start of this thread, namely high and low pass filtering.
I'm assuming the high pass (DC) filter needs to be applied to the signal coming in from the RCA socket. I believe I placed two whacking great caps on the signal path to counter this when making my Tangent variant of the CMoy headphone amp. However, I have subsequency read a number of posts (here and elsewhere) saying that caps in the signal path are to be avoided. So what's the best way of addressing DC offset?
In terms of low pass filtering, I have gone some way to address RF by buying a power inlet module which incorporates a filter. However, as was pointed out earlier in this thread, there are other sources of RF (RCAs and speakers?). What's the recommended way of intercepting these sources of RF?
The simplest soft start circuit I can find is this one by Rod Elliot, where A is the live and SA is the soft live.
It is placed in series with the supply to the transformer. More details here.
I'll have a go at calculating the resistor values (I will probably get this wrong, so do not use as a guide unless confirmed by a more knowledgable poster)....
I = VA / V (1) Where VA is the VA rating of the transformer, and V is the mains voltage used
Therefore,
I = 160 / 240 = 0.67A
At a limit of 200% of full power current, this is 1.3A AC. Using
R = V / I (2)
gives...
R = 240 / 1.3 = 180 Ohms
This suggests that I can use a single 180 Ohm resistor for the above circuit.
Earlier I bought a 5W resistor for use with my disconnecting network. This is massive. Can I use a 2W version....and how does one go about calculating this?
An externally hosted image should be here but it was not working when we last tested it.
It is placed in series with the supply to the transformer. More details here.
I'll have a go at calculating the resistor values (I will probably get this wrong, so do not use as a guide unless confirmed by a more knowledgable poster)....
I = VA / V (1) Where VA is the VA rating of the transformer, and V is the mains voltage used
Therefore,
I = 160 / 240 = 0.67A
At a limit of 200% of full power current, this is 1.3A AC. Using
R = V / I (2)
gives...
R = 240 / 1.3 = 180 Ohms
This suggests that I can use a single 180 Ohm resistor for the above circuit.
Earlier I bought a 5W resistor for use with my disconnecting network. This is massive. Can I use a 2W version....and how does one go about calculating this?
if you are using a 160va transformer and the chipamp psu you will not require a softstart.
will you be running a preamp/buffer ? as these will cause power on 'pops'
"caps in the signal path are to be avoided" in theory is true as adding anything into the circuit will contribute it's own distortion. In practise it's just bad publicity in my opinion and comes down to the quality of the cap, but others will disagree
i've used a 3.3uf similar to these as the input dc blocking capacitors. As used in Rod Elliot's chipamp.
This capacitor forms a high pass filter with R1 (22k) so low frequencies (in this case <2.2Hz) will be attenuated
will you be running a preamp/buffer ? as these will cause power on 'pops'
"caps in the signal path are to be avoided" in theory is true as adding anything into the circuit will contribute it's own distortion. In practise it's just bad publicity in my opinion and comes down to the quality of the cap, but others will disagree
i've used a 3.3uf similar to these as the input dc blocking capacitors. As used in Rod Elliot's chipamp.
This capacitor forms a high pass filter with R1 (22k) so low frequencies (in this case <2.2Hz) will be attenuated
PJ,
the input filtering does two different things.
The high pass filter determines the low frequency foll off and also blocks DC from the source, if any.
The low pass filter determines the high frequency roll off and also attenuates RF/interference coming in through the interconnect or from a source.
So the 4 components needed at the input do in total four jobs. Can't ask for better value than that.
If you know that all your sources can NEVER pass DC on to the next stage, you can delete the DC blocking capacitor from the power amp input. But you still need to determine the low frequency roll off of the amplifier.
The choice becomes yours once you have informed your self of the way your sources and your power amp interact.
the input filtering does two different things.
The high pass filter determines the low frequency foll off and also blocks DC from the source, if any.
The low pass filter determines the high frequency roll off and also attenuates RF/interference coming in through the interconnect or from a source.
So the 4 components needed at the input do in total four jobs. Can't ask for better value than that.
If you know that all your sources can NEVER pass DC on to the next stage, you can delete the DC blocking capacitor from the power amp input. But you still need to determine the low frequency roll off of the amplifier.
The choice becomes yours once you have informed your self of the way your sources and your power amp interact.
Pj,
the 160VA transformer should never draw more than 667mAac of current if it is working to it's maximum rating.
A T800mA fuse is adequate for this.
Overload the transformer and eventually the T800mA fuse will blow.
Try starting the amplifier with that correct fuse on the primary side. It may blow or it may blow at the seventeenth time of switching on.
To allow the correct rated fuse to be used you may need a soft start.
Don't believe all those posters that say you only need a soft start when the toroid exceeds 300VA. It depends on how the transformer has been designed and how unlucky you are with voltage at the time of switch on.
You may find that your amplifier will operate perfectly well with T600mA or even a T400mA fuse on the primary. I recommend that you fit the smallest fuse rating that allows your amplifier to play in all the situations (loudness) that you are likely to encounter.
If it won't start reliably (nuisance blowing) on this small fuse then add a delayed relay and some power resistors.
The delay can be between 100ms and 300ms. Some have suggested that the delay can be even shorter but I have not experimented with this.
The power resistors must be able to survive the transformer start up current for the time delay you have chosen.
They will generate some self heating during the delay time but if you keep it short, <=300ms, the resistors will be OK.
For bigger transformer I use a bank of 5off 10r 5W resistors in series. For your 160VA where the current to start the toroid can be much lower try using 4off 27r or 22r 5W resistors in series.
I do not recommend putting higher value resistors in parallel. The high value resistors are wound with very thin wire and will be less reliable than the thick wire low resistance version during the high current start up phase.
BTW,
I don't like ESP's use of an aluminium shroud around that mains connected resistors. I think that is an accident waiting to happen.
Fit a cover over the mains fuse holder.
the 160VA transformer should never draw more than 667mAac of current if it is working to it's maximum rating.
A T800mA fuse is adequate for this.
Overload the transformer and eventually the T800mA fuse will blow.
Try starting the amplifier with that correct fuse on the primary side. It may blow or it may blow at the seventeenth time of switching on.
To allow the correct rated fuse to be used you may need a soft start.
Don't believe all those posters that say you only need a soft start when the toroid exceeds 300VA. It depends on how the transformer has been designed and how unlucky you are with voltage at the time of switch on.
You may find that your amplifier will operate perfectly well with T600mA or even a T400mA fuse on the primary. I recommend that you fit the smallest fuse rating that allows your amplifier to play in all the situations (loudness) that you are likely to encounter.
If it won't start reliably (nuisance blowing) on this small fuse then add a delayed relay and some power resistors.
The delay can be between 100ms and 300ms. Some have suggested that the delay can be even shorter but I have not experimented with this.
The power resistors must be able to survive the transformer start up current for the time delay you have chosen.
They will generate some self heating during the delay time but if you keep it short, <=300ms, the resistors will be OK.
For bigger transformer I use a bank of 5off 10r 5W resistors in series. For your 160VA where the current to start the toroid can be much lower try using 4off 27r or 22r 5W resistors in series.
I do not recommend putting higher value resistors in parallel. The high value resistors are wound with very thin wire and will be less reliable than the thick wire low resistance version during the high current start up phase.
BTW,
I don't like ESP's use of an aluminium shroud around that mains connected resistors. I think that is an accident waiting to happen.
Fit a cover over the mains fuse holder.
Softstart:
The image you posted is only a small part of the total circuit, and you need at least 5W resistors for it (according to Rod Elliott). Given the information on the site you linked, I had calculated the resistors would see close to 1000W (total, not each) for an instant. I had done my own research into the pulse capability of power resistors and had chosen 3X 10W resistors that have a pulse capability of something like 250W or 300W. If you think 5W resistors are huge, you should see the bigger ones with heatsinks built in!
DC blocking / high pass input filtering:
An additional potential side effect is not only low frequency roll-off, but also low frequency phase shift. That said, AndrewT has great suggestions regarding low frequencies with correct component selection for the feedback components, input filtering components and power supply components (yes it matters!). Another option to get rid of DC without using capacitors in the signal path is to use a servo setup, but that is not really possible without the PCB being designed for it.
If you do not use DC blocking capacitors at any point in your setup, use a DC detection and protection circuit on the output!
The image you posted is only a small part of the total circuit, and you need at least 5W resistors for it (according to Rod Elliott). Given the information on the site you linked, I had calculated the resistors would see close to 1000W (total, not each) for an instant. I had done my own research into the pulse capability of power resistors and had chosen 3X 10W resistors that have a pulse capability of something like 250W or 300W. If you think 5W resistors are huge, you should see the bigger ones with heatsinks built in!
DC blocking / high pass input filtering:
An additional potential side effect is not only low frequency roll-off, but also low frequency phase shift. That said, AndrewT has great suggestions regarding low frequencies with correct component selection for the feedback components, input filtering components and power supply components (yes it matters!). Another option to get rid of DC without using capacitors in the signal path is to use a servo setup, but that is not really possible without the PCB being designed for it.
If you do not use DC blocking capacitors at any point in your setup, use a DC detection and protection circuit on the output!
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