Hello folks,
I have built a Class D amp with Hypex modules and SMPS. Since I was using unbalanced RCA inputs, the instructions said to have the 3rd prong of the power cord not attached, and to attach the outers of the RCA inputs to the case. They also said to electrically connect one of the stand-offs from the power supply to the chassis. ("J7 is connected to secondary ground with a 100nF capacitor. Connect J7 to chassis with a metal
spacer for optimum EMI performance. ")
The instructions further say to have class 2 double insulation. I am not sure how to implement this. My case is bare aluminum. The heatsink of the amplifier modules are connected to the case, although the transistors on them appear to be insulated. The SMPS is already sort of connected to the chassis via the standoff. Other parts of the SMPS are at least 1/4" away from bare metal.
I guess one concern is if somehow a high voltage touches the case. In that case, won't it fry my DAC, which is connected to the RCA?
If it's for shock protection of me touching the case, then should the case be coated with an insulator? But wouldn't my RCA outer and SMPS standoff still be connected to it?
I have built a Class D amp with Hypex modules and SMPS. Since I was using unbalanced RCA inputs, the instructions said to have the 3rd prong of the power cord not attached, and to attach the outers of the RCA inputs to the case. They also said to electrically connect one of the stand-offs from the power supply to the chassis. ("J7 is connected to secondary ground with a 100nF capacitor. Connect J7 to chassis with a metal
spacer for optimum EMI performance. ")
The instructions further say to have class 2 double insulation. I am not sure how to implement this. My case is bare aluminum. The heatsink of the amplifier modules are connected to the case, although the transistors on them appear to be insulated. The SMPS is already sort of connected to the chassis via the standoff. Other parts of the SMPS are at least 1/4" away from bare metal.
I guess one concern is if somehow a high voltage touches the case. In that case, won't it fry my DAC, which is connected to the RCA?
If it's for shock protection of me touching the case, then should the case be coated with an insulator? But wouldn't my RCA outer and SMPS standoff still be connected to it?
It is purely for electrical safety. Do you want/need to conform to formal safety regulations? If so, you pretty much have to connect the 3rd prong of the power connector to the chassis (and the instructions don't actually tell you you shouldn't, they just indicate precautions if you do). In that case, you should probably try to float the input connectors with the resistor and capacitor as described in the instructions.
Class 2 wiring describes the wiring between the power source and the connected equipment, usually loudspeaker wires. If you have mains gong to your amplifier box and it is metallic, exposed parts must be earthed for your own safety and to comply with regulations.
There's more;
The NEC defines a Class 2 circuit as that portion of the wiring system between the load side of a Class 2 power source and the connected equipment. Due to its power limitations, a Class 2 circuit is considered safe from a fire initiation standpoint and provides acceptable protection from electrical shock.
The Code defines a Class 3 circuit as that portion of the wiring system between the load side of a Class 3 power source and the connected equipment. Since the Class 3 circuits has higher levels of current than for Class 2 circuits, it specifies additional safeguards to provide protection from an electric shock you might encounter on the job site.
Power for Class 2 and Class 3 circuits is limited either inherently (in which no over current protection is required) or by a combination of a power source and overcurrent protection.
The maximum circuit voltage is 150VAC or VDC for a Class 2 inherently limited power source and 100VAC or VDC for a Class 3 inherently limited power source. The maximum circuit voltage is 30VAC and 60VDC for a Class 2 power source limited by over current protection, and 150VAC or VDC for a Class 3 power source limited by over current protection.
For example, heating system thermostats are commonly Class 2 systems and the majority of small bell, buzzer, and annunciator systems are Class 2 circuits. Class 2 also includes small intercom phone systems in which a battery and the ringing circuit supply the voice circuit.
Where a Class 2 circuit is routed a distance where voltage drop becomes a problem (by not providing a voltage that will energize the equipment), Class 3 circuits are sometimes used to provide the necessary voltage and current. Class 3 circuitry and accessories can be designed to alleviate the problem of excessive voltage drop.
See WHAT IS CLASS 2 WIRING
Use your head and all will be fine.
Class 2 and 3 circuits are defined as the portion of the wiring system between the power source and the connected equipment. Because of the power limitations of Class 2 circuits, many consider them to be safe from a fire initiation standpoint and to provide an acceptable level of protection from electrical shock. - See more at: Class 2 and 3 Circuits | EC Mag
There's more;
The NEC defines a Class 2 circuit as that portion of the wiring system between the load side of a Class 2 power source and the connected equipment. Due to its power limitations, a Class 2 circuit is considered safe from a fire initiation standpoint and provides acceptable protection from electrical shock.
The Code defines a Class 3 circuit as that portion of the wiring system between the load side of a Class 3 power source and the connected equipment. Since the Class 3 circuits has higher levels of current than for Class 2 circuits, it specifies additional safeguards to provide protection from an electric shock you might encounter on the job site.
Power for Class 2 and Class 3 circuits is limited either inherently (in which no over current protection is required) or by a combination of a power source and overcurrent protection.
The maximum circuit voltage is 150VAC or VDC for a Class 2 inherently limited power source and 100VAC or VDC for a Class 3 inherently limited power source. The maximum circuit voltage is 30VAC and 60VDC for a Class 2 power source limited by over current protection, and 150VAC or VDC for a Class 3 power source limited by over current protection.
For example, heating system thermostats are commonly Class 2 systems and the majority of small bell, buzzer, and annunciator systems are Class 2 circuits. Class 2 also includes small intercom phone systems in which a battery and the ringing circuit supply the voice circuit.
Where a Class 2 circuit is routed a distance where voltage drop becomes a problem (by not providing a voltage that will energize the equipment), Class 3 circuits are sometimes used to provide the necessary voltage and current. Class 3 circuitry and accessories can be designed to alleviate the problem of excessive voltage drop.
See WHAT IS CLASS 2 WIRING
Use your head and all will be fine.
Class 2 and 3 circuits are defined as the portion of the wiring system between the power source and the connected equipment. Because of the power limitations of Class 2 circuits, many consider them to be safe from a fire initiation standpoint and to provide an acceptable level of protection from electrical shock. - See more at: Class 2 and 3 Circuits | EC Mag
That is UL class 2, but what is clearly being discussed here is class II (Double insulated appliances), not the same thing at all.
Personally I take the view that all DIY needs to be class I if in a metal case, there are just too many ways to get class II lethally wrong.
Regards, Dan.
Personally I take the view that all DIY needs to be class I if in a metal case, there are just too many ways to get class II lethally wrong.
Regards, Dan.
That's good advice.
Even if the european protection class II in would allow metal casings without PE (protective earth), the catalogue of details how to meet the requirements of double isolation is really no fun.
No matter if the Hypex SMPS meets the requirements, most DIYers will mess the safety by their surrounding implementation when trying to realize class II. Even most EE are struggling hard to get it right.
Already a class I set up has enough points to mess, but usually remains by far more forgiving than a wrongly done class II build.
Metal cased class II is seen (Lots of commercial hifi stuff), but it is very subtle to design, I cannot reccommend going there.
Stick to class I, it is harder to screw up and can be at least as quiet if done right.
Regards, Dan.
Stick to class I, it is harder to screw up and can be at least as quiet if done right.
Regards, Dan.
umm, sorry, what do I need to do for Class I?
Here is the Hypex wiring guide:
http://www.hypex.nl/docs/wiring.pdf
"When using RCA inputs do NOT connect chassis to safety earth to avoid ground loops. Amplifier must be build according to double insulation safety standards"
Also This:
http://www.hypex.nl/docs/appnotes/earth_appnote.pdf
Here is the Hypex wiring guide:
http://www.hypex.nl/docs/wiring.pdf
"When using RCA inputs do NOT connect chassis to safety earth to avoid ground loops. Amplifier must be build according to double insulation safety standards"
Also This:
http://www.hypex.nl/docs/appnotes/earth_appnote.pdf
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Yep Hypex are in my view somewhat irresponsible for suggesting that class II is a suitable safety architecture for DIY (Especially in a small note on the bottom of a page of instructions).
The safety earth connection should be involate, there are other ways to keep earth loops under control that do not leave the inexperienced trying to do what the professionals are reluctant to do.
Regards, Dan.
The safety earth connection should be involate, there are other ways to keep earth loops under control that do not leave the inexperienced trying to do what the professionals are reluctant to do.
Regards, Dan.
I would not call Hypex irresponsible.
In fact I am glad that Hypex has some models of SMPS, which are suited for class II and are constructed without obvious short comings.
Bruno's advice on earthing and wiring might not satisfy a safety engineer,
but at least it describes the fundamental idea of an extra line of defense and gives a rough help how to settle it with or without protective earth.
May be he should push unexperienced DIYers slightly stronger to class I, true.
IMHO a DIYer who decides to DIY a mains powered device, has to accept some responsibility and shall learn the basics first - at least by google, wikipedia, books etc.
I strongly disagree against the growing habbit to sue knowledgeable people for the ignorance of others.
P.S.
... I am afraid of the amount of transformers or SMPS which are are constructed for classI, but have been implanted by DIYers in classII...
In fact I am glad that Hypex has some models of SMPS, which are suited for class II and are constructed without obvious short comings.
Bruno's advice on earthing and wiring might not satisfy a safety engineer,
but at least it describes the fundamental idea of an extra line of defense and gives a rough help how to settle it with or without protective earth.
May be he should push unexperienced DIYers slightly stronger to class I, true.
IMHO a DIYer who decides to DIY a mains powered device, has to accept some responsibility and shall learn the basics first - at least by google, wikipedia, books etc.
I strongly disagree against the growing habbit to sue knowledgeable people for the ignorance of others.
P.S.
... I am afraid of the amount of transformers or SMPS which are are constructed for classI, but have been implanted by DIYers in classII...
..and some more adders to Bruno's hints for builds with single isolation, which require to have the chassis connected to protective earth.
==> Class I
- Make sure that all conductive parts of the enclosure have a robust connection with low electrical impedance to the earth wire of your power cord.
Use crimping and screws for these connections and ensure wires of at least 0.75sqmm. (Soldering is regarded as insufficient.)
- Make sure that you always keep the 3mm creepage of N&L vs the chassis or any secondary side area - pay special attention to this when connecting the mains switch.
- Keep the 3mm creepage also between unisolated parts of N vs. L (i.e. at the mains switch)
- Make sure that the power cord has a proper strain relief.
- Do not pass single isolated mains wiring over the top of your secondary side audio circuitry.
Inside the mains plug of the power cord:
-Make sure to keep the length of PE wire inside the connector at least 10mm longer than N&L. This will ensure that N&L get disconnected first in case someone pulls the wire out of the strain relief.
-Make sure that the strain relief is fastened.
-Do not solder the strands of the litz before screwing, but use wire ferrules.
Note:
The required creepages and clearances may vary slightly depending on the chosen safety standard. 3mm refers to Bruno's paper.
When looking for basic isolation of mains up to 250V/AC in EN60065 I am finding 2.5mm for the creepages and 2mm for the clearances (Table 8 & 11).
Disclaimer:
The above rules are intended to prevent the worst, without guarantee for completeness or full compliance with relevant safety standards.
==> Class I
- Make sure that all conductive parts of the enclosure have a robust connection with low electrical impedance to the earth wire of your power cord.
Use crimping and screws for these connections and ensure wires of at least 0.75sqmm. (Soldering is regarded as insufficient.)
- Make sure that you always keep the 3mm creepage of N&L vs the chassis or any secondary side area - pay special attention to this when connecting the mains switch.
- Keep the 3mm creepage also between unisolated parts of N vs. L (i.e. at the mains switch)
- Make sure that the power cord has a proper strain relief.
- Do not pass single isolated mains wiring over the top of your secondary side audio circuitry.
Inside the mains plug of the power cord:
-Make sure to keep the length of PE wire inside the connector at least 10mm longer than N&L. This will ensure that N&L get disconnected first in case someone pulls the wire out of the strain relief.
-Make sure that the strain relief is fastened.
-Do not solder the strands of the litz before screwing, but use wire ferrules.
Note:
The required creepages and clearances may vary slightly depending on the chosen safety standard. 3mm refers to Bruno's paper.
When looking for basic isolation of mains up to 250V/AC in EN60065 I am finding 2.5mm for the creepages and 2mm for the clearances (Table 8 & 11).
Disclaimer:
The above rules are intended to prevent the worst, without guarantee for completeness or full compliance with relevant safety standards.
OK, just to get this straight:
The outer of the RCA jack is now connected to the case via a resistor and capacitor. What values?
The input on the amp modules have three wires: +,-,shield. What does the shield wire attach to now?
Also, if I get the case hard anodized - would that count as insulation?
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The Hypex data sheet recommends 100 ohm and 100 nF, and I don't see any reason not to use those values, but I am pretty sure they aren't critical.
The chassis.
No, not form the point of view of safety regulation, and I would definitely not bet my life on it.
Julf, if they have used feedback post filter, why they "ommited", to put in that pdf a 10Khz square wave tests, to observe rise and fall times?
You said about feedback in mine post, so postfilter being almost perfect, why they didn't do that test?
In that case, on squarewave output signal, the form of signal must be almost in concordance with input signal, that I don't believe...
Why in the "wonderfull specifications" they didn't sau anything about rise and fall times, or slew rate?
Those are parameters very important too!
You said about feedback in mine post, so postfilter being almost perfect, why they didn't do that test?
In that case, on squarewave output signal, the form of signal must be almost in concordance with input signal, that I don't believe...
Why in the "wonderfull specifications" they didn't sau anything about rise and fall times, or slew rate?
Those are parameters very important too!
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