Also, I'd like to use ESP's soft start circuit here:
http://sound.westhost.com/project39.htm
Can I replace the transformer and rectifier with a wall-wart DC supply? And how does the earthing work?
http://sound.westhost.com/project39.htm
Can I replace the transformer and rectifier with a wall-wart DC supply? And how does the earthing work?
How about this instead?pacificblue said:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=CP-1036-ND
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=CP-1236-ND
The non-locking ones are rated at only 1 A (I'm assuming per pin) for some reason, while this one does twice as much. Amphenol makes one rated at 5 A but I don't want to pay 3x as much. The shield I can use as the earth, while I can use two pins each for +, 0, and - for 4 A each. Is this OK?
Or should I use the 8-pos version, with two pins each for +/- and 4 pins for 0?
Those DIN connectors were used instead of RCA connectors for line level signals in the past. Ratings go from 30 to 100 V and 1 to 4 A depending on manufacturer and type. The plastic-housed have poor mechanical stability, while the metal-housed demand good soldering skills to not result in shorts.
Some British manufacturers still use them for signals and Mission uses the 5-pole versions for their PSX-R power supply, so they should work.
Some British manufacturers still use them for signals and Mission uses the 5-pole versions for their PSX-R power supply, so they should work.
I'd like to use this:pacificblue said:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=PB1044-ND
One on the +, one on the -, none on the two 0, right?
Terrible drawing (forgot the earth on the connector):
Attachments
Well, just put it in between the fuses and the caps, then.Hi 454,
First, You probably don't need a Safety Loop Breaker Circuit at all - it is a remedial fix if you are connecting to a device that has a Pin 1 Problem.
However, if you do want to have a SLB circuit, its purpose is to isolate the safety ground (and the chassis) from the audio grounds. Therefore it should go between the system star ground and the safety ground. If you have a separate power supply chassis, and the system star ground is in the amplifier chassis (most probably) then the SLB circuit should be there and connected to the extension of the safety ground in that chassis.
Dave
First, You probably don't need a Safety Loop Breaker Circuit at all - it is a remedial fix if you are connecting to a device that has a Pin 1 Problem.
However, if you do want to have a SLB circuit, its purpose is to isolate the safety ground (and the chassis) from the audio grounds. Therefore it should go between the system star ground and the safety ground. If you have a separate power supply chassis, and the system star ground is in the amplifier chassis (most probably) then the SLB circuit should be there and connected to the extension of the safety ground in that chassis.
Dave
Thanks, Dave. What's the practical difference between putting it in the PS chassis as my (and gni's) diagram shows and putting it in the amplifier chassis? I don't see much of a system/audio star ground in gni's diagram, so how would I implement that?David Davenport said:
Anyway, is the fusing OK?
Hi 454,
It is important to carefully design your grounding so that you do not have any loops or any ground current flowing where it doesn't need to flow. The best way to do this is to have a star ground somewhere in the device. The rest of the grounding can be busses or stars-of-stars, but it should all come back to this single system star ground at some point.
Having a separate power chassis does not change things. Design your grounding and make a map of the grounding and power on a piece of paper. Then draw a line around what you want in the power supply chassis (or vice verse, what you want in the amplifier chassis). Anything that crosses the line is in the cable.
Your system star ground should have going to it:
- All signal references
- All power commons
- All shields of single-ended interfaces
- Safety ground and chassis (Think of these as a single entity)
If you have a separate power supply chassis, there MUST be a separate wire from the safety ground lug on the power supply chassis to a lug on the amplifier chassis.
If you want a Safety Loop Breaker Circuit, disconnect the safety ground and chassis from the star ground and insert the SLB circuit between the star ground and the safety ground and chassis.
Your system star ground could go in either chassis but it makes sense to put it in the amplifier chassis to cut down on the number of wires in the cable. Your SLB could go in either chassis. If you put it in the amplifier chassis then both things you want it to go to (safety ground and star ground) are in that chassis. If you put it in the power supply chassis then you would need to add a wire to the cable to go from the star ground in the amplifier chassis to the SLB in the power supply chassis.
In a very simple system, assuming that the power common wire goes to the star ground, you might be able to cheat a little and use the power common wire in the cable as also the wire between the star and the SLB (with the SLB in the power supply chassis). However, using a wire for double-duty in grounding is a sloppy design practice and at some point will bite you. Also, there is no need to do this because you can put the SLB in the amplifier chassis and save the extra wire.
Dave
It is important to carefully design your grounding so that you do not have any loops or any ground current flowing where it doesn't need to flow. The best way to do this is to have a star ground somewhere in the device. The rest of the grounding can be busses or stars-of-stars, but it should all come back to this single system star ground at some point.
Having a separate power chassis does not change things. Design your grounding and make a map of the grounding and power on a piece of paper. Then draw a line around what you want in the power supply chassis (or vice verse, what you want in the amplifier chassis). Anything that crosses the line is in the cable.
Your system star ground should have going to it:
- All signal references
- All power commons
- All shields of single-ended interfaces
- Safety ground and chassis (Think of these as a single entity)
If you have a separate power supply chassis, there MUST be a separate wire from the safety ground lug on the power supply chassis to a lug on the amplifier chassis.
If you want a Safety Loop Breaker Circuit, disconnect the safety ground and chassis from the star ground and insert the SLB circuit between the star ground and the safety ground and chassis.
Your system star ground could go in either chassis but it makes sense to put it in the amplifier chassis to cut down on the number of wires in the cable. Your SLB could go in either chassis. If you put it in the amplifier chassis then both things you want it to go to (safety ground and star ground) are in that chassis. If you put it in the power supply chassis then you would need to add a wire to the cable to go from the star ground in the amplifier chassis to the SLB in the power supply chassis.
In a very simple system, assuming that the power common wire goes to the star ground, you might be able to cheat a little and use the power common wire in the cable as also the wire between the star and the SLB (with the SLB in the power supply chassis). However, using a wire for double-duty in grounding is a sloppy design practice and at some point will bite you. Also, there is no need to do this because you can put the SLB in the amplifier chassis and save the extra wire.
Dave
Hi 454,
Is the fusing OK?
I don't know. A fuse is there to protect something - ask yourself, what is it that you want to protect?
The main fuse in the IEC power receptacle will blow if something gets shorted to the chassis. It is sized to support the current draw of the whole device.
Additional fusing is needed for very sensitive things to be protected. For example, if your whole unit draws 5 Amps and you have a very sensitive device inside that draws 10mA that you want to protect, you would want to separately fuse the 10mA circuit because without that additional fuse the sensitive device would fry before the 5A fuse blew.
Remember, the chassis is connected to safety ground so you have protected yourself from a shock.
Dave
Is the fusing OK?
I don't know. A fuse is there to protect something - ask yourself, what is it that you want to protect?
The main fuse in the IEC power receptacle will blow if something gets shorted to the chassis. It is sized to support the current draw of the whole device.
Additional fusing is needed for very sensitive things to be protected. For example, if your whole unit draws 5 Amps and you have a very sensitive device inside that draws 10mA that you want to protect, you would want to separately fuse the 10mA circuit because without that additional fuse the sensitive device would fry before the 5A fuse blew.
Remember, the chassis is connected to safety ground so you have protected yourself from a shock.
Dave
So I DON'T need to fuse the transformer secondary, even as a good practice?David Davenport said:
If I put the breaking circuit in the PS chassis, I need 4 wires (+, 0, -, gr/PE). I need 3 minimum, so if I reduce the number of wires, that means I'm going to be shorting 0 and PE together inside the PS chassis?David Davenport said:
Hi 454,
You will need a minimum of four wires in the cable: safety ground, + voltage, - voltage and power common (0 volts) no matter if you have an SLB or not, of if you have an SLB, where it goes.
Good grounding practice would have five wires if the SLB were in the power supply chassis, and four wires if the SLB were in the amplifier chassis.
If you want to use an SLB, you can not double duty the power common and safety ground because these are what you want to isolate with the SLB. Also, as I said before, it is not a good idea to double duty any ground wiring.
If the secondary of the power transformer is shorted, that short will be reflected onto the primary and the main fuse will blow. There is no need for an additional fuse to protect the transformer.
Dave
You will need a minimum of four wires in the cable: safety ground, + voltage, - voltage and power common (0 volts) no matter if you have an SLB or not, of if you have an SLB, where it goes.
Good grounding practice would have five wires if the SLB were in the power supply chassis, and four wires if the SLB were in the amplifier chassis.
If you want to use an SLB, you can not double duty the power common and safety ground because these are what you want to isolate with the SLB. Also, as I said before, it is not a good idea to double duty any ground wiring.
If the secondary of the power transformer is shorted, that short will be reflected onto the primary and the main fuse will blow. There is no need for an additional fuse to protect the transformer.
Dave
454Casull said:
That is, if you answer the questionDavid Davenport said:
with: You want to protect the transformer from shorts, but not from overload.David Davenport said:
The trouble with transformers is, they cannot be protected against overload on the primary side, because their high start-up current forces you to use a fuse well above their nominal rating.
Here is, where your own assessment comes into play. Analyze the circuit you feed from the transformer. Is it possible to overload the transformer? E. g. if an output transistor shorts, there will be rail voltage across the speaker -> I = U/R -> I = rail voltage/Rspeaker. Is that current within the transformer rating?
If yes, skip the secondary fuse, but consider the use of a speaker protection, which could be a different fuse at a different place.
If no, will the current be big enough to trip the primary fuse?
If it is, skip the secondary fuse, and again consider the use of a speaker protection.
If it is not, decide, whether it is worth to protect the transformer or if you rather run the risk of damage in exchange for saving on the fuses.
You may come to the conclusion that you don't need the overload protection, because everything before the output transistors can only short and will always trip the primary fuse, and the output transistors get their own protection. Or you may come to the conclusion that Murphy's Law applies and you will get overload through some fault that you did not foresee and use an overload protection just to be on the safe side. Or you can come to the conclusion that you don't care about the transformer, and if it overheats and burns your house down, so what? I. e. if you never liked the house anyway.
Balderdash!David Davenport said:
A fuse is there to stop the house burning down.
It's purpose is not to protect something downstream.
A fuse disconnects a circuit that has already been abused and/or damaged.
A fuse must be rated less than the minimum current rating of any cable downstream that does not have separate fusing.
Hi Andrew,
There are a lot of commercial appliances that do not have a fuse and will not burn the house down. If a fuse was needed for safety in an audio amplifier, the standards organizations would produce a standard specifying such fusing.
Pacificblue made an excellent case that you might want to protect a speaker. I know from unfortunate experience that a speaker coil will open before there is a fire. However, this has happened to me only once in my fifty plus years in audio, so I don't deem it necessary to have a speaker fuse in my amplifiers.
Yes, it protects the circuit from further damage.
So, you are protecting the cable?
The cable should be designed such that it will withstand an overload long enough for the main component fuse to blow.
Dave
AndrewT said:
There are a lot of commercial appliances that do not have a fuse and will not burn the house down. If a fuse was needed for safety in an audio amplifier, the standards organizations would produce a standard specifying such fusing.
AndrewT said:
Pacificblue made an excellent case that you might want to protect a speaker. I know from unfortunate experience that a speaker coil will open before there is a fire. However, this has happened to me only once in my fifty plus years in audio, so I don't deem it necessary to have a speaker fuse in my amplifiers.
AndrewT said:
Yes, it protects the circuit from further damage.
AndrewT said:
So, you are protecting the cable?
The cable should be designed such that it will withstand an overload long enough for the main component fuse to blow.
Dave
Hi 454,
The SLB should go between the system star ground (with all of the audio grounds) and the safety ground.
If the system star ground is in the amplifier and the SLB is in the power supply chassis, you would need a wire to connect them. This is the fifth wire.
If both the system star ground and the SLB were in the amplifier then the fifth wire in the cable would not be needed.
Dave
454Casull said:
The SLB should go between the system star ground (with all of the audio grounds) and the safety ground.
If the system star ground is in the amplifier and the SLB is in the power supply chassis, you would need a wire to connect them. This is the fifth wire.
If both the system star ground and the SLB were in the amplifier then the fifth wire in the cable would not be needed.
Dave