@kodabmx:
the 1st one is a DC in / DC out converter and I made the same experience as you. These are ZVS converters, Zero Voltage Switching; means switching frequency is not constant, but varies with load; moreover, regulation is done such that there are bursts of fast switching followed by gaps (pause) with no switching at all; at least my specimen did that; it is neither a flyback nor a classic boost converter;
the switching as such is not audible but the repetition frequency of the gaps falls in the audio range - depending on load - and may vary randomly ...
couldn't use it as B+ supply so it found it's place as PS for a tube tester.
the 2nd one however is a DC in / AC out converter aka inverter to run mains equipment from a car battery. Output is most likely 60/50 Hz "modified sine" aka sort of square wave. How do you propose to use it for audio ? Add a bridge rectifier and conventional CLC filter ... ?
the 1st one is a DC in / DC out converter and I made the same experience as you. These are ZVS converters, Zero Voltage Switching; means switching frequency is not constant, but varies with load; moreover, regulation is done such that there are bursts of fast switching followed by gaps (pause) with no switching at all; at least my specimen did that; it is neither a flyback nor a classic boost converter;
the switching as such is not audible but the repetition frequency of the gaps falls in the audio range - depending on load - and may vary randomly ...
couldn't use it as B+ supply so it found it's place as PS for a tube tester.
the 2nd one however is a DC in / AC out converter aka inverter to run mains equipment from a car battery. Output is most likely 60/50 Hz "modified sine" aka sort of square wave. How do you propose to use it for audio ? Add a bridge rectifier and conventional CLC filter ... ?
Thanks guys for all of the education and design/product suggestions. I have a question that I tried to ask earlier, but maybe not clearly enough.
Most of the info I've found on the internet explaining the safety aspect of isolation transformers key on the fact that they don't share a common neutral/ground. So that if you were to touch one of the secondary-side leads while standing on "ground"/earth you wouldn't get a shock (hence isolated). But the design of all of the amps that we build with transformers has us attaching audio circuit grounds to the chassis, which is attached to the primary side neutral wire through the earth ground wire (which is also attached to the chassis). So doesn't this negate the primary safety aspect of the isolation transformer? What am I missing here?
Most of the info I've found on the internet explaining the safety aspect of isolation transformers key on the fact that they don't share a common neutral/ground. So that if you were to touch one of the secondary-side leads while standing on "ground"/earth you wouldn't get a shock (hence isolated). But the design of all of the amps that we build with transformers has us attaching audio circuit grounds to the chassis, which is attached to the primary side neutral wire through the earth ground wire (which is also attached to the chassis). So doesn't this negate the primary safety aspect of the isolation transformer? What am I missing here?
dancemyth,
USA
Ground and Neutral are not the same thing in the US.
Not if you are meeting the current up-to-date legal standards for home wiring.
You do not connect the amplifier directly to the circuit breaker panel in your home (which is the Only place that Ground and Neutral are the same, at one place inside that panel).
Old grandfathered amplifiers are one thing, most have 2 wire power cords.
If you have correctly wired 3 wire Hot, Neutral, Ground 120V power outlets in your home then use a 3 wire cord to the amp if you are able.
In the US . . . Connect Hot to fuse, then to power switch, then to power transformer primary. Connect Neutral to the other end of the power transformer primary (power return).
Do not use Ground as a power return. Ground is for safety, and also can sometimes reduce noise and ground loops.
If you can use the amp with 3 wire setup, connect Ground (safety ground) to the chassis.
Most turntables, CD players, tuners, preamps, etc. use 2 wire power cords. Many of those do not even have the wider Neutral tab (in that case, the hot and neutral tabs are the same width).
If the Neutral tab is wider, and you have a correctly wired 3 wire outlet, use the 2 wire power plug as it was designed, wide tab to wide outlet slot. do not modify that.
If the Neutral tab is not wider than the Hot tab, you can not tell which is which. The plug can be inserted either way. Use the way that gives the best noise and ground loop reduction.
Do not use those ground lift adapters. If you use them the worst that can happen is the "surviving spouse syndrome". I hope that does not require explanation.
Isolation transformers are best used by qualified personnel in special applications.
There are special power outlet conditions; old equipment that has hot chassis like old radios that do not have power transformers; and the other application is for Test and Measurement conditions.
Any of this needs to be set up by knowledgeable persons who can give guidance as to safe usage, and safe operating procedures.
Using an isolation transformer and the equipment that is powered by it . . . if done improperly can still result in someone receiving a shock.
Safety first.
USA
Ground and Neutral are not the same thing in the US.
Not if you are meeting the current up-to-date legal standards for home wiring.
You do not connect the amplifier directly to the circuit breaker panel in your home (which is the Only place that Ground and Neutral are the same, at one place inside that panel).
Old grandfathered amplifiers are one thing, most have 2 wire power cords.
If you have correctly wired 3 wire Hot, Neutral, Ground 120V power outlets in your home then use a 3 wire cord to the amp if you are able.
In the US . . . Connect Hot to fuse, then to power switch, then to power transformer primary. Connect Neutral to the other end of the power transformer primary (power return).
Do not use Ground as a power return. Ground is for safety, and also can sometimes reduce noise and ground loops.
If you can use the amp with 3 wire setup, connect Ground (safety ground) to the chassis.
Most turntables, CD players, tuners, preamps, etc. use 2 wire power cords. Many of those do not even have the wider Neutral tab (in that case, the hot and neutral tabs are the same width).
If the Neutral tab is wider, and you have a correctly wired 3 wire outlet, use the 2 wire power plug as it was designed, wide tab to wide outlet slot. do not modify that.
If the Neutral tab is not wider than the Hot tab, you can not tell which is which. The plug can be inserted either way. Use the way that gives the best noise and ground loop reduction.
Do not use those ground lift adapters. If you use them the worst that can happen is the "surviving spouse syndrome". I hope that does not require explanation.
Isolation transformers are best used by qualified personnel in special applications.
There are special power outlet conditions; old equipment that has hot chassis like old radios that do not have power transformers; and the other application is for Test and Measurement conditions.
Any of this needs to be set up by knowledgeable persons who can give guidance as to safe usage, and safe operating procedures.
Using an isolation transformer and the equipment that is powered by it . . . if done improperly can still result in someone receiving a shock.
Safety first.
Last edited:
Simply. You connect the "box" chassis or whatever to Earth ground. The use of isolation makes it safer byjust that... galvanic isolation. This means no matter how you connect the power (non polarized plug?) you still won't get a damaging shock. So called "death caps" used to fudge this to try and kill hum. Now they tend to kill humans...
Without isolation, most modern power supply designs would result in a short to ground, too.
In this case, without the transformer, and knowing one side of the "transformer" is tied to ground at the panel, half the supply would be a short, no? Or not... What do I know
Without isolation, most modern power supply designs would result in a short to ground, too.
In this case, without the transformer, and knowing one side of the "transformer" is tied to ground at the panel, half the supply would be a short, no? Or not... What do I know
Attachments
Last edited:
dancemyth, perhaps a different explanation.
We cannot eliminate the risk of electrical shocks. However, we can minimize them. Every simple minimization is both imperfect, and doggoned cheap insurance.
One risk of shock is conducting power from the outlet through your body to another ground, like a concrete floor. Mechanically connecting the chassis to an actual ground reduces the chance of this. An isolation transformer also reduces this risk.
We are not connecting the neutral wire, we are connecting the ground wire. Neutral wires are not necessarily "neutral", in spite of connections, and therefore not necessarily grounded. Proper ground wires are always grounded.
Under the wrong circumstances, both the "hot" wire and the "neutral" wire may have a voltage differential to the ground wire. Think unbalanced loads and less-than-perfect wiring connections. Yes, this means that sometimes you can test the outlet voltage, and there will be a voltage differential between the "ground" wire and the other two wires.
Stuff fails. Wiring insulation breaks, or wears through, and fails. If the piece of metal the wire shorts to is connected to ground, then a fuse blows, instead of killing you when you touch it while powered off.
A properly operating isolation transformer limits the power on the "out" side of the transformer to the circuit. Connecting to a proper ground changes nothing. It is unlikely that an isolation transformer will short out and carry high voltage outlet power through you to an external ground. Unlikely, but horrifically expensive. If all it does is kill you, that might be the cheapest alternative. Balance the cost of paying for killing somebody's kid, in the millions of dollars, against the cost of an isolation transformer. Even tiny likelihoods are horribly expensive.
How about a short inside the crossover network in a speaker? Never seen it happen, and don't want to. It only needs to happen once to ruin your life. Explaining to my daughter after my amplifier kills my grandson? Not enough money in the universe.
Grounding the speaker wire to the chassis means blowing a fuse before hurting someone.
It is those rare circumstances that seem to happen far too often, in spite of your best, most diligent efforts.
And if you balance the costs and decide not to use all the safety equipment, plan now. Plan how you are going to explain to your brother that your DIY equipment killed your neice. What, exactly, are you going to say?
We cannot eliminate the risk of electrical shocks. However, we can minimize them. Every simple minimization is both imperfect, and doggoned cheap insurance.
One risk of shock is conducting power from the outlet through your body to another ground, like a concrete floor. Mechanically connecting the chassis to an actual ground reduces the chance of this. An isolation transformer also reduces this risk.
We are not connecting the neutral wire, we are connecting the ground wire. Neutral wires are not necessarily "neutral", in spite of connections, and therefore not necessarily grounded. Proper ground wires are always grounded.
Under the wrong circumstances, both the "hot" wire and the "neutral" wire may have a voltage differential to the ground wire. Think unbalanced loads and less-than-perfect wiring connections. Yes, this means that sometimes you can test the outlet voltage, and there will be a voltage differential between the "ground" wire and the other two wires.
Stuff fails. Wiring insulation breaks, or wears through, and fails. If the piece of metal the wire shorts to is connected to ground, then a fuse blows, instead of killing you when you touch it while powered off.
A properly operating isolation transformer limits the power on the "out" side of the transformer to the circuit. Connecting to a proper ground changes nothing. It is unlikely that an isolation transformer will short out and carry high voltage outlet power through you to an external ground. Unlikely, but horrifically expensive. If all it does is kill you, that might be the cheapest alternative. Balance the cost of paying for killing somebody's kid, in the millions of dollars, against the cost of an isolation transformer. Even tiny likelihoods are horribly expensive.
How about a short inside the crossover network in a speaker? Never seen it happen, and don't want to. It only needs to happen once to ruin your life. Explaining to my daughter after my amplifier kills my grandson? Not enough money in the universe.
Grounding the speaker wire to the chassis means blowing a fuse before hurting someone.
It is those rare circumstances that seem to happen far too often, in spite of your best, most diligent efforts.
And if you balance the costs and decide not to use all the safety equipment, plan now. Plan how you are going to explain to your brother that your DIY equipment killed your neice. What, exactly, are you going to say?
@kodabmx: you should check that frequency;
what they picture on the bay shows 5.6nF / 4.3k / 200R for the timing components, which according to SG3525 D.S. gives 50kHz osc. freq. which results in half (!) of that for the PP outputs i.e. 25kHz;
actual builds may vary:
mine was populated with 10nF / 3.3k / 100R which gives the advertised 37kHz for the osc. but again output is half at 18kHz;
did you experience any problems with inrush currents into bigger electrolytics after the rectifiers ?
there does not seem to be any provisions for current limiting ... ?
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.