I am wiring a transformer for an amplifier and just want to make sure that I'm not making a mistake.
Here is a copy of the diagram on the transformer.
It can be either setup in parallel or series.
On the right I have connected the red and orange to the earth of the amp. Should I also connect them to the mains earth? The black and yellow are connected to one of the AC IN of the amp (which has the smoothing caps integrated in it) each.
For the left side of the transformer the brown goes to live and blue to neutral. As for the gray and violet they are connected together but I'm not sure if they should be connected to ground or not.
I am in Ireland so have 240V mains. The tordial transformer is 90VA. Is a 5A slow blow fuse sufficient on the live wire?
Here is a copy of the diagram on the transformer.
It can be either setup in parallel or series.
On the right I have connected the red and orange to the earth of the amp. Should I also connect them to the mains earth? The black and yellow are connected to one of the AC IN of the amp (which has the smoothing caps integrated in it) each.
For the left side of the transformer the brown goes to live and blue to neutral. As for the gray and violet they are connected together but I'm not sure if they should be connected to ground or not.
I am in Ireland so have 240V mains. The tordial transformer is 90VA. Is a 5A slow blow fuse sufficient on the live wire?
Build and use a Mains Bulb Tester.
Building a Gainclone chip amp power supply.
Use it to power on every new project and every time you modify a project.
Even just checking the wiring of a mains transformer can benefit from using the tester.
Building a Gainclone chip amp power supply.
Use it to power on every new project and every time you modify a project.
Even just checking the wiring of a mains transformer can benefit from using the tester.
You need to check what AC input the amp requires. Most likely is three wires (black, red+orange, yellow), but it is just possible that it requires four (black, red to one pair; orange, yellow to the other). Check the datasheet.
The amp datasheet should include grounding details. It is likely that there is some connection to mains earth, but this almost certainly will not require you to directly ground the red/orange wires. Get the grounding wrong and you get hum/buzz. Get the grounding seriously wrong and you get danger.
Build and use a lamp limiter. I always use this when messing with mains PSUs, and I only have nearly 50 years experience of electronics.
The amp datasheet should include grounding details. It is likely that there is some connection to mains earth, but this almost certainly will not require you to directly ground the red/orange wires. Get the grounding wrong and you get hum/buzz. Get the grounding seriously wrong and you get danger.
Build and use a lamp limiter. I always use this when messing with mains PSUs, and I only have nearly 50 years experience of electronics.
Than you all for the replies.
When I have finished the wiring I will test it with a bulb tester.
I am recycling the transformer form an old circuit (I didn't make that circuit) so I don't have the data sheet. All that I have is a sticker with the image that I included in my first post (which is a copy which I made using Power Point as a photo would not have been very clear). The GRY and VIO wires were connected together when I took the transformer out of the old circuit so I left them like that for now (and that way it will take an input of 240 VAC).
The amplifier is a TDA7294 which I bought on AliExpress. The bridge rectifier and smoothing caps are included so I just have to connect a transformer to it. The inputs are 2 AC INs and 1 GND.
Looking at this project the GND should be connected to the mains Earth. I believe that floating ground is illegal in Ireland so I have left it to be sure.
When I have finished the wiring I will test it with a bulb tester.
I am recycling the transformer form an old circuit (I didn't make that circuit) so I don't have the data sheet. All that I have is a sticker with the image that I included in my first post (which is a copy which I made using Power Point as a photo would not have been very clear). The GRY and VIO wires were connected together when I took the transformer out of the old circuit so I left them like that for now (and that way it will take an input of 240 VAC).
The amplifier is a TDA7294 which I bought on AliExpress. The bridge rectifier and smoothing caps are included so I just have to connect a transformer to it. The inputs are 2 AC INs and 1 GND.
Looking at this project the GND should be connected to the mains Earth. I believe that floating ground is illegal in Ireland so I have left it to be sure.
Connecting the transformer secondary centre-tap directly to chassis is about the worst possible place in an audio circuit to make the connection from signal ground to safety ground. It almost guarantees buzz or hum. Maybe that is why it is popular in guitar amps?
Should I just leave the connection from the transformer to ground out then? If I would do that then the amplifier wouldn't be connected to Earth at all. Would that be a problem?
If you have no enclosure during the build/testing phase, then there is nowhere to connect that PE wire.
Once you put the amplifier into an enclosure, that becomes the time you connect that enclosure to the Mains PE wire.
But long before that you have a transformer. Test it alone to check your primary wiring.
Add on the rectifier and test again. Then measure the output voltage at the +ve and -ve of the rectifier. This confirms you have wired the secondaries correctly.
Then add the smoothing capacitors. Test again, measure the voltages. This checks you have wired the whole PSU correctly.
Only AFTER you have proved the PSU, do you start connecting one amplifier.
Once you put the amplifier into an enclosure, that becomes the time you connect that enclosure to the Mains PE wire.
But long before that you have a transformer. Test it alone to check your primary wiring.
Add on the rectifier and test again. Then measure the output voltage at the +ve and -ve of the rectifier. This confirms you have wired the secondaries correctly.
Then add the smoothing capacitors. Test again, measure the voltages. This checks you have wired the whole PSU correctly.
Only AFTER you have proved the PSU, do you start connecting one amplifier.
I have everything connected and attached to an enclosure (except for the Earth to the case which I will obviously do before testing).
Seems like it is time to build the mains build tester.
Seems like it is time to build the mains build tester.
The case must be grounded, to the incoming mains ground conductor.
The circuit may be grounded (to the case) and in most cases should be grounded, but exactly where you do this will affect hum, noise etc. As I said, the secondary CT is about the worst possible place to do this. At the input or the output is usually better.
The circuit may be grounded (to the case) and in most cases should be grounded, but exactly where you do this will affect hum, noise etc. As I said, the secondary CT is about the worst possible place to do this. At the input or the output is usually better.
Ok, so I will connect the Audio In to the Earth/case as well. This would mean that the ground from my computer audio output (the amplifier input will to the output from my computer once I have tested the amp) will be connected to Earth.
A mains powered computer is already connected to the PE wire.
This is done inside the SMPS.
The Audio from a mains powered computer may, or may not, be connected to the protected chassis.
This is done inside the SMPS.
The Audio from a mains powered computer may, or may not, be connected to the protected chassis.
I will connect the amplifier Audio In to the case then to be sure as I won't always be connecting it to something which is connected to Mains Earth (e.g. for the final steps of testing it will be connected to my old phone).
I am making a shopping list of the things for the mains bulb tester. Would it be possible to use a large plastic lunch box as the enclosure for it? I'm just trying to think of how I could get plastic box easily.
I have a small loose lead version that I can stick in a bag to take on site visits. I use this portable one as the heater for making joghurt.
My semi-permanent version is installed in the same box that holds the Variac. The box is an old speaker cabinet.
You need a mains plug top, a bulb holder, a socket outlet and some 3core double insulated cable/cord.
My semi-permanent version is installed in the same box that holds the Variac. The box is an old speaker cabinet.
You need a mains plug top, a bulb holder, a socket outlet and some 3core double insulated cable/cord.
Thanks. I have a spare kettle lead so I was planning of just cutting it in two and connecting the tester in-between both parts. That way I could avoid getting the mains plug, cable (I have spare insulated copper wire for the internal connections) and IEC connector.
use the wires in the old iec lead.
Two go straight through, the PE wire and the Neutral wire.
The Live wire goes into the bulb holder and the other half of the Live lead comes out of the bulb holder.
If you can strip off about 100mm of the outer insulation without damaging the inner insulation you don't need to cut the N+E. Just cut the Live. Prepare the two ends to fit the bulb holder.
Two go straight through, the PE wire and the Neutral wire.
The Live wire goes into the bulb holder and the other half of the Live lead comes out of the bulb holder.
If you can strip off about 100mm of the outer insulation without damaging the inner insulation you don't need to cut the N+E. Just cut the Live. Prepare the two ends to fit the bulb holder.
Add a double layer of insulation tape around all the single insulated wires.
And at least two layers of double insulating tape over bare metal connectors.
Do you have a fuse in your plug top?
If not, then use a fuse somewhere upstream of the bulb tester. It might get abused by repeated rough handling.
And at least two layers of double insulating tape over bare metal connectors.
Do you have a fuse in your plug top?
If not, then use a fuse somewhere upstream of the bulb tester. It might get abused by repeated rough handling.
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