Hi all, new here. I'm trying to build an amp with PCBs purchased to make up the amp and the power supply board. An 80va dual toroidal transformer is recommended.
I've put the circuits together and have now managed to burn 2 toroidals and one other transformer too!
I'm not sure what I'm doing wrong but have posted an image of my setup here (excuse the poor quality!)
The project is a guitar amp in a wooden box. I've inserted a metal plate to have a ground point for incoming 240AC.
The transformer is mounted vertically on the back wall of the amp.
Any advice is greatly received!!
I've put the circuits together and have now managed to burn 2 toroidals and one other transformer too!
I'm not sure what I'm doing wrong but have posted an image of my setup here (excuse the poor quality!)
The project is a guitar amp in a wooden box. I've inserted a metal plate to have a ground point for incoming 240AC.
The transformer is mounted vertically on the back wall of the amp.
Any advice is greatly received!!
Must be a wrong connection, either for the input AC power, or on the secondaries.
Perhaps the primary windings are not phased correctly.
But it all depends on the transformer color coded wires being connected to the right points.
Do you have fuses on the input?
Suggest that for the next transformer, draw an actual schematic diagram and post it here.
Which one will you use?
Perhaps the primary windings are not phased correctly.
But it all depends on the transformer color coded wires being connected to the right points.
Do you have fuses on the input?
Suggest that for the next transformer, draw an actual schematic diagram and post it here.
Which one will you use?
The transformer is
Initially I fitted a transformer that came off an old sub woofer (not a toroidal) and that also sent up smoke!
I had fused the grey and violet on primary side of the above toroidal to have the transformer in series. And black and yellow on the secondary side to give the 0v ( as advised by supplier of the amp kit).
Here’s the data sheet, I haven’t added any fuses on either side of the transformer.
VIGORTRONIX 80 VA Mains Toroidal Transformer 2 x 115 V : 2 x 25 V VTX-146-080-225
It has an internal thermal fuse fitted.Initially I fitted a transformer that came off an old sub woofer (not a toroidal) and that also sent up smoke!
I had fused the grey and violet on primary side of the above toroidal to have the transformer in series. And black and yellow on the secondary side to give the 0v ( as advised by supplier of the amp kit).
Here’s the data sheet, I haven’t added any fuses on either side of the transformer.
That's absolutely essential: it will protect the transformers in case of misconnection.
Otherwise, use a dim lightbulb tester to weed out spurious issues
Secondary connection may be wrong as in pic. disconnect bridge rect. and measure the sec./output voltages with voltmeter (0-25-25-50).
Ok, thanks!
What type of fuse and do I put them on each of the primary wires or just the grey and violet?
What would be the recommended amp value for the primary side?
What type of fuse and do I put them on each of the primary wires or just the grey and violet?
What would be the recommended amp value for the primary side?
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the metal plate. How is the transformer mounted? Are you magnetically shorting the transformer? Post pictures of actual unit under test please.
Slow blow fuse on the hot lead for the transformer primary, guessing a 1.25A rating given the 80VA transformer. Fast blow for the return leg on the primary, guessing a 0.5A.
Dim-bulb tester highly recommended.
Step 1. Start with just the power inlet and transformer, power up and measure the voltages on the secondaries. See if it pops a fuse.
Step 2. Power down.
Step 3. Add rectifier circuit and power up. measure voltage on output of the rectifier circuit and see if bulb tester stays lit or fuses pop.
Step 4. Power down and discharge any PSU filter caps.
Step 5. Add amp board. Power up. Check if bulb tester stays lit or fuses pop.
Step 6. power down and discharge any PSU filter caps.
If the fuses don't pop or the dim-bulb tester dims, keep adding more boards until everything is installed, repeating the same power down and power up procedures. Once you add something and a fuse pops or the bulb tester stays lit, you know where the problem is.
Again, pictures can be very helpful.
Caveat: I am not a licensed electrician and accept no liability for advice given.
Slow blow fuse on the hot lead for the transformer primary, guessing a 1.25A rating given the 80VA transformer. Fast blow for the return leg on the primary, guessing a 0.5A.
Dim-bulb tester highly recommended.
Step 1. Start with just the power inlet and transformer, power up and measure the voltages on the secondaries. See if it pops a fuse.
Step 2. Power down.
Step 3. Add rectifier circuit and power up. measure voltage on output of the rectifier circuit and see if bulb tester stays lit or fuses pop.
Step 4. Power down and discharge any PSU filter caps.
Step 5. Add amp board. Power up. Check if bulb tester stays lit or fuses pop.
Step 6. power down and discharge any PSU filter caps.
If the fuses don't pop or the dim-bulb tester dims, keep adding more boards until everything is installed, repeating the same power down and power up procedures. Once you add something and a fuse pops or the bulb tester stays lit, you know where the problem is.
Again, pictures can be very helpful.
Caveat: I am not a licensed electrician and accept no liability for advice given.
And the 9V step down buck - that looks suspicious to me as dual supply buck converters aren't very common and don't normally take a dual supply input...
Did you measure any of the secondary-side voltages before things cooked?
Earth connection needs to be direct to the case if its metal, crimped and bolted securely, and ideally tested.
Did you measure any of the secondary-side voltages before things cooked?
Earth connection needs to be direct to the case if its metal, crimped and bolted securely, and ideally tested.
One usually uses only slow (T) fuses on the primary side of toroidal transformers because of their large inrush current. Probably 400 mA T for 80 VA at 230 V, but it is usually specified by the transformer manufacturer.
6sX7's remark about mounting is a very good one. If the mounting hardware and enclosure somehow form a conducting ring through the hole of the transformer, you have an unintended shorting turn.
6sX7's remark about mounting is a very good one. If the mounting hardware and enclosure somehow form a conducting ring through the hole of the transformer, you have an unintended shorting turn.
Your "9V Step-down buck" converter is suspicious. It could short the -V in to the -V out to the Preamp ground to the power amp ground to the main supply ground. You need more detail about what these blocks are. A "buck converter" does not isolate the inputs from outputs. Does it output one 9V or two, ie +/-9V?
It is also worrisome that the transformer is rated 230V and the power is 240V, because toroids can have inrush problems, but if the same thing happens with an E-core then that is not the problem.
It is also worrisome that the transformer is rated 230V and the power is 240V, because toroids can have inrush problems, but if the same thing happens with an E-core then that is not the problem.
The whole case is wooden, hence I added a metal plate to attach earth to from mains side. Do I need to earth/ground the dc side to same point?
It is 240V, always has been. Appliances are rated for 230V showing they are compatible with both mains standards. The mains voltage and its frequency are strongly related by the hardware in the system, so you can't just dial down the voltage without replacing vast amounts of infra-structure (and incurring increased system power losses). They now describe UK mains as 230V +10%/-6%, which is 216--253V, which is also 240V +5%/-10%. But nothing has changed physically. You could call it 220V -2%/+15% if you wanted, but its still 240V and not suitable for 220V-only appliances.
Today my local mains is 243.7Vrms...
Today my local mains is 243.7Vrms...