Hi just finished building my first amp ever- telos clone. I am using 2 toroidal transformers 500VA, 50VACx2. It is working fine ,dc offset measures 5mV both channels. The only thing i noticed is each time i turn the amp on there is smoke coming from the resistor until the relays kicks in then it is ok. Is there anything i should worry about? Should i change to a higher power rating resistor? 
Quan,
Amateur here but I'll volunteer an answer. Put a meter across the resistor and turn on the amp. The inrush current will be high to begin with so note what is the highest voltage at turn on. Then figure your maximum amperage, voltage/resistance. Then multiply that amperage times the voltage supply to give you the maximum wattage at start up. I would then double that wattage for the new resistor.
Amateur here but I'll volunteer an answer. Put a meter across the resistor and turn on the amp. The inrush current will be high to begin with so note what is the highest voltage at turn on. Then figure your maximum amperage, voltage/resistance. Then multiply that amperage times the voltage supply to give you the maximum wattage at start up. I would then double that wattage for the new resistor.
Sounds like you need higher powered resistors.
I use 4 x 68 ohm 10 W (jaycar wire wound) in parallel with lots of air around them feeding a pair of 300VA transformers. That gives me about 10A peak on the first half cycle (depending on where in the half cycle it is powered up) falling rapidly to the idle current. The relay switches after about 100mS. No noticeable resistor heat.
The soft start circuit and pcb are my own design and I am intending to use it unchanged for a 2 x 500VA Leach clone currently under construction.
Cheers
John
I use 4 x 68 ohm 10 W (jaycar wire wound) in parallel with lots of air around them feeding a pair of 300VA transformers. That gives me about 10A peak on the first half cycle (depending on where in the half cycle it is powered up) falling rapidly to the idle current. The relay switches after about 100mS. No noticeable resistor heat.
The soft start circuit and pcb are my own design and I am intending to use it unchanged for a 2 x 500VA Leach clone currently under construction.
Cheers
John
hey, you got good answers, so I guess its allowed to smile now
but without the smiling, in worst case it could cause a fire
hey, you got good answers, so I guess its allowed to smile now
but without the smiling, in worst case it could cause a fire
Yes ,definitely . i need to work out why it puffs a smoke when turns on otherwise definitely no sleep. I am not so sure now. I took another closer look . The smokes actually come from either the X2 capacitor which rates at 0.6uF 250VAC or the 3W resistor parralel to it( value of 470K/3W). I don't know what to do now. It is not coming from the load resistor which points out earlier as 10W/68R
:scratch. I replace another unit which i bought from the same vendor , again the magic puffs of smoke appear again. I am getting nervous as this is my first ever amp build.quan
I am begin to believe it is the dodgy X2 class capacitor which lets out the smoke every time power on until the primary of the trannies are in direct connect. The first X2 capacitor was a Carli brand , the other one is a RIFA TYPE. I am not sure is it just faulty which is so usual for 2 separate types of X2 capacitor or the rating of the cap is exceed with the initial surge?
quan
quan
Personally, I don't like those aluminium clad resistors connected to mains wiring.
I believe there is too much metal too close to the mains wiring for good safety.
I use resistors that are clad in fireproof insulation material, with only the connection wires made of conductive material/metal. Much easier to make safe during the build.
I believe there is too much metal too close to the mains wiring for good safety.
I use resistors that are clad in fireproof insulation material, with only the connection wires made of conductive material/metal. Much easier to make safe during the build.
Oh dear.
With the mains voltages, I cannot advise LIVE measuring of what is happening after the capacitor.
I would bin all the smoked caps. I have no idea what damage the heat has done inside the caps/s
With the circuit completely disconnected from the mains, can you measure component values?
Can you inject a current controlled 12Vdc on to the bridge rectifier?
A damaged/faulty/fake component downstream may be overloading the capacitor. The esr in the capacitor times the current flowing will heat the cap. That could be the smoke.
With the mains voltages, I cannot advise LIVE measuring of what is happening after the capacitor.
I would bin all the smoked caps. I have no idea what damage the heat has done inside the caps/s
With the circuit completely disconnected from the mains, can you measure component values?
Can you inject a current controlled 12Vdc on to the bridge rectifier?
A damaged/faulty/fake component downstream may be overloading the capacitor. The esr in the capacitor times the current flowing will heat the cap. That could be the smoke.
I've used that circuit with two mods - instead of the resistors I used two CL60 themistors in series. I found that the dc voltage was high and if I can remember correctly I put a 24V zener across the relay. It has been working now for 3 month without an issue. Check that nothing is connected to earth.
What caps are you using?
What caps are you using?
The kit is simple enough to build which i did build twos and they both smokes at x2 cap at turn on. The soft start still work but like you say how long would it last before it caught fires. I am not sure regard the ESR of the cap? Is it the one down the stream ie 470uF/50V. They came with the kit just typical no name caps. When i power it up for the first time using the variac there is no smoke at all.
quan
quan
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