Hi ....
i have retired service of my LM1875 and decide to replace it with a TPA3116D2 board i have in handy ... origninally this old amplifier uses 26VDC optained from a toroid power transformer which has secondary of 18V AC 0 18VAC and some other bunch of lower voltages for preamp and other misc uses ... so after rectification it gives around 26V DC at no load
so at this 26V DC is it safe to operate and use it along with the TPA3116D2 module? thanks
i have retired service of my LM1875 and decide to replace it with a TPA3116D2 board i have in handy ... origninally this old amplifier uses 26VDC optained from a toroid power transformer which has secondary of 18V AC 0 18VAC and some other bunch of lower voltages for preamp and other misc uses ... so after rectification it gives around 26V DC at no load
so at this 26V DC is it safe to operate and use it along with the TPA3116D2 module? thanks
Remember to account for both higher than normal mains voltages and also the fact that an 18 volt transformer will be specified at full load meaning the open circuit (or light loading) voltage is higher by factor called the 'regulation' value. That will be given in the transformer data sheet.
At face value 26 volts is at the top of the recommended range and given the above could be to closer to the 30 volt absolute maximum rating.
At face value 26 volts is at the top of the recommended range and given the above could be to closer to the 30 volt absolute maximum rating.
It means if the transformer is a nominal '18 volt' type then that will be at its maximum current rating into a resistive load when fed with its rated AC line voltage.
So if it is a 200va type with a regulation figure of say 5% regulation it means you get a voltage of 18.9 volts AC at low or light loads.
If the transformer has a 230 volt primary and your actual line voltage is closer to 240 then the transformer voltage rises again by a similar percentage, perhaps almost another volt.
So that 18 volt transformer could be giving nearer to 20 volts AC output.
It is up to you. 30 volts dc is the absolute maximum and 26 volts dc is the maximum recommended. Normally it is better to not push things up to the safe limits but to derate them a little.
A 15 volt transformer would probably be a safer option... but its your call 🙂
So if it is a 200va type with a regulation figure of say 5% regulation it means you get a voltage of 18.9 volts AC at low or light loads.
If the transformer has a 230 volt primary and your actual line voltage is closer to 240 then the transformer voltage rises again by a similar percentage, perhaps almost another volt.
So that 18 volt transformer could be giving nearer to 20 volts AC output.
It is up to you. 30 volts dc is the absolute maximum and 26 volts dc is the maximum recommended. Normally it is better to not push things up to the safe limits but to derate them a little.
A 15 volt transformer would probably be a safer option... but its your call 🙂
Don´t guess, measure [TM]
1) make a full wave rectified supply
2) turn it ON, measure unloaded voltage.
3) load it somewhat, use a 24V truck/bus lamp , 12W to 25W or so
Measure loaded voltage.
Post both results.
1) make a full wave rectified supply
2) turn it ON, measure unloaded voltage.
3) load it somewhat, use a 24V truck/bus lamp , 12W to 25W or so
Measure loaded voltage.
Post both results.
Without load 25.3 Vdc .. when loaded with 2 units of 12v dc fan in series it dropped to 23.7 Vdc ... So ??
Already tested 24v dc working ok ... But now run into another problem that when it was turned up loud ... The amp will just shut down and turn up itself again ... Seems like kinda protection ... Replaced thermal paste and tried using lower voltage supply still same problem ... Any ideas?
Already tested 24v dc working ok ... But now run into another problem that when it was turned up loud ... The amp will just shut down and turn up itself again ... Seems like kinda protection ... Replaced thermal paste and tried using lower voltage supply still same problem ... Any ideas?
There could be a few possibilities.
The load impedance might be to low or perhaps the supply is being modulated (its voltage is dipping to much under load) and that momentarily cause the amp to shut down.
Also 'loud' is very subjective. What really matters is what the voltage swing across the load is when this happens. That is one for a scope (and always remember that the load is not ground referenced in most Class D amps).
You could try adding a small value resistor in series with the load as a test. Try something like 3.3 to 5.6 ohm and see if the amp still shuts down.
The load impedance might be to low or perhaps the supply is being modulated (its voltage is dipping to much under load) and that momentarily cause the amp to shut down.
Also 'loud' is very subjective. What really matters is what the voltage swing across the load is when this happens. That is one for a scope (and always remember that the load is not ground referenced in most Class D amps).
You could try adding a small value resistor in series with the load as a test. Try something like 3.3 to 5.6 ohm and see if the amp still shuts down.
It'll run down to a 2ohm load...
You def said it was a 200VA TX ?
Monitor your supply voltage as you crank it up and take it to shut down,
You def said it was a 200VA TX ?
Monitor your supply voltage as you crank it up and take it to shut down,
A 4 ohm speaker could see the impedance dip way below that nominal value. That is why you need to test it properly.
The chip probably has very aggressive protection circuitry in the way it operates.
The chip probably has very aggressive protection circuitry in the way it operates.
Variety of power supplies ranging from desktop power supply to laptop 19.5v high current besides the linear 24v yields same result ... Increase impedance by adding another speaker in series still same problem ... I guess the chip might have toast