assuming the supply voltage is more suitable for an 8-ohm load than a 4.
This is the complete circuit for 1 channel.
Thanks a lot.
This is the complete circuit for 1 channel.
Thanks a lot.
To be on the safe side, the mains transformer's VA rating should be twice the power output you're aiming at.
Best regards!
Best regards!
Assuming you are going for the maximum 68w dissipation available out of an lm3886.
Then you want a transformer with dual secondaries no higher than 25vac.
Ideally slightly lower if 4 ohm loads will ever feature.
A general rule of thumb is to over rate your power transformer by at least 1.41 due to the power losses when rectifying into a capacitive load. 68w x 1.41 = 96va. Round that up and 100va would be the minimum to prevent overheating of the power transformer. Also to prevent excessive voltage sag under load and therfore clipping.
Ideally 120-150va if the budget allows as this provides more safety margin.
You can go higher if you wish but there won't be much benefit for the extra expense.
This would be per channel.
Then you want a transformer with dual secondaries no higher than 25vac.
Ideally slightly lower if 4 ohm loads will ever feature.
A general rule of thumb is to over rate your power transformer by at least 1.41 due to the power losses when rectifying into a capacitive load. 68w x 1.41 = 96va. Round that up and 100va would be the minimum to prevent overheating of the power transformer. Also to prevent excessive voltage sag under load and therfore clipping.
Ideally 120-150va if the budget allows as this provides more safety margin.
You can go higher if you wish but there won't be much benefit for the extra expense.
This would be per channel.
Transformer size will vary with your power supply voltage. So higher voltage will invoke higher current on the output side of the amp.
Calculate and you will have your answer. Music is variable signal, not fully loaded all the time, current spikes will be due sudden dynamic changes, so average value is a litle bit lower.
Design your voltage according the load and maximum rating of the LM3886. Load is your speaker impedance which which determine current flow with amplified voltage on the output. If you have ampacity then you will have correct value for the power size.
Is it correct to put 100VA transformer for the LM3886 with dual 17Vac, and 4 ohm load, yes, because transformer with 85VA is sufficient. For dual 12Vac and 4 ohm load, transformer with 50VA is OK (calculated value is 40VA). Your rectifier defines power factor and VA multiplied with power factor gives W which will be on the output.
Calculate and you will have your answer. Music is variable signal, not fully loaded all the time, current spikes will be due sudden dynamic changes, so average value is a litle bit lower.
Design your voltage according the load and maximum rating of the LM3886. Load is your speaker impedance which which determine current flow with amplified voltage on the output. If you have ampacity then you will have correct value for the power size.
Is it correct to put 100VA transformer for the LM3886 with dual 17Vac, and 4 ohm load, yes, because transformer with 85VA is sufficient. For dual 12Vac and 4 ohm load, transformer with 50VA is OK (calculated value is 40VA). Your rectifier defines power factor and VA multiplied with power factor gives W which will be on the output.