ROOSIE Posted April 11, 2017 Share Posted April 11, 2017 What I have:• A transformer rated at 150VA / 30V (center tapped) / 5A• Speaker rated at 30W / 8 ohms (measured 6.3 ohms with my multimeter)Will use class AB amplifier:• LM4780 • Question:If I send +30V & -30V to this chip, I will get 45W at 1%THD+N: Is it possible to keep +30V & -30V but limit the maximum power to 30W? Is it by playing with the gain (feedback resistor value)?I read somewhere "...power amps at lower gains requires more input voltage to get the same power output, with the same speaker impedance".How to adjust/calculate the gain so that I get a maximum of 30W output with +30V / -30V power supply? I own the transformer already so I plan to use it as the power supply (+30V / -30V). It is center tapped. It is 30V-0V-30V. Quote Link to comment Share on other sites More sharing options...
Don Richard Posted April 11, 2017 Share Posted April 11, 2017 A long as you don't play full blast you will be OK with the 30V supply. What speaker are you using? Quote Link to comment Share on other sites More sharing options...
No.4 Posted April 11, 2017 Share Posted April 11, 2017 This is all from memory. Your rectified voltage with a transformer with 30V secondaries will be more like 42V. Quote Link to comment Share on other sites More sharing options...
No.4 Posted April 11, 2017 Share Posted April 11, 2017 The usual recommended AC voltage on the secondaries is between 20-25V for this chip. I used antec 22V transformers when I built this chip to push speakers from 4 to 8 ohm. Your mains power at the wall will also have an affect on the output of your transformers. Again this is from memory, I built this chip over 5 years ago. Are you using a pcb or wiring point to point? Quote Link to comment Share on other sites More sharing options...
babadono Posted April 11, 2017 Share Posted April 11, 2017 If the secondary of the transformer is really 60V center tapped to get 5amps out it would have to be a 300VA transformer. Are you sure it is 30-0-30? If it is you will get approx + and - 42 volts as No.4 stated. From the second page of the data sheet it looks like a pretty standard high power op amp. So given a known amplitude input signal you can adjust the gain to give a desired output signal power. The caveat is with too much input DC and lower output power the device must dissipate more heat. Also from the data sheet it looks like at +/- 42 volts input power you are real close if not at it's maximum rating. Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted April 11, 2017 Share Posted April 11, 2017 11 minutes ago, babadono said: If the secondary of the transformer is really 60V center tapped to get 5amps out it would have to be a 300VA transformer. Are you sure it is 30-0-30? If it is you will get approx + and - 42 volts as No.4 stated. From the second page of the data sheet it looks like a pretty standard high power op amp. So given a known amplitude input signal you can adjust the gain to give a desired output signal power. The caveat is with too much input DC and lower output power the device must dissipate more heat. Also from the data sheet it looks like at +/- 42 volts input power you are real close if not at it's maximum rating. You beat me to it Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.