I have an LM3886 amplifier driving a 4-ohm subwoofer speaker, and think that high distortion at low volume levels is caused by my low power transformer. I know it puts out 25-0-25, at I think a little below 1 amp. Can I connect two of the same transformers in parralel, anotherwords connect the three outputs of each together to double the power into the rectifier?
Or would this not be a cause of the distortion?
Thanks, Mike
Or would this not be a cause of the distortion?
Thanks, Mike
the problem with this is that it is akin to putting 2 voltage sourece in parallel, only with a small resistance in between. If you can determine the difference in actual output voltages, you can begin to analyze the feasibility of this endevor. either the resistance between transformers must be increased, or a resitor must be added in series with 1 primary (to lower voltage at the econdary. make sure phase isn't affect though!
i would just get a larger transformer though.
i would just get a larger transformer though.
The very best thing you can do is to use two recifier bridges. Then you totally safe but if the transformers are identical it's usually no so bad connect the windings directly in parallel. You should bebeware of potential risk of having currents flowing from the one transformer to the other. The only side effect you will get is warmer transformers.
I heard a funny story once about someone bringing a small power plant online in Idaho. It seems that he connected the leads together while his station was still 30 degrees out of phase with the rest of the world.
20 miles down the road, a transformer the size of my house, picked itself up off the ground and rotated 30 degrees before setting itself back down.
Your phase has GOT to be exactly right.
20 miles down the road, a transformer the size of my house, picked itself up off the ground and rotated 30 degrees before setting itself back down.
Your phase has GOT to be exactly right.
Phase is like polarity for AC. Pretend there's a + and a -. If you connected two batteries in parallel, but had + to - and - to +, that would be bad. It's the same with transformers.
If the transformers are identical, you should be able to find and connect the exact same wires together. As an experiment, maybe put a 1K resistor or something between each connection the first time you hook them up - there should be very little voltage across each resistor.
If the transformers are identical, you should be able to find and connect the exact same wires together. As an experiment, maybe put a 1K resistor or something between each connection the first time you hook them up - there should be very little voltage across each resistor.
Yes, peranders is right. I am just building a simple power supply, not some power plant. I am not skilled enough to know how to use 2 rectifiers, and since the wires connect into the transformer inside and they come out a hole in the bottom, there is a 50% chance of the phase not being right. I dont really like the idea of a subwoofer picking itself off of the ground and doing somersaults across the room. 
I think that I will just take the easy and expensive way out by buying a larger transformer.
I think that I will just take the easy and expensive way out by buying a larger transformer.
> think that high distortion at low volume levels is caused by my low power transformer.
No. Distortion at low levels (without distortion at high level) is oscillation or a bad part (cap or chip).
> I have an LM3886 amplifier driving a 4-ohm subwoofer speaker, ...{transformer} puts out 25-0-25, at I think a little below 1 amp.
Yes, that will distort at high level. The effective impedance of a power amplifier to its power supply is about 6 or 7 times the speaker impedance. Around 50Ω for an 8Ω load, more like 25Ω for a 4Ω load.
The transformer is 50 Volts AC, will rectify and capacitor up to about 70 Volts DC.
The 1 amp AC winding is good for 0.6 to 0.5 Amps DC in a rectifier capacitor power supply.
Your supply wants to see a 70V/0.6A= 116Ω load, your 4Ω amplifier presents about a 25Ω load.
Wait a second: a 70V DC supply on a 4Ω load is 156 Watts output. Which isn't going to happen from a chip. Very likely, you are tripping the protection circuits. I think for 4Ω load on a reasonable heatsink, you want to run the chip on more like +/-25V, not +/-35V. So you need a 18-0-18 VAC transformer. You want about 2Amps DC, so you want 3.2A to 4A AC rating.
No. Distortion at low levels (without distortion at high level) is oscillation or a bad part (cap or chip).
> I have an LM3886 amplifier driving a 4-ohm subwoofer speaker, ...{transformer} puts out 25-0-25, at I think a little below 1 amp.
Yes, that will distort at high level. The effective impedance of a power amplifier to its power supply is about 6 or 7 times the speaker impedance. Around 50Ω for an 8Ω load, more like 25Ω for a 4Ω load.
The transformer is 50 Volts AC, will rectify and capacitor up to about 70 Volts DC.
The 1 amp AC winding is good for 0.6 to 0.5 Amps DC in a rectifier capacitor power supply.
Your supply wants to see a 70V/0.6A= 116Ω load, your 4Ω amplifier presents about a 25Ω load.
Wait a second: a 70V DC supply on a 4Ω load is 156 Watts output. Which isn't going to happen from a chip. Very likely, you are tripping the protection circuits. I think for 4Ω load on a reasonable heatsink, you want to run the chip on more like +/-25V, not +/-35V. So you need a 18-0-18 VAC transformer. You want about 2Amps DC, so you want 3.2A to 4A AC rating.
What I meant about distortion at low levels is that the low levels to me are pretty high to others. It can shake the the floor 20 feet away, and still be able to go a bit louder. I will probably just get a larger transformer.
Also, I might just use the two rectifiers, I am not sure yet.
Thanks for the help, Mike
Also, I might just use the two rectifiers, I am not sure yet.
Thanks for the help, Mike
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.