Absolutely correct!
But you wouldn't want to do that.
As the rail voltage gets higher, most (including the LM3876) chipamps have a harder time driving lower-impedance speakers. In a perfect world, with a completely smooth and resistive 8-ohm speaker (Which doesn't exist) you could run the rails at the max and get a lot of power out of the amp.
But the normal speaker in the world these days is a 4-ohm, and the easiest way to accommodate that is lower rails.
The 30v rails you are planning are fine. A few volts lower would be slightly better. But lowering the voltage with a 3-pin regulator like a 317 won't really work in your situation, as you will probably shut them down because you are pulling too much current through them.
Get a single bridge and a couple of 10,000uf 50v caps. It's much cheaper and much simpler, and will work very well with no fuss.
You're not wrong.
And at a much higher output impedance with the added complexity of the transients as the reg switches on and off as it tries to track the PSU ripple on the input.
Don't ever allow the regulator to "drop out" if you want good performance.
Point taken.
However a purely resistive speaker is rare, and so the normal precautions on a chipamp (output zobel, film bypass caps on the smoothing caps, etc...) should be taken, as well as having a rail voltage appropriate to your load.
This is taken from the LM3876 datasheet --
The important thing to realize is that with higher voltage rails into a lower-ohm speaker the chip will eventually run out of oomph and cut off. In order to get it to operate with the widest range of speakers, it is advisable to have lower voltage rails.
The important thing to realize is that with higher voltage rails into a lower-ohm speaker the chip will eventually run out of oomph and cut off. In order to get it to operate with the widest range of speakers, it is advisable to have lower voltage rails.
Revised modification of the modified revision.
OK You guys have convinced me. I dropped the voltage regulators. As to what I am trying to do, here's a rough description. I am trying to build a cheap and easy Bass guitar amplifier. Not big, about 50 watts or so. Using parts that I scrounge from friends, without being to obvious about it. The amp will replace one I borrowed from a friend, and am now using at church, so it doesn't have to be very loud. Also, I have already built a speaker cabinet, utilizing the Thiele-Small parameters. It's only a 50 watt speaker, 8 Ohms impedance, but it's louder than most 100s. (I cannot jack it up all the way in our church, which is held in a small basketball court/gymnasium, because it's so loud it drives everyone out.) I hope to have the amp schematic on line in the proper forum shortly.
I'm an old grouchy retired engineering technician whos retirement plan flew out the window. So "cheap" is the operative word. Therefore, I scrounge a lot. For example, I plan on using GBU4J rectifiers. Why? Because I already have them. And from everything I've read, they will work. They might be overkill, but they're free and they will work. In other words, it doesn't have to be latest high tech and perfect. It just has to work without burning the house down.
I thank all of you for your comments and advice. And I plan on working on this until I get it working, to my satisfaction, and yours, maybe. So, on with the show. Included is the latest and greatest schematic for the power supply. I have a feeling that I'm supposed to put some large resistors from the leads to ground, but I don't know what size or why. Any Ideas?
Thanx
The Happy Hippy
OK You guys have convinced me. I dropped the voltage regulators. As to what I am trying to do, here's a rough description. I am trying to build a cheap and easy Bass guitar amplifier. Not big, about 50 watts or so. Using parts that I scrounge from friends, without being to obvious about it. The amp will replace one I borrowed from a friend, and am now using at church, so it doesn't have to be very loud. Also, I have already built a speaker cabinet, utilizing the Thiele-Small parameters. It's only a 50 watt speaker, 8 Ohms impedance, but it's louder than most 100s. (I cannot jack it up all the way in our church, which is held in a small basketball court/gymnasium, because it's so loud it drives everyone out.) I hope to have the amp schematic on line in the proper forum shortly.
I'm an old grouchy retired engineering technician whos retirement plan flew out the window. So "cheap" is the operative word. Therefore, I scrounge a lot. For example, I plan on using GBU4J rectifiers. Why? Because I already have them. And from everything I've read, they will work. They might be overkill, but they're free and they will work. In other words, it doesn't have to be latest high tech and perfect. It just has to work without burning the house down.
I thank all of you for your comments and advice. And I plan on working on this until I get it working, to my satisfaction, and yours, maybe. So, on with the show. Included is the latest and greatest schematic for the power supply. I have a feeling that I'm supposed to put some large resistors from the leads to ground, but I don't know what size or why. Any Ideas?
Thanx
The Happy Hippy
It is just a safety precaution.
If ever the power supply is powered without a load (i.e. without the rest of the amp), they will stay charged for a long time after shutdown.
This creates an irritating spark when connecting the power supply back to the main circuit or a nasty bang when accidentally shorting the caps.
Adding ~4.7k, 1/2W drain resistors will instead slowly discharge the filter capacitors.
Add a series LED to each and you will have a useful reminder that there is juice.
That will do.
Most people will only use one fuse on the primary side.
A small refinement is to add a 0.1 to 0.22 ohm resistor between the two capacitors on each rail, creating an RC-RC filter (first R being part of the transformer). These should be 5 W to 10 W units.
Also use the rightmost junction on the ground network as your 'star' ground point, not where the ground symbol is shown now.
Attached drawing
Yes, thats pretty much what I've got, except the 120v side of the transformer is all one coil. Does that make a difference?
Also, I've kind of decided to not use a voltage regulator, and just go with big caps. Thanks for your interest, tho.
Thanx
The Happy Hippy
Yes, thats pretty much what I've got, except the 120v side of the transformer is all one coil. Does that make a difference?
Also, I've kind of decided to not use a voltage regulator, and just go with big caps. Thanks for your interest, tho.
Thanx
The Happy Hippy
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