LM3876 power supply

[happy hippy]

Here's the modified revision of the revised modification of the....oh never mind. Here is the new power supply. All comments, criticisms, and changes will be appreciated.

Thanx
The Happy Hippy

[discrete]

That is a center-tap transformer, not a dual secondary.
Remove one of the rectifier bridges and tie the secondary center tap to the ground bus, like figure 2 at the bottom of this page:

60-80W Power Amplifier

Other than that lots of power is wasted in the regulators....better to get the correct transformer and not use any regulation?

Edit: If you must go with regulators, do not forget the protection diodes around the regulators.

[Puffin]

Why?

[benb]

I agree, substantial power will be dissipated in the regulators, especiallty the first set with the +/-35V output that presumably powers the chipamp. Looking at the transformer voltage, I wonder what the max input-output differential voltage on the LM317 - it looks like a lot, and keep in mind that when first turned on the +35V output will actually be at zero volts.

I'd rather eliminate these and use a transformer that gives the desired output directly. I presume the +/-15V is to drive a few opamps, and those regulators sholdn't need nearly as much heat sinking as the others would.

The schematic shows a center-tapped transformer with TWO bridge rectifiers. Tracing through it shows the transformer output gets shorted through the ground connection. It either needs two separate secondary windings, one for each bridge, or a single bridge between the end winding connections and the + and - rails with the transformer center tap connected to ground.

Puffin, presuming you're asking about the protection diode, a regulator cvan be damaged if the input voltage drops below the output voltage (which is especially likely with the second set of regulators), and the backwards diode between input and output prevents that by conducting when the input drops lower than the output.

[Puffin]

No. I can't understand why it has to be so complicated. The mantra is KISS.

[6L6]

A center-tapped transformer only needs one bridge. I'm not entirely sure it will do anything but release the magic blue smoke if you connect it as drawn.

Why on earth are you making it so intensely complicated? And again, as we have all said before, this (Chipamp PSU) is not the right application of a 317/337 regulator.

Use a 2nd transformer for the tone control circuit.

[happy hippy]

The operative word is "cheap", i.e., utilizing things I already have or can get free or cheaply. For example, a Hammond 56v -1.8a transformer is roughly half the price of a 50v - 2a transformer. So I have to go with the 56v unit. But that means I have to knock the DC voltage down from 39.5v per side to 35v. That means regulators. And I have or can get those free. I have lots of resistors, caps, diodes, etc. And I have heatsinks for the TO-220 chip pieces. See my thread in this section on the 317 regulator, part 48, for a longer explanation. I don't mind using lots of parts, if I already have them. Yes, some people say use a transformer from a wall wart for the 15v op amps, but others say knock it down with a regulator from the 35v rails.
I used to have a sign in my office that said "Sooner or later the time comes to shoot the engineers and build the *%&!#* thing." So if I finally get a design the will work, I'll build it. I don't care if it's complicated or not esthetically pleasing, or the latest technology. Just so it works.
I don't mean to put down or belittle anyone, and I certainly thank all of you for your advice, and I hope you will continue to respond to my obviously amateur attempts.

Thanx
The Happy Hippy

[discrete]

Nothing wrong with cheap.

But do realize that you will be power limited by the 1.5 A regulators and 1.8 A transformer.
Lets say the transformer and regulators can (optimistically) push 2 A peak for short periods, that is 16 W into an 8 ohm speaker, assuming a separate power supply for each channel.
Also realize that for 16 W into 8 ohm, 20 V rails are quite sufficient and the 35 V rails will never be fully utilized.

[6L6]

As somebody else mentioned, here is the proper connection of a center tapped transformer as a bipolar supply --


(From Elliot Sound Products)

[happy hippy]

Originally Posted by discrete

Nothing wrong with cheap.

But do realize that you will be power limited by the 1.5 A regulators and 1.8 A transformer.
Lets say the transformer and regulators can (optimistically) push 2 A peak for short periods, that is 16 W into an 8 ohm speaker, assuming a separate power supply for each channel.
Also realize that for 16 W into 8 ohm, 20 V rails are quite sufficient and the 35 V rails will never be fully utilized.

Where does the 16 watts come from. 35 volts a side = 70 volts, x 1.5 amps = 105 watts. And what is "each channel"? There is only one channel. I'm beginning to think we are talking apples and oranges here. Are we talking about the same thing?

Thanx
The Happy Hippy