Simple Chip Amp for P to P wiring

[coldcathode]

I would like to build this.

Can we substitute a cap for the inductor resistor?

What is issue if I remove it altogether. That needs to be a BIG resistor.

[danielwritesbac]

Originally Posted by coldcathode

I would like to build this.

Can we substitute a cap for the inductor resistor?

What is issue if I remove it altogether. That needs to be a BIG resistor.

Output stuff = stabilizers.
Yes, the output resistor needs at least a 5w rating. There's a cheapskate solution. Use 2 of cheap ceramic resistor. A parallel pair of cheap resistor at the output will pass signal intact. Don't forget the inductor. These three units all have inductance; however, since they are all in parallel, inductance decreases dramatically.

The output zobel needs only a cheap 5w ceramic resistor and a cheap polyester cap. *If you make an overspend for a polypro cap, change the resistor value to within the range of 5R to 10R. And, here's why. . .

Problem: The National Semiconductor datasheet assumes mass production of television amplifiers or economy home theater units and so there wouldn't be a single piece of polypropylene accounted for. Polyester has extremely high internal resistance, ESR. This is reflected on the resistor value of the speaker output zobel in the datasheet. Using a different type of cap will remove the ESR and you must compensate the resistor value accordingly, else too much load at the output.

The LM3886 is inherently unstable and we're cutting the gain on it. In this case, I think that stability enhancement parts are required rather than optional. Fortunately, the needed parts are very economical, as well as giving us a better chance of success.

[coldcathode]

Heres what I have decided to build.

[coldcathode]

I have seen plenty of designs without the inductor and resistor. The Zobel should prevent oscillation?

[coldcathode]

Originally Posted by JPeitzman

...digging...
index
It is about three fourths of the way down the page.
James

James,


How about a SolidState Output WILLIAMSON???

[danielwritesbac]

More simply put. . . once you have about 4 ohms in series with the output, the LM3886 behaves. Adding the inductor decreases the effectiveness (but restores the power output), and so a 10 ohm resistor is used. We're tricking it, but that will cool it off.

[danielwritesbac]

Also, when the amp runs nicely it will last longer. That's much better than sticking one of its output transistors 5 months from now and burning through our woofer. Additionally, Thiele-Small and Boucherot work together, because they're a magnitude less effective otherwise.

This link contains a great deal of blather on the topic: Embedded.com - IC Audio Power Amplifiers and Zobel Networks: One Size Does Not Fit All All of which is irrelevent because it doesn't directly relate circuit values to benefits. They've assumed that the reader will do this automatically, given the formulas that look so much like http://www.youtube.com/watch?v=rwrVcR8MZZI ; however, . . .

Your temperature probe (the one that's fastened to your heatsink) and your ears (if running the amp full band) are quite relavant.

Somewhere between technical blather and end results are the means to employ thiele-small boucherot components at the output of the amplifier. And, here's why. . .

These will help us cut the gain while keeping the amp stable. You wanted less contribution from the chipamp and more contribution from the tube, right?

Wow. These comments are so unlike me. I'll bet that AndrewT's eyebrows went up when he read all that. Normally, I'm the first to break the rules and that last to insist on them. However, I do need a chance for this project to work.

Um. . . simply put: With LM3886, try it right first and bend it later, because the other way around results in masking.

[Juergen Knoop]

I have used a 10R 2W resistor with success. It doesn't see very much power, because it is shorted with a wire (the coil!).
The output coil seems to scare lots of people, but it is only 0.7uH (microhenry). This is almost nothing. Yet it helps a lot and doesn't do any harm at all.
A fart you can't smell, but it releaves you from a lot of inner pressure so to speak.
regards

[MJL21193]

Amplifier basics 101:
The output inductor//resistor isolates capacitive loads from the amplifier feedback loop. Also to isolate the internal feedback loop of the amplifier from external RF signals picked up by speaker wiring, crossover coils, driver voice coils, etc.

"Fart you can't smell...: priceless

[Juergen Knoop]

sometimes it helps to speak a less technical language