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Old 5th January 2015, 10:45 AM   #1
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Default Which LM3886 circuit is better?

I was following the guide on circuit-projects site to build my first Hi-Fi Amplifier. The Circuit there is based on the Typical Application circuit from the datasheet. Click the image to open in full size.
The Circuit is minimal and easy.

But Later I saw there was a PCB for LM3886 on sale on ebay. It would save me a lot of time but I am unsure of the circuit and if it's better or worse than the minimal one! It has a dc blocking capacitor.. Does it make it inferior to the first circuit? or should i avoid it and use a preamplifier? Here's the circuit..
Click the image to open in full size.
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Old 5th January 2015, 11:19 AM   #2
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You've opened a can or worms. On the question of "which circuit to use?" feelings run high.

Here's one vote for: a) Use the factory circuit, it was developed by the same team of engineers who created the chip in the first place. b) Most of the worry about using capacitors is urban legend. The real gurus (Pass, Self, etc) don't hesitate to put in a capacitor when they need one, so how bad can they be?

Just to mention it, Radio Shack's perfboard is something of a best kept secret. If you're not wiring up circuits for a jet fighter it will do the job for you: Pre Punched IC Spacing Perfboard 2266451 | eBay
.
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Old 6th January 2015, 04:21 PM   #3
tomchr is offline tomchr  United States
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The typical application circuit will work fine, provided that you decouple the supply, use the Zobel (R+C to ground) and Thiele (L||R in series with the output) networks on the output, provide the LM3886 with a good sized heat sink, and pay attention when wiring it up. Basically: Read the data sheet (in particular the application section in the back) and follow the advice given there.

I have tons of information available here: Taming the LM3886 Chip Amplifier

You may also find these DIY Audio threads interesting:
LM3886 PCB vs Point-to-Point (with data)
LM3886 Thermal Experiment (with data)

~Tom
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Last edited by tomchr; 6th January 2015 at 04:35 PM.
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Old 6th January 2015, 04:34 PM   #4
tomchr is offline tomchr  United States
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Quote:
Originally Posted by bentsnake View Post
.b) Most of the worry about using capacitors is urban legend. The real gurus (Pass, Self, etc) don't hesitate to put in a capacitor when they need one, so how bad can they be?
They can be quite bad if you choose the wrong type. Douglas Self touches on this in his Power Amplifiers book and even more in his Small Signal Audio book. He backs up his claims with data (which I like).

The bottom line is: Dielectrics matter. Parasitics matter. Brands and snake oil do not.

If you use electrolytic capacitors in the signal path, ensure that the pole or zero caused by them is way outside the audio band. For a DC blocking cap, this means the pole is placed in the single-digit mHz range in a high-performance amp. Also ensure that no significant DC voltage can develop across the electrolytic cap if used this way.

Polypropylene capacitors are transparent for audio. They don't cause measurable distortion when used as coupling caps.
C0G/NP0 dielectric ceramic capacitors can be used for compensation caps (and coupling caps in low-voltage circuits) as they don't cause measurable distortion either.

If you're curious about the performance of components such as resistors and capacitors, I recommend reading the relevant chapter in Self's "Small Signal Audio" book. He just released a new edition of it.

~Tom
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Modulus-86: Composite amp achieving 0.000067 % THD. Damn Good 300B, Novar Spud, 21st Century Maida Reg., Filament Reg., etc.
Neurochrome : : Audio - http://www.neurochrome.com - Engineering : : Done : : Right
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Old 6th January 2015, 10:51 PM   #5
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Did anybody see the part about "build my first Hi-Fi Amplifier"? Sounds like a fun weekend project, huh? But no, instead let's send some poor guy off into a 6-month study course. Because that really is helping a guy out, isn't it?

ayushextreme, do as you think best, of course. But I can tell you that if you build an amp with Mylar film capacitors for small values, and electrolytics for large values, you'll be pleased as punch with the result. Your wife will be impressed, your kids will be proud of dad, your friends will envy you.

Some links that might help. Disclosure: I have no association with these people, except I send them money sometimes.

Mylar Film Capacitors: items in store on eBay!

Electrolytic Capacitors: items in store on eBay!

As for what anybody else tells you, well, that's what they tell you.
.
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Old 7th January 2015, 03:17 PM   #6
tomchr is offline tomchr  United States
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Quote:
Originally Posted by bentsnake View Post
You've opened a can or worms. On the question of "which circuit to use?" feelings run high.
I guess so.

~Tom
__________________
Modulus-86: Composite amp achieving 0.000067 % THD. Damn Good 300B, Novar Spud, 21st Century Maida Reg., Filament Reg., etc.
Neurochrome : : Audio - http://www.neurochrome.com - Engineering : : Done : : Right
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Old 10th January 2015, 02:42 AM   #7
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Please don't buy any components on ebay. Try Mouser, Digikey, MCM, or even Parts Express.
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Old 10th January 2015, 04:12 AM   #8
djoffe is offline djoffe  United States
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The schematic found in this manual stays pretty close to the data sheet recommendations, with some enhancements:

http://www.akitika.com/documents/***...101rev1p38.pdf

It has a few years of successful use by satisfied customers.
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Old 10th January 2015, 09:24 AM   #9
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Quote:
Originally Posted by tomchr View Post
They can be quite bad if you choose the wrong type. Douglas Self touches on this in his Power Amplifiers book and even more in his Small Signal Audio book. He backs up his claims with data (which I like).

The bottom line is: Dielectrics matter. Parasitics matter. Brands and snake oil do not.

If you use electrolytic capacitors in the signal path, ensure that the pole or zero caused by them is way outside the audio band. For a DC blocking cap, this means the pole is placed in the single-digit mHz range in a high-performance amp. Also ensure that no significant DC voltage can develop across the electrolytic cap if used this way.

Polypropylene capacitors are transparent for audio. They don't cause measurable distortion when used as coupling caps.
C0G/NP0 dielectric ceramic capacitors can be used for compensation caps (and coupling caps in low-voltage circuits) as they don't cause measurable distortion either.

If you're curious about the performance of components such as resistors and capacitors, I recommend reading the relevant chapter in Self's "Small Signal Audio" book. He just released a new edition of it.

~Tom
I think the circuit diagram was not visible before..
Click the image to open in full size.

It has a Zobel and theile network but i am unsure of the mute circuit.
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Old 10th January 2015, 10:50 AM   #10
Mihkus is offline Mihkus  Estonia
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That 220pF capacitor should be between ground not negative feedback. Its like that on TI's datasheet but It would be better to put it like that... AndrewT commented about that once I think...
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