LM3886 Class AB Amplifier

[Kannan_madhu]

I bought a pair of LM3886 kits about fifteen years ago but never got around to building them, as I ended up using eight audio assembled boards instead. While cleaning recently, I came across the ICs again, but the PCBs and other components were missing. So, I thought of designing a new board for them. I referred to the official reference design, Tom Christiansen’s work at Neurochrome, Scott Campbell’s article on Circuit Basics, and Rod Elliott’s detailed write-up on the LM3886. All of them shared a wealth of information on LM3886-based amps. I designed the board keeping their suggestions in mind, using my favourite layout program, EasyEDA. I left the project aside for a few months, but recently got the test PCB made again. Today it was raining heavily from morning so I thought it was the perfect time to finally finish it.

 

[Kannan_madhu]

Powered it up and, as usual, I didn't get any sound. Most of my diy won't work in the first run one of the power supply cords was broken, replaced it and it worked

 

[kaushik]

Upper later pcb u can coat with two paints white and black.
( before u fit the parts)
Use a laser from nearby engraver.. U can burn blacks to make white parts marking.. Giving it a pro look

 

[arunlouie]

Nice it is taking life after all these years. I remember FM Sachin used to offer nice kits on LM3886.

 

[IndianEars]

Just curious, are these ICs still easily available in India?

Any idea of the price?

 

[diyaudio]

Just google.

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[availlyrics]

Just curious, are these ICs still easily available in India?

Any idea of the price?

There was a shortage post lockdown.
Buy genuine ICs from RS Components, Mouser or Digikey (700-800Rs)
Local Lamington market (RK, Matrix) stuff should cost you around 300 Rs (not recommended). LM3886T has a metal tab , so heatsink becomes negative & the LM3886TF ver. has a plastic tab but it has a higher thermal resistance
You can also buy TDA7294 , similar performance.
I'm palnning to make dual monobloc on XY LM3886 PCB

 

[availlyrics]

Scott Campbell’s article on Circuit Basics,

What are your thoughts on Cc, Cf? I'm planning to use 220pF, 47pF COG SMD capacitors, soldered close to IC pins

 

[diyaudio]

These ICs LM3886, TDA7293 and TDA7294 were excellent class AB ICs. They had everything in a small package. The performance was great because they were from good technology companies and everything was on the same silicon and temperature tracking was good, hfe matching etc was not needed. All protection was built in. The distortion was too low to be noticeable. When implemented with the right PCB as per their app notes, one could easily make amplifiers rivalling high end ones. These were underrated ICs.

Now technology has moved on.

History is repeating itself, Class-D has taken over, making the amplifiers very compact and very efficient. The chip amps from TI are great. It would be hard to differentiate a good class-D from TI vs a high end amplifier in a blind test.

IMHO, if we put LM3886/TDA729X/TPA3116 and a high end amplifier and do a blind test never bringing any amplifier to near clipping then no one would be able to pick out one in the blind test.

Of course, there will be a separate market for 'high-end' boutique amplifiers, that's a different matter altogether.

 

[diyaudio]

What are your thoughts on Cc, Cf? I'm planning to use 220pF, 47pF COG SMD capacitors, soldered close to IC pins
View attachment 91430

Never seen D1 anytime, whats its role? Also, IMHO, the feedback loop components should form as small a path as possible, pls check guidelines in datasheet.

 

[availlyrics]

Class D are hard to beat and are well suited for compact BT spk, sound bar , multi ch. HT setup` and the best part is that they are perfectly suited for battery based operation. I will definitely do a blind test with 3118 based Allo Volt amp vs LM3886

 

[availlyrics]

Never seen D1 anytime, whats its role?

The 16 V Zener diode (D1) blocks current flowing out of pin 8 until the diode’s breakdown voltage (16 V) has been reached. This produces a soft start/stop effect that gradually increases or decreases the volume instead of abruptly cutting it.

https://www.circuitbasics.com/design-hi-fi-audio-amplifier-lm3886/#The-Mute-Circuit

 

[availlyrics]

Now technology has moved on

I was also under the same impression, but any chipamp's damping factor and ruler flat FR over varying load impedance is way better than any 3116/8 or 3255 Class D based amps.

 

[IndianEars]

There was a shortage post lockdown.
Buy genuine ICs from RS Components, Mouser or Digikey (700-800Rs)
Local Lamington market (RK, Matrix) stuff should cost you around 300 Rs (not recommended). LM3886T has a metal tab , so heatsink becomes negative & the LM3886TF ver. has a plastic tab but it has a higher thermal resistance
You can also buy TDA7294 , similar performance.
I'm palnning to make dual monobloc on XY LM3886 PCB

Thanks for the detailed info.

There is also a High Voltage version of the LM3886 if I remember... It has a particular alphabet as a suffix after 3886.

Also, are LM3886/TDA729X/TPA3116 pin compatible / drop in replacements ?

 

[availlyrics]

There is also a High Voltage version of the LM3886 if I remember... It has a particular alphabet as a suffix after 3886.

Max. operating voltage (+/-42V) is same for both LM3886T & TF version, no other high voltage ver. was ever released. Recommended voltage is +/-35V for 8 Ohms, +/-28V for 4 Ohms , limited max. supply voltage and output current is the main drawback of any chip amps

There is also a High Voltage version of the LM3886 if I remember... It has a particular alphabet as a suffix after 3886.

Also, are LM3886/TDA729X/TPA3116 pin compatible / drop in replacements ?

No, they are not pin compatible.

 

[diyaudio]

I was also under the same impression, but any chipamp's damping factor and ruler flat FR over varying load impedance is way better than any 3116/8 or 3255 Class D based amps.

Agreed, the frequency response of class-d is irregular at the extreme highs
Question is when we cant listen past 15Khz does it matter?? I mean that's hardly a peak or dip even at 20Khz.

And damping factor of amplifier is related to Qe of the loudspeaker when connected. Nobody complains that there is 4 ohm or 8 ohm in the coil. It is in series with the amplifier. What happens to damping between the two? Does anybody care? If an amplifier has 1 ohm resistance (just exaggerating) just add to the 4 ohm or 8 ohm and remeasure Qe and its time to move on. Also, damping factor just changes bass just a little bit. It is overrated like most things in audio. Its all about making the right compromises in the end and class-d chip amps from good companies like TI has done that very well.
ClassA/B chips have become vintage if we notice their prices, they will continue to sell at higher and higher prices without any sonic perceivable difference with Class-D. I said perceivable, not measurable, pls note.

And isn't it true that if we increase bandwidth of the amplifier to lets say 100Khz, it has a higher chance of oscillating? Isn't the bandwidth limited by design to a lower value in class AB for safety?

 

[diyaudio]

It would be interesting to compare distortion profile of TPA3116/TPA3255 vs LM3886

 

[diyaudio]

PFFB reduces that 'irregularity' in frequency response to 1.2dB at 20Khz for 8 ohm and 0.8dB for 4 ohm

 

[availlyrics]

Question is when we cant listen past 15Khz does it matter?? I mean that's hardly a peak or dip even at 20Khz.

Uneven FR is a bit step backward when compared to Class AB. But in furure , Im sure this tiny FR gap will become unmeasurable . As for me, I can't hear past 16K Hz and can barely notice any difference below 0.5dB. Textbook 20-20KHz human ear response is slightly exaggerated , considering how uneven human ear's FR is

they will continue to sell at higher and higher prices

Just like Tubes & Vinyls.
BTW I give more importance to objective measurements than what I can hear or not hear and absolutely zilch to esoteric boutique parts / system.

As for damping factor , while designing, anything less than 20 should be best avoided and above 400 has no major effect (laws of diminishing returns) . For 4 ohms , the outout impedance of the amp should be less than 4/8 or 0.5 Ohms, similarly for 8 Ohms it should be less than 1 Ohms. Without the output inductor, LM3886 DF can easily go above 400 @ 1KHz . Pracyically , DF of 100 -200 is good enough. Cable length and contact resistance of connectors would have more effect in this regards

And isn't it true that if we increase bandwidth of the amplifier to lets say 100Khz, it has a higher chance of oscillating? Isn't the bandwidth limited by design to a lower value in class AB for safety?

Any good amp designer would roll off FR above 25-30Khz range, to avoid blowing up tweeters due to oscillations

 

[availlyrics]

It would be interesting to compare distortion profile of TPA3116/TPA3255 vs LM3886

The joy of DIY chipamp with specs reaching the hifi territory is immense