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Author Topic: LM 3886 current feedback poweramp  (Read 853 times)

Manfred

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LM 3886 current feedback poweramp
« on: June 19, 2017, 03:26:22 AM »

I found this schematic in an old topic.
Who knows the value of the resistor which is covered by the lettering "STORE"?



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Enzo

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Re: LM 3886 current feedback poweramp
« Reply #1 on: June 19, 2017, 10:24:36 AM »

Why not tell us what the schematic was for and which old topic you found it in, we might have the direct information you seek.

Meanwhile the datasheet and application notes for the part should have sample circuits.
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Manfred

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Re: LM 3886 current feedback poweramp
« Reply #2 on: June 19, 2017, 03:36:20 PM »

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J M Fahey

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Re: LM 3886 current feedback poweramp
« Reply #3 on: September 15, 2017, 09:20:28 PM »

The 8085 circuits schematic makes not sense and the half covered one is unavailable, Roly too :(
Just look at the impedance correction networks in any practice TDA2030/2050 Guitar amp (Peavey/Fender/Marshall/Crate/Laney/etc.) and use the same with the LM3886 , they will work properly

All these chipamps are "powerful Op Amps" , just varying in supply and power output, same design rules apply to all.
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tarahall

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Re: LM 3886 current feedback poweramp
« Reply #4 on: September 19, 2017, 08:45:52 PM »

All these chipamps are "powerful Op Amps" , just varying in supply and power output, same design rules apply to all.

JM can you please clarify this. When data sheets (and I quote the LM3886 here) says things like:

 "68W cont-avg-output power into 4 ohms" or "38W cont-avg-output power into 8 ohms"

what does the term "cont-avg-output power" mean?
is that their way of saying 68w RMS or 38 RMS?

TIA Gavan.
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phatt

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Re: LM 3886 current feedback poweramp
« Reply #5 on: September 19, 2017, 09:49:14 PM »

 (cont-avg-output power) = Continuous Output Power.

So a sine wave input would be "Continuous" but music is unlikely to ever be Continuous.

Regarding your Q of RMS output others here will know more,,
I just look at these as a ~40Watt chip.
Also remember that the whole power thing is governed by the power supplies ability to deliver that power so a larger transformer is the key if you want max Wattage. (no free power 8|)
Then you will need a lot of heat sink if you intend to run them hard.
Phil.
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Enzo

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Re: LM 3886 current feedback poweramp
« Reply #6 on: September 20, 2017, 12:03:36 AM »

Just for marketing, somethimes they come up with some sort of spec where for one glorious nano-second the thing can be measured as putting out a thousand watts.  COntinuous output power means it can actually produce it.

A real world example.  I had an upright piano fall over on its back in our truck.  it pinned the toe of my boot.  Damned thing weighed 900 some pounds.  I could get my fingers under the edge.  I was able to jerk up on it just enough to free my boot.  Now I cannot lift 900 pounds, and certainly can't hold it up.  But I can apparently for just an instant peak my lift at 900 pounds.  SO in one sense, i can lift 900 pounds, but in any real sense I cannot.  Just so continuous versus peak power coming from an amplifier.
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J M Fahey

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Re: LM 3886 current feedback poweramp
« Reply #7 on: September 20, 2017, 10:58:55 PM »

Quote
JM can you please clarify this. When data sheets (and I quote the LM3886 here) says things like:

 "68W cont-avg-output power into 4 ohms" or "38W cont-avg-output power into 8 ohms"

what does the term "cont-avg-output power" mean?
is that their way of saying 68w RMS or 38 RMS?
They are speaking with the Dictionary in hand, which is fine with me.
Quote
cont-avg-output power
is what average people on the street (and thousands of brohures, magazine articles, user manuals and probably even some books) calls "RMS power".

Strictly speaking there is not such a thing as RMS power, but RMS voltage or current.

That said, what everyday talking "RMS power" actually means (or should) is "power calculated using RMS voltage, sustained during a reasonable time"

personally if if I check an amp puts out 20V RMS, when fed some classic test tone, usually 1kHz or 400/440Hz , into a 4 ohms resistive load, without visible clipping and for at least 10 minutes, would prefer at least 1 hour, then *I* won´t argue at all if you say it is a "100W RMS amplifier".

There´s been tons of arguments lately arguing gramatics while the real problem lies in the monstrous fantasy claims posted everywhere using undefined, pure fantasy numbers.

Arguing against a time tested, **easily repeatable and consistent** system which has been used for decades and does not require hard to find equipment , difficult Math and on which most agree (or have agreed since forever until the latest Revolution)  sounds stupid and dangerous to me, because after dissing and putting out of the way a stable and repeatable test procedure, anything else goes.

FWIW the FTC itself has dropped **officially** any pretense of measuring or norms enforcement.  :grr
« Last Edit: September 23, 2017, 01:22:19 PM by J M Fahey »
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tarahall

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Re: LM 3886 current feedback poweramp
« Reply #8 on: September 21, 2017, 07:37:00 AM »

Agree on LM3886 opinion, but I guess I found the reason: LM3886 is simpler to use and it boasts 50 or 60W RMS ,
Now TDA7293/4 claim 100W RMS which simply is asking too much from the exact same package.

Thanks to y'all for your explanations.
If I want a 60W "RMS" into 8 ohms output stage which of these chips would be the most suitable:- LM3886, TDA7293 or TDA7294.

TIA
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phatt

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Re: LM 3886 current feedback poweramp
« Reply #9 on: September 22, 2017, 09:32:35 AM »

The difference between 50 and 60Watts is hardly noticed in a live situation,, I doubt you would pick the diff in a blind test.
If you want louder use 2 speakers,, want more? use a quad box,, want to really go crazy? then use high SPL speakers.
A vox AC30 is louder than a 40 watt fender deville.  :o

Up to you?? but the LM3886 has 11 pins while the TDA7293/4 have 15pins.
The LM3886 is likely easier to route tracks on the PCB design.

the trick is to focus the tone shaping. so if you want it to cut through then design and test you preamp until you get the right balance and you will never miss the extra 10watts.

The aim of the game is to transfer electrical watts into acoustic SPL.
To get the full 100Watts from a 100Watt head you need 2 quad boxes.
IF you use the very same amplifier to drive 1x12 combo it will never come close to the same power output.
Again tone shaping is the key to great sound I've heard massive wattage rigs which are just dead pan boring and dull while others rip your ears off with ice pick fizz. you want to aim for balance.
Phil.
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Jazz P Bass

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Re: LM 3886 current feedback poweramp
« Reply #10 on: September 22, 2017, 10:09:41 PM »

Good to keep in mind that the IC output potential is totally dependent on the power supply voltages into a load.

Within the limits defined in the datasheet.
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sajy_ho

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Re: LM 3886 current feedback poweramp
« Reply #11 on: September 28, 2017, 06:06:23 AM »

 Hi, I've recently built a combo using 3886 in mixed feedback mode; here is the project file if anyone is interested:
https://www.dropbox.com/s/o8oe5be7xn0ycqc/LM3886%20Guitar%20Amplifer.pdf?dl=0
« Last Edit: September 28, 2017, 06:19:36 AM by sajy_ho »
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J M Fahey

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Re: LM 3886 current feedback poweramp
« Reply #12 on: September 30, 2017, 09:39:05 AM »

Thanks Sajy  :dbtu:

Now we need some pictures of the completed build and the cherry on the cake would be some tasty guitar playing demo  :dbtu:
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sajy_ho

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Re: LM 3886 current feedback poweramp
« Reply #13 on: September 30, 2017, 07:45:15 PM »

Thanks Sajy  :dbtu:

Now we need some pictures of the completed build and the cherry on the cake would be some tasty guitar playing demo  :dbtu:
Thanks man, here are some pics:
https://www.dropbox.com/s/7y0yxbi1y7fbp2z/20170912_215828.jpg?dl=0
https://www.dropbox.com/s/7twizvnunrvuehx/20170912_215846.jpg?dl=0
https://www.dropbox.com/s/27vcaq5ql3jfjw2/20170926_212818.jpg?dl=0
https://www.dropbox.com/s/o93el7x2wxknoc8/20170926_212848.jpg?dl=0
https://www.dropbox.com/s/amqx3744svgakjp/20170926_213010.jpg?dl=0

It's the so called 3886 power amp and before that I'm using ROG Thunderbird and Rebote 2.5 delay as preamp.
I wish I was a good player so I could post a video :'( but I will try my best soon :duh
« Last Edit: September 30, 2017, 08:12:18 PM by sajy_ho »
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J M Fahey

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Re: LM 3886 current feedback poweramp
« Reply #14 on: October 01, 2017, 07:16:23 AM »

Cool project, congratulations  :tu:

By the way, nice carpets, where are you from?

Always fill Country/City information in your user profile ... sometimes we are surprised :)
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