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Chip Amps Amplifiers based on integrated circuits

LM3886*T* without mica foil - working!(?)
LM3886*T* without mica foil - working!(?)
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Old 20th May 2019, 02:35 AM   #11
kokoriantz is offline kokoriantz  Lebanon
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Lm3886 became famous because gaincard amplifier 3000$ was using it (3875) . It functions at very high temperature as the outputs are not ordinary 150C ones but 250C and protected . The datasheet gives the smallest heat sink to be used . As long as the temperature of the heatsinks don't exceed 70C you don't need to bother about.
As you chose nonisolated version you can get advantage of the case and power the negative not by pin 4 but from the heat sink . Apply the negative lead of the bulk capacitor directly to the screw by round terminal. The positive pin 1 can be enforced by soldering the bulk capacitors lead up to the root from external edge of the IC and solder the incoming +V to the capacitors lead.
To enhance the sound , try lower gain , down to 2.8 by 180 ohm 1w feedback resistor and 100 ohm W shunt resistor grounding without capacitor. It is perfectly stable , compare the sound with others , if you prefer it than either amplify the input signal by a driver high quality op amp as AD826 or apply a step up transformer as I do 600/10k .
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Old 22nd May 2019, 05:58 PM   #12
SchiZoID is offline SchiZoID  Germany
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I think the only disaster that could happen is a chip burning for 5$ - ok the speakers would be financially critial (and I already lost one...)
And no 34V you just do not feel - even with wet hands and no shoes.

@kokoriantz
Ok I see what you are trying to tell me here: lower the gain of the final stage and giving more power with my preampstage!? I already use a pair of AD826 to drive my crossover and filter network - but several notchfilters lower the signal voltage noticeable. I still have a pair of LT1028s and a coolable LME49720(TO) at Home to build preampstages that could come after the crossover for the two channels... maybe I'll give it a try, thanks!

And yes I drive the LM3886s at a remarkably high gain (10k and 680R).
So you say high supplyvoltage AND high gain are an ill match!?

And I will remove the caps that ground the signal path in the middlepieces - only used them as an attempt to kill noise that eventually came from a bad grounding (loops - caps too far - PSU too close etc..) -which is now stable.

What I don't get: why using the sinks as powerinput? doesn't make a difference does it?

Last edited by SchiZoID; 22nd May 2019 at 06:07 PM.
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Old 22nd May 2019, 06:16 PM   #13
Panelhead is offline Panelhead
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[QUOTE=SchiZoID;5799195]I think the only disaster that could happen is a chip burning for 5$ - ok the speakers would be financially critial (and I already lost one...)
And no 34V you just do not feel - even with wet hands and no shoes.

@kokoriantz
Ok I see what you are trying to tell me here: lower the gain of the final stage and giving more power with my preampstage!? I already use a pair of AD826 to drive my crossover and filter network - but several notchfilters lower the signal voltage noticeable. I still have a pair of LT1028s and a coolable LME49720(TO) at Home to build preampstages that could come after the crossover for the two channels... maybe I'll give it a try, thanks!

And yes I drive the LM3886s at a remarkably high gain (10k and 680R).
So you say high supplyvoltage AND high gain are an ill match!?

And I will remove the caps that ground the signal path in the middlepieces - only used them as an attempt to kill noise that eventually came from a bad grounding (loops - caps too far - PSU too close etc..) -which is now stable.

What I don't get: why using the sinks as powerinput? doesn't make a difference does it?[/QUOTe


It is your amp. If mine the LM3886 would have mica insulators, proper shoulder washers, and thermal paste. Then all the individual heat sinks would be be connected electrically and grounded.
I will take your word on touching the heat sinks with wet hands and feet.
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Old 24th May 2019, 03:06 AM   #14
tomchr is offline tomchr  Canada
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I don't see the point of creating a deathtrap to save a few bucks on mica washers (or thermal pads). That's flat-out negligent.

Tom
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Old 24th May 2019, 03:09 AM   #15
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by SchiZoID View Post
What I don't get: why using the sinks as powerinput? doesn't make a difference does it?
The die in most ICs is connected to the lowest voltage in the circuit. In this case, that's VEE. To get low thermal resistance between the metal back of the package (the die attach paddle or DAP), the chip is likely soldered to the DAP. That creates an electrical connection. It's up to the end user to isolate the package electrically from the heat sink.

Tom
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Modulus-86, 186, 286, 286 Kit, & 686: 40-240W (8Ω) at <-120dB THD. HP-1: 3W/20Ω, -130dB THD, 128dB DNR.
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