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Old 17th September 2008, 10:00 PM   #21
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Quote:
Originally posted by lineup
The problem with LM3875 / LM3886 /LM4780 is the

1. Too high slewrate + high bandwidth
... which makes a noisier sound and not as musical

2. SPiKe protection electronics = garbage in Output Stage.
Which 'cuts' the peaks in music.
Like in a badly processed CD disc. . . with compressed sound & not perfectly dynamic sound waves.
. . .
Hey man, if there's some of the signal that's un-desired and all other means have failed, it might be a good time to admit this, and improve the efficiency by slagging that screaming sucker's NFB. Like this:
From -input, a resistor from 22k to 27k
From this resistor, a capacitor from 10nF to 15nF
From that capacitor, a resistor of about 150k (or a dial)
From that resistor, the speaker +
And that is a tone control--gage to use it at the point where it "just barely" takes audiable effect and you'll have wiped out the screech without seriously harming the music. I'm saying "just barely take the edge off," because if you went farther, it wouldn't be hifi.

This is on the side of the NFB that can say "don't do it" to the amplifier.
Removing un-desired signals improves efficiency.

There are also artificial means to clear up the smashed bits of the signal, without dropping the gain on them (like we just did).
Parallel amp and/or blackgate input filter capacitor (or brainy little matching device) can hash/divide up the signal going in so that it won't get full of sine waves going out. Theoretically, any multipath arrangement can do this, and its up to you whether its a distortion or whether its a more-desired signal.

On the capacitance you mention, one way to avoid trouble is to avoid promoting it. Larger contacts are less condusive to capacitance and that most certainly includes the spacing inside your resistors. Some people believe to pass as much signal as possible. But, in this case, I'd like less trash signal and more audio signal. The popular band-aid fix is a large Caddock or the equally good 1/2w 1/2cent carbon film. Both are carbon, with larger spaced contacts and both are tube-amp centric. If these are mixed with metal film, you have a voltage divider that promotes the errata of the larger carbon resistor (hopefully accentuating its ability to remove or reverse a noise). Its this technique a distortion or is it quantity versus quality? Once again, its not for me to decide what sort of signal is the most efficient. That's up to you.

But, the LM3886 itself is just fine. If you can't hear its lovely bass and baritone, then cause a situation where you can. Cheers!
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Old 17th September 2008, 10:02 PM   #22
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Did I just say that LM3886 + terrible cheating "could" make better fidelity than any TDA7294? Yes. And, I apologise if that offends anyone. The comment was directed towards Lineup because he and I both have similar audio preferences (of what is and isn't a desired signal).

EDIT: I think that "favorite" is about desire of relating to the efficiency of a "most desired" signal.
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Old 17th September 2008, 10:37 PM   #23
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Quote:
Originally posted by danielwritesbac


differences:
In my opinion, most of the audio variances between the different model chips can be negated via the power supply or power circuit choices; however, LM1875 and LM3875 alike, are still less powerful than LM3886 by 3 to 4 decibels output. The optimized power circuits, for these to produce high fidelity audio, are all probably quite different. To me, the quote above looks like one of the National Semiconductor chip amps has facilited the use of a favorite power circuit.
Right, even if conditions look the same at first sight, they often are not if you look into details. So I think the whole discussion here will not help to find "the best" chip, because we have allot of different impressions (a question of taste) and allot of different conditions... which powersuply, which external components, which layout, which music and which loudspeakers have been used? So my comment was just my impression and everybody can make his own research. Maybe someone will see different results or will prefer somethig different. I did the test before I started to build my amplifier and finaly i ended up with the LM3875 for the Mid and High chanels and pralell LM3886's for the bass on a 3way system.
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Old 18th September 2008, 05:10 AM   #24
dynabok is offline dynabok  Hong Kong
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Seems different combination of component will have different sounds?
But for my own opinion, I believe that "simple is the best", if too much component inside the circuit, will pickup more noise, is it?

I agreen with "Tranceformer", as we are using different power supply, different component, so it is hard to compare, can we have a way to test different sound of each chip?
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Old 18th September 2008, 05:24 AM   #25
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Quote:
Originally posted by dynabok
I agreen with "Tranceformer", as we are using different power supply, different component, so it is hard to compare, can we have a way to test different sound of each chip?
I think your thread is really valid just like it is. For instance, Lineup and I and many others, have a lot of fun causing LM1875 and TDA7294 to mimic the sounds of tube amplifiers. EDIT: Those chips have facilited efficiency via helping create "a more-desired signal" for their given application.

And, without those chips, I'd be buying tubes because I'm just not smart enough to trick a transistor.

EDIT: So howabout the chipamp and its application listed together, like Tranceformer's inspired application of both LM3875 and LM3886, showing how they are used?
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Old 18th September 2008, 05:54 AM   #26
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My votes are for the LM1875 and the OPA549

The OPA549 is very transparent but must be run at lower gain so you need a good pre. It can deliver a pile of current with the right power supply.

The thing I like most about the 1875...apart from the sound is only 5 pins (as are some old STK3875 chips manufactured for Sony).
In my experience the 3875 is quite punchy. I was not fond of my parallel LM4780....but it makes a great sub amp.

They are all fun to try, I'm sure the differences are mostly in the individual application, as any of them can be made to sound good. I don't truly believe there is a "best".

G.
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Old 18th September 2008, 09:48 AM   #27
digi01 is offline digi01  China
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i like all of overture series chipamp,especially LM4780.

and,the STK4xxx series still in my memory,a sweet memory... when I was 16 years old I play these big cakes
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Old 18th September 2008, 11:05 AM   #28
lineup is offline lineup  Sweden
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Quote:
Originally posted by dynabok

But for my own opinion, I believe that "simple is the best", if too much component inside the circuit, will pickup more noise, is it?

I agreen with "Tranceformer", as we are using different power supply, different component,
so it is hard to compare, can we have a way to test different sound of each chip?
Quote:
Originally posted by danielwritesbac

EDIT: So how about the chipamp and its application listed together,
like Tranceformer's inspired application of both LM3875 and LM3886,
showing how they are used?
Like dynabook and others,
I want to keep it as simple as possible, while still make it good audio.
My rule is
Quote:
Do not use more force & complicated gears
than the demand of the situation
calls for
Yeah, some would use even Schumacher Formula One Ferrari car to go shopping.
It will possibly work. But is this the best solution?
Is this even one desired, wanted way to do it?

I can use one gigantic truck weight 10 tons (10000 kg)
to move away some old junk from my garden.
Junk, that I can put into the back of my Toyota Corolla.
And transport it where I want it.
-----------------------

danielwritesback
thinks Tranceformer have a good idea:
So how about the chipamp and its application listed together,
showing how they are used?


I think this is the best idea

Just tellling: This or that Transistor is best one.
Really does not give any good information, at all.
We should put the device in its CONTEXT.

In what situation, in what audio chain, environment,
would this chip LM1875 perform very good?
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Old 18th September 2008, 11:35 PM   #29
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OK Guys, I can tell a bit more about my Chipamp.
In the beginning I used a big 600W transformer, fast diodes, big capacitors and so on. I designed a PCB and started to run some tests. Beside listening to music I tested the noise with a open input. I connected a headphone and spent allot of time by optimising the cabeling and shielding the transformer. But I was not 100% happy with the results because I still did hear some 50Hz hum and noise on the headphone. The next stage was a regulated power supply which was an improvement but not the final design. After several experiments I ended up with switch mode power supplys and a new PCB design.
I agree to what dynabok said : simple is the best
So I changed my first design to a inverting design which saved a cap in the signal path and I removed the pots and used resistors for a fixed gain. I am using a digital x-over inside the amp to get the signal for my 3-way speakers. In the whole path from the digital input (spdif) to the loudspeaker there is only one capacitor.
As a conclusion I would say the same that people here said before: THE DESIGN ARROUND THE CHIP CAN BE MORE IMPORTANT THAN THE CHIP ITSELF.
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Old 19th September 2008, 11:03 AM   #30
dynabok is offline dynabok  Hong Kong
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You are using switching power supply, is it will noise? I also think about to use switching power before, but I am afraid it will pickup a lot of noise? how can you do it?

By the way, I come up with a idea, is it possible that we can make them as module, for example: make power supply as a module, make regulator as a module and make chip amp as module(1875 chip amp as a module, 3875 chip amp as a module, 3886 chip amp as module).
so that we can change the chipamp and hear different sound from different chip and different circuit design? and also we can change the different regulator to see how it can affect the sounds, how about this idea?
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