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Old 29th July 2012, 09:51 AM   #11
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Quote:
Originally Posted by ataul View Post
.Why some amp sounds sweet? what is the magic behind this?
Its not magic, rather attention to details of controlling noise sources. PSRR of chipamps also is not good on -ve supply rail at higher freqs, inadequate power supply regulation can harm the sound.
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Old 29th July 2012, 03:09 PM   #12
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Quote:
Originally Posted by ataul View Post
Daniel,At least 10years back i tried with this LM1875 that was nothing special I remembered that sound was very clean but something missing.. . .
Maybe the NFB cap (if that's missing, so are your dynamics)? Maybe the input load too light? Maybe the negative feedback current too heavy? All of those occur with common/free/datasheet designs. OR, with the Quasar Kits #50 (K50 kit), the feedback current is insufficient (or possibly the feedback shunt current is too light).

SO, try this:
330uF power caps directly at the chip (range 220uF to 470uF) and of course you'll want some bigger capacitance added nearby.
One 4.7uF 250v cap from v+ to v- (noise filter)
33nF polyester caps for power decoupling right at the chip.
Feedback resistor in the range of 47k to 100k
Feedback shunt resistor in the range of 2.2k to 3.3k
NFB cap in the range of 120uF to 470uF
10k input load resistor (range 5k to 12k)
3.3uF input cap (range 2.2uF to 4.7uF)

There is ranges of values. I'd suggest to experiment within the range and see if you can get LM1875, LM675 or the similar 5 pin chips from ST to have a very pleasant sound. LM1875 doesn't want gain over 48 (45 and less sounds better than 48), LM675 doesn't want gain over 15 (LM675 can boost a headphone amp), and most of ST's don't want gain over 23 (compensations sealed inside little black chip). So, if you've got Computer, digiplayer or iphone source, use LM1875 for its big gain capacity. The smaller your feedback shunt resistor the bigger your NFB cap needs to be (examples: 120uF+3.3k, 220uF+2.7k, 470uF+2.2k, and nearby values work fine). Figures are approximate. Basically I'm just saying you do have options to explore and these options all sound different.

Chips don't make just one sound. They do whatever you ask.
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Last edited by danielwritesbac; 29th July 2012 at 03:12 PM.
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Old 29th July 2012, 03:47 PM   #13
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The chip amp doesn't make any sound... that's what the loudspeaker does.

You might think about your question. I don't believe that you are asking the right one(s).

You need to think more in terms of how much power you need, and the distortion (and what kind of distortion) will be produced at low, medium, and high power outputs (relative to what the chip amp is capable of). That, and the noise (from the layout of the board and power supply) of the amp are about all you should be concerned with.

Think about your loudspeakers and the room they are in. Executing the loudspeaker and its crossover correctly have a large influence on the sound. These things are vastly more important with regards to "sweet sound" than the amplifier.

-Charlie
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Old 29th July 2012, 04:27 PM   #14
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He said Active Crossover, and the TDA2030A (and similar from ST) does have some crossover examples with its documentation. If given an Active Crossover, it seems like whatever fine job you do on the amplifier can be swamped (made less important) by RC and EQ distortions that are usually much worse than passive crossovers. Good luck.
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Old 5th August 2012, 12:54 PM   #15
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danielwritesbac,

Do you have schematics for the 1875 chip that you suggeted or is it text book lm1875 schematics but use the parts per your suggestion. Thanks.
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Old 5th August 2012, 11:15 PM   #16
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Fairly well described in post #12. However, if you have a k50 kit or other LM1875 board, I could give component values if you like.
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Old 21st September 2012, 08:22 AM   #17
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Quote:
Originally Posted by ataul View Post
TDA 2009 have some magic of sweetness in 8Ohm load but very low power, only 6+6 watts into 8Ohm.
It isn't especially low power in bridge config.

The magic sweetness, like TDA2003, is singleton sound. Amplifiers that may sound similar include Singleton input, NTP input, SSA input, and many tube amplifiers. On all of the examples, regulated power, K-multi power, or capmulti power is suggested, especially for singleton.

Perhaps you already have a good power amp and it needs a Singleton Preamp or a Triode Preamp to make sound like you expect?
It is not expensive:
MooseFET Preamplifier
Try it with:
IRF510
Nichicon ES 0.47u input cap
Elna Cerafine 16v 47u // Nichicon ES 1u output cap
Multi-Turn trimmers
Low ESR caps, such as Panasonic FC

Big soundstage and good tone is not necessarily about singletons and triodes. It is more likely to be related to whatever is most helpful to the source device. A Diamond buffer can do it. Have a look at these:
Improved Diamond Buffer Design
For power, I'd choose OnSemi MC7815, MC7915 regulators, since excellent quality power is the other half of the job.
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Old 21st September 2012, 11:47 PM   #18
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I'm really surprised no one has contributed this yet, so I guess it's up to me.

The MyRef series of amplifiers, originally designed by Mauro Penasa and offerred by him here for DIY, is perhaps the finest implementation of power chips available. Do a little research, as there are several threads dedicated to it and its most recent incarnation as the MyRef FE developed by Dario (ClaveFremen).

I have owned massive tube amps and multi-thousand dollar power amps, and this little amplifier, when properly constructed with quality components, equals or surpasses all of them in almost every way. It is easy to build, inexpensive, reliable, efficient, and sounds beautiful: sweet, spacious, accurate, detailed without brightness or fatigue.

The basic design is readily available for private use, and several group buys have allowed many happy builders to purchase PCB's or entire kits. The configuration I currently use is identical to what you have described, with the monoblock amps directly coupled to active xovers, all in the same chassis.

Peace,
Tom E
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Old 22nd September 2012, 02:20 AM   #19
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Quote:
Originally Posted by madisonears View Post
The MyRef series of amplifiers, . . . sounds beautiful: sweet, spacious, accurate, detailed without brightness or fatigue.
Thanks for the review!
Yes, "spacious with good tone" and sufficient power are what he's looking for.
So, your answer is very good.

Perhaps the current pump topology, and pedantic attention to component detail provides an "out of the box" hi-fi experience. However, the constructor must avoid substitute parts and also is required to follow known successful examples for power and wiring layout. . . so as to achieve the documented outcome. Even so, I think it wonderful that the majority of the fine tuning work is already done and already documented.

MyRef-LM3886T: Much faster trip to hi-fi and much less financial risk to use known good.

P.S.
Given this news, perhaps it is time to exhume/reboot the Nested LM1875 project, which isn't a current pump like the MyRef, but does have a small signal "pilot amp" (nested pre) like the MyRef. To compete on current, we'd probably have to do a parallel amp, which may be more complex. Like Ataul pointed out, the LM1875 by itself is an "almost" home run but Not competitive to the singleton chips (TDA2009, TDA2003) for "Spacious" soundstage feature. We need to widen that a bit, per each speaker and that feature must be provided by whatever pilot/pre amp is chosen.
Such work has already been done for the MyRef-LM3886T.
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Old 22nd September 2012, 08:16 AM   #20
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Quote:
Originally Posted by madisonears View Post
......................The MyRef series of amplifiers,............. is perhaps the finest implementation of power chips available. .................
if these really are the finest, then I'm of the opinion that the best chipamps perform far worse than the good discrete designs available.
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