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Old 18th July 2003, 12:46 PM   #21
Previously: Kuei Yang Wang
 
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Konnichiwa,

Quote:
Originally posted by millwood
I wish National can do the same with its class ab chips - not to integrate the output devices on the chips - much like their Class D offerings.

That way, you just go find your own power BJTs and you have one wonderful, versatile, and powerful amp.

we can all dream, cannot we?
Hmmm. I think I prefer NS doing what they did. As they did their homework and implemented the quasi complementary output stage properly, with correct thermal tracking and equal speed devices for both halve waves, plus minimised crossover distortion it is very hard to do better discrete.

You will do usually much worse due to problems with thermal coupling at low levels unless you run a significant class A current and should you be deluded enough to use complementary devices you will have added assymetrical timing in the output stage, which matters if there is no NFB but ballses up things royally when there is NFB around the Output stage.

I'd prefer to have the Output Stage of the NS Chip as Power chip and the ability to have a choice of drivers....

Sayonara
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Old 18th July 2003, 12:52 PM   #22
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Eric wrote:

Quote:
Also nowadays many modern PA amplifiers incorporate internal soft limiting stages and this can help to idiot proof live systems.
You who do make a living of servicing equipment should be aware that it is impossible to make anything idiot proof since idiots are much too inventive !!!

A friend of mine is doing P.A. work for a living. He is in the sales and rental busines. He once had a customer (small music club) he had sold a processor P.A. (Audio Performance, something like a Swiss made Meyersound P.A.) to.
Some day one of the guys there found out that he can remove a specific cable and that he would have much more bass (it was the control line from the LF poweramp's output to the processor). It didn't last very long though.......


Regards

Charles
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Old 18th July 2003, 01:25 PM   #23
Previously: Kuei Yang Wang
 
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Default Re: summarizing...

Konnichiwa,

Quote:
Originally posted by carlosfm
Guys, I assume this thread was started with a domestic point of view. 50 watts RMS is more than enough for your room.
This is a little too blanket. If your speakers are 97db/W/m and your amp's have > 6db dynamic headroom (subjectively not distorted with music) you need only 5 - 6W RMS. Now if your Speakers are 87db/W/m and there is NO or little dynamic headroom (most SS Amp's) you need around 200W....

So, the 25W gaincard with it's around 3db dynamic headroom (very soft supply, sustains only 25W RMS, but handles short peaks of > 50W RMS equivalent) needs at least (in my estimation) 93db/W/m speaker efficiency to allow sufficient dynamic range.

A 50W RMS Amp with no dynamic headroom BTW also needs 93db/W/m speakers....

BTW, this not to say that Gaincard/Gainclone are not good Amp's, HOWEVER, they do not like low impedance speakers or low sensitivity speakers (but then, who apart from Don D'Agostino does and he likes them only because they make him sell his Amp's).

Quote:
Originally posted by carlosfm Anyway, thinking of an ideal amplifier (when are we going to have a wire with gain? ), I will point out two main advantages of chip amps:

1. Short signal path.
2. Much less components.
[/B]
Ahhhm. Actually, most chip amp's have many more parts than most discrete, but of course, you don't see these parts as they are inside the "black box".

For example, contrary to most discrete Amplifiers the NS LM38XX series Amplifiers use current source loads EVERYWHERE possible. Contrary to most dicrete Amp's the NS LM38XX series Amplifiers use Emitter followers (usually current-source loaded) in front of EACH AND EVERY amplification stage, killing (okay, drastically reducing) the effect of the nonlinear Beta (current gain) of the Bipolar trasistors. They also cascode a few things.... All measures that enhance the inherent circuit linearity NO END.

Few discrete circuits can afford that kind of attention to detail and consequent dealing with problems. Also, any "differential pair" in a chip amplifier tends to be tightly matched and tightly thermally coupled....

Quote:
Originally posted by carlosfm Anyway, thinking of an These should theoretically make very hard for you to make a discrete design to be as good as the best chips.
[/B]
Practically too, for the reasons listed above.

Quote:
Originally posted by carlosfm Anyway, thinking of an BTW, Kuei, your pre was reviewed in Hi-Fi World.
They say it's very good.[/B]
Yes, thanks to both MF Audio for making my ideas into products and to HFW for accepting a "hairshirt" passive pre.

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Old 18th July 2003, 02:13 PM   #24
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Quote:
Anyway, thinking of an ideal amplifier (when are we going to have a wire with gain? ), I will point out two main advantages of chip amps:
1. Short signal path.
2. Much less components.
This cracks me up...
As was pointed out, there are many times more components internally in the "little black box".
Minimalist chip amps are a contradiction of terms.
In my opinion, there are two schools of thought when it comes to amplifier design:
1- True minimalist- as in the fewest series gain devices possible, and minimal feedback.
The point being that the fewer gain devices (which, as Nelson Pass says, are most responsible for distortions in the amp) the least amount of damage to the signal.
2- Lowest measured distortion- This school of thought uses all the tricks- current sources, mirrors, active loads, etc. If another stage will lower the distortion, go for it! Feedback in whatever amount gets the job done is acceptable.
Op amps fall into this category, no matter how much (or little) wire you use to hook them up.
I won't be the one to say which is the right way. I guess it depends on who you are, and your preferences. Maybe the truth is somewhere in between?
I fall into the first category, which is inherently discrete by nature. My reasoning is:
1. I believe that greater amounts (but not ridiculous amounts, of course) of low order distortion is preferable to smaller amounts of higher order distortion.
2. I believe that feedback, which is a subtractive process, tends to subtract more than just distortion when overused.
With these "I believes" it sounds a little like religion, and that might not be far from the truth.
Anyway, if I were to build a "type 2" amp, I would probably not bother using discretes, because it is pointless. If you're going to use multiple gain devices, etc. you might as well go with those with the best matching (and all the other benefits mentioned before).
So, my vote is- discretes are better for minimalist techniques, and chips are better when the numbers matter more than the sound.
Just my opinion, of course.
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Old 18th July 2003, 02:20 PM   #25
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Quote:
Originally posted by phase_accurate
Eric wrote:
You who do make a living of servicing equipment should be aware that it is impossible to make anything idiot proof since idiots are much too inventive !!!

A friend of mine is doing P.A. work for a living. He is in the sales and rental busines. He once had a customer (small music club) he had sold a processor P.A. (Audio Performance, something like a Swiss made Meyersound P.A.) to.
Some day one of the guys there found out that he can remove a specific cable and that he would have much more bass (it was the control line from the LF poweramp's output to the processor). It didn't last very long though.......
Regards
Charles
Yeah, who was it that said there is an idiot born every minute !!!.
Live sound guys are usually pretty responsible so long as the drinks rider is after the show (most live engineers know not to drink on the job - bad for the rep) and DJ's are the worst - if there is a way to overdrive and break a system they will find it - cloth ears and too much chemical enhancement is the cause as I understand it.

Eric.
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Old 18th July 2003, 02:54 PM   #26
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Default Re: Re: summarizing...

Quote:
Originally posted by Kuei Yang Wang
If your speakers are 97db/W/m and your amp's have > 6db dynamic headroom (subjectively not distorted with music) you need only 5 - 6W RMS. Now if your Speakers are 87db/W/m and there is NO or little dynamic headroom (most SS Amp's) you need around 200W....
Don't let the specs fool you.
I was very sceptic too, before doing my GC, that they would drive my Epos 11 speakers properly. (8 ohms, 86~87db).
I read the datasheet of the LM3875 and wasn't convinced.
I can tell you I never thought it was possible that these speakers could deliver such an impressive dynamics.
My Nad amp (about the same power) wasn't man enough.
My LM3875 GC is.
I think that more important than power is current delivery.
But even than, the LM3875 is nothing special in this field.
Strange animal...
How could he drive some tiny Tangent 3 speakers (10cm woofers, 87db, 8 ohm) on a 25 square meter room in a way that it made us (I was not alone) preffer their sound to a pair of Tannoy (91db) and a pair of Allison (90db) speakers?
I can't explain this by maths or physics, you really have to listen.
I repeat: it's a strange but beautiful animal.

Quote:
Originally posted by Kuei Yang Wang

Ahhhm. Actually, most chip amp's have many more parts than most discrete, but of course, you don't see these parts as they are inside the "black box".
I know .
But still, it's a shorter signal path, isn't it?
It would be impossible to make today a Pentium 4 processor as they did CPUs until about 30 years ago: discrete, on big boards.
And today CPUs are much faster.
Impossible to get with discrete components.
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Old 18th July 2003, 03:27 PM   #27
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Quote:
Originally posted by nobody special
Minimalist chip amps are a contradiction of terms.
I agree. my experience with gainclones has not been exactly stellar but I wasn't expecting more to begin with.

However, I do think as a DIYer, discret amps are much fun to work with and give more freedom to the builders.

But if you don't need tons of power, I don't think you can tell the two apart.
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Old 18th July 2003, 03:38 PM   #28
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Quote:
Originally posted by mrfeedback

Yeah, who was it that said there is an idiot born every minute !!!.
Live sound guys are usually pretty responsible so long as the drinks rider is after the show (most live engineers know not to drink on the job - bad for the rep) and DJ's are the worst - if there is a way to overdrive and break a system they will find it - cloth ears and too much chemical enhancement is the cause as I understand it.

Eric.
Funny you should mention that...
I had a really interesting experience when my band was playing out one night. The lead singer's friend's band asked us to open for them, as kind of a favor. We showed up, and there were no soundguys anywhere! They had a massive system, made up of mostly JBL stuff, and it was a huge system! We got everything set up, and finally the sound guys show up- drunk off their *****, of course.
We had NO monitors... it sounded completely AWFUL! They were able to make great equipment sound like the worst garbage. It was so bad that the other bands packed up their stuff and left before they were supposed to go on!
I'll never forget that, hehe.
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Old 18th July 2003, 03:42 PM   #29
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Quote:
Originally posted by millwood
But if you don't need tons of power, I don't think you can tell the two apart.
the other advantage for chip amps is that you are more likely to get consistent results from them. For a 4-channel discret amp, it is much harder.
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Old 18th July 2003, 04:04 PM   #30
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Quote:
We got everything set up, and finally the sound guys show up- drunk off their *****, of course.
This is a really good way to ensure that you don't get any live mixing work !.

BTW, it is quite normal for the support act to be intentionally made to sound inferior to the main act.
A muso friend of mine did a support act for a big international touring show and sounded so good that the main act production guys cut him off early half way through his show because he was sounding too good.

Eric.
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