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Old 31st August 2013, 06:58 PM   #1
rsavas is offline rsavas  Canada
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Default Elektor Q-Watt project

Hello,
I subscribe to Elektor, noticed this project, so while looking for the documentation, I see that they opened this one up for everyone to download. Looks to be very nice implementation of the LME49811.
Q-Watt Audio Power Amplifier - ELEKTOR.com | Electronics: Microcontrollers Embedded Audio Digital Analogue Test Measurement
I noticed that they used one pair of bjt's in a TO-3P package, so I was surprised at the Q-Watt ratings using only one pair of o/p's. Went looking for the o/p bjt's Semelab MG6330-R/MG9410-R, Farnell has them pretty cheap, as well.
These are 200W/260V/15A parts. I also noted that they make a 300W part in TO-3P and a 400W (MAG6332/MAG9412 in a TO-264.
Might have been nice if they mentioned these facts in the article.
The hfe is very linear, beta droop is good, Ft is good. ( I guess Ring Emitter equiv.) No Spice models. From what I see, cost/performance is a bit better than OnSemi.
One critisism that I have with this Elektor project, is it is only a pcb or assembly, leaves the readers to figure out all the rest, PS,chassis.
At least DIYAudio forum, have got it figured out, offering sources for cases/HS/PS's assemblies, etc.

Last edited by rsavas; 31st August 2013 at 07:04 PM.
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Old 3rd September 2013, 09:24 PM   #2
dangus is offline dangus  Canada
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The parts list does include a suggested transformer, rectifier, and filter caps. It'll probably all add up to much more than buying a used amp, though.
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Old 6th September 2013, 02:42 PM   #3
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Hmmm???

I just photoshopped the two PCB sides on top of each other,
and realised that they have actually routed the audioground to the star point via the chips GND pin???
I have let myself understand that that pin actually emits noise from the chips internal guts...

Any opinions on that?
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Old 8th September 2013, 02:34 PM   #4
rsavas is offline rsavas  Canada
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Does not seem to matter too much based on the measurement results.
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Old 16th December 2013, 09:43 PM   #5
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Quote:
Originally Posted by palstanturhin View Post
Hmmm???

I just photoshopped the two PCB sides on top of each other,
and realised that they have actually routed the audioground to the star point via the chips GND pin???
I have let myself understand that that pin actually emits noise from the chips internal guts...
Any opinions on that?
Chip guts does not emit noise. Noise in circuits is generated by unwanted or extended current loops. Therefore when designing PCB, current loops should be avoided as much as possible. This particular circuit topology (by looking at schematic and drive IC datasheet) determines current loops to be minimal if common ground point is designed around audio ground of the chip. And that is exactly what author did.
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Old 17th December 2013, 06:11 AM   #6
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Does the chip use its GND pin for the audio signal?
Or does it use it for something else?
I have let myself understand that it does not use it for the audio signal.
It uses it for something else, which emits noise...

I might have let myself understand the purpose of the chips GND pin wrongly.
But I still try to keep it clear from the audio signals in my designs...
Which should then be a huge problem.
However, by luck I have managed to keep that mistake unmeasurable.
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Old 17th December 2013, 11:17 PM   #7
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Ground pin on integrated chips like this one is the common return for all other signals this chip has. This means, the sum of all out and incoming currents (minding the direction) from/to this chip is equal to common current flowing to ground pin. The LME49811TB itself is just integrated power amplifier, therefore current flowing from its speaker output will return to its source through ground pin. So it is used for audio signal as you refer. There is no "something else" within the LM amp, it is simple integrated circuit with no built in high frequency noise sources which would couple to audio circuits.

I am no sure what you mean by keeping ground clear from audio signals, but you might be misunderstanding the concept of common return in electronics circuits which some of these are named ground like on this example.

As for the subject, I have decided to build this amplifier as its parameters are amazing in terms s/n ratio and distortion level. Simplicity of this design with careful selection of external power transistors should produce same results as listed in Elektor article. In fact, being Elektor reader since 1996, this is the first time power amplifier design is worth checking out. I expect to achieve results which should surpass many commercially available amps I had in past 20 yrs.

The pcb's and components are on the way.
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Old 18th December 2013, 05:57 AM   #8
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Hey, I have to agree with you, this amplifier being the best of the Electors implementations ever, I have been reading Electors since the beginning of the -80ies... Need some old issues??? ;-)

Anyhow,
I have let myself understand, that the chips GND-pin is the return to the ShutDown of the chip.
Hence everything injected to the ShutDown will be sent out from the chips GND. So if one wants to return the shutdown directly to the audio ground, the Electors way is a good way to do it, in my oppinion, but hey, I might still be wrong here...
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Old 18th December 2013, 07:34 AM   #9
Art M is offline Art M  United States
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Quote:
Originally Posted by rsavas View Post
Hello,
I subscribe to Elektor, noticed this project, so while looking for the documentation, I see that they opened this one up for everyone to download. Looks to be very nice implementation of the LME49811.
Nothing Free here. Have to Join or Buy something. Best move on to Vendor Forum.
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Old 18th December 2013, 07:56 AM   #10
Mooly is offline Mooly  United Kingdom
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