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goldyrathore 27th February 2003 01:15 PM

Pls comment on "Compact audio amplifier" from Elektor
 
Hi,

Some years back Elektor had published a MOSFET (20GTD201)based amp called "Compact Audio Amplifier". Has anyone built it? According to Elektor it is the best high end amp published by them in terms of its sonic abilities. The MOSFETS are so damn expensive and I probably need 10 amps for 5.1 setup. I hope the amp is worth what I invest.

Thanks in advance

halojoy 27th February 2003 01:35 PM

Re: Pls comment on "Compact audio amplifier" from Elektor
 
Quote:

Originally posted by goldyrathore
Hi,

Some years back Elektor had published a MOSFET (20GTD201)based amp called "Compact Audio Amplifier". Has anyone built it? According to Elektor it is the best high end amp published by them in terms of its sonic abilities. The MOSFETS are so damn expensive and I probably need 10 amps for 5.1 setup. I hope the amp is worth what I invest.

Thanks in advance

It uses IGBT transistors. Not easy to find.
And according to Nelson IGBT is so good Transistors.
Not for Audio.

Better is to use Conventional Bipolar Output transistors
or real MOSFETs.
---------------------------------------------------------

Yes, that amp is a nice construction, I Know about it.
And I am sure it has good performance/price.
It is a good amplifier.
-----------------------------------------------------------

But this would not be my choice, if I needed 10 amps.
A power IC design would be the right thing.

TDA2050, as I have said earlier
or LM3875.
You will have ALL the help and experience you need here at forum,
if you build 10 of LM3875 amps.
You need not mess things up, by building INVERTED LM3875.
Nothing to gain by that. Can give you PROBLEMS and headache.


That the inverted should have any "better sound"
is just a product of vivid imagination.
As many other ideas in the audiophile world.
-----------------------------------------------------------

Build TDA2050 or LM3875 amplifiers. Use the recommended circuit.
Will give you well over average listening pleasures.
PCBs you will get from several guys, if you wish.

/halo - why make it harder, than it has to be?
- let's make it normal, simple and good ;) :cool: ;)

sangram 28th February 2003 05:20 AM

"That the inverted should have any "better sound"
is just a product of vivid imagination.
As many other ideas in the audiophile world."

Halo, I politely differ. I find the inverted opamps have a cleaner sound, more musical. Less fatiguing... Also there are practically no differences between the inverted and non-inverted configurations in terms of component count, ease of construction. Some component values differ, but I do find a difference in the sound, and not in ease of implementation - the inverting and non-inverting are the same easy layout. Unless you use a 10K pot for volume control.

I like the sound of Keui's unity gain config the best, even though it is a bit of a psuedo method at first sight, after building and extensive listening to all three configurations (inverting, non-inverting, and unity-gain) I find the normal x10 inverting config the least troublesome (no additional amplification needed for full output) and best-sounding...

At the kind of prices that these chips are nowadays, it is best for goldy to build one and then decide whether he wants to use + or - config. Just two solder joints to undo...

"You need not mess things up, by building INVERTED LM3875.
Nothing to gain by that. Can give you PROBLEMS and headache."

Specifically, what problems and headaches do you allude to? I am curious because I may be building more of them in the future and would like to be warned of any issues with this configuration. I assume issues with the inverted 3875 would also be issues with inverted 1875, 2030, 2050 etc...

halojoy 28th February 2003 10:50 AM

an answer
 
sangram,
I notice that you say they sound better in inverted.
Well, a listeningtest - that is not even blind.
Does not convince me!

Nowhere I have seen a comparing test
that shows any tendency of better figures for inverted.

If there is such figures, I am sure there is other figures
that are worse for inverted mode.
This usually the case, when there is a difference.
You get some, but lose some other thing.
---------------------------------------

Here I can say, that I think that the non-inverted mode
sounds much better. This goes for my OPamps as well as my Power ICs.
So what would this prove?
Just as much as subjective listening test in general.
Which is not much. :D :D

So I would not say this.


As I can not leave garanti the my listening experience
is due to the model I use in my OPamp circuit.

I want something else.
At least a theory, a hypothesis
and I would be please to find that some evaluation
had been done.
Giving some figures that would tend to say the theory
might be valid.
---------------------------

There is a lot of circuits I could say sound better
than another circuit. Just to promote my way of doing things.

I would have much harder to explain and show data.
:D Especially if these data is not better. :D

---------------------------------------
Quote:
Specifically, what problems and headaches do you allude to? I am curious because I may be building more of them in the future and would like to be warned of any issues with this configuration. I assume issues with the inverted 3875 would also be issues with inverted 1875, 2030, 2050 etc...

sangram,
for the normal builder it is always good to use
the recommended setup - gives fewest problems.
But even "normal configuration" can of course
raise some question, for the the normal DIY-builder.


What problems?
I thought you had followed those threads with discussions
of Power ICs in inverted mode.
Do that! And you will see, what I mean with "headache".

/halo - has not as much headache - as :D some guys have :D

Rudy 28th February 2003 11:14 AM

Re: Pls comment on "Compact audio amplifier" from Elektor
 
Quote:

Originally posted by goldyrathore
Hi,

Some years back Elektor had published a MOSFET (20GTD201)based amp called "Compact Audio Amplifier". Has anyone built it? According to Elektor it is the best high end amp published by them in terms of its sonic abilities. The MOSFETS are so damn expensive and I probably need 10 amps for 5.1 setup. I hope the amp is worth what I invest.

Thanks in advance


Nice amp, very very very detailed sound, altough it has a chilly sounding like a transistor amp, doesn't have the warm feeling like a mosfet amp. Sounds very powerfull for a 50 watt amp.

Not an amp i would suggest when you dont have a lot of experience, other words, don't build this if it is your fisrt amp.

On the IGBT's, nothing wrong with them, these are the only one's usefull for audio-applications. And these are very hard to find, try to find them first and then start bying the rest.

Greetz Rudy

Tube_Dude 28th February 2003 09:18 PM

Inverted or not inverted!
 
I donīt use to express myself concerning subjective sound quality issues.Thats too subjective!...How many times i went to dealers and hi-fi shows and i see people hearing in a religious way systems that for my ears sound like crap.
As many things in life one man ceiling is another man floor!
In case of the invertid amplifier there is a reason for to my ears, it sounds more intermodulated then the noninverting amplifier.
The reason is that the EMF from the loudspeaker can find the way to the preamplifier or CD thay is driving it and that to my ears causes euphonic sound that is the result of that dinamic intermodulation (of course many people seams to prefer melow sounds).
Regards
Jorge Santos
PS: of course i have nothing against an inverted amplifier if it is not connected to a reactif load as a loudspeaker.

P.Lacombe 28th February 2003 11:17 PM

Halojoy,

In correctly designed amps, inverting configuration exhibit better distortion figure than in non-inverting ones. This is caused by the cancellation of the common-mode distortion at the input of the amplifier, and nothing to do with the absolute phase of the signal, indeed.

This can be clearly seen in some Linear Technology Application Notes, for instance, with distortion figures as low as 0.0001% in the inverting configuration.

This phenomenon has been discovered long time ago, and the famous Electrocompaniet 25 W designed by Dr Matti Otala in 1975 was an inverting amplifier.

Inverting amplifiers with parallel feedback are frequently used in scientific equipment and measuring instruments because of the improved linearity.

Regards, Pierre Lacombe.

halojoy 1st March 2003 12:44 AM

Pierre always uses inverted mode configured AMPs.
 
So mon ami Pierre,
why is non-inverted configuration used 98% of all amps?
You did not leave out som drawbacks with inverted, did you?
--------------------------------------------------------------
And if it is so very much better,
I suppose, Pierre always uses inverted mode configured AMPs.

And most amplifier/soundsystem constructors are so ignorant,
that they mostly uses NON-inverted design.

Anything else would be UN-logical, wouldn't it?
Who wants un-necessary bad figures, when things could be better?

---------------------------------------------------------------

I can see one drawback:
You have to turn the signal back into phase.
Either in the actual channel,
or in all other channels that can be in your soundsystem.

This means that you have to have another inverter amplifier (or many),
which signal will pass.
And will make signal pass a quite a number more devices,
making signal way longer.
So that has to be added to your figures.
-----------------------------------------------
You can of course do the trick of reverse the LSP connections.

But I prefer to have all my parts in my system "in phase".
This way exclude that you forgot what the actual phase is.

/halo - uses the inverted mode in very low volt designs
- like +- 1.5V or +-3.0V battery amps.

P.Lacombe 1st March 2003 10:35 PM

Halojoy,

I know that serial feedback is very useful, but this cann't establish that it's the best solution.

Mahatma Gandhi has explained that it's not because error is very common, that it becomes truth............

Regards.

FunkyStu 2nd March 2003 09:16 PM

Re: Pls comment on "Compact audio amplifier" from Elektor
 
Quote:

Originally posted by goldyrathore
Hi,

Some years back Elektor had published a MOSFET (20GTD201)based amp called "Compact Audio Amplifier". Has anyone built it? According to Elektor it is the best high end amp published by them in terms of its sonic abilities. The MOSFETS are so damn expensive and I probably need 10 amps for 5.1 setup. I hope the amp is worth what I invest.

Thanks in advance


I've heard this is a pretty good amp. I'm currently in the process of building one myself. The only problem is that the BF871 and BF872 transistors are no longer available. I wrote to T.Giesberts at Elektor and here is his reply:

Quote:

Hello,
Try to find MPS-U10 (NPN) and MPS-U60 (PNP), but these are probably hard to
find (or not at all: no longer produced by Motorola).
An untested alternative: types MJE340 (NPN) and MJE350 (PNP) in SOT32 casing
(TO225AA) and are also produced by ST Microelectronics. Additional (little)
heatsinks are needed. Please inform me if this helped you (or not). I've
found no Japanese transistors that are equivalent or come close.

Ton Giesberts
Hope this helps...

Let us know if you have any other info regarding this amp.

- Stu - :clown:


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