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Pls comment on "Compact audio amplifier" from Elektor
Pls comment on "Compact audio amplifier" from Elektor
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Old 2nd March 2003, 09:53 PM   #11
Rudy is offline Rudy  Belgium
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Join Date: Feb 2003
Location: Belgium
Default Re: Re: Pls comment on "Compact audio amplifier" from Elektor

About the BF871 and BF872...

If you don't mind to lose some bandwith then there will be no problem replacing them by the MJE340 and MJE350.

Orriginally the amp had a bandwith of 1.5Hz...270Khz

Sow losing some wouldn't mind that mutch.

Greetz, Rudy
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Old 3rd March 2003, 08:20 AM   #12
sangram is offline sangram  India
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Join Date: Sep 2002
Location: India
Default Re: Pierre always uses inverted mode configured AMPs.

Originally posted by halojoy

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".
Unfortunately I could find nothing after searching for 'Inverted Gainclone'. Only Paul Hilgeman has thrown up some problems with phase, which may or may not be related to the actual circuit, and it is not a known issue as I see he has not got any revolutionary or path-breaking answers, either.

In the meanwhile I have completed building a stereo bridged amp using TDA 2030 (In the past I have used TDA 7294 with decent - not excellent - results, using PCBs with the stock circuit) in inverted configuration.

I am stunned, in a word. Not that it will compete with a great amplifier, but for the money you pay, it is a knockout. This has been built after extensive experiments using the same chip in non-inverted, inverted and the Keui unity gain mod.

I like the unity gain mod the best sonically, but unfortunately the requirement of an additional gain stage for full power output is unappealing. Therefore the decision to go for normal (x10) inverting. The more I listen, the more I like it.

Originally posted by P.Lacombe
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...
True. This reason has also been mentioned earlier, by Thorsten/Keui as well as others earlier. The other issue is of the input impedance, at the inverting input is lower. This creates issues with volume controls etc. It is not possible to have amplifier with high input impedance at the inverting configuration.

Some small signal opamps also have considerably less noise in non-inverting mode than inverting, as per National's opamp book. But that is not an issue in power opamps...

Originally posted by halojoy
I can see one drawback:
You have to turn the signal back into phase.

... You can of course do the trick of reverse the LSP connections.

If you are constructing the amp yourself all you have to do is to reverse the polarity inside the amp, to solder the output wire to the black terminal, and the ground to red.

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