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LF: RE: LF Amplifiers etc

To: [email protected]
Subject: LF: RE: LF Amplifiers etc
From: "Talbot Andrew" <[email protected]>
Date: Wed, 3 May 2000 14:59:50 +0100
Reply-to: [email protected]
Sender: <[email protected]>
Thanks for that, you've just saved me some work.  I'm playing with a
TDA2005 bridge audio amplifier for 10 watts off a 12v rail (since I had
one spare), but that older device is a bit prone to instability into
anything other than a perfect resistive load.
The simplicity of the LM1875 circuitry makes the effort of using a 30V
rail (via a switch mode PSU from 12V) worthwhile.

Farnell do this device too, and also I see in their catalogue the LM1876
which appears to be a pair of '1875 types in one package.   50 watts
from a bridge perhaps ?

On the subject of linear amps.  I'm also investigating the idea of a
pulse width mod. voltage controller for class D PAs.  Then by separating
out envelope and phase information from complex modulation waveforms, an
efficient PA could be used without the trouble of going through SSB
driver stages and probably a transverter.   The authors of a lot of the
modem software could hopefully be persuaded to make amplitude and phase
info available separately.

Watch this space.

Andy  G4JNT

----------
From:   Andre' Kesteloot[SMTP:[email protected]]
Reply To:       [email protected]
Sent:   2000-05-03 13:17
To:     [email protected]
Cc:     lf-amrad
Subject: Re: LF: beacon power control
Rik Strobbe wrote:

> [...]
> As the beacon is meant to be low-power (10mW and less) a relative
small TX
> power can be used (50 Watts and less), so it can easily be
overdimensioned
> to provide extra safety.

Maplin has a small class A amplifier using a LM 1875 that easily puts
out 25
watts at 136 Khz. It is stable, has automatic current limiting and
overheating
protection. Because it operates in class A, the output can  be
controlled simply by a step attenuator at the  _input_   of the
amplifier.


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