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I recall at one point folks in the Bitx20 boards were discussing a simple hack to avoid blowing out eardrums on transceivers lacking AGC - They would simply use a couple diodes between the headphone lines to ground, so higher voltages would get bled off through the diode.? I don't recall the precise details, but the principle seems like it might work.

Obviously it is a kludge and probably sounds terrible when it gets to audio limiting, but it might at least prevent you from getting blasted off your chair by a sudden loud CW signal...

Thoughts?
-N1EDC

It would be similar to this technique to protect ADC inputs with a couple Schottky diodes:

https://www.analog.com/en/technical-articles/protecting-adc-inputs.html

I used 2 schottky diodes in antiparallell on my QCX-mini.?
It does save your ears from audioshock!?
It does not influence audio quality under normal operation, since the diodes are not clipping the waveform.?
But you still have large variations in audio level when tuning across the band.?
When the AGC-Boards became available I installed one of them, and it makes a world of difference! Now you can comfortably tune the bands

SM5EIE /Gunnar?

Friends , Romanos,? ?Gentlemens? ---? lend? me one buck I can do it for you because that's the Ebay price for the Tda7052AT?

BUT it , the design,? works ONLY with the AT variant ,? not the bare 7052 because the latter has no mute input.?

Here's the cct that the? MST 2 from Australia used to? use - a fine cct but Ozqrp shut down when the owner , Leon , retired.

Note that the? LM08 psu is critical? . This device will NOT withstand 12V.? ?the Audio? is 500% better than the crap you will get out of an LM386 cct
no wining noises , no biasing in favour of the? HF elements of the AF band because of capacitive coupling, because there ain't any.?
Note how there is? provision for Tx on muting.? this damned cct has everything.

Fly in ointment - the chip is obsolescent.? BUT it rides at night on Ebay and varous SE asian sources . Futurlec.com does not list it but often he can get not too hard parts if you pester him.? Don't buy? one unless they are rationed get two or three.? Note that i adding AGC to an existing say LM386 cct you may have to just abandond what is there and make up a replacement amp on a piece of veroboard.? Don't forget the support holes.

TE. Fidler

The AGC kits don't work on the QMX though, do they?

Nope.

-mike/w1mt

All,

I would recommend patience.? The QMX has a very capable processor to process the audio.? Hans will add the AGC into the software at some point.? This should be much better than the simple diode limiter developed for the QCX.? Otherwise, you must hack a very tight board to add the limiter.

73
Evan
AC9TU

ND6T has pointed out that this can be done with an external adapter that will leave no permanent modification to your rig and could be used with any homebuilt rig.

http://www.nd6t.com/qrp/speaker.htm