LM386 low noise alternative?

[neazoi]

Two parallel diodes wired opposite ways around across the headphone is the simplest solution but you MUST add a series resistor or risk the amplifier dumping high current into them.

The trouble with RF AGC is:
1. changing the pre-amp characteristics will alter the detector stage so you need to keep an uncontrolled buffer stage between them. In other words add AGC to a new stage before the existing pre-amp.
2. where do you get the signal strength measurment from? You might be able to extract some RF from the emitter of the detector stage but you would again have to buffer it to reduce it's loading effects then rectify and probably amplify it as well.
3. consider what happens to the perceived signal strength when you deliberately increase the regeneration to receive CW or SSB. The oscillation would be thousands of times stronger than the signal you were trying to measure. The AGC would be the oscillator level, not the incoming signal level.

If you are still there right now, I am monitoring 14.255MHz at the moment but only for a short while!

Brian. (GW6BWX)

We cross posted. Yes I see the limitations with it, I would better not use it at all.

I am at work right now, so I have no access to the transceiver. I built a simple box that converts CW tone to PTT and has some transformer isolation for the audio. It works ok for ON/OFF keying but not for SSB, so I will do it by ON/OFF the TX not modulate it by the tones.
I have not done any test on air, but we won't go high speed CW anyway.
I just found your website, I will send you a PM there to arrange the QSO, to test the Schematix program.
Regards!
Kostas sv3ora

 

[betwixt]

The frequency was clear when I posted but is now a 'pile up' of stations contacting a station in Spain anyway!

Let me know when you are available.

Brian.

 

[neazoi]

The frequency was clear when I posted but is now a 'pile up' of stations contacting a station in Spain anyway!

Let me know when you are available.

Brian.

I've sent you a message through the website http://www.atv-projects.com and a way to chat live, which will help on the QSO, since we can't communicate by phone.
Regards
Kostas sv3ora

 

[Audioguru]

If you use BC549C and BC559C transistors with a max allowed current of only 100mA as the output transistors in the discrete audio amplifier then they will probably burn out if the pot is set for too much current. The amplifier uses 2N2222 and 2N2907 transistors that have a max allowed current of 800mA so that it can drive an 8 ohm speaker with 530mA peak current for 1.1W. 0.1W is loud in headphones. Even the 470uF output capacitor is calculated to produce bass sounds in an 8 ohm speaker, it produces earthquake sounds down to 11Hz into a 32 ohm headphone.

 

[pgamage]

With all these changes the volume is nice, sometimes ear-splitting when a good signal is received.

Overall success!
?

Can you share the diagram of final product you built?