The 10pF capacitor in the anti-hiss circuit seems to be waaaaaaaaaaaaaay too low to be an effective. Its turnover frequency appears to be around 1.5 Mhz.
Substitute it for 1,000pF and then 10,000pF and let's see what happens.
Perhaps if you told us the impedance of your headphones it would help. If you are unsure, even a resistance measurement might give a clue.
All these amplifiers are fine for their intended purpose - driving small loudspeakers with reasonable volume, noise and distortion. They are for use in consumer equipment where cost is more important than quality. It isn't really fair to condemn them, they serve a pupose admirably, it just isn't the right one for Neazoi's needs.
Brian.
The TDA7052 is also cheap and noisy. It is bridged so you need to wire it differently from the way shown in its datasheet to drive headphones that have only 3 wires, not 4 wires.
Why is that?You should NEVER Connect Headphones direct to the Output of Any Power Amp.
A power amp, even as small as an LM386 can seriously damage your hearing, either by simply producing too much volume or by becoming unstable and sending loud (possibly beyond audible frequency) oscillations down your ears!Why is that?
A power amp, even as small as an LM386 can seriously damage your hearing, either by simply producing too much volume or by becoming unstable and sending loud (possibly beyond audible frequency) oscillations down your ears!
The problem with all the proposed designs so far is they are intended to push high currents through low impedance loads. That is exactly what is needed in a power amplifier but your needs are different, you want lots of amplification (high sensitivity) and reasonably high voltage output but into a higher impedance load. 32 Ohms resistance implies the impedance is at least 32 Ohms so it moves the target more towards a voltage amplifier than a power amplifier.
I would propose you use a dual op-amp and see if that is sufficient. You can use the first stage to give say 30dB gain and the second stage to give say 20dB gain. The second stage connecting to the headphone through a resistor to isolate the reactive effects of the load and provide the essential safety feature. I am thinking of an amplifier something like a TL072/TL082 or equivalent. There is at least one commercial product doing just that, using a TL072 and costing around 1,000 Euros (~$US 1,000). Of course the manufacturer claims they use specially selected resistors to justify the price!
Brian.
--> read post#25You mentioned a series resistor, is it enough to place it in series with the headphones and what value?
Hi,
--> read post#25
Klaus
Your discrete amplifier in post #26 has a very low input impedance of only 1k ohms (because it is an inverting amplifier) that kills the audio level from the high impedance radio output and 10k volume control. If you use an input transistor with higher hFE like a BC549C (it also has low noise) then you can increase the values of the 1k and 680k resistors and reduce the loss of level.
Completely wrong.Excellent! This will also save me from having to buy another type of transistors, since my radio uses bc549C transistors as well.
Ok so I will replace the 2n2222 ones with bc549 and the 2n2907 with a bc559. Then I will increase the input resistor to 10k and the 680k to 6.8k?
How does it sound to you?
Completely wrong.
You need to change only the input transistor Q1 to a BC549C, not a BC549 because only the "C" has high hFE. The other two transistors are fine as a 2N2222 and a 2N2907.
Then increase the 1k resistor to 4.7k and increase the value of the 680k resistor to 2.2M. Then the input impedance will be 4.7k and the gain will be closer to 2.2M/4.7k= 468 times.
The 680k, 2.2M or 3.3M resistors are for negative feedback (gain) and for biasing. 680k provides a bias current to the first transistor of 5.6uA and a 2N2222 transistor in that circuit needs about 17uA so it was designed wrong and some 2N2222 transistors might work and many will not work. A BC549C transistor needs a bias current of about 3.3uA so the 2.2M is good and some BC549C transistors will work with 3.3M ohms and have a little more gain.
The output transistors are emitter-followers that have a voltage gain of 1 so changing the 2N2222 and 2N2907 to BCxxx will make no difference.
"Sometimes ear-splitting"? See, a real AM radio circuit has automatic volume control so that a weak distant station sounds as loud as a strong local station. Your simple regenerative circuit does not have it.
You ideally want to use RF AGC to optimize the receiver and have a peak limiter on the audio. The problem is that in a regenerative receiver it is difficult to derive a suitable signal for AGC and even if you were sucessful, applying it would change the operating parameters. For example, imagine your regeneration was set too low and the recovered AGC voltage was 20mV, you increase the regeneration to best point and the AGC rises to 50mV, you go a little too far (as for receiving CW/SSB) and the AGC suddenly jumps to 2,000mV because it is now based on the circuit working as an oscillator. The increased AGC kills all the preamplifier gain and probably (depending on the time constant) turns the whole receiver into an unstable, pulsed oscillator.
Brian.
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.Can a simple peak limiter be made on this audio circuit?
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