I assume you are not expecting it to be louder than it should because any radio can distort when the input signal is too high.
I'm expecting it to be louder
when operated on cassettes (it uses a separate preamp, with one IC and one transistor) , not the radio of course, on radio it's overdriving the speaker
I would use a similar method of sound injection and sampling with a high impedance pre-amp and speaker or headset if I did not have a scope, to zero in on the faulty node..
So you say to use a high impedance input, (oscilloscope is perfect for this), like some old headphones or a separate high impedance amplifier.
Unfortunately, I only have some generic pc headphones (they have an impedance of ~30ohms).
I don't think I have some high impedance amps, only amps from radio receivers and car amplifiers.
I think I can make one using some audio transformers and some driving circuitry?
As a side note, I measured some components in the preamp stage, they all look good:
To clarify some things:
The problem of this radio is that at volumes over 15%, it begins to distort the audio, at 50% its very bad, the speaker has so much base present that it just makes aggressive back and forth moves (like a trampouline), and extremely high volume. (on AM and on FM)
If I hook audio at its input, it amplifies very good the audio (and loud), but if I increase
a lot the audio input, the amplifier makes the exact same distortion as above.
If I hook the audio present at its input to another amplifier, it does the exact same distortion at high volumes...
When playing cassettes it doesn't distort the sound, only the head needs cleaning (along with pinch rollers etc)
So either the amplifier is not working as it should, overdriving, with the audio present at its input (which I don't believe, because, with 3-4mv at its input, it is outputting 900mv, as it should) either the signal present at its input is too high, overdriving any amplifier.
If I attenuate the input signal with a potentiometer, will it do something?
I'll go tomorrow to see if there are any oscilloscopes left in an old deposit.
Many thanks
Sunnysky and
73's de Edd !!