No there is no whistles. Something I forgot to mention:
- I used LM358 as a pre-amplifier, is it possible that this what makes the sound so noisy?
- Somewhere else, I read that the 20khm: and 50khm: variable resistors have to be one linear and the other audio (may be logarithmic). My question how can I differentiate.
- For the above variable resistors i used similar type and value (50khm: )
The lousy old LM358 is half an old LM324 quad opamp.
They are the first low-power opamps.
Their low current causes noise and crossover distortion.
Their output cannot swing at high level above only 5kHz.
I use TL071 single, TL072 dual and TL074 quad low noise, low distortion and wideband (100kHz) opamps for audio.
The lousy old LM358 is half an old LM324 quad opamp.
They are the first low-power opamps.
Their low current causes noise and crossover distortion.
Their output cannot swing at high level above only 5kHz.
I use TL071 single, TL072 dual and TL074 quad low noise, low distortion and wideband (100kHz) opamps for audio.
The pins numbers are exactly the same.
Use a lousy old LM358 if you want want hiss and crossover distortion, or use a low noise TL072 if you want high quality. I think they cost the same, peanuts.
You forgot to post the schematic of your preamp so we can't see if the opamps are biased correctly for a TL072 to be used. A TL072 doesn't need a negative supply if its inputs are biased at half the supply voltage and coupling capacitors are used.
The minimum recommended supply voltage for the TL072 is 7V.
The TL071 is a single opamp, the TL072 is a dual and the TL074 is a quad.
The pins numbers are exactly the same.
Use a lousy old LM358 if you want want hiss and crossover distortion, or use a low noise TL072 if you want high quality. I think they cost the same, peanuts.