So your point is that the resistors are still too low and that it makes more sense to do experiments, such as trying different op-amps, after that is fixed? Sounds logical.
Thanks for digging up these data. Is there a typo in the capacitance column, should nF really be pF?
With 8.26 H, 107 nF and 15.9 kohm, the humbucker would be almost critically damped, be at about -5 dB around 169 Hz, be quite insensitive to cable capacitance and have an impedance maximum of just over 20 kohm.
With 8.26 H, 107 pF and 15.9 kohm, it would resonate around 5354 Hz and be quite sensitive to cable capacitance and amplifier input resistance.
What is "filter open"? Maximum bandwidth? Disconnected?
Yes, if the source is disconnected the hiss is high, and higher on '5532. You don't play that way.
Also: is that 'scope showing "RMS = 1.32V"? Hiss should be low milliVolts at that level, 1/1000th of signal, and not visible on a linear display. I wonder if you are seeing room-hash or even an unshielded prototype. LOW-hiss building is never shake-and-bake cookery.
Open means connected but no frequencies are cut off, all frequencies are passed through.
RMS is for the input signal (1)
By hiss/noise I mean the FFT (2). But I don't think that this noise really matters in every day use.
For this test I installed a 1M bias resistor.
There is an annoying noise on the output of the TDA7267, when powered with a regular 12 V wall wart power supply.
It looks like a 700 to 800 Hz frequency triangle wave.
When I remove C9 the noise is much quieter, but then the signal is distorted.
I also tried different cap sizes across the power rails. No difference.
Has anyone experienced similar noise issues?
Any help is appreciated.
It looks like a 700 to 800 Hz frequency triangle wave.
When I remove C9 the noise is much quieter, but then the signal is distorted.
I also tried different cap sizes across the power rails. No difference.
Has anyone experienced similar noise issues?
Any help is appreciated.
What do you mean by "the noise is much quieter", is there still a beep but a soft one, or do you only get random noise, that is, hiss?
In the second case, it could be that the capacitive load is too large for the power supply. You could then check what happens with a smaller value for C9.
In the second case, it could be that the capacitive load is too large for the power supply. You could then check what happens with a smaller value for C9.
Indeed, the power supply noise is different with other power adapters.
But first I want to get the input stage right.
And here I noticed a weird thing going on.
The setup is like this:
R1 and C2 form a low pass filter. But when R1 falls below a certain value (in this case ~16 ohm) the high frequencies get amplified.
When I set this up on the breadboard and turn R1 down the signal gets severely distorted.
Is this what is referred to as "oscillation" ?
Why is that?
Could someone please explain?
Thanks!
Even an OP07 can't drive 16 Ohms. 2,000 Ohms is a better bet. 16 is way past the end of the graph:
Is also a stability issue because OP07 output impedance is 60 Ohms so 16r to a large cap load is severely sucking-down the opamp. +
You also need a bias resistor on the input. SPICE may not complain but in real life it will work poorly if at all.