Adding low pass filter to Fortin 33 copy (high freq noise/hiss problem)

[rankot]

Ok guys I did some testing...

Connecting pin 1 to +V on TC1044 does nothing.

Best solution I foud is connecting pins 2-6 on TL071 using 1.5 nF cap, I wonder if using 2.2nF, 5nF, or even 10+nF cap will reduce this noice even further?

It will, but it will also reduce the bandwidth of your preamp! Anything above 100p will cut the highs. Try using LT1054 instead of LTC1044, of even better TC7660H (works at 120kHz).

And if using LT1054, in case you don't need too much current and can live with some loses, you can even push switching frequency further: https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/837081/lt1054-increase-lt1054-oscillator-frequency

[anotherjim]

Isn't Q1 collector signal inverted? So any noise on Vref gets differentially amplified across the opamp inputs instead of common-mode rejected?

[PRR]

> noise on Vref gets differentially amplified

Only if gains are matched. I see different gains, factor of 50 or more.

IAC, I think RF squeal due to builder layout is far more likely than a design mistake.

[m4268588]

It seems that fixed VREF is not necessarily good.

Modified@2022-01-03: This simulation is incorrect.

Please try as many things you can undo it.

[m4268588]

[amptramp]

Is it that much of a hassle to run the unit off three 9-volt batteries in series?  They would last longer due to elimination of the inefficiencies of the charge pump and at a fixed voltage output, if the voltage in is reduced (to 9 volts), the current has to increase, so battery drain is a problem.  If you are operating off a wall wart supply, I have 24 VDC wall warts that I am using on a test setup for antique battery radios.  Open circuit, they are good for 32 volts.  Like others have said, eliminating the cause of the problem is better than trying to fix the problem later.

[iainpunk]

yesh, i'd either go for a better wall wart/power supply of a stack of batteries, for the higher voltage, instead of a charge pump.

i use an 19.1v laptop charger for an overdrive/distortion i build a few years ago, i just really wanted that headroom. (free interpretation of the Centaur) it worked fine, no whine, no hiss, no intermittent switching.

also, do you need to run it on the higher voltage? iirc it runs quite well with only 9v.

cheers

[m4268588]

I hate charge pump.
I don't use charge pumps because I don't see the point in raising the noise floor in exchange for headroom, ...and
they sound bad (not that I'm trying to get others to agree).

But still, I have to point out the errata of VCC.

If trust this schematic