Mosfet

[audioguru]

If the output of this amplifier is shorted or has a load resistance too low then the gate-source voltage could become higher than the maximum allowed for the Mosfets. The zener diodes limit the maximum gate-source voltage to 9.1V.

 

[Pim Driessen]

Hello mr Audioguru,

I'm curious about your opinion on the RC filter, and the negative feedback capacitor.

First I made the counter-coupling capacitor of 47 pF.

Then the 1K5 resistance of the RC filter replacement at the entrance by two adjustment potentiometers 2K.

After that I value changes until I had a nice square wave at 1 KHz and 20 KHz.

I arrived at a resistance of 330 ohms, rather than 1K5.

Is this metode reasonably reliable for a good outcome ?.

Have attached two pictures of the square wave, 1 Khz and 20 Khz.

Sincerely,

Pim

 

[audioguru]

Why are you making a discrete preamp with hundreds of parts instead of using an opamp?
Why must the output voltage swing need to be so high?

 

[Pim Driessen]

Hello mr Audioguru,
The starting point for me is the highest possible quality, and that is not possible with an ic I think.
Have in the past tried but it was never comparable to a discreet built preamplifier.

The output voltage of an average CD player is around 1 volt, which is the reason that I with 1 volt input voltage test.

See also prefer the output of a tuner, or a turntable that light a little more at a lower level than the CD player.

Sincerely,

Pim

 

[audioguru]

There are many excellent audio opamps such as the OPA2134 dual that has distortion of only 0.00008% and very low noise. Audiophools think its distortion is too high! You might be able to hear 0.1% distortion on music if you have good hearing.
The last time I played my turntable was about 20 years ago and its high gain preamp uses a Japanese audio IC that sounds great.

Your preamp has a gain of 7.7 times so if its output of 7.7V feeds a power amp with a gain of 20 then the output power into an 8 ohm speaker is 3kW! If you use a piece of wire as a preamp then it has no distortion and the 1V output of a CD player into a power amp with a gain of 20 produces a reasonable 50W into 8 ohms.

Why does your preamp have such a high supply voltage?

 

[Pim Driessen]

Hallo mr Audioguru,

The gain goes down, is still in the test.
The high voltage is actually emerged after visiting AJ van den Hul 20 years ago, my preamplifier then had a supply voltage of +18 volts and - 18 volts, he advised me on increasing the supply voltage to 33 volts + and -, which I did and was very positive about the dynamic behavior of the preamplifier.
With the op amps I'm going to set up a test plate.

Greeting,

Pim