Diy preamp for Amplifier IRFP240/IRFP9240

[mprivitera1]

Most likely some grounding issues. Are you powering it with regulated power suuply?

..use this power supply schematic for the Buffer and Preamp ...

 

[mosfet54]

your grounds must be collected into one big point 😱

offtopic -> satellite ->

(one ground)

 

[minek123]

..use this power supply schematic for the Buffer and Preamp ...

For a pre-amp I would suggest using good quality regulated PSU, preferably shunt PSU.
Example: http://www.diyaudio.com/forums/power-supplies/286425-shunt-regulator-15v.html

With preamp with non regulated PSU you are always going to have some hum..
If it's excessive hum, grounding/shielding of signal cables may also be a factor.

 

[mprivitera1]

For a pre-amp I would suggest using good quality regulated PSU, preferably shunt PSU.
Example: http://www.diyaudio.com/forums/power-supplies/286425-shunt-regulator-15v.html

With preamp with non regulated PSU you are always going to have some hum..
If it's excessive hum, grounding/shielding of signal cables may also be a factor.

ok ... thanks for advice

 

[minek123]

ok ... thanks for advice

Here is another good regulator, and it's +-24V, just like you need:

http://www.diyaudio.com/forums/power-supplies/164365-class-preamp-psu.html

 

[mprivitera1]

Here is another good regulator, and it's +-24V, just like you need:

http://www.diyaudio.com/forums/power-supplies/164365-class-preamp-psu.html

Yes, right

 

[mprivitera1]

Here is another good regulator, and it's +-24V, just like you need:

http://www.diyaudio.com/forums/power-supplies/164365-class-preamp-psu.html

PSU excellent , the best APEX ... but there is a simpler?

 

[mprivitera1]

Exactly - you need to lower the output impedance.
Here is a top quality buffer for your purpose.

Cheers,
Valery

you think ... it can be used as a preamp by connecting a potentiometer ?

 

[minek123]

PSU excellent , the best APEX ... but there is a simpler?

The simplest, and still good enough would be one zener + one transistor
regulator. or maybe 2 transistors (darlington).
See:
Transistor-Zener Diode Regulator Circuits

Or even simpler - use LM7824 chip (for positive rail) + corresponding negative IC for negative rail.

 

[minek123]

you think ... it can be used as a preamp by connecting a potentiometer ?

I would assume you can put volume pot between your buffer, and the pre-amp.

 

[mprivitera1]

The simplest, and still good enough would be one zener + one transistor
regulator. or maybe 2 transistors (darlington).
See:
Transistor-Zener Diode Regulator Circuits

Or even simpler - use LM7824 chip (for positive rail) + corresponding negative IC for negative rail.

yes....it is simpler

 

[mprivitera1]

I would assume you can put volume pot between your buffer, and the pre-amp.

because the volume pot between the buffer and preamp?

 

[vzaichenko]

because the volume pot between the buffer and preamp?

Yes, makes sense. I would recommend a 100k pot for the best performance. Input impedance of the buffer is 850 KOhm within at least 300KHz bandwidth.