All Jfet Buffer Balance Line Amp
October 20, 2009 - filed under: Other Amplifiers
This is also Borbely Erno Design Jfet Buffer and I use this to make my pre-amp. I use two low noise regulator and 4 buffer module to become a full balance pre-amp. The sound is very good and distortion is also very low. I have tried to use a transistor second stage but the sound become aggressive and harsh. Thus all Jfet is my choice!
Jfet regulator Circuit *updated on Dec 23, 2009*
Jfet Buffer PCB Errors *updated on Jan 15, 2010*
FFT jfet buffer xlr log at 10V
Update on Oct 20: After redo a bit on the wiring of power supply and put a NTC from star ground to the casing, the distortion has improved to below 0.0001% at 10Vrms output balance mode. Distortion is also very low at 0.0026% at 1Vrms output. The good thing about this pre-amp is that the higher the output level, the lower distortion it will be.
Some FFT measurement after improvement:
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All Jfet Line Amp with NO FEEDBACK
October 19, 2009 - filed under: Other Amplifiers
This is a Borbely Erno design SE all jfet line amp in one of his article. I have been using this as a pre-amp since 2006 with Pass power amplifiers like Aleph 60, F4 & F5. The gain of this pre-amp is quite high and thus it can be used to drive F4 to sufficient loudness.
The distortion level is also very low at around 0.003% at 1V and 0.026% at 4V output at balance mode. I am only using +28V dc due to transformer only at 25V x 2 AC.
This pre-amp sound very smooth due to no global negative feedback! But you see the distortion will increase quite fast as the output level increase!
Last update: 20th Sept, 2010: This is the pre-amp that I am still using at this moment as I like the sound of NO Feedback!!
Borbely Erno All JFET SE line amp Details Updated Sept 21, 2010
Was completed 2006/9/16, update FFT measurement on Oct 19, 2009.
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All Jfet Buffer SE Line Amp
October 16, 2009 - filed under: Other Amplifiers
This preamp is same as the All Jfet Buffer Line Amp except it is only for Single Ended input and output (RCA input/output sockets). An old Alps volume ( 100K type A) is used at the input instead of step attenuator.
From the picture, you can see there is one single 25V x 2 30VA transformer and two Borbely low noise regulators and two buffer modules are used. It is very simple but it sound also wonderful when driving a F5.
The FFT measurement show that the hum noise is very small and also distortion is very good at 0.0035% at 1Vrms output level. At 10Vrms output, the distortion rises to about 0.009%. Hum and noise is at about 1.2mVrms at maximum volume.
FFT output at 1V, 12k load lin
FFT output at 1V, 12k load log