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Old 14th December 2003, 05:25 AM   #1
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Default Current feedback amp, pcb files included

Howdy guys,

I have put the protel pcb layout files up on my ftp site of the current feedback amps I use. I have also included a schematic, but it is hand draw sorry. Between the schematics and pcb files I think everything is labeled. Sorry for the quality of the hand drawn schematic.

Feel free to use as you wish. Few things, watch the grounding, make sure you use star grounding when ever you can. The transistors mentioned are not too easy to obtain somethimes, I have no ideas for substitutions, but anything similar will work. All the small transistors are either NEC or Toshiba, with output transistors being Sankens.


With a 4.7pf cap in the position of the 10pf cap, it will oscillate very slightly when cold at turn on, but will settle down to work perfectly after a 5 minute warm up. Running it on the edge of stability sounds best to my ears. If you are not confident, I have used the adjustable trimmer caps in the 10pf and 39pf positions. a 50pf trimmer or similar. When happy with value, shove in a cap of choice. I like silver micas, from RS Components.


An cro is strongly reccomended for this project. The amp is a blend of Analog Devices' current feedback ideas, and of Sony's TA-N1 current feedback amp. It exhibits super low distortion that doesn't rise with frequency like tranditional solid state amps, and a frequency response to 900khz, if allowed to oscillate you will upset more then a few radios. Even with an amp this fast, hard bias into class A still sounds the best.


I have not heard a better amp then this one so far. I have built many amps from these protel pcb files, only difference is I don't use the power supply regulators, I prefer just a emmitter follower with a LED array generated voltage reference, bypassed by lots of caps. Think the amp is faster then the power supplies that are laided out here.


The servo loop should me used with a higher value then 2M2 resistor, otherwise the phase rotation from the servo amp will cause the bass to be less then strong. Suggest something like 20megs. Replacing the 0.1uf cap for a bipolar is not reccomended, as leakage from the cap and distortion will do more harm then good.


Feel free to email me with any questions, hope this is a good starting point for people. If you don't use protel, but PADS or similar, email me and I will export you a copy if I can.

Mark Hathaway


current feedback amp Protel 99se pcb files

current feedback amp protel DXP file

current feedback schematic
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Old 14th December 2003, 06:42 AM   #2
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