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Old 18th June 2015, 03:25 AM   #1
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Default erno borbely super shunt regulator

I purchased 320 Phono and EB906/255 super shunt regulator from Erno Borbely a few years ago. Last year, I changed the regulator to Dexa and put aside the 255. Recently, I wish to use it again for another diy kit but I could not find the 255 circuit diagram again. The new diy kit uses only 20mA that the current setting at 240mA would make the power transistor red hot.

I remember there is a formula to calculate the resistor value but I can't find it. Can anyone give me the formula, or the value for 30mA or Erno's email addres (I wonder if he still reply email today).
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Old 18th June 2015, 03:57 AM   #2
GaryB is offline GaryB  United States
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You can find a schematic for the EB906/255 on the old Borbely Audio website. That website is no longer online but you can find it either in the web archive or you can download a copy of the website from Zenmod's website Zen Mod Blog | Buddha is everywhere …….

Once you find a copy of the old Borbely website, look under the "Special Articles" section for the article by Are Waagb on Shunt Regulators.

Resistors R1 and R2 set the total current available to the load and to the shunts. The total current is roughly -.6v/R1. So if you are sourcing about 240ma then R1 should be around 2.5 ohms. Raising R1 to 15 ohms would set the total current available to 40ma which should be fine for a 20ma load.
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File Type: jpg LOW_CURRENT_SHUNT_REG.jpg (139.6 KB, 251 views)

Last edited by GaryB; 18th June 2015 at 04:14 AM.
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Old 18th June 2015, 03:04 PM   #3
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Thank you very much.
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Old 18th June 2015, 05:52 PM   #4
CBS240 is offline CBS240  United States
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I like the circuit very much but those complementary matched J-fets......hard to come by these days. I'd probably have to change the Zener voltage reference with lower noise CCS/resistor.
All the trouble I've ever been in started out as fun......
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Old 18th June 2015, 10:10 PM   #5
mlloyd1 is offline mlloyd1  United States
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you're definitely right about the jfet pain, cbs240
for this circuit, i would cheat and make 2 positive regs with separate transformer windings, separate rectifiers and caps.

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Old 19th June 2015, 10:00 AM   #6
AndrewT is offline AndrewT  Scotland
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The low gm cascodes Q7, 8, 9 & 10 are still available in P & N channel.
The high gm Q6a & Q6b will be the difficult to source Pchannel.
Even the dual Nchannel high gm (Q5a&b) will be rare and probably expensive.
make 2 positive regs
will at least ease the component sourcing.
regards Andrew T.
Sent from my desktop computer using a keyboard

Last edited by AndrewT; 19th June 2015 at 10:03 AM.
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