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Old 22nd February 2010, 02:07 AM   #1
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Default Borbely Class A question

Ok I'm getting parts together to build this amp but there is one thing I'm not sure about. D5 and D6 say LM336 which seems to come in two flavors, 2.5 and 5 volts. So which one is correct?
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Old 22nd February 2010, 02:45 AM   #2
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It doesn't look like a real Borbely, op amp should be jfet, and would have 2sk216 and 2 sj79 drivers after the VAS, changed input and VAS devices and several other changes. It looks like cross between one of his line amps and one of his power amps................................... Erno now uses blue LED for cascode voltage reference for jfet/jfet cascode - Erno's power amp VAS use jfet/mosfet cascode with higher cascode reference voltage because of using the mosfet for higher power / voltage handling-

the jfet /jfet cascode should be ok for 24 volt rails

Last edited by ticknpop; 22nd February 2010 at 03:09 AM.
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Old 22nd February 2010, 06:50 AM   #3
h_a is offline h_a  Europe
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I'm not really familiar with this VAS, but it seems to me 2.5V allow larger voltage swing and 5V are maybe a little bit more linear. I would try 2.5V first.

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Old 22nd February 2010, 07:07 AM   #4
boholm is offline boholm  Denmark
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The principle is described here:

http://www.essex.ac.uk/csee/research...%20cascode.pdf

Due to the low voltage of 25 volts and not having a separate PSU for the pre-stages, 2,5 volts seem to be the right choice. 5 volts will result in lower output voltage, as h_a states.
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Old 22nd February 2010, 07:38 PM   #5
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Thanks everyone. Guess the title should have said "based on Borbely". I just ordered parts last night and only gave it a thought afterward. Of course I picked the 5v version but oh well. Here is a link to where the boards came from.

DC All FET Cascode class A amplifier PCB Borbely ! - eBay (item 220494425166 end time Mar-11-10 23:46:13 PST)
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Old 22nd February 2010, 07:56 PM   #6
Zen Mod is offline Zen Mod  Serbia
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somehow I have doubts that they asked Papa Borbely for permission - to make pcbs for his design
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