Borbely Class A question

astouffer · 22nd February 2010, 02:07 AM

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?

ticknpop · 03:09 AM

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

h_a · 22nd February 2010, 06:50 AM

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.

Have fun, Hannes

boholm · 22nd February 2010, 07:07 AM

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.

astouffer · 22nd February 2010, 07:38 PM

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)

Zen Mod · 22nd February 2010, 07:56 PM

somehow I have doubts that they asked Papa Borbely for permission - to make pcbs for his design

22nd February 2010, 02:45 AM	#2
ticknpop diyAudio Member Join Date: May 2005 Location: toronto	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.

22nd February 2010, 07:07 AM	#4
boholm diyAudio Member Join Date: Apr 2004 Location: Copenhagen	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. __________________ Best regards Bo

22nd February 2010, 07:56 PM	#6
Zen Mod diyAudio Member Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain	somehow I have doubts that they asked Papa Borbely for permission - to make pcbs for his design __________________ my Papa is smarter than your Nelson ! tnx to clean thread ; Cook Book ; PSM LS Cook Book ; Baby Diyaudio FORUM ; Mighty ZM's Bloggg;I'm dumb

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
FS-Borbely Class A mosfet	nicoch58	Swap Meet	8	29th September 2009 09:45 AM
Little Class D question	The Dragon	Class D	4	16th May 2007 09:01 PM
Another question about class A.	boxedin	Solid State	72	10th January 2006 11:58 PM
Question on PS for class AB vs class A	Duck-Twacy	Solid State	7	10th June 2004 10:44 PM
Borbely DC-50 Class-A 20watts	PassFan	Solid State	5	6th January 2002 11:59 PM


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

22nd February 2010, 06:50 AM	#3
h_a diyAudio Member Join Date: Sep 2006 Location: Graz, Austria	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. Have fun, Hannes

22nd February 2010, 07:38 PM	#5
astouffer diyAudio Member Join Date: Jun 2004 Location: Pittsburgh, crumbling wasteland	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)

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read