Source follower thermal cycling?

wildswan · 25th October 2009, 08:16 PM

Hi,
I'm using the simple source follower below as a output driver for a tube preamp, but the output voltage seems to be wandering up and down a few volts (With a load of 50k or so)

Now it seems that this might be caused by thermal cycling (the fets and resistors are a couple of centimeters apart....but it seems very severe for a follower!

So far I've tried lowering the gate-souce resistor to 100k and put in new fets, but nothing changes. I was expecting some offset but the wandering bias is surprising me........Can't seem to find any thermal data on ss jfets.

Very confused

Has anyone had this problem before?

peranders · 25th October 2009, 08:37 PM

R3 should be connected to signal ground.

wildswan · 26th October 2009, 02:39 PM

Thanks Peranders!

Pretty dumb when I think about it :-) Of course any offset will produce offset at the gate too!

Down to about 10mV or so for the record now, using 2sk369

25th October 2009, 08:37 PM	#2
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	R3 should be connected to signal ground. __________________ /Per-Anders (my first name) or P-A as my friends call me

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
Some other Source Follower COnfigurations	EUVL	Pass Labs	375	20th January 2012 11:35 AM
Source follower and common source output stages	slogan2112	Pass Labs	2	9th October 2008 08:19 PM
Aleph-type current source, but source follower this time	tschrama	Pass Labs	4	29th July 2005 12:55 PM
cheapest source of heatsink/thermal pads?	DonoMan	Solid State	7	16th July 2005 08:50 AM
Source follower electret mike -> use with current source?	capslock	Solid State	1	28th February 2003 12:54 PM

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


	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

26th October 2009, 02:39 PM	#3
wildswan diyAudio Member Join Date: May 2006	Thanks Peranders! Pretty dumb when I think about it :-) Of course any offset will produce offset at the gate too! Down to about 10mV or so for the record now, using 2sk369

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)