Buffer with Dual N-Ch Jfets and Dual Power Supply

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
The ,215 parts come on a reel of 3,000. The ,235 parts come on a reel of 10,000. If you are producing large numbers of final product, you may find that ordering a reel of 10K gives you different statistics for part-to-part variation than three or four reels of 3,000. If you are buying a couple of dozen for your personal projects, I suspect the difference is irrelevant.
 
Member
Joined 2000
Paid Member
I wimped out and only picked up 25 qty BF861 and 25 qty J113. Also 50 SOT-23 to SIP adapters. Still have a bunch of 2SK170 ranging from 3mA to over 20mA Idss.

Soekris DAC's output is off the R2R array and said to be 1.2V. Can a buffer be made with 15v rails that will produce at least that much output from the buffer?
B1 does it with +19v, so I'm guessing +/-15v rails can achieve at least 1.2v output.
 
Member
Joined 2000
Paid Member
Getting better results with BF861b jfets.
By that I mean I have 2sk170 b grade jfets that potentially match up with bf861b.
 

Attachments

  • bf861B_idss_01.jpg
    bf861B_idss_01.jpg
    392.7 KB · Views: 337
Member
Joined 2000
Paid Member
Built the buffer from figure C. Used 2sk170 with 9.76 idss on top and a BF861 with 9.64 idss on the bottom. Offset is 63mV.
Ran audio through the buffer to an amp and speakers, and then shut off the buffer and audio stopped. It works! Had this thought that the signal might somehow bleed thru to the amp, but it didn't. :D
 

Attachments

  • Buffer_sk170_bf861.jpg
    Buffer_sk170_bf861.jpg
    482.3 KB · Views: 278
Member
Joined 2000
Paid Member
No cap. I let the circuit run for 1 hour.
Thought someone said a cap on the output would degrade a simple circuit like this?

I have the higher idss j113, but they are in the 20mA range. The bf861-b are pretty much 6mA to 10mA range, for the 15 pieces I tested. I might have 2sk170s that are 15mA or more. Part of the fun is using jfets that are available for not a lot of money. :)

For the dropping resistor, are there any other considerations besides simple ohms law?

I'll check out the links. Thx.
 
Official Court Jester
Joined 2003
Paid Member
will cap degrade or not is one issue , while completely other issue is output DC offset, of much greater importance to solve , even with cap if there is no other way

do what Patrick wrote - choose adquate specimens for CCS , then introduce source pot to set Iq , thus output offset

it must be close to 0 , except when you deliberately are choosing different voltage level , but even then you must make it in a way that it's settable
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.