Tweakers' Asylum

Absolutely Not !!!

205.175.225.5

djk

In Reply to: RE: Update posted by bevo on October 26, 2007 at 16:00:53

Those guys don't have a clue.
Pin 4 of the original part is the + input, pin 3 is the - input, pin 6 is +35V. pin 1 is ground, pin 5 is the output.
Pins 3,5,10,12 at the + inputs, pins 2,6,9,13 are the - inputs, pins 1,7,8,14 are the outputs, pin 4 is +35V, pin 11 is ground.
Most opamps don't have the current to drive the outputs, this one does (with all four sections).
The diodes and resistor replace the bias circuit in the old chip.

http://www.national.com/images/pf/LM837/00904702.pdf (Open in New Window)

Edits: 10/26/07

Follow Ups:

Addendum - djk 17:47:34 10/26/07 (2)
Upon further thought, some more changes.

When adding the diodes (instead of R21), just use one with a 33 ohm resistor in series with it. Stand one lead of both the diode and resistor in the air and connect to each other. There are no emitter resistors on the outputs so we don�t want all the bias, a 1N4001 type diode will be fine here.

When hooking all the outputs of the LM837 together, use a 100 ohm resistor on each output of the opamp. Where all four resistors hook together now goes to the base of Q3.
- WOW, am I glad I asked again - bevo 18:06:57 10/26/07 (1)
  Okay, this makes a bit of sense since I did realize that the MFC has on-board biasing and the other did not. So on the LM, I bridge those pins into a single trace, right? So the same input will be fed into each of the 4 quads and the outputs of the quads feed into one as well, correct? Thanks again for all your time and effort in helping me out on this.
  - RE: WOW, am I glad I asked again - djk 18:46:27 10/26/07 (0)
    Yes, parallel all 4 inputs as shown, all 4 feedback pins as shown, and all 4 outputs (don't forget the resistors on their output pins).
    
    The 1.5K pull-down provides optimal class B bias, and forces the LM837 into class A at low levels.
    
    If you need new outputs I would consider the MJE15030/31 pair.

Post a Followup:

FAQ

Post a Message!

Forgot Password?

Moniker (Username):
Password (Optional):
	Remember my Moniker & Password (What's this?) Eat Me
E-Mail (Optional):
Subject:

Message:	(Posts are subject to Content Rules)

Optional Link URL:
Optional Link Title:
Optional Image URL:
Upload Image:
E-mail Replies:	Automagically notify you when someone responds.

To view your new posting or follow-up, click on the RELOAD or REFRESH button on your browser.

This post is made possible by the generous support of people like you and our sponsors:

The Cable Cooker