Source for LM709?

Hi All,

I've just started teching at a studio in town that's got a 20 channel Electrodyne board. Primarily 709 channels, but 4 of them are 711s.  We've also got 6 limiters that use the A-1000. Surplus of A-1000s is nonexistant and I'm looking into the feasability of manufacturing some myself.

If it's going to be a pain to acquire some I may just work on designing around a different op amp, but I think it would be nice to keep it original. Maybe there are old pieces of gear that have a bunch in them that are available really cheap these days that I could scavenge?

Hi,



    http://www.cricklewoodelectronics.com/Cricklewood/search.php?mode=search&page=1




  kindest regards,





        ANdyP

and LM711




  http://www.cricklewoodelectronics.com/Cricklewood/search.php?mode=search&page=1

Cool, thanks. If nothing else I might go through them. Anyone know of a similar place in the US? I'll see what google turns up for me...

Seems like there's plenty of these hard to find component sites on the web. Thanks, I'll check some out.

Are your lm709's in a dip-14 package? I may have a few - I'm sure I lost some when I took them out of my Auditronics console. How many are looking to get?
This is from Larry Devivo's "The History of Electrodyne Quad-Eight and Sphere"

It turned out John was one of the designers of the discrete op amp used in the early Electrodyne modules.  As John tells it, “The 709 was an IC designed by Bob Wiler at Fairchild and used in the original Electrodyne 709 module.  We redesigned it as a discrete monolithic op amp [with much better performance specs] and that’s what we used in the early Electrodyne 709 (line amp module), 710, 711 and 712 mic/line/EQ modules.

Click to expand...

The lm709 can be replaced with a 5534 style opamp with some minor changes to the surrounding circuitry. The 5534 footprint fits inside the lm709 footprint. I have some documentation from Auditronics detailing the replacement procedure. It just involves removing the compensation circuitry and adding a cap in parallel with the feedback resistor to limit bandwidth (and thereby prevent oscillations). 
Best, Ben

Well I have one A-1000 that wasn't fully potted. The 709 inside is the H version (round can). 7pins I think?

I'd be looking for 10-20.

What values of feedback components does your documentation specify? I was thinking about just subbing another opamp here, but I thought I'd try seeing if I can get any 709s and keep the circuit original.

-Best, Ben

+1

If ever an opamp screamed out for a modern substituion, the 709 needs to be replaced (with all due respect of course).

JR

Cool, thanks.

That's interesting that the A-1000 contains an lm709...
Best, Ben

It's a 709 followed by a set of push pull transistors. The A-2000 (in the 711 modules we have) is a discrete op amp.

> If ever an opamp screamed out for a modern substituion, the 709 needs to be replaced (with all due respect of course).

I started on 709, appreciated the virtues of newer chips, but respect is due.

Flaws:
Totally NOT short-proof.
Teeny devices mean high OSI.
Semi-nasty underbiased output stage.

Virtues:
If you can under-compensate, it potentially has more gain-bandwidth than any common chip made over the next 2 decades.
Taking output single-ended (as in the buffers above) moots the output underbias and leaves a neat simple signal path.

It's a flint knife against steel blades. A good flint-knife butcher can reduce a buffalo as fast as a guy with a new-tech steel knife. It just works different.

I'm glad to see the factory-approved 5534 mod. It is not a downgrade, and won't offend any ear.

> Maybe there are old pieces of gear that have a bunch in them that are available really cheap

I'm sure there must be some geomagnetic telemeter that had a dozen, and got surplused-off for the value of the case. In the 1970s I used to see such boards (and passed them by). Good luck getting so lucky.

I know RCA sold a large radio console, with IIRC 10 or 11 709s in the whole thing. They were fairly expensive in their day, not sprayed-on like modern chips.

We have been making new A1000 opamps for almost 10 years (Since we took over Electrodyne and its subsidiaries) and have limited inventory of NOS 709 DIP8 as well as TO99 741.
Please let us know what we can be of assistance with.

Thank you,

Ken Hirsch / Director of Engineering
Orphan Audio LLC www.orphanaudio.com
Quad-Eight Electronics LLC www.quadeightelectronics.com
Electrodyne Audio www.electrodyneaudio.com (a division of Orphan Audio LLC)
email: [email protected]
mobile/text: 818 632-2496

"Education is the cure for everything"