Best IC replacement for 709c? For use in a Quantum QM8

FollowFarnsworth · Post by **FollowFarnsworth** » Sun Dec 28, 2014 5:27 pm

Best replacement for 709c opamp? Quantum Audio Labs
Hey guys,
I have an early Quantum Audio QM-8 with 709c op amps. I have the full manual and schematics. I was wondering if I should replace them or what I could use to replace them. Could I replace them with a discrete opamp?

The Real MC · Post by **The Real MC** » Sun Dec 28, 2014 10:02 pm

Pretty much any modern opamp will work fine, just make sure you remove any frequency compensating caps on pins 1, 5, and 8. The TL07x is a popular opamp used in many audio gear.

The Scum · Post by **The Scum** » Sun Dec 28, 2014 10:11 pm

Are they 8 or 14 pin 709s?

Back in the day, the 741 was an upgrade for the 709.

If you're clever & persistent enough, you can replace almost any opamp with any other opamp, discrete or otherwise. You might learn an awful lot about 'lectronics in the process. Have you ever designed a PCB?

MC is correct, the 709 has some historic baggage in the frequency compensation pins that almost no other opamp has. You'd be wall advised to remove it before subbing anything else in. Be perticularly careful if you sub in tl071's, because they use the same pins for different purposes.

So what happened to the ADM?

FollowFarnsworth · Post by **FollowFarnsworth** » Mon Dec 29, 2014 4:16 am

Thanks guys!

I still have the ADM and am weighing my options. I just don't know which one to peruse.

FollowFarnsworth · Post by **FollowFarnsworth** » Mon Dec 29, 2014 4:16 am

Thanks guys!

I still have the ADM and am weighing my options. I just don't know which one to peruse.

Sean Sullivan · Post by **Sean Sullivan** » Mon Dec 29, 2014 7:00 am

I remember seeing a post awhile back where Jim Williams reworked a QM8. I think he's rates are very reasonable, considering all the headaches that can arise when modifying equipment. You may want to call him and get him to do a channel and maybe the center section and see how you like it.

Jim Williams · Post by **Jim Williams** » Mon Dec 29, 2014 8:16 am

14 pin 709's have the correct 8 pin DIP opamp layouts on the inside pins. Use a machine socket.

I diconnect the pad switch and add a 10k reverse log pot for a 20~60 db variable mic preamp gain control. The switch becomes phantom power (requiring a power supply for that).

FollowFarnsworth · Post by **FollowFarnsworth** » Mon Dec 29, 2014 9:31 am

Thanks for your reply Jim!
These 709c opamps are in the T05 can format.

Jim Williams · Post by **Jim Williams** » Tue Dec 30, 2014 7:52 am

Use either an adaptor or use machined wire wrap 8 pin DIP socket with the leads bent into a circle. I cut off pin's 1, 5 and 8, don't need those.

LME49710 is a good replacement.

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Best IC replacement for 709c? For use in a Quantum QM8

Best IC replacement for 709c? For use in a Quantum QM8

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