Stacking OP amps?

[kramer5150]

can it be done... in a cmoy?
Ive been getting conflicting information.

Thanks,
Garrett

 

[MisterX]

No.
You need resistors to balance the output currents or the opamps will fight with each other until one or both of them smokes

 

[kramer5150]

thanks

 

[ozshadow]

I tried it, sounded worse. It won't give you an A47.

 

[mono]

Yes you can do it, sort-of.

When stacking them, you don't directly solder adjacent pins together, essentially you'll be air-wiring on some resistors as in the A47 schematic. I can't find the one I did at the moment but if memory serves correct, I bent some pins sideways for the air-wiring, snipped off the excess, and the two were put into a socket (as part of the stack), which THEN plugged into the 2nd opamp socket (on the CMOY). Unfortunately even if I find it I can't post revealing pics as after I air-wired the resistors on I slapped some epoxy on the area to secure it, so it ended up just looking like two opamps stacked in a socket plus epoxy.

 

[kramer5150]

Quote:

Originally Posted by mono Yes you can do it, sort-of. When stacking them, you don't directly solder adjacent pins together, essentially you'll be air-wiring on some resistors as in the A47 schematic. I can't find the one I did at the moment but if memory serves correct, I bent some pins sideways for the air-wiring, snipped off the excess, and the two were put into a socket (as part of the stack), which THEN plugged into the 2nd opamp socket (on the CMOY). Unfortunately even if I find it I can't post revealing pics as after I air-wired the resistors on I slapped some epoxy on the area to secure it, so it ended up just looking like two opamps stacked in a socket plus epoxy.

Is it even worth the effort??

That doesn't sound too hard, with SMT resistors being as small as they are. At least physically. Sonic perfection however is a whole nother' world.

Garrett

 

[mono]

Quote:

Originally Posted by kramer5150 Is it even worth the effort?? That doesn't sound too hard, with SMT resistors being as small as they are. At least physically. Sonic perfection however is a whole nother' world. Garrett

That's a loaded question. I don't think an A47 is worth it in general, unless the target is the cheapest way to get some voltage gain while running off an unregulated wall wart (which is of course to be avoided, but IF those were the criteria then the buffered ground gets rid of quite a bit of line hum. That is A47's forte, IMO. Then again, I don't think CMOY is worth it as a final amp rather than a beginning exercise before moving on to better things. It is a good teaching tool, IOW.

Even so, someone looking at a CMOY and wanting just a little more current, sure, it'll do that. I made mine because I felt it not a fair comparison to judge CMOY's one opamp vs a different amp, in isolating the benefit of dual/dual opamps it needed to plug into same amp.

SMT is not easier, you'd end up soldering leads to the SMT, ending up with an even cruder version of a leaded resistor. Look at the A47 schematic to see what needs be done, it's pretty straightforward, just bending out at 90' any pins not allowed to connect to the corresponding pin on the opamp socket-as-carrier. Trimming them off later is only a matter of compacting the stack so it looks better and fits closer to other parts beside the amp's opamp socket.

 

[Andrea]

I'd much rather use a high current op-amp (AD8655/6, OPA551/2, LM6171/2, LT1363/4, AD8397, AD45048 ...). I think that this alone can transform a cmoy (but with a TLE rail splitter at least) into something far more 'fit' & satisfying.

 

[JahJahBinks]

or adding a current buffer

 

[mono]

Quote:

Originally Posted by Andrea I'd much rather use a high current op-amp (AD8655/6, OPA551/2, LM6171/2, LT1363/4, AD8397, AD45048 ...). I think that this alone can transform a cmoy (but with a TLE rail splitter at least) into something far more 'fit' & satisfying.

Agreed, I'd use different opamp or buffer to get more current, but considering the typical CMOY build instead of one slighly more elaborate on a custom board, these better (for the purpose) opamps may not be stable.