Annoying Question

[chrisaxeman]

I know Robert Keeley mods get brought up often,but this "stacked" chip mod in the SD1 that he is doing has me interested.

Is it actually a case of piggy backing the two chips,or is there more to it?

Anyone tried it?

I've done the "Fullclone" mods in my SD1,but was going to put an OPA2134 in,so while fiddling,I thought this might be interesting(the dual opamp bit) if I equipped the pcb with a removable IC socket.

Thanks in advance.

Chris....

[DougH]

There have been threads on here from a few years ago about "stacking" or "parallel" op amps. It's old news at this point, really. You may be able to find some info by searching the archives.

[Mark Hammer]

I've attempted some op-amp stacking, with mixed results, using NE5534 op-amps.  The gist of it is that the paralleled outputs produce a higher current output.  Now, what the impact of that higher output current might be would depend very much on the context.  For instance, in the Super-Buffer that Jack Orman has at AMZ, you see several op-amp stages paralleled to provide enough drive current for travelling over a very long cable without losing bandwidth.  You will also see paralleled invertor stages in some analog time-based effects that need to send a higher-current clock signal to counteract input capacitance from a BBD.

One should, in my estimation differentiate between running op-amps in parallel and the way in which that parallel operation is configured.  Dave Barber's original suggestion here was just to stack a pair of same-pinout opamps and solder/sweat the pins together.  In that usage, they are treated as if they were simply paralleled power transistors or tubes.  In Jack's Super Buffer ( http://www.muzique.com/lab/superbuff.htm ) the input pins of the multiple op-amps may be tied together, but the inverting pins and the utput pins are not.

[Minion]

One problem with Stacking opamp is the Outputs will not be equal(because of varying device charictoristics) so the outputs will be Fighting each other and one or both of the opamps can eventually die...In most Paralell configurations there is a Low value Resistor on each of the output pins which helps share the load evenly...so if you do this you may get better result....

Cheers

[Gus]

Keeley?

http://www.barberelectronics.com/parallelopamps.htm
http://www.diystompboxes.com/smfforum/index.php?topic=51862.0
http://www.diystompboxes.com/smfforum/index.php?topic=60569.0

All three links are from here
http://www.diystompboxes.com/wiki/index.php?title=Simplemods

[DougH]

Wow, time flies... I didn't realize this stuff came up here 5 years ago.

FWIW, Matchless did this sort of thing with the preamps in their guitar amps. They would parallel both halves of a dual triode to drive more current and increase SNR.

[chrisaxeman]

Thanks Guys'

Excuse the lack of search function-it's a big data base,especially when not sure what should be searched for(for 30-odd posts in a few tears,might be ademonstration that I use search often )

Cheers

Chris....

[DougH]

Forums can sometimes be difficult to search and don't necessarily make good archives. I think the wiki (at the top of the page) is a good place to look for reference info. It's kind of an "organized interface" into the data contained in the forum that makes finding information a little easier.