freestompboxes.org

Keeley is a great guy, not shy of sharing some trick with the public. That's great, but had some déjà vus when reading his site:

Boss Stacked SD-1 with Diode Switch

Description
New as of August 2007--we're introducing a new feature now included in our SD1. We're now stacking two TI4558P chips. These two TI chips work in parallel, mounted on top of each other and soldered together. Many hi-fi stereo enthusiasts enjoy this technique for noise reduction (read The Art of Electronics for some really technical data!) and it’s been done in a couple of other boutique effects too. The same Keeley SD1 tone is still there, now with noticeably BETTER DISTORTION, LESS NOISE, ARTICULATION and TRANSPARENCY! This tone is so good we've decided to stop including the Burr Brown chip. (Don’t feel like you’ve missed out; this new version and technique is truly better sounding in the SD-1.)

Yes found it! Here:

bajaman

Replies: 13
Views: 406
PostForum: Boutique Stompboxes dissected... Posted: 12 Aug 2007 01:51 am Subject: Way Huge - Green Rhino
Hi Dirk
Op amps are strange things Wink
OPA2134
LM1458
TL072
NE5532
LF442
LM833
JRC4558
LF353N
all sound different in the same circuit - use a socket and try - you WILL hear the difference.

Then try "stacking" them - my personal favourite is an OPA2134/LM1458/LM833 stack.
One disadvantage - they draw more current - so if you are using battery, it will not last as long Wink
Cheers
bajaman

Just thought to give this idea some more circulation, maybe somebody would like to experiment. I had a hard time stacking something on my DS-1 7pin opamp, but will have to try it soon.

modman

thanks bajaman, for daily inspiration days after even

credit where it is due - I believe it was the Barber site that first mentioned the idea of stacking op amps

I had to laugh at Keeley's bullshit though - those two TI4558 ICs cost a lot less (about a quarter of the price ) than the Burr Brown OPA2134 IC he was referring to, and that he was previously using mojo = more money
bajaman

I like the idea of this, yet another way to find interesting tones.

Has anyone stacked two LF353 op amps? I'm wondering what that would sound like but I only have one at the moment

I killed one stack because of overheating it seemed. Second attempt went better and I was as smart to assemble the IC stack outside of the socket. But then you have to be careful that the lower pins are cleared so they can be socketed.

Any practical hints, Baja?

Any practical hints .....

Yes, simply forget this mojo-sh*t.... if you want to parallel opamps you need at least summing (current-limit) resistors (e.g. 470 Ohm) at the output(s)....

analogguru

yes and you can stack many of them,,,, I remember when this came up years ago it was either barber or Orman that stacked 7 or 8 of them , just to be silly drilled a whole in the box for them to poke out like a Muscle Car air scoop .....


and you can have some fun photographing them as mating spiders....

And you won't play any better at the end of it!

A question: (for when designing/planning a build)

Wouldn't it be the same as if you parallel two opamps from a package, i.e. two opamps from the tl072? So no "soldering from the top" ?

Any opinion on that? Wouldn't it be technically the same?

Any opinion on that? Wouldn't it be technically the same?

yes - it will work, but the best sounds are found by stacking disimilar op amps - for example - try stacking an LM1458 and a TL072 and listen to what you get
bajaman

What about the "noise reduction" aspect? Would f.e. "paralleling" two TL062 lower the noise in an onboard guitar circuit versus a single TL061? Afaik the price is basically the same for a 061 and a 062 ... bateries would last half, that's for sure, but longer than with a single "non-parallel" TL071, right?

The most widely mentioned technique for sound improvement was a pulldown "class a" resistor afaik, what would happen in such case: for "parallel" opamps there should be half-value pulldown resistors, right?

Battery sales would go up for sure ...



Edit: otoh, I was somehow planning to play around with the "4049" distortion circuit. Would that work if "paralleling" the unused inverters with the ones that do the work? Would that be possible or will be there some smoke-signals? Offtopic, but somewhat similar.

Stacking opamps work but the input impedance is much lower, resulting in less treble and often a muddy sound. You need to alter the part values for a compensation.

There are some articles with good sample circuits about opamp stacking on the web.

You can build other curcuits with a dual opamp (the 2 halves work similar like 2 trannies), for ex. a MU-amp. You can bootstrap a single opamp too for more gain and a bit more distortion.

JHS

I'm curious about stacked op amps. Is this something that offers any benefit in tone? A google search reveals some old threads where it gets debated and I know that some of the popular Boss mods utilize stacked op-amps. Is this something I should experiment with or has it been settled that there is not much benefit in tone?

Merged for a good old necrobump