Let's discuss RAT OpAmp options

[Gus]

The sound change is not the chip alone.

This is a good circuit to try out different opamps as many have posted years ago R.G. Jack..... it is about the recovery and other aspects of the  opamp when driven to clipping and what load it is driving.

use a socket and drop in different opamps for test then solder in the one you like that works with you amp and guitar.

[grolschie]

My Rat came with a OP07DP. I tried a NE5535A and a LM308. They all sound very similiar to my ears, except that the Lm308 sounded a little more tubey - less brittle.

[bwanasonic]

I agree with you!  But many guitarists are a obsessive bunch and can tell the different where as the audience wouldn't care.

Well, they certainly like to think they can tell the difference. In my experience, many of these perceived differences don't hold up in double-blind (or even single-blind) conditions. Take a dozen identically packaged Rats, the only difference (aside from part tolerance differences) being six have opamp x, and six have opamp y. It would be interesting to see how well most guitarists (or anyone for that matter) would do at telling them apart by ear. My guess is probably no better than chance.

Kerry M

[dosmun]

Quote from: tonefreak on March 14, 2007, 01:36:35 PM
I agree with you!  But many guitarists are a obsessive bunch and can tell the different where as the audience wouldn't care.

Well, they certainly like to think they can tell the difference. In my experience, many of these perceived differences don't hold up in double-blind (or even single-blind) conditions. Take a dozen identically packaged Rats, the only difference (aside from part tolerance differences) being six have opamp x, and six have opamp y. It would be interesting to see how well most guitarists (or anyone for that matter) would do at telling them apart by ear. My guess is probably no better than chance.

+1000 to that

[Mark Hammer]

I agree with you!  But many guitarists are a obsessive bunch and can tell the different where as the audience wouldn't care.

Well, they certainly like to think they can tell the difference. In my experience, many of these perceived differences don't hold up in double-blind (or even single-blind) conditions. Take a dozen identically packaged Rats, the only difference (aside from part tolerance differences) being six have opamp x, and six have opamp y. It would be interesting to see how well most guitarists (or anyone for that matter) would do at telling them apart by ear. My guess is probably no better than chance.

Kerry M

While golden ears exist, even "golden ears" are subject to oxidation.  Remember that the ability to make sonic distinctions when playing solo at practice levels with no other concurrent sound sources is not necessarily predictive of the ability to make those same sonic distinctions when the volume goes up another 9db, and the pedal is "heard" in the midst of keyboards, drums, crowd noise, and an overly strident PA system.  The human ear follows relatively predictable rules, and as the number of overlapping sound sources increases and the volume level goes up, the capacity to discriminate goes down.

So, I have absolutely no doubt whatsoever in the noticeability of op-amp changes in a wide variety of distortion pedals.  I even posted a wavfile I recorded last year where I subbed several different op-amps in my Distortion+ pedal and the difference was easily audible.  Buit what you can hear in circumstances designed to hear it, and what you can hear in circumstances NOT designed to hear it, are two different things.  A half teaspoon of salt in a pot of coffee is dead easy to notice.  The same half teaspoon of salt in a pot of 5-alarm chili...not so much.

A 308-equipped Rat *does* behave differently.  The question is whether that difference remains audible under the conditions in which you intend to use it.  For home studio, a 308 will likely make an audible difference.  If its a barband gig pedal, use what you got and don't sweat it.

[WGTP]

The slew rate of the OPO7DP is pretty dismal, as is the 2262.

I have subjected my family and friends to op amp tests and they seem better able than I to "hear" a difference in op amps (my hearing ain't what it used to be).  Once they even commented on the pleasantness of the noise generated by some where as others were harsh.  Whether this can be heard in the midst of presentation, is ...   

I've noticed in some op amp material reference made to fast recovery and a value sometimes given.  Is that what we are talking about in terms of some sounding better than others?

I also noticed reference to "phase invertion" upon hitting the rails, which is hypothesized as potentially having a sonic effect.   

[MartyMart]

Well they dont call me "Bat ears Marty" for nothing !!!
In "clinical" studio situations the differences are often VERY audible to me, as Mark says
within a band rehearsal/Gig probably not audible at all.
TL070 and 308 seem like the "right" contenders for me though, possibly the 301 is fine too
though I have not checked the spec on that.
I like the look of Dano's new FKR - Rat, that seems like a "fun" project !

MM.

[stm]

I also noticed reference to "phase invertion" upon hitting the rails, which is hypothesized as potentially having a sonic effect.   

Sorry to disagree, but phase inversion is a real issue with JFET opamps.  I've experienced it and seen it with oscilloscope happening on TL072's.

This image illustrates the phenomena:
http://www.analog.com/library/analogDialogue/Anniversary/Graphics/figure19lg.gif

The full explanation and conditions under which it may occur are near the end:
http://www.analog.com/library/analogDialogue/Anniversary/6.html

It is not something you may like unless you are fond of gated octave effects during the peaks of your playing.  Anyway its cure is pretty simple: a 10k in series with the (+) input of the opamp is all it takes, if I'm not misktaken (guess I read it on a TI technote).

[MartyMart]

Thanks Sebastian, interesting little read !
MM.

[WGTP]

Sorry, I didn't mean to imply that it was bogus.  It was a reference to my own lack of understanding of this complicated stuff I found on the TI site.  Another parameter is settling time.  Somewhere R.G. was discussing the phase inversion issue in a previous op-amp thread and it definitly "sounds" like something that would be undesirable.