oops, put the wrong ic in my tube screamer clone

[Andy]

I forgot to plug my 4558 chip into the socket when I finished my clone earlier and nothing happened when I went to fire it up.  I thought "oh crap, no wonder.  The chip is sitting right over there"  I grabbed the chip I saw laying on my desk and put it in.  The pedal fired up right away but it sounded BETTER than the clone I built last week!!  I thought, "man, something sounds good!."  I thought it was the choice of diodes I used this time and last time but later, much later, I looked at the chip for some reason and noticed I stuck in a tl072cp!!  I immediately thought two things:  1.  did I screw up all my hard work by using the wrong chip or did I screw up my chip? and 2. where the heck is my 4558 (which is in the bag of parts I made up).  anyhoo, has anyone ever done this?  Can anyone tell me why it works and why it works so much better?  Is it in fact the choice of diodes I used making it sound different?  I used 1n4001's last time and 1n914's this time.  I actually learned something else. the true bypass works VERY well because I could play my clean guitar though the chip was out!!!

[aron]

The TL072 and many other op amps are pin for pin compatible.

YES, this means you can use many other types of op amps in there to get different sounds.

Could be the chip, the diodes will sound different as well.

One way to find out, put in a 4558.

[Ge_Whiz]

You've just learned, unlike some who hang out here, that ears are a better guide to sound than part numbers and their associated folklore.  :twisted:

[acromarty]

I have modified my TS9 TubeScreamer to use red/green leds for the clipping diodes and a TS952 cmos opamp. The different colour leds give some asymmetry to the clipping because they have slightly different forward voltages. The opamp is designed for rail-to-rail operation on low voltage power supplies, so it behaves predictably under overload transients or clipping.
It sounds wonderful, it gives me a smooth lead sound with endless sustain and no harshness. Seems to work best with the clean channel of my amp.
I usually take it along to the local jam night where there is a small and much-abused Fender amp (I think it's a Champ 12), and other players have several times asked how I get that sound.

I have since acquired a TS9DX cheap in Japan, done the same mods, it sounds just as good.

Cheers,

[Andy]

what does "rail to rail" mean?  I've seen that before.

[drew]

"Rail-to-rail" means that an opamp can output a maximum and minimum voltage which is close to its supply voltage. If you power an opamp with +9v/-9v, then its maximum output should be close to those values.

As an example, if you input a 1V P-P signal with a gain of 100, the opamp won't output 100V... it will output as close as it can get to its supply voltage. (Which, obviously, causes clipping.) In an opamp designed for "rail-to-rail" operation it will output values close to its supply voltage.

In a gain of 100, the difference between +8v/-8v and +9v/-9v isn't much, but if you want more "headroom" (gain before clipping) it does matter. A regular opamp might clip at lower gains where a rail-to-rail opamp won't clip. And, generally speaking, people like the distortion of diodes/transistors/etc. more than that of opamps when designing pedals. (GENERALLY speaking.)

Sorry if that was too many details and you already knew most of that...


drew
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