TL071 vs. TL072

[loki]

Hi everyone,
I'm thinking about building a Craig Anderton's De-Scratcher for my old morley volume pedal. I just have 1 question: the original CA's schematic lists a TL071 OpAmp, while Tonepad Layout changes it to a TL072, so i'd like to know what difference is there between the two (except for the fact they have different pinout, right?)
I read the specs sheet but couldn't undetstand much (i ain't really an expert) so i'm just wondering is using one instead of the other will sensibly change the way the volume pedal will work (maybe more gain, or such...)
thank you!  

[Travis]

The pinout is different because the TL072 is the dual version of the TL071.  TL071=single  TL072=dual.

A single section of either should behave in an identical manner.

edit:  I just noticed that this was for the old Morley volume pedal.  I've never seen an old pedal (chrome job) that used a pot, though I wouldn't be incredibly surpised if I came across one.  They are all LED/LDR combos, with a (pedal controlled) fabric screen between the two.  I have come across all kinds of problems with these, but you should NOT have any pot problems.

In what way is it scratchy?

[jimmy]

theyre both the same stats wise, but the TL072 has 2 opamps onboard while the TL072 has 2  

if you look on the data sheet it might have a picture of a triangle inside the chip on the 071, but on the 072 there are 2 triangles?

thats all. if i had to choose id use the TL072 on the tonepad pcb.

good luck!
Jim

[loki]

edit:  I just noticed that this was for the old Morley volume pedal.  I've never seen an old pedal (chrome job) that used a pot, though I wouldn't be incredibly surpised if I came across one.  They are all LED/LDR combos, with a (pedal controlled) fabric screen between the two.  I have come across all kinds of problems with these, but you should NOT have any pot problems.

In what way is it scratchy?

oh yeah, mine uses a pot... i opened it up. the model is CVO (compact volume pedal), black, and it has a 50k slider pot (it says A, so i believe it's audio taper). the slider pot's shaft is glued to a small spring which in turn is connected to a nylon thread attached to the pedal.
and well it scratches in the most standard way i think, when you rock the pedal back and forth...    i tried cleaning the pot but nothing changed...

so thank you both guys, i think i'll go with th TL072
bye!

[Mark Hammer]

There is no performance difference between them.  Since the price tends not to be different between them either, you will find many layouts calling for a TL072 when only a TL071 is really needed, simply because it's easier and more convenient to just order/buy a bunch of duals and use either both halves or one as needed, and because some layouts are much easier to do when the input and output pins are on the same side of the device (true of the TL072) than when they are on two sides (true of the TL071).

Though not a complaint, those among us who are ambitious and generous enough to design PCB layouts should probably consider including (where feasible) some sort of "mini-kluge" capability when using only half of a dual op-amp in the layout.  For instance, you'll find layouts for the Orange Squeezer and Dist+/DOD280 that use a dual op-amp and only one half is needed.  In such instances, the other half can be put to productive use if there are a few extra pads/traces provided for adding components to the unused half.  Think of it as "reserve capacity" or "design headroom".

[nooneknows]

and it has a 50k slider pot (it says A, so i believe it's audio taper)

I wouldn't want being wrong but A should be  linear and B  Log (or not?)

[Paul Marossy]

"A" usually indicates audio/log and "B" indicates linear.

[stm]

As Mark said, having a dual opamp instead of a single may give you reserve or additional capacity, but don't disregard that power consumption of the TL072 (dual) is twice of that from a TL071 (single), so if your goal is maximum battery life, you go for the single op-amp. This is the case where both options work, despite there are design tradeoffs involved.

[Hal]

FYI, a TL074 is just what you would expect, a quad op-amp.  4 in one package.  Its a DIP-14, though, not DIP-8

[sir_modulus]

I'd go for the TL-072, as Dual Opamps are common, and if you want a different sound, you can ask around the forum, as there are many compatible Other Dual OA's.

[loki]

ok, thank ya all for your suggestions, i think i'll use the TL072, since the tonepad layout for it is already done (though i'll have to change it since i'll built it on  a perfboard, still i have a base to start from)
i've no probs about power consumption, i'm a wall wart guy   and my wonderful digital power supply is 1.7 A, so there's plenty of power
then, as i intended it, i don't think changing the opamp would affect the sound... afterall it's just a volume pedal de-scratcher....
bye!

[jjs]

I have a question about the TL071. What are the two pins labeled OFFSET N1 / N2 for? The dual- and quad- opamps (72/74) don't have them.

[loki]

I have a question about the TL071. What are the two pins labeled OFFSET N1 / N2 for? The dual- and quad- opamps (72/74) don't have them.

OFFSET N1 is Pin 1, and OFFSET N2 is Pin 5, what they are for maybe you can check here
http://www.linuxfocus.org/common/src/article251/TL071.pdf

[Torchy]

I have a question about the TL071. What are the two pins labeled OFFSET N1 / N2 for? The dual- and quad- opamps (72/74) don't have them.

These are offset-nulls. If an op-amp (which is actually a difference amplifier) had both inputs shorted to each other and earth, we would expect zero output. Practically, this never happens and to achieve zero output we have to "offset" one of the inputs with a small voltage to "null" the output. This is done internally to the op-amp and is achieved by wiring a pot between the O/N1 & O/N2 pins and adjusting for zero (null) output with zero (null) inputs.

More info on op-amps here http://www.allaboutcircuits.com/vol_3/chpt_8/3.html

[stm]

If you look at the TL071 datasheet on the application circuits section, you should find that a pot placed across the offset pins allows for trimming the offset at the output.

In other words, you expect to have exactly 0V at the output for 0V input (assuming +/- power supplies), but in practice, and depending on the type of op-amp and the circuit gain, you can have as much as 100 mV (0.1V) at the output for 0V input. You use this pot for nulling this voltage out.  This is intended for precision applications, and in practice you don't need it for guitar effects, unless you need a full wave rectifier accurate to the millivolt level.

TL072 are relatively low offset, so they don't have the nulling pins to save pins and reduce the IC footprint.

[jjs]

Thanks! Quite interesting page link, by the way!

PS: You are too fast for me. Every time I wanted to post a reply, in the topic review was another new post answering the question I just wanted to ask.