Favorite 2N7002 or dual 2N7002?

[phasetrans]

Mouser has thirteen different dual 2N7002 in ready availability. Anyone have a favorite brand / PN for 2N7002 or dual 2N7002? Schematic I'm working on is attached, if you're interested in the application:

[phasetrans]

Replying to my own thread. I changed the design approach and slimmed it down, and also checked all the available SPICE models. Still debating on whether to spin a test board to jumper in all the various dual 2N7002s that can be purchased.

[bluebunny]

Anyone have a favorite brand . . . ?

The thing about the BG3309* is that it conforms to the specs of a BG3309, otherwise it isn't a BG3309.  The name or logo on the front isn't part of the spec.

I'd buy the cheapest. 

___
* insert your part number here...

[phasetrans]

Anyone have a favorite brand . . . ?

The thing about the BG3309 is that it conforms to the specs of a BG3309, otherwise it isn't a BG3309.  The name or logo on the front isn't part of the spec.

I'd buy the cheapest. 

They're all pretty cheap, LOL.

Five of the six spice models are close enough to each other that I should just start with a couple parts and see...

[duck_arse]

Anyone have a favorite brand . . . ?

The thing about the BG3309 is that it conforms to the specs of a BG3309, otherwise it isn't a BG3309.  The name or logo on the front isn't part of the spec.

I'd buy the cheapest. 

They're all pretty cheap, LOL.

Five of the six spice models are close enough to each other that I should just start with a couple parts and see...

"Supertex inc." is my fave, cause they sent me some free samples. of 2N7002's. this doesn't mean that I will ever be able to get supertex's from tayda, for inst, but, they are my favourite.

[PRR]

> ....it conforms to the specs of a...

Exactly.

Any "well designed" circuit, the designer writes SEX6969 on the part list, the Purchasing Manager buys the cheapest SEX6969 he can find, and it will work.

Sometimes not that easy. The datasheet may not set limits on some parameter we need. We know that Peavey (like most audio companies) had a Qualified Parts program. JR would ask for samples and try them. Maybe maker D's parts rattled, F's parts hissed, the others were all about the same, so makers A B C E and G got Approved SEX6969 Vendor status. But this can be VERY application specific. A little hiss is bad in a mike preamp, moot in a headphone amp or servo. Potentiometer scratch may be tolerable in a fixed (set and forget) school PA, distressing in a mixer, and fatal in a guitar.

And then there is the question: was the *circuit* designed per the datasheet? If so, it will "work". If not, the Designer has some explaining to do. Maybe it DOES give the super-groovy sound when *selected* parts are used. Your plan has a *fixed* 1.3V difference in bias to M2 and M3. But Vgs(off) of 2N7002 is 1V-2.5V, a 1.5V spread. Throwing perfectly good 2N7002s in there, you have a high chance of one or the other device being full-OFF, no signal. You have a slim-to-none chance of finding two devices with a 1.3V offset, which would cause equal currents and "optimum" linearity (which is maybe not "optimum" for guitar effects). The design causes an uncontrolled variable either-way distortion characteristic.

So: sort 2N7002s for desired offset? Or put in a trimmer on the free Gate? If you have a robot sorter and many-bin trays, that can work. In small production, even though trimming is tedious(costly), trimming is probably the way to go. By inspection and guesswork: trim for Drain voltages equal to a "Gold" prototype. Or trim to maximum output and total clarity, then turn for an approximate drop of output and increase of "tone".

Dual 2N7002s exist to cut costs. The one I looked at has NO specification for matching. Maybe you get one dual-FET chip and that is likely to match. I have also heard of 2-die duals, luck of the draw.

[Rob Strand]

Five of the six spice models are close enough to each other that I should just start with a couple parts and see...

If you believe spice models represent reality  .  Which they don't for a lot of MOSFETs running low currents.

[phasetrans]

Five of the six spice models are close enough to each other that I should just start with a couple parts and see...

If you believe spice models represent reality  .  Which they don't for a lot of MOSFETs running low currents.

I don't believe the models, hence the question... They all magically have Vth of 2V, too :-)

Apparently I shouldn't try my hand at comedy

[phasetrans]

> ....it conforms to the specs of a...

JR would ask for samples and try them.

John Roberts, eh? Wow, world's collide... The 2N7002 specs are pretty dreadful by modern FET standards, which is why they piqued my interest.

Your plan has a *fixed* 1.3V difference in bias to M2 and M3. But Vgs(off) of 2N7002 is 1V-2.5V, a 1.5V spread. Throwing perfectly good 2N7002s in there, you have a high chance of one or the other device being full-OFF, no signal. You have a slim-to-none chance of finding two devices...

Or maybe I like a lazy way to change the bias voltage and observe the general effects...

Otherwise everything is else is true if it were for production, which it isn't. A BJT version would probably make more sense in that context.

Dual 2N7002s exist to cut costs. The one I looked at has NO specification for matching. Maybe you get one dual-FET chip and that is likely to match. I have also heard of 2-die duals, luck of the draw.

The whole idea started on this very question, "are the dual packages actually single die, and do they match at all?"

I've not subjected a pile of them to the transistor tester yet. Obviously ones that matched would be a pleasant surprise.