Fairchild Photo FET

[Pushtone]

Our head engineer excitedly came up to my desk today.
This guy is in his late 50's and dosen't get excited about anything.

He brought news of a "new" semiconductor.

Fairchild H11F3M
http://www.fairchildsemi.com/ds/H1/H11F3M.pdf

Check it out.

At first I though It could be used to make a buffer without DC decoupling caps.
Looking at the applications in the data sheet I don't think it can do that but there are some audio apps in there.

Besides a volume pedal, there might be some cool stompbox applications, given the ingenuity and talent of this group.

Geeks, enjoy!

[dxm1]

He brought news of a "new" semiconductor.

I'm hoping you quoted the word "new" because you're aware the H11 devices have been around for years...

If I'm not mistaken, RG mentioned them in a GEO article about mic mutes or some such, about a decade ago?

[Faber]

I think I have an idea!
Anyone know where to get these?

[Ry]

Http://www.smallbearelec.com/Detail.bok?no=702

[R.G.]

The H11Fx series is ...great... for switching.

They're pretty good for linear resistances, except that the voltage across the FET must be kept below 25-50mV to get that "99.9% distortion free" they talk about up at the front of the datasheet. It's the small signal capability, smaller than guitar signal even, that keeps these from being the only good answer to tremolos, phasers, etc.

[Pushtone]

I'm hoping you quoted the word "new" because you're aware the H11 devices have been around for years...

No.
I guess he isn't either.

The conversation was focused about how these are cheaper than the opto-couplers he currently uses for our custom media matrix switchers.
So switching was the application.
I'll dig through geofex.com and show our engineer the article if I find it.

Sorry about the false announcement.

[dxm1]

I'll dig through geofex.com and show our engineer the article if I find it.

My bad - it was only 8 years ago...

http://geofex.com/article_folders/automike/automike.htm

I'm surprised a 50 year old engineer using optoisolators in current production hasn't seen the H11 products... Maybe because they're _so_ old?  When it comes to optos, I admit to having BiPolar syndrome - I'm a TIL111-113 kinda guy.  But then, we're talking switching, not linear control, and the TIL parts are as ancient as the HF11's.

What we need to see is a photoFET that acts like a CLM6000...

[soggybag]

I have a few of these I used to experiment. There is an app note for a sample and hold. I tried it, and managed to get it to work.

I have often wondered about the usefulness, for stompbox related stuff, of all of the opto transistors I have seen listed. There seems to be many and varied types of these. There BJTs, FETs, Darlingtons and more.

[zachary vex]

H11s are a sure way of turning a sine wave into a triwave.  Pretty amazing that way.

[Paul Perry (Frostwave)]

Zach, I bet you need pretty accurate level control to get that 'sine to triangle" to work.

[DimebuGG]

here ya go:

http://www.stinkfoot.se/andreas/diy/articles/vlbypass.htm

http://www.geofex.com/article_folders/bypass/bypass.htm

[Mark Hammer]

There is a temptation, or rather will be a temptation, to use these like Vactrols.  While they can be used that way in principle, on top of the caveats that RG mentions, an aditional caveat is that they respond bloody fast.  Why is that a problem?  Well, normally, the slight sluggishness of the LDR in a Vactrol-type optoisolator adds some lag to the settling time required for the LDR to return to full "off" resistance.  In most typical uses for folks like us, that helps to smooth out the envelope ripple often found in half-wave rectifier circuits during the decay phase of a note or strum.  Sadly, the speed of photo-FETs permits them to translate every nuance of the envelope, including the ripple at the end.  So, they CAN be used in place of a Vactrol, but do pay attention to whatever additional steps can be taken to minimize audible ripple because these guys are likely to be unforgiving.

Having said that, consider a circuit like the Funny Cat, where the envelope ripple is used specifically for the manner in which it can seem to produce a "soft distortion".