"Rock Face" - J Hollis's temp stable FF Review ...

[MartyMart]

http://www.diystompboxes.com/smfforum/index.php?topic=27176.0

Here's the circuit and some comments, I didn't find much about this at all
in a search, only "three" mentions ..

At first glance it seems like an awful lot of extra parts, to get a good temperature
stable Fuzz Face, perhaps there's more to the IC/LED/LDR than just that ?
Anyway, I built one on vero ( of course ) this morning, with only two changes from
the original circuit :
A TL071cp  single op-amp and a 1N34A Ge diode from base to ground on Q 1, which
perhaps screws the whole idea, as this is a temp fix also for ge trannies !!
Q1 - GT309A Ge russian   hfe 90
Q2 - GT309B Ge russian   hfe 116
LDR one of the cheaper 2.50 buck ones from smallbear and a 3mm Red LED, for
which I have no data, it's just a Maplins "cheapie" standard LED

Well it sounds very, very good and I think it's the best of the three "FF's" that I've
built ... by far 
With the fuzz pot left flat out, there's lots of control and tones between 8/10 on
the strat volume, "bright clean" to just a touch of drive, then Fat and quite full
sounding fuzz at 10, this could be a bit thinner for me and a touch brighter, but
it's just about perfect "vintage fuzz" IMHO   
Also, it seems to let the Strat's tone come through, like it's not "masked" by too
much fuzz tone ( dare I say transparent !! ) never noticed this before on such a
fat sounding fuzz circuit !!
Perhaps this is more due to the Transistor choice, as those russian 309's seem to have
a lovely tone to them,
I've had it right next to the heating in the studio for half an hour and it sounds
exactly the same as when i first plugged in ! ... no splatting or tone change at all
RESULT  !!   
The temp stable diode trick mostly works for me so far, but perhaps this is the
"Rolls Royce" of stable Fuzz Faces  ??
If you've got time/space for that LDR/IC I'd give it a try, you can also reverse a few
connections/caps and build it with NPN Ge's like AC127's or OC140's too, then its
normal "negative" ground.
Thanks John Hollis for another very interesting circuit and everyone else here
who's made it possible for me to build almost anything from a schematic  ! 

Marty.

[MartyMart]

UPDATE
I did get this circuit to go A.W.O.L earlier ..... by blasting it with a hair dryer !!
Had to heat it up for about two minutes, but it settled down quite quickly
I don't expect it will ever recieve that anount of heat in a gig situation though !!
( unless there's a parcan lamp right nest to it ! )
MM.

[jimbob]

Great review.

[jmusser]

You're one of the few people that I've ever heard that built this, and maybe the only one to have luck with it staying stable. I'd say if you had to cook it with a hair dryer to get it to crap out, then you've definitely got the temperature stabilization problem whipped! I always thought that the Optoisolator was sort of a tone oriented feature like the one in the Ugly Face, and not an actually part of a temperature compensation circuit. I never paid that much attention to it, because it always had problems, like the Ring Frob and Nurse Quacky. Thanks for the comprehensive report. I happen to know another guy who has the weird Russian germaniums. in fact, he just got in some GT308Vs today to wring out