Tech21 XXL schematic unveiled

[J. Luja]

I picked up a broken one cheap -check R31 on the board scan, it's the second one I've seen like this, I'd assume it's caused by a wrong polarity adapter that's been daisy chained with another pedal -toasts the resistor, but the effect will still run on battery power.
that block of epoxy just made me all the more curious to see what what was under it, here's what I got

[Marcos - Munky]

Thanks a lot. Looks very interesting. Did yoy tried to breadboard it?

[Joep]

NICE ONE!

[Arno van der Heijden]

Nice! :mrgreen:

How do you know the correct opamp type?

[aron]

That's pretty amazing. I have one here, but since it's not mine, I didn't have the nerve to remove the epoxy.

[Ben N]

Wow!  So the warp control just messes with the biasing of the drive opamp, and not a clipper in sight!  Now what I would have expected.  Can anyone tell us what is happening in there?
Thanks, J.
Ben

[stm]

My 2 cents:

This Warp control and its surrounding resistors look strange to me.  I would expect that on one end of the pot rotation the biasing would be Vcc/2 (symmetrical clipping).  In fact, the values shown allow for positive and negative biasing around Vcc/2, which would produce basically the same sound.

Apart from the above, thanks for sharing it  

STM

P.D.  Some logical values in terms of the above would be:  22k for the upper resistor, then the 100K pot, then a 120k resistor.  In this way, with the pot at minimum you have 22+100k above the wiper, and 120k below, giving perfect symmetry to the biasing.  On the other end, you would have 22k on top, and 100k+120k below, giving a biasing point of 9V * 220/(220+22) = roughly 8V.

EDIT:  I checked Tech 21 site and in fact the "middle" or normal position is slightly OFF-CENTER to the left, as the resistor values indicate!  Perhaps they left the provision to be able to go to the LEFT of the CENTER position to absorb the tolerance of the pot.  For instance, pots are specified usually as +/- 20% tolerance, so a 100k pot could be perfectly between 80k and 120k, which could not allow to get to the "CENTER" biasing in all production units.  My approach, if I were to build something like this, would be to include a trimmer to take into account for pot tolerance and make sure one end of the pot is really the CENTER biasing point.

[birt]

stupid question: what is it? :oops:

[stm]

Read here:

http://www.tech21nyc.com/xxl.html

Samples are available also.

[Marek]

That 'Warp' thing sounds like a 'Presence' pot being turned fully down.

Whatever the circuit says...

[toneman]

Nice work!!
THanx 4 posting!
T

[strungout]

Thnx for sharin

The clips sound pretty cool.

[J. Luja]

Marcos - no I haven't breadboarded it, it's fairly straightforward and I didn't really have any doubts about my tracing

Arno - once I got to the point where I took the scan, I did some more carefull excavating with a dental pick and got enough of the numbers to make an educated guess. I also measured the current draw of the originals and compared them to others I had on hand. plus I later installed full size sockets to try different opamps and my ear agreed with that combo

STM - yeah, I was a bit puzzled by the "warp" implementation, my guess is it allows two simple "presets" for guitarists averse to knob twiddling - full anti-clockwise is pretty much the sweet spot, clockwise is full blown fuzz, the two sounds most would be looking for basically -if I were to build it I'd use an opamp to set the voltage division for either end of the pot, cheaper than a trimpot

-Jeremy

[stm]

Jeremy, I agree entirely with your opinion on the preset settings. You did a very nice and thorough job on backtracing the circuit.  Thanks again for sharing it.

Now, on another line of thought, everytime I see these Surface Mount guitar circuits I can't believe they will sound as good as if they were made with full-sized through-hole components.  I can feel the mojo of through-hole!  Of course someone 20 years older than me will make the same comparison between Solid-state and Valve circuits  :lol:  Does anyone here feel like me?

[bwanasonic]

I spent some time with an XXL a few years back. I remember liking it direct into the fx return of my Rivera. Nice find for cheap, and thanks for the work you put into this.

Kerry M

[Paul Perry (Frostwave)]

, everytime I see these Surface Mount guitar circuits I can't believe they will sound as good as if they were made with full-sized through-hole components.  I can feel the mojo of through-hole!  Of course someone 20 years older than me will make the same comparison between Solid-state and Valve circuits  :lol:  Does anyone here feel like me?

Personally, I prefer surface mount! but my commercial products are either through hole or a mixture (some useful components are ONLY made in surface mount now).

[stm]

I agree certain IC's are mainly available in SMT, but what about metalfilm caps and stuff like that?

[bwanasonic]

Since I have my boards made, I suppose it would be feasible to attempt some SMT circuits, at least with some of the larger SMT parts. It might be an interesting experiment to make a couple simple booster/distortion circuits, making a SMT and a traditional thru-hole version of each, trying to keep the part value differences to a minimum. Then *taste test* them. Which reminds me, I need to get one those desk lamps with the big magnifying glass in the middle.

Kerry M

[petemoore]

I got a huge desk mount light/magnifier for Xmas...have no place to install it...has a large countersprung 'elbow arm' so you can bring it in' over the work and away...four screw mounting plate at it's base.
 If you're interested in an unused unit, drop me a line...make an offer...It'd be nice, if I had a place for it.

[MartyMart]

I just got some 14 pin high quality dual op-amps from Ti, unfortunately they are SMD ( only available now in that format )
anyone know a "quick'n dirty" way to expand that out to a 14 pin dip socket
"Dead bug" wiring, would that work ?
I'm thinking of a couple of "Craig Anderton" builds.....

Marty