Author Topic: Tech21 XXL schematic unveiled  (Read 19923 times)

J. Luja

Tech21 XXL schematic unveiled
« on: January 24, 2005, 01:37:48 PM »
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

Tech21 XXL schematic unveiled
« Reply #1 on: January 24, 2005, 01:59:28 PM »
Thanks a lot. Looks very interesting. Did yoy tried to breadboard it?

Joep

Tech21 XXL schematic unveiled
« Reply #2 on: January 24, 2005, 02:01:18 PM »
NICE ONE!

Arno van der Heijden

Tech21 XXL schematic unveiled
« Reply #3 on: January 24, 2005, 02:19:11 PM »
Nice! :mrgreen:

How do you know the correct opamp type?

aron

Tech21 XXL schematic unveiled
« Reply #4 on: January 24, 2005, 02:28:09 PM »
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

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Tech21 XXL schematic unveiled
« Reply #5 on: January 24, 2005, 03:25:30 PM »
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

Tech21 XXL schematic unveiled
« Reply #6 on: January 24, 2005, 04:59:43 PM »
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  :D

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

Tech21 XXL schematic unveiled
« Reply #7 on: January 24, 2005, 05:22:55 PM »
stupid question: what is it? :oops:
http://www.last.fm/user/birt/
visit http://www.effectsdatabase.com for info on (allmost) every effect in the world!

stm

Tech21 XXL schematic unveiled
« Reply #8 on: January 24, 2005, 05:26:44 PM »
Read here:

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

Samples are available also.

Marek

Tech21 XXL schematic unveiled
« Reply #9 on: January 24, 2005, 05:34:21 PM »
That 'Warp' thing sounds like a 'Presence' pot being turned fully down.

Whatever the circuit says...

toneman

Tech21 XXL schematic unveiled
« Reply #10 on: January 24, 2005, 05:35:53 PM »
Nice work!!
THanx 4 posting!
T
TONE to the BONE says:  If youTHINK you got a GOOD deal:  you DID!

strungout

Tech21 XXL schematic unveiled
« Reply #11 on: January 24, 2005, 05:49:40 PM »
Thnx for sharin :D

The clips sound pretty cool.
"Displaying my ignorance for the whole world to teach".

"Taste can be acquired, like knowledge. What you find bitter, or can't understand, now, you might appreciate later. If you keep trying".

J. Luja

Tech21 XXL schematic unveiled
« Reply #12 on: January 24, 2005, 05:56:27 PM »
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

Tech21 XXL schematic unveiled
« Reply #13 on: January 24, 2005, 07:37:22 PM »
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

Tech21 XXL schematic unveiled
« Reply #14 on: January 25, 2005, 12:31:54 AM »
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)

Tech21 XXL schematic unveiled
« Reply #15 on: January 25, 2005, 07:22:16 AM »
Quote from: stm
, 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

Tech21 XXL schematic unveiled
« Reply #16 on: January 25, 2005, 09:40:38 AM »
I agree certain IC's are mainly available in SMT, but what about metalfilm caps and stuff like that?

bwanasonic

Tech21 XXL schematic unveiled
« Reply #17 on: January 25, 2005, 01:20:06 PM »
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

...
« Reply #18 on: January 25, 2005, 01:26:49 PM »
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.
Convention creates following, following creates convention.

MartyMart

Tech21 XXL schematic unveiled
« Reply #19 on: January 25, 2005, 03:38:39 PM »
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
"Success is the ability to go from one failure to another with no loss of enthusiasm"
My Website www.martinlister.com