Tech21 XXL schematic unveiled

[toneman]

several companies make SMT to DIP adapter pcbs.
One i can think of right off the top is Aries adapters.
I think DIgikey, mayB Mouser, sell them.
Little on the pricy side.
Google "smt adapter" & C what U come up with.
I designed an adapter for 16pin SMT to 16pin DIP for a TI
headphone amp, but never etched it cause i ended up buying
an evaluation pcb.
Also, i discovered, i couldn't solder the SMT---ultra small..
staydownsized
tone

[Paul Perry (Frostwave)]

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 ???Marty

For 'cheap' go 'ghetto'!
that is, get an old computer board with smt parts, remove the components with a heat gun, and cut off a chunk that has the pattern you want. Then you solder your smt chip to the board fragment and either glue it to the main board & run wires off to the relevant places, or soleder on stiffer wires & pretend they are legs.
You DID say CHEAP right? (yeah, i have done it for protos..)

[wcampagner]

Does anybody know what's the FET transistors used in this stompbox to make the bypass circuit?

Thanks,
Wagner.

[amz-fx]

I don't know anything about the XXL specs but typically the J111 is used in similar switching arrangements...  you can also use the J113  ---  DOD uses both of these for switching.

Boss uses the 2SK30A and Ibanez sometimes uses the 2SK118.  

regards, Jack

[SonicVI]

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?

I don't like the look of them either, my Korg DT-10 tuner has them too, but then again I just think about how frickin small electrons are and I don't really worry about it.

[DavidS]

You could always make it true bypass, or use mechanical switching in place of the FETs.

[aron]

The Insanity pedal was designed after I had an XXL here. (of course) I liked the Insanity a lot better than the XXL.

[Rodgre]

Maybe now I can figure out how to clean it up. I like the tone of the XXL, but even at the lowest gain setting, it's way too dirty for me.

Roger

[Lee_ranaldo]

i've used that pedal a few times
i had the chance to compare with a bd-2 , green bigmuff, vintage bigmuff, and ds-2, including a classic tech 21.(in realtime)

it's not really special, sounds buzzy and has one sound for it.

it's gainy and buzzy without an special character.

[Mark Hammer]

Maybe now I can figure out how to clean it up. I like the tone of the XXL, but even at the lowest gain setting, it's way too dirty for me.

(Assuming the J. Luja draw is 100% accurate) The first stage has a default gain of 100, and the second stage can't go any lower than a gain of 10 (albeit with a bit of attenuation between stages).  No wonder it never really cleans up.  Perhaps replacing R8 with 10k instead of 3k3 might help.

Um, are you sure those component values are right? With C10 = 47nf and R8 = 3k3, that gives a low end rolloff of 1026hz.  While this is sort of counterbalanced by the high end rolloff at 4.8khz caused by C7, I'm not quite sure those components would yield anything more than a whiny tone.  Is it possible that C10 = 470nf?  Not questioning anyone's integrity, just the limits of the human eye when it comes to those SMT parts.

[J. Luja]

Wagner, I didn't make note of the fet part number, sorry, but as Jack has pointed out, there are several substitute parts that should work fine.

Roger, I agree with you there's not much range in the drive control, a good mod would be to add another gain control for the first stage. though all the important parts are under a brick of epoxy, you're better off building a clone and modding that.

Mark, I'm fairly certain of the component values, each of the caps were unsoldered and measured one at a time (there's no label, you wouldn't want a mix up) and the resistors are very clearly marked, especially on my high resolution scan. also a 470nf cap would be farily large for a ceramic smt I think they would more likely choose a tantalum package, as they did on the double drive. check out the interesting tone control though, it seems to compensate for the pre-emphasis and attempts to keep the perceived volume the same throughout its range.

-Jeremy

[Mark Hammer]

Well, you're right about the interesting tone control.  Kinda clever.  I like clever tone controls.

If my calculated roloff is accurate, boy oh boy that's a weird one.

[Khas Evets]

If I'm reading this correctly, the input cap/resistor (C12/R21) form a high pass filter with a corner frequency of 590Hz. That not only feeds the circuit, but it feeds the bypass. I think I'll true bypass this one.

[J. Luja]

If I'm reading this correctly, the input cap/resistor (C12/R21) form a high pass filter with a corner frequency of 590Hz.

nah, you got the math right, but you're reading it incorrectly. R21 is in series with R20 and R10, which (ignoring C11,C8, R12 ,the position of the warp control and the input impedance of the opamp for simplicity) makes the coner frequency at around 12Hz.

[bwanasonic]

Maybe now I can figure out how to clean it up. I like the tone of the XXL, but even at the lowest gain setting, it's way too dirty for me.

While I had the XXL on loan, I was considering using it just for it's high-gain, smooth *lead* tone (somewhere between Santana and Fusion), using other methods for edge-of-breakup and *crunch* sounds. But I found the GT2 I already had to be much more versatile overall, as it will actually clean up with the guitar volume.

Kerry M

[Ken]

G'day all,

To build this pedal true bypass would I be right in assuming that I would

leave out the two fets along with the input buffer and just hard wire the

level pot to the output buffer.

Cheers Ken.

[Khas Evets]

I was about to ask the same question. Is the output buffer required? I was thinking about just putting a coupling cap and a pull down resistor.

I was also thinking about using one side of the TCL2262 to replace the TL072, but that will probably change the character of the circuit.