Build report: Q-Tripper

[Mark Hammer]

An envelope-controlled filter (autowah) from a Japanese designer (K & R) that Mark M graciously made a PCB layout for.

http://www.aronnelson.com/gallery/main.php/v/MarkMs-Gallery/album15/album76/Q_Triper_LAYOUT.jpg.html

http://www.aronnelson.com/gallery/main.php/v/MarkMs-Gallery/album15/album76/Q_Triper_TRANSFER.gif.html

http://www8.plala.or.jp/KandR/cir_q-triper.html

A quick glance at the schematic shows it to be a close relative of the Dr. Q, with a JFET input stage, similar to Jack Orman's Dr. Quack.  Rather than the dual-position filter mode switch on the Dr. Q, this design has a kind of blend control they've labelled "Mix", which appears to blend between the two types of filter modes.  Not sure I find it especially useful at this point, but I might after some more extened playing.

Unlike the Q/Quack/Nurse Quacky, this one uses a JFET as the voltage-controlled resistance that changes the center frequency of the bandpass filter.  The schemaic shows one of those fancy-schmancy selected 2SK30ATM-GR types.  I just popped in a garden variety non-selected 2SK30AY and it worked fine from the get-go.  Same thing with the diodes.  I just used 1N914 types and it was fine, and also stuck a 22uf in for the Vref smoothing cap (C13) instead of the 100uf shown.  If you can't locate K30s where you are, consider using a 2N5457, and let us know how that works out for you.  I would imagine it'd be fine for the input stage, though I can't predict how well it will work for Q2.  it might, it might not.  Unlike the Dr. Q, this one is very comfortable with a 4558, and that is what I used, without any problem. 

One of the nice things about this design is that, with the sole exception of the K30 JFETs, the unit uses some very standard parts and values.  I picked up a Velleman 480 resistor pack over the weekend and was able to completely outfit the unit's resistor requirements with the standard values in that assortment.

The "Depth" control tunes the starting point of the sweep, and is more useful than adjusting the trimpot is on a Dr. Q, since the entire range of rotation provides a usable adjustment, unlike the 15-degrees or so on the Dr. Q trimpot.

This thing fired up properly right away.  Well, after I dissolved some of the flux away and was able to spot a solder bridge it fired up right away.  On the whole, this is a nice musical-sounding autowah that seems to work well for neck or bridge pickup.  Very much in the spirit of the Guyatone Wah-Rocker.  The decay time is fixed by R16, and could likely add to the versatility of the unit by being replaced with 18k in series with a 100k-250k variable resistor for a broader range of decay times.  As with the Guyatone guitar and bass Wah Rockers, changing the two .0047uf filter caps for .01uf will allow it to work better for bass.

Many thanks to MarkM for a nice layout that made the build very easy.  The board may be a bit too wide for a 1590B but will most certainly fit into a 125-style box. 

[Morocotopo]

Nice Mark (both of you!).
How about the ripple? I´m thinking of making an autowah to replace my Meatball, that´s nice but way too big for the pedalboard, and too many controls to bother about. And it has ripple, more than I´d like.

By the way, I have a borrowed Boss one (don´t remember the model), and they managed to make ripple almost inexistent.

[fuzzo]

looks really interesting. I really like that kind of effect since I built the dod 440.

That's not really on the subject, but , Mark  have you made the bi-filter ? there's a document with  your modifications (I think) based on the one made by EHX,  but it says "no tested" , looks also really interesting to insatll it in a rack enclosure I have.  

[Mark Hammer]

I'm not sure that my name is connected in any way with the bigger rackmount EHX Bi-Filter.  It is, however, associated with some useful mods to the Craig Anderton Bi-filter Follower.  These share some portion of a name, and the fact that they employ dual filters, but there the similarities end.

The ripple seems to be minimal.  This is partly because of the use of a larger averaging cap, and a fast decay.  As with any ECF, part of any ripple heard stems from stuff like strings, use of palm muting, etc.  I doubt that this pedal would eclipse the Meatball, but it could count as a really good, finely tuned, well-behaved Dr. Q.

[fuzzo]

Sorry I meant the one designed by Anderton , yes.

I remember I had some strange distortion when I made the doctor Q on breadboard  . I attenuated that noise creating simple high cut filter .I can have the same issue with the jfet using in that schematic  ?

Increasing the two 4n7 cap in feedback loop will change the frequency cut , right ?

[Mark Hammer]

Increasing the value of the two 4n7 capacitors will shift the entire range of the sweep downwards.  Making the caps smaller in value will shift the whole range upwards.

The susceptibility of any envelope-controlled device, whether filter, compressor, noise gate, etc., is at its greatest during the decay of the note.  The first few hundred msec are usually "safe", but once you strum a chord and hold it, many different sources of ripple can occur.  One way to tackle that is to use a larger value averaging capacitor that smoothes out all the little fluctuations which produce what you heard as "distortion".  Another way is to make the decay fast so that the filter sweeps back down before the fluctuation (ripple) starts.  They both work, however each solution works better for some contexts than others.  If you are playing rhythm and want chords to linger a bit, then you wan to use a larger cap to reduce ripple.  If you want a more synth-like sound for leads, that calls out for a faster decay.  You can get a faster decay by making the averaging cap smaller in value (e.g., 4u7 instead of 10u), OR by using the same cap value and sticking a medium-value resistor (22k-47k) in parallel to drain off the stored current quickly.

[fuzzo]

thanks Mark for all thoses explanations !   

I think I may try the circuit on breaboard.

Actually when I say "distortion" I mean a kind of "scratchy" sound , the same I have on my DOD440 ( noise a lot of people had with the circuit,  by the way). I don't know if you talk about the same "distortion".

the best way , would be put a decay put to have choise between all possibilities.

[deadastronaut]

yep i know its old but... .a shot in the dark...


@mark : or anyone!... do you have a sound clip of the q tripper?..i can't find anything audio/video on it

i'm still on my quest for an EF...(that works well with an off biased fuzz after) ....cheers



edit: no worries i just breaded it...sounds ok, now for modding it.....and try and get a down sweep too


its pretty cool, pretty much like the mutron v ,  works on the top strings too...which is a bonus as others ive tried failed at that..

i may be some time, had to use the 2sk30a's though,  clip later..

[deadastronaut]

ok heres an ''exclusive'' clip of this ''elusive'' effect.. Q-TRIPPER

as mark said above, it has 2 filters adjustble by the mix control, (which i shall mod to my liking) the thin one is just too thin imo, and lacks balls..

the thicker filter is much better. more usable.

the clip starts with thick filter, then thin, then a blend of both...this has no 'ripple'' whatsoever as far as i can tell at the mo, its a nice filter ripe for modding.

and is pretty much in the realm of the mutron v....

https://dl.dropbox.com/u/7464107/qtripper.mp3

i shall have a tweak and see how i get on,  any suggestions for reversing the sweep ?

[deadastronaut]

i thought i'd try the R16 decay mod as mark suggested.

here i'm changing the R16 (22k) on schematic   Q-tripper into fuzz)

first is just 2 chords  switching 10k  22k  33k 47k 56k. to show the variable decay.

then rythm/lead in the same values.

https://dl.dropbox.com/u/7464107/R16changes.mp3

lots more tweaking to do.....but i'd like to nail the down sweep!!.



nobody likes me....i don't blame ya!.

[deadastronaut]

just for my own reference......completely butchered, but much better imo... a one pot wonder...




hands up who knows how to reverse the sweep!!!!..come on!.

[Mark Hammer]

There would be two ways.  One is to have an "opposite" DC voltage that the envelope subtracts from (what the Mu-Tron and similar do).  Another is to have a control element that behaves in "opposite" manner.  Didn't Tim Escobedo show a way to use N-vs-P channel FETs to achieve "opposite" sweep?

BTW, it would appear that you kind of like a fast decay, eh?

[puretube]

flip the diodes (+caps)?

[deadastronaut]

 Didn't Tim Escobedo show a way to use N-vs-P channel FETs to achieve "opposite" sweep?

BTW, it would appear that you kind of like a fast decay, eh?

hmmm not sure on that, i'll have a look about..  have you a link to that?

fast decay?...i'd prefer adjustable..( need to tinker with that a bit more) ..it does go from fast to slow though,


@puretube:   i'll try that cheers.


edit:  tried flipping the diodes/cap no joy..hmmm...