Build report - Univox Squarewave

[Mark Hammer]

I had put the circuit together on a piece of perfboard a while back, and was looking for quickies to finish up over the weekend in between trips out to my sister's to fix her video setup, and running family errands.  There are days when you want something that you can thoroughly complete, instead of something that gets oart of the way there and gathers dust while you try and find a free weekend.

As builds go, this one is pretty damn easy.  As a two transistor fuzz (one JFET, one NPN), perfboarding it is dead easy, with most components being placed almost identically to the schematic drawing.  The resulting board, even if you don't try to conserve space via the usual tricks (verticaly mounted resistors, etc.) is small enough that it will fit inside a 1590B quite comfortably.

I think you have to place this one in among the pantheons of two-knobbers to appreciate it.  It also has two controls, but where others had a distortion amount and output level control, this one has a preset degree of distortion (http://www.univox.org/pics/schematics/squarewave.jpg), but includes the typically missing "tone" control in addition to a volume level control.  So, while a 2-knobber in design and spirit, it had one "twist" to distinguish it from others.

Judging from its full-out sound, my guess is that the subtler tones, even were one to arrange them by tinkering with gain-altering components, would not be especially inspiring.  Although the longer I look at it, the more it seems to employ a quasi-Fuzz-Face topography with a FET in the second position, so I should see what sort of tone one gets by lifting the diodes.

The tone control is bonehead simple: a variable resistance in parallel with a bypass cap.  Turn up the resistance and what makes it through to the volume pot via the bypass cap is mids and highs.  So the tone control is essentially a bass cut.

In the stock version (I used a 2N5088 and 2N5457 rather than the japanese transistors indicated in the linked schem), with full bass and full volume, there is a noticeable boost, but it wouldn't be describable as having "gobs of gain".  Indeed, turn the tone down and you need to crank the volume to have matching effect/bypass levels.

To remedy this, on mine I put in a toggle to select between Si and Ge diode pairs.  As predicted, the use of Si diodes results in much higher output levels, and a slightly warmer crunchier tone because of the higher clipping threshold.

This is generally in the same ballpark as a Distortion+ in the sense that it creates its effect via diodes just prior to output.  Much like the Distortion+, you can probably also goose the output level by increasing the volume pot from 50k to 100 or so.

What does it sound like?  With bass fully cut, this is mosquito fuzz territory.  Similar to a BMP with the tone fully-treble.  So, aimed at those who like "sick" fuzzes, and not at all the sort of set and forget type of pedal....unless you play in a 1966-pre-psychedelia band like the Electric Prunes or something.  Not inspiring, but for what it costs to make one in terms of money and time, not a waste of time either.  I stuck mine in a plastic chassis with a hunk of copper shim for shielding inside, and used rub-on lettering and clear matte lacquer as a fixative.  Estimated total build cost?  For me, about $12, with the $3.75 X-wing stompswitch being the most costly part.

Probably lots of territory for modding, well beyond the diode types: the gain structure, the value of the bypass cap, etc.

[MartyMart]

I know this is an "old one" but just wanted to say that i found your comments quite
useful 
Implimented the "s idiodes" option and a 100k vol pot helps some too.
I didn't change the "gain" structure yet, but I guess swopping that 3k9
for a 5k pot would be fine, also using a 22uf for the 33uf ? doesn't seem
to be a problem !
Quite a good "Fat/rich" fuzz tone I'd say ... my "tone" doesn't get quite
as "mosquito like" with a 4n7 cap at the back end 
Dragonfly's layout was great, just watch for the "680 ohm" off Q1
which it should be ... not 680k  !! 

Marty.

[jmusser]

Thanks Mark for the review, and the mods. I built mine a year and a half ago from the http://www.diystompboxes.com/pedals/square.gif which I believe was drawn up by Brad Fajardo. It calls for a  2N5088 for Q1, and a 2N5458 Q2. It has nice warm tone to it, but one you wouldn't really associate with being a squarewave tone. It is on the very bottom of the buzzy scale (if at all), when compared to Tim's Simple Square Wave Shaper, and Digital Octaver Fuzz, and the Optimum Fuzz (AKA Triggered Squarewave Fuzz). Mine gets no where close to mosquito land. I don't know if the 2N5457 is a higher gain device and would help this circuit out or not. I will play with putting in Si diodes. All in all with building to that schematic, it's pretty bland.

[R.G.]

I have one of the originals, and it's not too buzzy either. I thought something was wrong with it.   

[jmusser]

Thanks R.G. It's not like this is a horrible sounding effect or anything, but with it being dubbed "Squarewave" you'd think it would really be a radical heavy buzz, and it ends up being sort of "Squarewave Lite". Tim's Simple Squarewave Shaper's tone to me would typify what I would expect out of a squarewave. Of course with his, it actually generates a totally new wave form from the original input, where this one may just be heavily clipped off wave form that happens to look square on the scope. I don't know. I honestly thought I may have missed a step while building it!

[MartyMart]

It's a great tone though Jeff, not "subtle" at all it's pretty much
"flat out crunch/fuzz" no matter where the gtr vol is !!

MM.

[Toney]

Ah, Im glad this one came up...I built it from this layout:

http://aronnelson.com/gallery/album17/UNIVOX_SQUAREWAVE_FUZZ

But was puzzled by the arrangement of components off Q2 s source. Looking at the schem
http://www.univox.org/pics/schematics/squarewave.jpg

It seemed to me that the 560k resistor had to connect at the junction of the 100k and 270k at the base of Q1 and at Q2s source simultaneously with the 33u cap and the 3.9 k res. Ie the 33u and 3.9k should directly connect to the Q2 source, not via the 560 k.

Like this... sorry for hasty cut and splice

http://photobucket.com/albums/y16/stm88/?action=view&current=univoxsquare.jpg

Any input much appreciated.

Toney.

[MartyMart]

I looked at the schem and did the same thing !
I used a jumper from Q2 to the 3k9/33uf and placed the
560k "just like" the schem ... on its side from junc of 100k/270k to
the top of 3k9/33uf, with a "cut" in that strip ....

IT MADE NO DIFFERENCE AT ALL   
It's the same connection "nodes" and was doing the same job !

MM.

[Toney]

  Right!
Gonna have another go a this one.
Got me a 680ohm resistor to replace the 680k......didnt pick that up fr the schem.
When debugging I was sure the problem was Q2s source so I guess I overlooked this.

[MartyMart]

Toney, that will sort it out 100% 

Marty.