Univox Square wave hosed up

[jmusser]

I built the Square Wave last night, and finally got it hooked up to my fixture for a test drive. First, the volume would go all the way up, but the tone would only go up about a 1/4 of the way before it cut off the whole effect. I started looking around , and found out the ground from the circuit board wasn't hooket up to the jack sleeves and chassis. I thought, Ahh Haa. I hooked that up, cranked it up, and had full volume, except now, when I hit the strings, all I get is a real loud "splat" that instantly decays. Hopefully I'll get some time to go through the schematic and do some circuit tracing this evening or tomorrow, to see what's miswired. I will let you know what I found, in case somebody ever wants to build a "Splat Box"! I will ask one question, that may remedy the problem. I am using a 2N5458 Jfet in this circuit, which I can only assume is correct, and that the 2N545B is a misprint on the schematic. Is the pin out for this device the same aas a mosfet like J201? I have it oriented, so if the flat part of the transistor is facing me, the Drain is the left leg, Source middle, and Gate on the right leg.

[b_rogers]

how bout voltages for all D,G,S?


When my effects "splat" its usually a bias problem...


Brent

[jmusser]

I'll check tomorrow on what the voltages are, but for now, do I have the SDG oriented correctly for that jfet?

[Lonestarjohnny]

on some jfet's you will find a wrong data sheet that will give you the incorrect pinout, Just a word to let you know that not all Jfet's are pinned out alike, make sure of the brand your useing and use thier data sheet, not the 1st one that pop's up. this has been discussed on several threads here in the past.
who's schematic are you useing ?
if the original univox, the tranny's were 2SK***, I cant remember if they are 538's or not, but without knowing which schematic your useing it's hard to trouble shoot.
Johnny

[jmusser]

The, schematic I used is on http://www.diystompboxes.com/pedals/square.gif.  I got the jfet from Small Bear. I didn't know that different companies had different pin outs, so I guess that's why I ask these silly questions. I will check the jfet for a manufactuer, and go to their web page. Hopefully this pinout orientation is the problem. For the most part, if that jfet is not the problem, then I'll just have to do some good old circuit tracing to see what I've miswired.

[StephenGiles]

Interesting - "to hose down" in England means to wash with with water from a hose, like a car for instance. Nothing to do with distortion, but I thought that I would mention it all the same. Pirates would hose down their ship............ooooooooooooooops, musn't mention pirates, Johnny Kidd & the PIRATES, PIRATES of Penzance, pirate CDs............I slap my face, especially those.................bootlegs.......that's OK!!!!!!!!!!!!!!
Stephen

[Lonestarjohnny]

J, you got a good plan for getting the circuit working, Let us know what you find. and a lot of time's it will be a simple mistake that happen's to me if i get in to much of a hurry, LOL !
Johnny

[jmusser]

I checked the TO-92 packaging of the jfet on the Fairchild site. The transistor I have has a capital "F" then B411 , then 2N5458. I'm guessing F means Fairchild, but it could mean Franks Transistor Imporium. Anyway, it shows the flat side down being GSD from left to right. In a jfet, does the "source" act like an emitter, and the "drain" like the collector of a standard transistor? I'm wondering that, because the schematic shows pins 1,2, & 3 on the Brad Fajardo schematic on Aron's site for that jfet.

[jmusser]

I went back through this thing with a fresh schematic and highlighter. Unless I have the jfet wired wrong, I have no wiring errors. However, I did find out that the 3K9 resistor tied to the 33uf capacitor was the wrong value. I had put in a 39K instead. Hopefully when I get time to trade this out, this will have caused the misbiasing problem that one of the other guys talked about, that is giving me the splat sound. Right now, I have the 2N5458 oriented to the schematic symbol, as 1=Drain, 3= Gate, and 2=Source. If that's correct, then the resistor being off by a factor of 10, should be my only problem. I traced it out on my lunch hour at work.

[Lonestarjohnny]

J, I think you found your last problem, hopefully, and you should get some tone now, I'm rootin for ya anyway, make's you feel good when you hear somethin you built come to life and work right,I know when I make a mistake it's because i loose concentration. and sometime it take's awhile to find 1 or 2 small mistake's,
but i think that resister will cure your bais problem,
Johnny

[jmusser]

IT'S ALIVE!!!!! (insert Gene Wilder in Young Frankenstein). That was it, just the resistor value. I changed the 39K to 3.9K and man what a fuzz! I'm on 12 hour night shifts from 6 P.M. to 6 A.M. I only got about 5 hours sleep today before my next 12, but I had to see if that was the culprit. I read somewhere where this circuit was not supposed to have much sustain, but mine has gobs  It's a real seathing, unruley type tone, and there is some noise in there, but not in a bad way. It's just good old late 60s early 70s classic rock stuff. As for now, It has the coolest tone of any fuzz I've made to date. The Buzz Box is great and is at the nasty end of the spectrum, where the Easy Face is smooth as silk, and basically noiseless. This hits right in the middle with it's sort of unsuffisticated raw tone. If you hit the bass E open (neck pickup), the note will sustain, and even eventually get louder before it breaks up. This thing is truly awesome in my book. Of course, tone and sound are in the ear of the beholder, but it's a tone I've been looking for, and I guess that's why we do this stuff.