This is a library of perfboard and single-sided PCB effect layouts for guitar and bass. I'm not an electrical engineer by any stretch of the imagination, just a DIY'er who likes drawing layouts. It is meant for the hobbyist (so commercial use of any of these layout is not allowed without permission) and as a way to give back to the online DIY community.

Friday, July 3, 2015

Univox SquareWave

This is a pretty unique fuzz from the mid-70s by Univox. It was designed by Shin-Ei and like a few other Shin-Ei designs it can suffer from volume loss. To get it back up to unity or above, DIYSB forum member LucifersTrip made some mods to the circuit that keep the original sound, but improve the circuit a little bit. (Here's the original schematic, and LT's schematic for reference)

Volume problem:
To increase volume, I slowly increased the vol pot. Even at 1M, it was still below unity. So, I added diodes in parallel. Finally it was above unity, but now the distortion (really a tone control...closer to 0K the more bassy) didn't give me a good sweep.  So, I simply increased the 27K cutoff to 100K and subbed a 1M distortion pot instead of the 250K. Beautiful!  That gave me a nice sweep from just barely too bassy to a nice thin fuzz.

Mild Gating Problem:
Anytime I see an odd small value from an emitter, base or collector to a rail, I always suspect it to be very sensitive, and it was...I slowly increased from 0K and hit a perfect spot around 2.6-2.8K. The mild gating and pick percussion were gone, resulting in a killer smooth fuzz with super long sustain.  It was nearly perfect, but a bit too harsh on the highs. A simple tweaking of the 680 gave me a sweet spot right around 1.8-2.2K. If you raise it much higher, you'll wind up with less power...and around 4-5K will start to gate again. Further, I increased the 2M to 3M, which gave a bit more richness to the higher strings. I tried up to 7M...still good (thicker on the high strings)  but I didn't want to take a chance it would change the tone too much.

 Here's a demo of the original:





If you want use this layout to build the SquareWave to original specs, follow the below value changes:

  • Change the 1.9k resistor to 680Ω
  • Change the 2.8k resistor to 3.9k
  • Change the 3M resistor to 2M
  • Use a 2N5458 for Q2
  • Jumper D3 and D4
  • Change the 100k resistor by the diodes to 27k
  • Use B250k pot for Distortion control
  • Use A50k pot for Balance control
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2 comments:

  1. UnknownJune 26, 2020 at 8:29 PM

    Will try it tomorrow, wish me luck!

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  2. JDTNovember 14, 2020 at 7:56 PM

    The top left 100k resistor should connect to the bottom of the 100nF capacitor (Row B, column B to row E, column F). With that change, the board works.

    I tried both versions on breadboard first. The original resistors and the 2N5458 make a very gated fuzz that won't quite reach unity volume, though it does sound good. LT's version solves the volume and gating issues as advertised. A 1.8K resistor off the Q1 emitter and a 2.7k resistor off the Q2 source got me pretty close to the voltages on the modded schematic.

    LT also came up with a second version that took out one of the diodes. In his words: "Well, there's no cheaper way to increase the volume than remove the diodes...and in this circuit, the diodes don't do nearly as much as others...just a bit more fizz."

    I made my perf version with LT's resistor values and a 2N5458, since they are still easily available in through-hole versions. I put a socket in for the diodes, but I think I'll leave them out. I also left a gap in the ground rail on the left side of the board so that I could put a pot in series with the 33uF cap as a gain control. The circuit doesn't have the typical Fuzz Face guitar volume clean-up, so the gain pot can tame the fuzz a bit.

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