Rosac Nu Fuzz with switchable Distortion Blender

[bmsiddall]

Greetings from Australia.  Long time no post- buying a house and moving in proved a small distraction 

Have finally gotten back into building fuzz pedals.  I've been interested in the Rosac Nu Fuzz as it seemed like a good way to get fuzzrite gnarl with versatility via a tone control.  Did a bit of web research and discovered an old Harmony Central thread on the Distortion Blender, which was described as a nu fuzz with an additional 2 transistors- a drive stage into the nu fuzz plus clean blend a la fuzzrite. Orright!

https://www.harmonycentral.com/forums/topic/1690410-first-impressions-on-the-rosac-distortion-booster/

As far as I can tell, there aren't any schematics for the Distortion Blender, so I took the values described in that thread and came up with what I guessed was a possible topology.  I couldn't imagine 4 boost stages in series so thought this schematic made sense.  The 1st stage is the clean blend, the 2nd stage is the distortion boost and the last 2 stages are the stock nu fuzz circuit.  I've made it switchable with a 3PDT allowing a choice of stock nu fuzz or Distortion Blender.


I've put it together and tested it and (of course) the nu fuzz is killer.  Before connecting the clean blend, I tested the 2nd stage into the nu fuzz- interestingly, it gave a somewhat nasty, more trebley distortion.  If I'd stopped there, I think I would have added a BC bypass capacitor on that extra stage.  Adding the clean blend seem to tame that aspect a little but I still might think about the capacitor.  I'll try and find some time to do a demo, but in the meantime, was interested in getting some feedback as to whether I might be in the ballpark on the schematic.  Suggestions, criticisms welcome.

Btw, transistors are BC114 with HFe from 160-220.

Cheers,
Brett

[antonis]

I was stuck on 1nF cap for more than 3 minutes till I realized it's a humble crackle-stop item..

[Mark Hammer]

That pair of caps and 500k pot over on the far right remind me of the tone control on the Univox Square Wave, which provides one path for full bandwidth and another for highs-only.  Where the SW precedes the tone control with a larger-value DC-blocking cap, Brett's drawing has the two cap values placed in parallel.  I might add this is also very similar to Joe Gagan's still-clever lo-blend addition to the input of the basic Fuzz Face.

[bmsiddall]

Bit of a whoopsy- forgot the 43K in the tone control.  It's just there to reduce the 500k volume pot value to about 40k or so, I guess.  Have also annotated the schematic so (I hope) it's a little clearer what I've done.

Looking again at the schematic, i think the distortion boost is still too much in circuit so have adjusted, adding SW3.  So, I need to order a 4PDT 



Here's the original Rosac Nu Fuzz trace for reference.



Cheers,
Brett

[duck_arse]

bms, I'm not sure the 1nF and the 10nF tone caps come from the same collector, do they? in the fuzzrite, they come one from each collector to give the in- and out-of phase mix.

[bmsiddall]

bms, I'm not sure the 1nF and the 10nF tone caps come from the same collector, do they? in the fuzzrite, they come one from each collector to give the in- and out-of phase mix.

d_a, they do if the hand drawn trace is correct (creepy fingers made one based on this trace, i think).  The fuzz is not a fuzzrite, and both caps form a tone control (not a blend), which incidentally works really well. The Distortion Blender (which came after the nu fuzz) incorporates the clean blend wrapped around the nu fuzz. 

I mentioned fuzzrite because it and nu fuzz were designed by Ed Sanner and both were nasty, 60s type fuzzes.  Hope this makes sense!

[iainpunk]

you can use Q2 as a buffer instead of a gainstage and save one switch, since you already use double throw switches, saves a little bit of hassle

cheers,
Iain

[bmsiddall]

you can use Q2 as a buffer instead of a gainstage and save one switch, since you already use double throw switches, saves a little bit of hassle

cheers,
Iain

That's a great idea- I might try it this week. Thank you!