Author Topic: Zvex Mastotron with blend control  (Read 2496 times)


Zvex Mastotron with blend control
« on: February 17, 2016, 10:32:06 AM »
Hello guys,

First post here on the DIYStompboxes. :)
I have been working on some fuzz boxes, I builded a Zvex Woolly Mammoth, a Mastotron and some Big Muffs. But for bass, it always lack some bottom end. So, the ideia here was to put a blend control on a Mastotron/Wolly Mammoth, as they are very similar circuits. I realy like the sound of those two fuzzes. And mostly when I push all the way to maximum the pinch, wool and tone controls. But when I use this parameters there is no bass. So the blend control will solve me this problem.
I tried different blend circuits but the one i liked the most was based on the Run off Groove Split and Blend. It really gives the sound that I need. I get a crazy, sintetized and treble sound from the fuzz, but with a clean bass blended. So the definition and bottom end remains unaltered. I really like.
I have breadboarded the circuit in order to tried different components, but for know this is the circuit that i have:

What do you think about this guys? If you have any suggestion i would appreciate very much.


Re: Zvex Mastotron with blend control
« Reply #1 on: February 17, 2016, 10:47:49 AM »
Many fuzz circuits depend on loading the guitar down to get their sound, if you buffer the signal in order to split/blend you end up with the fuzz being too fizzy because that loading has been removed by the buffering (that's what buffering is supposed to do). There are various suggestions on how to combat this but I bailed on the idea because none really worked for me - in other words I use the same type circuit you do for blending in pedals, just not fuzz pedals. However, I'm sure there are alternatives others suggest that work for many people so let's see what those are in subsequent replies. :)


Re: Zvex Mastotron with blend control
« Reply #2 on: February 17, 2016, 11:49:32 AM »
Thanks for feedback.
That was indeed one of my fears. I read some forums that said that many fuzzes need the pickup load like you are saying, and even requires passive basses to get a good sound of it. That happened to me on the wooly mammoth. I tried passive and active basses and the active basses was definitely to fizzy like you said.
But the mastotron adds a pot just after the input connector to regulate the power before entering in the transistor stage. I tried it and I think it really helped on the active bass. So i though.. if i use this in my active bass, that already have buffers inside, it will not make any difference if I add a buffer to split the sound.
But i really do not understand what that potentiometer do to the input impedance of the transistor. it increases the input impedance of the 2N5088?
One note: in the schematic is tagged two 2N5088 but i used two 2N3904.


Re: Zvex Mastotron with blend control
« Reply #3 on: February 17, 2016, 12:48:23 PM »

I had the same issue for a long time and tried different alternatives.

In the end I found the push pull at the input of the mastotron is the best solution.

I recommend you to install a 100k trim before the push pull. Put the blend all the way to the clean side and set the trim and the push pull pot at minimum. You'll probably hear the clean is not really clean because of the input impedance of the fuzz. Start turning the trim up until you get actually clean bass. Then you leave the trim on that position and can play with the push pull pot for active or passive basses.

Also for this hi gain circuits I think true 100% blend could have better performance (search panning for fun on geofex).


Re: Zvex Mastotron with blend control
« Reply #4 on: February 17, 2016, 01:53:38 PM »
You don't need the bottom two opamps, you can just connect the + side of C15 to the output of IC1A to get your clean signal.


Re: Zvex Mastotron with blend control
« Reply #5 on: February 17, 2016, 08:34:42 PM »
I am definitely going to try that option with the trimm.
I really liked the control that the push pull pot gave me using passive or active basses when I was trying the effect alone, but I was afraid that wasn't the best solution for the blend circuit.

I also read the article from geofex abut the pan. Great article!
In fact, I saw the same kind of circuit on the schematic of the full circle from BYOC, but I did not understood the circuit so I did not try it. Now I understand after reading the article. They use bipolar transistor instead of opamps but the idea is the same.
I will try both options with bipolar and opamps.

Thanks a lot