Whisker Biscuit schematic help?

[luciguci]

Thinking of making a Whisker Biscuit with two Bazz Fusses in series rather than one. However, I am still learning how to read circuits, so I was wondering if someone could help me isolate the Bazz Fuss from the Whisker Biscuit schematic? I think I could figure out the rest afterward.

[Pens]

From the second 100n cap to right before it goes into the tone stack, which is the split 33k resistor and the 4n7 cap. The full isolated circuit would have another 100n cap right there to prevent DC leakage.

If you wanted to do two in series, take it all from the second 100n cap up to where it splits to the tone stack, and repeat it.

[luciguci]

Alright, thanks! I wasn't sure if I was right with that, but you've confirmed it for me.

[luciguci]

Now, if I wanted to put a sustain pot, I would put it just before the second 100nF capacitor, correct? I feel like that's wrong, if so, explain where and how I would put in a sustain pot? Here's what the new schematic looks like:

[Pens]

If I recall right, the "sustain" pot was really a gain pot and in the BMP was just before the major gain stage. In other words, would be before the first Bazz Fuss stage. If I were you, that's where I'd put it here. It limits the amount going into the gain stages and thus making it not as raunchy sounding. Smaller signal == less clipping.

It ought to be a pot going into the top leg of it, with the wiper being the "output" going into the gain stage. Possibly a small resistor on bottom leg going to ground to provide a minimum gain.

[luciguci]

Great, that's what I was also thinking, especially after finding this this detailed explaination of the Big Muff circuit. At the bottom, there is a schematic for the Big Muff. In the Big Muff schematic, I see that going out of the first gain stage, there is a 1uF cap just before a 100k pot leading into the second gain stage and a 1k resistor bettwen the pot and ground, which I believe is what you mentioned with the resistor for minimum gain. So logically, all I need is to put that in the same place, correct?

Here's the new schematic in which I added a gain pot. I think this should work.

[NickS]

Wiper to the 100n cap, small resistor (1K) to the bottom of the pot is what he meant.

[JohnnyTheBoy]

This is fab! I've just read the Big Muff details and have got a better understanding of how these circuits are put together!..its all about the stages..
So thanks for posting! Yeh you gotta make this by the way...

[Pens]

Wiper to the 100n cap, small resistor (1K) to the bottom of the pot is what he meant.

Yep

[luciguci]

I fully intend to, but first, I will breadboard board the current circuit I have. Then, if it sounds okay, I plan to try out a few mods, one at a time, then all of them at a time if they work. I plan on making this thing some crazy ass customizable monster.

• ~A switch to turn each Bazz Fuss on seperately (BF 1/BF 1&2/BF 2)
  ~Two switches to change the diode in each Bazz Fuss (switch one - Si/none/Ge, switch two Si/LED/Ge)
  ~Tone bypass switch
  ~Switch to select between regular tone stack or flat mids tone stack
  ~Clean blend

I might also make the tone bypass switch or the flat mids switch foot switchable, depending on which one I like more. I see it in my head like this:

[Pens]

Wiper to the 100n cap, small resistor (1K) to the bottom of the pot is what he meant.

Yep

To clarify a bit more, you take the signal from the 1u cap into the "top" leg of the pot, attach the wiper to the 100n cap, a smallish resistor (1k is fine) to the bottom leg, then go to ground.

This creates a voltage divider, which will effectively cut the signal down into a smaller wave form when turned down.

[luciguci]

That's what I thought.

[Pens]

Oh, one tweak I would suggest to your schem is a large resistor to ground just in front of the first cap. I'm not sure what the purpose of that 33k in series with the signal is aside from input impedance, but it's generally a good idea to have a resistor in front of that cap to provide a path to ground for the other leg of that input cap. This helps avoid the "pop" you hear with some pedals when they are engaged, basically the cap charges on the other side of it but has no place to dump to until the pedal is engaged, which then dumps the charge into the signal path and makes the pop. I'd probably change the 33k up front there into a 100k to ground instead.

[luciguci]

I'll definitely try that once I get the parts.

[NickS]

Oh, one tweak I would suggest to your schem is a large resistor to ground just in front of the first cap. I'm not sure what the purpose of that 33k in series with the signal is aside from input impedance,

Yep, that's one reason why. Particularly with old low-gain germanium transistors, where the input impedance of the transistor is effectively gain x emitter resistor (100R). With higher-gain transistors it gets a whole lot more complicated

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but your input impedance is going to be the parallel combination of the 100K, the 470K divided by stage gain and the 100R x stage gain. Stage gain would be controlled by the ratio of the 10K to the 100R (more or less) i.e. around 100 except for the fact the 470K is providing negative feedback in a divider that includes 470K on one side and the parallel combination of the 100K, the 100R x stage gain and (33K plus the output impedance of the guitar) on the other. That reduces stage gain, so the transistor input impedance drops and is also in parallel with the 470K divided by the stage gain...

The other reason could be anti-pop (RC time constant of 33K + 100nF), but when these circuits were first designed it was assumed your instrument was always connected to the input (no TBP) so need for a bleed resistor.

[luciguci]

I've drawn out a couple of the mods that I've mentioned:

• ~two separate switches to bypass each gain stage
  ~one switch to bypass the tone stack

Looking at a schematic for the 1980's Big Muff with the Tone Bypass switch (lank) and I see that there is a 150k resistor in the path of the bypass, but I'm not entirely sure that might be the proper value for the caps and resistors in my tone stack.

Alternatively, I'm considering extending the tone bypass to include the last stage, which is essentially just an amp to bring counter act the volume cut that comes with the tone stack. Therefore, if I want to make the tone bypass footswitchable, I don't have to worry about the massive volume boost that happens. I guess I will just have to try it out myself, so I will post here when I do.

[NickS]

I fully intend to, but first, I will breadboard board the current circuit I have.

That's going to be interesting, as at full "Gain" the collector load on Q1 will be a little under 1K instead of the intended 10K. This reduces the open-loop gain by a factor of 10. You may find that the Gain control appears to do very little over a wide range, and that most of the stage gain has disappeared.

[Pens]

I fully intend to, but first, I will breadboard board the current circuit I have.

That's going to be interesting, as at full "Gain" the collector load on Q1 will be a little under 1K instead of the intended 10K. This reduces the open-loop gain by a factor of 10. You may find that the Gain control appears to do very little over a wide range, and that most of the stage gain has disappeared.

Yeah as drawn I don't see that gain control doing much. It needs to be a voltage divider there.

[luciguci]

So the resistor under the gain pot should be changed to 10k rather than 1?

[Pens]

No, the configuration of the gain pot is only going to change the amount of resistance going into the gain stage, which isn't going to do what you want it to do.

You need a voltage divider. Look at the below, at the Sustain knob, for how to configure this. You will keep that resistor there between the pot and ground, but this his how it ought to be set up.