Been Messing With The Bazz Fuss...

[Kearns892]

Alright this is a cool little circuit for what you get considering its simplicity. It also makes it the perfect place to start messing around with things. I've been reading up and I see a lot of things you can do with the Bazz Fuss, but not a whole lot of explanation of what's actually happening. So I was wondering if someone could tell me the role of the input and output capacitors, and why the diode is where it is.

I was also wondering about the gain knob in the Deluxe Bass Fuzz. I added it (1k value) on my stripped down Bazz Fuss (I'll draw up an exact schematic with values for what I'm doing in a minute) and it sounds really sputtery on everything except full gain. Suggestions for improving the gain pot? I also know noise when turning pots on single transistor fuzzes is the norm, but I was wondering if there is anything that can be done to reduce that noise.

And finally, I was showing this fuzz off to a friend of my mine on the breadboard, he plays bass and was very interested in it. He wants to see how it sounds through his bass and if he likes it he wants me to box one up for him. I was wondering if anyone had any suggestions for value changes for making the bazz fuss as Bass friendly as possible. Normally I would just tweak values myself and tune it to taste (which is kind of what I have done with my guitar), but I dont own a bass.

Again I will have the exact values of what I am using up shortly. Thanks

[Kearns892]

Here is what I am using right now. Sorry for the hand drawn schematic.



Oh, for testing purposes I left the Vol. pot off the breadboard (less alligator clips haha).

[ZombiCrow]

I read on one of the Bazz Fuss pages around that the gain sounded best full-up anyway, so I wonder if there is much range to that gain pot regardless of what value you throw in. Have you tried adding the "Thickness" control doesn't offer a little more flexibility?

The input and output caps on this are just tailoring the bass response while converting the DC to AC, right? Is the majority of the distortion here generated by the diode, or the Darlington'd trannies? I'm really interested in this little guy, and I'm going to look into the Whisker Bisquit, too!

[bobp1339]

This is one of my favorite distortion/fuzz boxes.  I have mine setup for guitar, but also built one for my bass player using .47uf caps.
I also use a 2n5088 and a 2n5089 and I get a little different fuzz than 2 2n5088.

BobP

[Kearns892]

Hmm I dont have any 5089s on hand I don't think. But would lowering the input and out put caps better tailor this for a bass? I swapped the 10uf caps for 1 ufs and I couldnt hear much difference at all.

[bobp1339]

The 10ufs should work for bass since they are much bigger than the .47uf my bassist is using. 
For my guitar I use .01uf.

BobP

[Kearns892]

Alright so for both Capacitors, higher values are recommended for lower frequencies?

[Havaden]

I allways put a fuzz face gain control at the bazz fusses i build, only with a 50K  pot. Works a lot better than a 1K pot alone.

[midwayfair]

I think that using the two 1k resistors has misbiased the transistor. Usually the Darlington version uses 10K on the collector and the emitter is GROUNDED. You've raised the emitter resistance AND lowered the collector resistance, so your collector is probably sitting at a very high voltage, like 8V, right? You need to raise the collector resistor again.

A potentially better gain control that won't misbias your transistor would be to put a 100K-250K voltage divider at the input of the circuit, like in the original version of the circuit. It's just a normal volume control, and it'll work like your guitar's volume control. It still might sound a little splatty at lower gain settings, but that's the nature of the circuit.

Your 10uF will sound just fine with a bass.

So I was wondering if someone could tell me the role of the input and output capacitors, and why the diode is where it is.

The transistor needs some positive bias to function, which is what the diode is doing -- it's just taking the place of a large resistor in a collector feedback bias. But a diode isn't a resistor, so it works differently at different frequencies and signal sizes (voltage).  The diode is where it is because it's the only way to safely get it to do what it does -- I believe you can't connect it right to the +9V source or it'll pop the transistor (IIRC). When the signal size at the collector exceeds the forward voltage of the diode for the portion of the wave that swings positive, it will conduct back to the base as negative feedback, clipping the output, and negative voltage that appears at the input that exceeds the diode's forward voltage will conduct to the collector, pulling it down further than usual on the POSITIVE swing of the wave (because the collector is reverse phase). The result is extremely asymmetric clipping with a transistor that is basically slammed in terms of gain, and since it's a very high gain transistor in that Darlington arrangement, that means that your signal produces an outrageous amount of distortion from only a single transistor and a relatively small input signal. [EDIT: Someone please correct me if I'm wrong on describing how it provides positive bias. There's also the fact that the guitar signal at the collector produces the current that biases the base, so I might be missing a step here.]

[PBE6]

Thanks for the explanation midwayfair, I spent yesterday trying to puzzle out the effect of the diode and your description certainly helps.

One thing I noticed while running some simulations is that the circuit does some goofy stuff without some form of resistance/impedance in front of it. It looks like passive guitars are fine in this regard, but active pickups or buffered precursors will probably sound broken (in a bad way) as-is. Interestingly, adding simple resistance anywhere from 2k to 150k seems to make the simulated circuit play nicely, with the added effect that increasing input resistance causes the (upside-down) peaks to shrink in width. Can't wait to breadboard a test circuit tonight and see how it sounds!