The Week on the Breadboard: Chuck's Buzzaround

[Chuck D. Bones]

Maybe we should hold a contest to come up with a better name.

Red Knob: LEVEL
Red Knob: TIMBRE
Red Knob: FUZZ
LED is a rainbow LED that fades from one color to the next. Very psychedelic.



I bought a pile of MP38As recently and decided to have another go at the Buzzaround. I looked at the various TB mk3 circuits and ended up with this. I replaced the Ge Darlington pair with a single high-gain low-noise Si transistor. The rest of it is pretty standard. It's negative ground, so no charge pump req'd. C3 rolls off the top end a bit, just like vintage Ge would do. This is a good circuit for leaky diodes, so I put in a Russian D2D. Q3 is optional. It's a unity-gain buffer that will keep the next device in the chain from loading down the TIMBRE circuit. J112 would also work. If you're driving an amp or high-impedance pedal, the buffer is unnecessary. I designed a Vero, but it's not yet verified. ♪ Inna Gadda Da Vida Bay-Beh! ♫

 

[szukalski]

I can't believe you didn't call it a Chuckaround!

 

[Chuck D. Bones]

And this is why we need a contest.

 

[spi]

And this is why we need a contest.

Why, Chuckaround is a winner. Or maybe bonearound.

 

[steviejr92]

May i ask does the Timbre knob make the Fuzz for lack of a better word "wooly"?

 

[Chuck D. Bones]

I suggest that you breadboard it and decide for yourself. My definition of "wooly" might not be the same as yours. Kinda like the way surfers describe waves.

To be analytical about it, the TIMBRE knob is mostly a treble control. At 7:00, most of the bass is gone; we get some high mids and a lotta treble. As you turn it up, the bass increases. Flat is somewhere around 1:00. Above that, there is a some slight treble cut. To recap: clockwise for fatness, counterclockwise for sizzle. Pretty much the same at the TIMBRE knob on every other TB mk3. Some of them get very thin when you turn TIMBRE down.

 

[steviejr92]

Got it! Going to breadboard this asap! By reading your analytical definition I’m thinking it’s doing exactly what i think it does. Only one way to find out!

 

[Chuck D. Bones]

C6 tunes the sizzle. Smaller for hotter, larger for fatter.
C2 controls the bottom end going into the distortion stage. Larger for a thicker bottom, smaller for a tight booty. Know what I'm sayin'?

 

[Bricksnbeatles]

I’ll be breadboarding this for sure, but I must ask: to me, the balance control is the heart and soul of a Buzzaround— is it worth putting a pot configured as a voltage divider in place of R8 to try to cop the effect of the balance control?

 

[Chuck D. Bones]

Ya know, in the beginning I had the BALANCE control on the breadboard. To me, all it did was act as a volume control. I expected it to alter the tone too, but I wasn't hearing that. If you're hearing something different, then maybe I need to have a second look at it. The main reason I ditched the BALANCE control in favor of the LEVEL control is it gave me a way to balance the bass and treble sides of the TIMBRE control. I copied the configuration from the Park Fuzz, Soul Bender, Sola Sound TB mk III, etc. You must have noticed the volume drop when you turn TIMBRE down on Buzzaround or Dizzy Tone.

[edit]
After a nap and further reflection, it occurs to me that we can still have the BALANCE control. To wit:

 

[Laundryroom David]

I can't believe you didn't call it a Chuckaround!

Why, Chuckaround is a winner. Or maybe bonearound.

I had almost recovered from Chuckaround when bonearound hit.

 

[Fingolfen]

Okay - this one screams for the dino treatment... I'm a big Robert Fripp / King Crimson fan...

 

[Coda]

I second the balance control. I built the PPCB Gnat, and didn’t “get” the circuit until I dimed the Level and used is as it was stock. You can get a lot out of depending on where the Balance control is…

 

[Chuck D. Bones]

Done. Check out the edit to post #10.

I'm just testing it now, so further tweaks may be in order.

 

[finebyfine]

Absolutely killer Chuck. I’ll play around with the ge parts on mine but the first leaky transistor and diode I happened to grab sounded amazing.




edit: tentative on further updates, buuuut

 

[Chuck D. Bones]

Nice layout, very symmetrical.

I might have one more change. Please standby...

 

[finebyfine]

Nice layout, very symmetrical.

I might have one more change. Please standby...

Gives me some time to make sure the transistor footprints can accommodate other pinouts, too

 

[Chuck D. Bones]

I think there is too much interaction between the BALANCE & TIMBRE knobs. I have one more trick up my sleeve...

 

[Chuck D. Bones]

OK, this is it:
BALANCE acts as both a volume and a bias control. FUZZ influences the bias also, particularly below noon. C9 was the latest addition. It helps keep the TIMBRE from changing when BALANCE is rotated. I tried several different transistors for Q3. My AC127s are very leaky and did not work at all in this circuit. Tried a 2N1308 and it was hot. Much too hot for my tastes. The MP38A I have in there now has Iceo = 240μA. Pick a JFET for Q3 that provides a source voltage between 3V and 6V. If you can't find a suitable JFET, omit Q3, R11, R12 & C7. Take the output from TIMBRE pin 2.

 

[finebyfine]

Gonna do a final once over on this tomorrow (caught pinout errors today that I'm not 100% sure I fixed) before I snag a few boards and share gerbers/diptrace files but can't help but tease it



edit: finally tracked down the post Chuck had a while back with the Celestial Engineering font (carolus) so that will be going on there too