This Week on the Breadboard: The Guitar PCB Beano Bundle

[Chuck D. Bones]

I pick up some GPCB Nostalgia Tone boards over the summer and have been breadboarding them. The Beano Bundle consists of a modified RangeMaster and a BluesBreaker. I breadboarded this (more-or-less) in its stock configuration. The only things I changed from the build docs was a C1K for HEAT and different transistor in the RangeMaster and different diodes (FD100 + 1N4003) in the BluesBreaker. You can find the schematics on the Guitar PCB website, so I won't repost them here. B1K also works well for HEAT. The various transistors I tried for Q1 are arrayed at the lower right (104NU71, MП38A, 2N2221, 2N222A, MPS6530, BC109C). They all worked well and did not require any biasing* changes. I ended up with a 2N1308 (HFE = 134).

* one could fiddle R4 to adjust the bias to taste. Because of their higher leakage & lower Vbe, the Ge transistors ran hotter (higher collector current). This lowers the voltage on Q1-C which produced more headroom for the resistor values shown. Higher HFE produced higher gain, but there was only a few dB difference between the transistors listed above.

Some great tones happen with the knobs set for just a touch of distortion. Cranking things up ain't bad either. Every knob does something useful. For the moment, I do not have the ORDER or BYPASS switches installed.

Knobs (L-R): VOL - TONE - GAIN - BOOST - RANGE - HEAT

 

[Gordo]

Curious Chuck, do you then go back and build the board up as you've breadboarded it? Or is this more of a "let's see what this sounds like" and then tear it up once you've beat it up enough?

 

[Chuck D. Bones]

Good question!
Most of the time, the "This Week on the Breadboard" project ends up being built on a production board or Vero. Sometimes, not very often, the circuit doesn't excite me that much and I disassemble the breadboard and move on. I keep records of the breadboards (here and on my HD) in case I decide to resurrect one of them. I learn something from each breadboard and that knowledge comes in handy for subsequent circuits.

I should add that I have a few goals with this exercise.

• See how the circuit performs before I commit to soldering parts
• See if there is something I want to change
• Explore in detail of how the circuit works
• Share the knowledge with the rest of you

And besides, breadboarding is FUN!

 

[Chuck D. Bones]

Here it is with the Bypass & Order switches installed. The order switch is in the middle and points the side that comes first (BluesBreaker, in this photo). The ORDER switch really does turn this into a completely different pedal. The RangeMaster circuit is capable of a much higher output than the BluesBreaker. With the RangeMaster first, it can be used as a gain boost or treble boost. With the RangeMaster last, it can be used as a volume boost. Depending on the setting of the BB's VOLUME knob and the RM's HEAT knob, the boost can be clean or dirty. The ORDER & BYPASS switch wiring is a bit of a rat's nest. Took a couple of tries to get it right. When the RangeMaster is last, the BOOST knob becomes the VOLUME knob. It's a bit touchy as a B10K, so I might try an A10K. Lotta fun, very versatile and highly recommended.

 

[HamishR]

Looking at the schematic of the Beano Bundle - specifically the BB side - I wonder why they use a 220nF>47K>220nF>47K chain (C5 & 6, R6 & 7) rather than the regular 100nF & 10K?

 

[Chuck D. Bones]

I thought the same thing. There is no good reason. Two caps & two resistors is a leftover from the original BluesBreaker design that kills the signal between stages when the pedal is in bypass mode. If we don't have the kill feature, then one R & one C will do. I built the breadboard with 10K + 220nF and I'll populate the PCB the same way.