This Week on the Breadboard: The Guitar PCB Beano Bundle

Chuck D. Bones

Chuck D. Bones

Circuit Wizard
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, 2N2222A, 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
Beano breadboard 06.jpg
 
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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!
 
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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.

Beano breadboard 08.jpg
 
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?
 
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 + 100nF and I'll populate the PCB the same way.
 
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I finally got around to building half of this today. I was interested to hear what the modified Rangemaster sounded like - it's very similar to a Red Rooster. I used the stock set up according to GPCB and a 2N2222A. I was surprised that it runs a fair bit quieter than any Red Rooster I've built - maybe it's the 2N2222A? I'm sure I've built a Red Rooster with a 2N2222A... Anyway, it's as good a treble booster as I've heard. Thanks for bringing it up, Chuck. I never would have heard of it otherwise!
 
It's harder to find a quiet Ge trans than a quiet Si trans. A low-leakage Ge trans is needed in the Rooster for low noise.

The Beano Rangemaster has fixed bias and a HEAT knob to control the gain. The Rooster always runs at max gain.

Those two factors cause the Rooster to be noisier. I ran a 2N1308 in my Beano and it was quiet.
 
Well I'm sold on this treble booster because it's whisper quiet. Maybe even quieter, depending on who's whispering. And it sounds alright too. I think I might have run out of 2N1308s.

I made two small changes. I changed the 1nF cap to a 470pF because I felt it bled off too much top end, and used a C500K for range and wired it to increase lows as you turn it clockwise.
 
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