My New Favorite, The Chickenhead

The Bias adjustment makes this circuit pretty flexible. Try any NPN germanium that you have. HFE in the 50 to 80 range is preferable. I built a similar boost and used a Russian MP38A with good results.
 
I finally built the pedal and agree: its absolutely killer! One thing: I‘ve got 2 OC140, one is 120 hfe and the other one 75. which one would you recommend for this circuit?
 
Either will work because the Bias trimmer can accommodate a range of hFE. Personally, I'd use the 75 because the old RangeMasters didn't have high-gain transistors in them. You most likely will not hear the difference. Save the higher gain OC140 for a pedal that will benefit from it.
 
In general, would you set the bias for 4.5 volt operation with this? or slightly lower for more compression? The demos for the Red Rooster do not sound squished so I would think the bias would be at half the incoming voltage.
 
For maximum headroom, we want the collector voltage 1/2 way between the power supply and the emitter voltage. In this circuit, the emitter will be around 1V, depending on hFE, so we shoot for 5V on the collector. Setting the bias higher or lower will reduce the headroom, increasing compression. Transistors clip a little softer when biased cold, meaning less collector current. For that, you would set the collector voltage higher. I'd say start at 5V, see how you like the sound and then tweak from there. Be sure to explore the RANGE settings as well as the guitar's Volume and Tone controls because this circuit interacts with the guitar's pickups and controls.
 
Thanks. Yet another pedal wanting to be the first effect in the chain. : ^ ) I had noticed that the voltage on the emitter was staying close to 1 volt when adjusting the bias.
 
HamishR said:
I've built a few of these on vero and can attest to their wonderfulness. Absolutely my favourite booster. I always build 'em NPN and have used AC127 and MP38s with excellent results. I've even built some with a 2N2222A and a cap on the output to lose some of the highs to make it sound more Ge. It actually works really well! And you can obviously make it slightly brighter sounding than a Ge pedal if you want and with less noise.

The best thing about this booster is that you can bump up the lows to fatten up a Strat or drop it down a bit to get that classic Beano kinda sound with a Les Paul. It sounds so authentic. I share your enthusiasm.
Click to expand...

Sorry to revive an older thread but I'd love to hear more about the output cap you're using for the 2n2222a builds! I'm doing a build with those already and since they're cheap and Tayda stocks them I was thinking about having a go at this circuit with them. I'm guessing without the cap it still sounds pretty decent? Thanks!
 
Eric it sounds excellent with the 2N2222A and no treble snubber. It's just brighter than a stock Red Rooster. The 1nF to ground can go from Boost 3 or the Collector and I would recommend it.
 
HamishR said:
Eric it sounds excellent with the 2N2222A and no treble snubber. It's just brighter than a stock Red Rooster. The 1nF to ground can go from Boost 3 or the Collector and I would recommend it.
Click to expand...

That's great news! I'll play around with it, thanks for the reply!

The more I think about it the more upset I am they didn't name the original the "rooster booster." Huge missed opportunity.
 
So, I just built one of these boards up for a friend and in testing, I am hearing a pretty prominent ocean/white noise sound when I am not playing. I can mitigate it a little by turning the gain way down (where is the fun in that?) or biasing it to a very low voltage, but I am wondering if I got a bad transistor (got mine on Reverb as well) or wired it up wrong. I notice yours has the red dot on the right side of the PCB, and I assumed the red dot goes to the tab side of the PCB footprint. Or does it matter with these transistors? I have not taken the time to desolder and swap it yet, but thought I'd ask here how much noise is "normal" and what is the correct orientation for that CV7112?

Edit: I just found this, which confirms you can put the CV7112 in either orientation:

About Ge OC140 (CV7112 black glass military germanium)

About Ge OC140 (CV7112 black glass military germanium)
www.diystompboxes.com

I'll have to look at the schematic. It could be I have it in the higher gain orientation, which is causing the noise.

Thanks!

-Bret

Jovi Bon Kenobi said:
Sweet baby Jesus this pedal sounds incredible! I couldn't even wait to label it to share my excitement. I haven't even biased it yet! I built it stock with no alterations. The hard to find 5nF cap was from Smallbear. The NPN germanium CV7112 was from reverb. The HFE is 88 and the leakage is zero! It's dead quiet except for a wee bit of crackling when turning the boost knob. I don't mind. If you haven't built a Germanium treble booster I can't recommend this enough. The boost knob is sort of like a volume and gain rolled into one. The other knob is "range" and boosts certain frequencies and can add the most creamy and warm bass or perfectly musical treble I've ever heard from a pedal. There is not a bad setting at either end of each knob. It's my new favorite sounding pedal I've ever built.

View attachment 2171
View attachment 2172
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IMG_5517.jpeg IMG_5516.jpeg IMG_5515.jpeg
 
Last edited:
Ok, never mind. I flipped the transistor and the noise is gone. More importantly, it sounds SO MUCH BETTER. At first I was like, "Huh, this is what people are all crazy about?" Now I get it, really nice range of gain and tones available!

bretvh said:
So, I just built one of these boards up for a friend and in testing, I am hearing a pretty prominent ocean/white noise sound when I am not playing. I can mitigate it a little by turning the gain way down (where is the fun in that?) or biasing it to a very low voltage, but I am wondering if I got a bad transistor (got mine on Reverb as well) or wired it up wrong. I notice yours has the red dot on the right side of the PCB, and I assumed the red dot goes to the tab side of the PCB footprint. Or does it matter with these transistors? I have not taken the time to desolder and swap it yet, but thought I'd ask here how much noise is "normal" and what is the correct orientation for that CV7112?

Edit: I just found this, which confirms you can put the CV7112 in either orientation:

About Ge OC140 (CV7112 black glass military germanium)

About Ge OC140 (CV7112 black glass military germanium)
www.diystompboxes.com

I'll have to look at the schematic. It could be I have it in the higher gain orientation, which is causing the noise.

Thanks!

-Bret

View attachment 5272View attachment 5273View attachment 5274
Click to expand...
 
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