Chuck D. Bones
Circuit Wizard
Left: Variac with auto-balance & Germanium final stage. Built on a Big Noise board from Cooder.
Middle: Brownout OD.
Right: Boneyard Suburban Decay Maniac. Last stage uses blue LEDs as a soft clipper in place of the differential pair. Built on Vero.
Like most JFET-based pedals, getting the biasing right is essential. Plan on selecting JFETs and/or tweaking source resistors. On the Brownout, I have the drains of Q1 & Q2 set at 5.4V and 5.0V, respectively. Because the drain resistors are so large, you must use a DMM with 10MΩ input resistance to measure the drain voltage. The cheap DMMs with 1MΩ input resistance will read 10% too low. Q3, Q4 and Q7 should have low Vp (<1V) and Idss > 2mA.
I used selected 2SK193s for all five JFETs in the Big Noise Variac. Source resistors on the first two stages were tweaked to achieve the desired bias. Slight retuning of the Tone Stack. Differential stage has two 104NU71 Germanium transistors. The auto-balance keeps the Ge transistors at the correct bias point. Board has true-bypass relay switching.
I followed the Brownout build docs except for the transistors. I used selected 2N5246s for Q1 & Q2. None of the 2N5457s I had came anywhere close to biasing correctly in the 1st two stages. The other three JFETs are selected PF5102s. The diff pair is a vintage dual matched pair Silicon transistor.
The Suburban Decay Maniac uses the same 1st two stages with selected JFETs and tweaked source resistors. I rescaled and retuned the Tone Stack and added in the MID control. I replaced the diff pair 3rd stage with an LED soft clipper.
The left and middle Variacs sound very similar. The Maniac on the right has more gain and compression in the last stage and is a little darker compared to the two Variacs. I think they all sound great. Distortion is easily controlled from the guitar and the two gain knobs. Note decay is very smooth and natural sounding, no fizziness.
I had a problem with high-freq oscillation in the Maniac due to trace proximity on the Vero. The trace for Q1's gate ran right next to the trace for Q2's drain. One cut fixed that.
Middle: Brownout OD.
Right: Boneyard Suburban Decay Maniac. Last stage uses blue LEDs as a soft clipper in place of the differential pair. Built on Vero.
Like most JFET-based pedals, getting the biasing right is essential. Plan on selecting JFETs and/or tweaking source resistors. On the Brownout, I have the drains of Q1 & Q2 set at 5.4V and 5.0V, respectively. Because the drain resistors are so large, you must use a DMM with 10MΩ input resistance to measure the drain voltage. The cheap DMMs with 1MΩ input resistance will read 10% too low. Q3, Q4 and Q7 should have low Vp (<1V) and Idss > 2mA.
I used selected 2SK193s for all five JFETs in the Big Noise Variac. Source resistors on the first two stages were tweaked to achieve the desired bias. Slight retuning of the Tone Stack. Differential stage has two 104NU71 Germanium transistors. The auto-balance keeps the Ge transistors at the correct bias point. Board has true-bypass relay switching.
I followed the Brownout build docs except for the transistors. I used selected 2N5246s for Q1 & Q2. None of the 2N5457s I had came anywhere close to biasing correctly in the 1st two stages. The other three JFETs are selected PF5102s. The diff pair is a vintage dual matched pair Silicon transistor.
The Suburban Decay Maniac uses the same 1st two stages with selected JFETs and tweaked source resistors. I rescaled and retuned the Tone Stack and added in the MID control. I replaced the diff pair 3rd stage with an LED soft clipper.
The left and middle Variacs sound very similar. The Maniac on the right has more gain and compression in the last stage and is a little darker compared to the two Variacs. I think they all sound great. Distortion is easily controlled from the guitar and the two gain knobs. Note decay is very smooth and natural sounding, no fizziness.
I had a problem with high-freq oscillation in the Maniac due to trace proximity on the Vero. The trace for Q1's gate ran right next to the trace for Q2's drain. One cut fixed that.
Last edited:
