Chuck D. Bones
Circuit Wizard
Here it is, the famous (infamous?) Monarch. Now that I have it working, I'm really liking this pedal. It's a great dirty boost that cleans up pretty well. Good control ranges.
Like many EQD pedals, this one requires mods to make it work right. The starting point is this schematic from Effects Layouts. Effects Layouts (Tangerine), Pedal Parts (Orange King) and Stewmac offer, or have offered Monarch kits. They all match the schematic below, except for one resistor value (R6). It's a simple design. 1st stage is basically a SHO. Next comes a James tone stack, followed by a gain control. After that we have a mu-amp, a source-follower and finally a mild low-pass filter.
How does this thing even work?
Major design flaw #1: no DC bias path for Q2's gate. Easily fixed by jumpering C9, Removing R11 and replacing C10 with a 10K resistor. The 10K resistor is a "gate stopper" that prevents RF oscillations.
Major design flaw #2: no DC bias path for Q4's gate. Easily fixed by replacing C12 with a 10K resistor. Again, the 10K gate stopper prevents RF oscillations.
With those changes the circuit works great. But why stop there?
FET Substitutions
Q1 is a MOSFET in the original circuit. Depending on whose schematic you're looking at, R6 is either 33Ω or 330Ω (see schematic above). The difference is about 8dB gain. MOSFETs and JFETs have the same transfer function (relationship between input and output), but JFETs are quieter and have more gain at these currents. I breadboarded it both ways and they sounded the same. I ended up going with a JFET. The biasing is slightly different, as you can see in my schematic. I selected a value for R6 that put Q1's drain voltage at 5V for maximum headroom. Different JFETs may require different resistor values. R6 ended up being large enough that it reduces the 1st stage gain, so I added bypass cap C19. That took the gain up to around 32dB, same as the MOSFET with R6 = 33Ω. I put a 470Ω resistor (R18) in series with C19 to bring the gain down to 24dB. Both settings sound good, so I added a switch to my breadboard that allows me to switch Q1's gain from 24dB to 32dB by shorting out R18. The lower gain setting (switch open) provides more headroom in the 1st stage if you want to play clean. The higher setting has a little more bite. You could go with the switch or hard-wire it for either gain.
There is nothing magic about the 2N5457 and since I don't have any, I tried PF5102 and MPF4393. Both work, but the PF5102 has slightly higher gain in this circuit so I went with that one. Other JFETs will also work. NB: not all 2N5457s will work in this circuit because their Vp range is so large. Whatever JFET you use, we want one with Vp no larger than 2V or we start losing too much headroom.
We set the drain current in the 2nd stage by selecting Q3 and/or adjusting R14. I went with 560Ω on my breadboard, although 1K works well too. I found that setting the current in the 2nd stage between 1mA & 2mA gives good results. An easy way to measure the 2nd stage drain current is to measure the voltage across R14 and divide by R14's resistance. On my breadboard, that voltage is 637mV. 637mV / 562Ω = 1.13mA.
Q4 does not need to be a JFET, a BJT works the same, sounds the same, has slightly more headroom and doesn't need a gate stopper resistor. I used a 2N5089. Just about any NPN will work, I even tried germanium and that worked too! But seriously, don't waste a germanium transistor here. It's just an emitter-follower, you won't get any extra mojo.
As always, mind the pinout when subbing transistors.
Tone Controls
They work pretty well. I have no idea how well their sound matches an Orange amp. The component values in the Monarch's tone stack deviate from the Orange amp somewhat. If you want the sound and feel of a Monarch, leave the values as-is. Otherwise, experiment! You can use Duncan's Tone Stack Calculator to see what happens when you changes the R's & C's. B1M pots may work better for BASS & TREBLE if you prefer settings at the top end of their ranges.
Level Control
At full boogie, this pedal makes well over 3.5Vp-p at the output jack. EQD put in a B-taper LEVEL pot. An A-taper is more appropriate in my opinion. Even with an A100K, unity is pretty low - between 8:00 and 9:00.
Presence Control
I added a PRESENCE control after Q4 to allow me to reign in the higher-order harmonics generated in the 2nd stage when the GAIN is set high. See my schematic above for the details. When PRESENCE is dimed, it is slightly brighter than a stock Monarch. At 4:00 it's about the same as the Monarch and it gets gradually darker as you turn it down. You could make PRESENCE an internal trimpot if you like. C16 & R17 don't do anything within the range of human hearing, so they're gone in my circuit.
Other Mods
Some of the capacitor values are a bit silly. C3 is 68nF in the Orange amp. 100nF has the same freq response as 470nF, so use whatever you have. C14 can be as low as 100nF and have the same freq response. I used 220nF for both.
I picked a value for C19 that provides strong bass response, even in the higher-gain mode. If you want less bass in the higher-gain mode, reduce C19.
C13 controls the bass response in the 2nd stage and dominates the pedal's overall bass response. Reduce C13 to tighten the bass and increase it to fatten the bass.
One more thought... That BALLS switch could be a stomp switch! We could add a pot to set how much gain boost we get when we hit the switch. Something like this:
At this point, I think I've made enough changes that I can make like JHS and claim this design as my own.
Like many EQD pedals, this one requires mods to make it work right. The starting point is this schematic from Effects Layouts. Effects Layouts (Tangerine), Pedal Parts (Orange King) and Stewmac offer, or have offered Monarch kits. They all match the schematic below, except for one resistor value (R6). It's a simple design. 1st stage is basically a SHO. Next comes a James tone stack, followed by a gain control. After that we have a mu-amp, a source-follower and finally a mild low-pass filter.
How does this thing even work?
Major design flaw #1: no DC bias path for Q2's gate. Easily fixed by jumpering C9, Removing R11 and replacing C10 with a 10K resistor. The 10K resistor is a "gate stopper" that prevents RF oscillations.
Major design flaw #2: no DC bias path for Q4's gate. Easily fixed by replacing C12 with a 10K resistor. Again, the 10K gate stopper prevents RF oscillations.
With those changes the circuit works great. But why stop there?
FET Substitutions
Q1 is a MOSFET in the original circuit. Depending on whose schematic you're looking at, R6 is either 33Ω or 330Ω (see schematic above). The difference is about 8dB gain. MOSFETs and JFETs have the same transfer function (relationship between input and output), but JFETs are quieter and have more gain at these currents. I breadboarded it both ways and they sounded the same. I ended up going with a JFET. The biasing is slightly different, as you can see in my schematic. I selected a value for R6 that put Q1's drain voltage at 5V for maximum headroom. Different JFETs may require different resistor values. R6 ended up being large enough that it reduces the 1st stage gain, so I added bypass cap C19. That took the gain up to around 32dB, same as the MOSFET with R6 = 33Ω. I put a 470Ω resistor (R18) in series with C19 to bring the gain down to 24dB. Both settings sound good, so I added a switch to my breadboard that allows me to switch Q1's gain from 24dB to 32dB by shorting out R18. The lower gain setting (switch open) provides more headroom in the 1st stage if you want to play clean. The higher setting has a little more bite. You could go with the switch or hard-wire it for either gain.
There is nothing magic about the 2N5457 and since I don't have any, I tried PF5102 and MPF4393. Both work, but the PF5102 has slightly higher gain in this circuit so I went with that one. Other JFETs will also work. NB: not all 2N5457s will work in this circuit because their Vp range is so large. Whatever JFET you use, we want one with Vp no larger than 2V or we start losing too much headroom.
We set the drain current in the 2nd stage by selecting Q3 and/or adjusting R14. I went with 560Ω on my breadboard, although 1K works well too. I found that setting the current in the 2nd stage between 1mA & 2mA gives good results. An easy way to measure the 2nd stage drain current is to measure the voltage across R14 and divide by R14's resistance. On my breadboard, that voltage is 637mV. 637mV / 562Ω = 1.13mA.
Q4 does not need to be a JFET, a BJT works the same, sounds the same, has slightly more headroom and doesn't need a gate stopper resistor. I used a 2N5089. Just about any NPN will work, I even tried germanium and that worked too! But seriously, don't waste a germanium transistor here. It's just an emitter-follower, you won't get any extra mojo.
As always, mind the pinout when subbing transistors.
Tone Controls
They work pretty well. I have no idea how well their sound matches an Orange amp. The component values in the Monarch's tone stack deviate from the Orange amp somewhat. If you want the sound and feel of a Monarch, leave the values as-is. Otherwise, experiment! You can use Duncan's Tone Stack Calculator to see what happens when you changes the R's & C's. B1M pots may work better for BASS & TREBLE if you prefer settings at the top end of their ranges.
Level Control
At full boogie, this pedal makes well over 3.5Vp-p at the output jack. EQD put in a B-taper LEVEL pot. An A-taper is more appropriate in my opinion. Even with an A100K, unity is pretty low - between 8:00 and 9:00.
Presence Control
I added a PRESENCE control after Q4 to allow me to reign in the higher-order harmonics generated in the 2nd stage when the GAIN is set high. See my schematic above for the details. When PRESENCE is dimed, it is slightly brighter than a stock Monarch. At 4:00 it's about the same as the Monarch and it gets gradually darker as you turn it down. You could make PRESENCE an internal trimpot if you like. C16 & R17 don't do anything within the range of human hearing, so they're gone in my circuit.
Other Mods
Some of the capacitor values are a bit silly. C3 is 68nF in the Orange amp. 100nF has the same freq response as 470nF, so use whatever you have. C14 can be as low as 100nF and have the same freq response. I used 220nF for both.
I picked a value for C19 that provides strong bass response, even in the higher-gain mode. If you want less bass in the higher-gain mode, reduce C19.
C13 controls the bass response in the 2nd stage and dominates the pedal's overall bass response. Reduce C13 to tighten the bass and increase it to fatten the bass.
One more thought... That BALLS switch could be a stomp switch! We could add a pot to set how much gain boost we get when we hit the switch. Something like this:
At this point, I think I've made enough changes that I can make like JHS and claim this design as my own.
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