Crunch Box/Angry Charlie/AT mid shift mod

[shredgd]

Hi everyone,

I want to share with you a very simple mod I recently came up with to overcome the slightly "scooped-mids" tone you normally get with this circuit, especially when played into a blackface style clean tone.

It only involves replacing the 22nF cap from the presence/air control to ground with a 12nF cap. This way the low pass filter formed by this cap and the 25k potentiometer changes its corner frequency from 290 to 530Hz, hence giving you some more mids and avoiding that sometimes boomy bass which becomes prominent the more you reduce the presence knob. I actually wouldn't call this really a presence control with the stock value cap: 290Hz is a very low pass corner!
I was inspired by the Bluesbreaker/King of Tone/Morning Glory tone circuit, which shows a similar 25k pot/10nF cap to ground low pass filter, but I found 12nF was really the "magic value" for this gainer circuit.
Making this mod switchable lets you toggle between the stock "modern" tone and a more "classic heavy rock" tone.

Enjoy!

Giulio

PS: this mod obviously doesn't apply to the JHS Angry Charlie V3, which already has an (active) mid control

[shredgd]

One more thing I recently noticed and I wanted to share is that, being the second gain stage an inverting type opamp stage, the 0.1uF cap and 10k resistor that precede it form an high pass filter, which is actually variable as you move the gain pot (the latter is not wired as a simple variable resistor for the first gain stage, but as a divider): the lower you set the gain the more series resistance is added to that 10k resistor, so the total series resistance varies from 110k (gain pot at min) to 10k (gain pot at max).
This means that at minimum gain we have an high pass filter with a corner frequency of 14Hz, while at maximum gain the corner frequency shifts to 159Hz, so a slight cut in the lows is made the more we increase the gain. The original Marshall Guv'nor/Drivemaster circuit featured a 0.22uF cap in series with that 0.1uF, which gives a total of 0.068uF. The corner frequencies were therefore 21Hz for minimum gain and 234Hz with the gain at max.
This might seem a little difference, but if we remember that those corner frequencies represent the point where a 3dB roll off happens (not the real point where frequencies start to be reduced), and if we consider the two low pass filters which are applied later in the circuit, the JHS higher cap value surely contributes to the heavy low-mids the Angry Charlie/Andy Timmons circuit has.
So if you use the Angry Charlie/AT pedal with the gain set lower than halfway as I do, or if you don't like the excessive bass this circuit has when the gain is set very low, then reducing that cap to the original Marshall value (or even lower!) might be your case.

Cheers!

Giulio

[Kipper4]

Schematic you are working from please or it has little context besides, "I like it better with my rig."

[shredgd]

Just google "Angry Charlie schematic" and it pops out!

Well, the "I like it better with my rig" is quite a constant for anyone, but in this case I'm also giving an explanation.

Have a nice day!

[Ben N]

... or Angry Andy for the AT schem.

[shredgd]

... or Angry Andy for the AT schem.

Exactly. All schematics around contain a mistake, though: the tone pot taper must be linear, not reversed log (I verified this by looking at a gutted AT pedal picture, which showed a 10kB pot). The reversed pot is very hard to dial and makes the pedal sound harsh for most of its range because the sweet spot is all shrinked towards "10 o'clock"... replacing it with the correct linear taper was a bless.
Also, I used 1N4148 diodes for the alternative clipping mode: I believe the BAT41s have too low forward voltage and are just another imprecision.

[Ben N]

Did you use the pedalpcb board? I have one on order.

[shredgd]

Did you use the pedalpcb board? I have one on order.

No, I use perfboard and I do my own layouts 

[ali1111]

I've  made a clone of Angry charlie V3, its sounds amazing and have a nice and warm  distortion but i think it has less treble, what is your recommendations for increasing about 30-40% treble to tone of this pedal?
https://www.pedalpcb.com/docs/AngryCharles.pdf

[PRR]

C3 is a heavy load on guitar, though not on most other pedals.

C17 shaves treble. Try smaller.