# PedalPCB Pendulum - fixing the midscoop?



## jesuscrisp (Dec 22, 2021)

As a preface, I'm really happy that the Pendulum came out right when I was looking into harmonic tremolos. Built it, sounds nice, very smooth and the simple controls are absolutely enough for some wobbly action! 

However, the pedal also seems to take out a big chunk of midrange (or maybe it emphasises bass and treble, same result though). This is especially apparent when played with distortion, fuzz or overdrive. Just has a tendency to get boomy and fizzy, which is a shame, since the harmonic tremolo effect in itself is pretty cool. If anyone else built it and has a fix, please let me know, otherwise I might just tack on a passive tonestack! 

Cheers and thanks in advance!


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## Robert (Dec 22, 2021)

You can shift the center frequency of the High Pass and Low Pass filters by adjusting the resistor/cap values of each filter.

C2 / R5 is the High Pass filter.
C3 / R6 is the Low Pass filter.


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## jesuscrisp (Dec 23, 2021)

That would however also change the way the phasing/vibing sounds as far as I'm concerned. When are the schematics going to be uploaded? 

Well maybe I'll be adding a little passive EQ at the end after all.


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## Robert (Dec 23, 2021)

The schematic is in the build doc now.


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## SYLV9ST9R (Dec 23, 2021)

jesuscrisp said:


> As a preface, I'm really happy that the Pendulum came out right when I was looking into harmonic tremolos. Built it, sounds nice, very smooth and the simple controls are absolutely enough for some wobbly action!
> 
> However, the pedal also seems to take out a big chunk of midrange (or maybe it emphasises bass and treble, same result though). This is especially apparent when played with distortion, fuzz or overdrive. Just has a tendency to get boomy and fizzy, which is a shame, since the harmonic tremolo effect in itself is pretty cool. If anyone else built it and has a fix, please let me know, otherwise I might just tack on a passive tonestack!
> 
> Cheers and thanks in advance!


I remember on my build, I first had done the DIY vactrol thing (LED and LDR enclosed in heatshrink), and I found that the volume was loud and distorted at high value, and the sound was quite boomy too. I then removed the heatskrink and spaced the LED and LDR just a bit, and then it sounded way better. You might want to try different "settings" for these.


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## cjonesplay (Jan 27, 2022)

SYLV9ST9R said:


> I remember on my build, I first had done the DIY vactrol thing (LED and LDR enclosed in heatshrink), and I found that the volume was loud and distorted at high value, and the sound was quite boomy too. I then removed the heatskrink and spaced the LED and LDR just a bit, and then it sounded way better. You might want to try different "settings" for these.


I changed the 18k to 22k in mine to make the low-end 330kHz instead of 440 and I used 5mm yellow LED’s. I also lowered the value of the 4.7k’s (these should have been trimmers) on each LDR in order to get more depth, since you can always dial it back. I settled on 1.5k for the high filter and 2.2k for the low filter. Now it sounds more like a Magnatone circuit to my ears, although not nearly as awesome as the digital vibrato found in the Module8. That was has a center frequency sweep and gets much chewier, I love it!


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## jesuscrisp (Jan 27, 2022)

Thanks for the tips guys! 

Have been experimenting myself with adding some passive tone shaping at the end in the meantime. Will try adjusting the LED/LDR combo mechanically, but otherwise I'll just go with the little EQ. The pedal has massive output volume anyway so adding a bit of high and low cut don't hurt too much.


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## Brent (Feb 9, 2022)

cjonesplay said:


> I changed the 18k to 22k in mine to make the low-end 330kHz instead of 440 and I used 5mm yellow LED’s. I also lowered the value of the 4.7k’s (these should have been trimmers) on each LDR in order to get more depth, since you can always dial it back. I settled on 1.5k for the high filter and 2.2k for the low filter. Now it sounds more like a Magnatone circuit to my ears, although not nearly as awesome as the digital vibrato found in the Module8. That was has a center frequency sweep and gets much chewier, I love it!


Are you referring to R7 & R8 to adjust the depth? Im thinking ill use a couple of 10k trims to set it to my taste


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## cjonesplay (Feb 15, 2022)

Brent said:


> Are you referring to R7 & R8 to adjust the depth? Im thinking ill use a couple of 10k trims to set it to my taste


Yes, the resistors feeding the LED’s. They can be 5k trimmers, but 10k is fine


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## jesuscrisp (Feb 20, 2022)

Tried physically adjusting the LEDs, but that just seems to make it sound thinner. Replacing the main signal IC with an LM348 sort of reduced some pluckiness, but still not a major fix. Replaced the LFO IC with an LM324 too, maybe a tad smoother wobble but may be placebo. 

Left the ICs in, but the major "fixes" to get it as "transparent" as possible are to put a 4n7 cap across the level pot to smooth out the treble and replacing the 1uF output cap with a way smaller value. I chose 68nF, but even 47nF isn't too thin sounding. If you want some slight fattening, I'd go for 100nF.

Now it's as transparent as harmonic trem can be. Actually prefer it to my harmonious monk in that regard. Doesn't quite have the vocal, round smoothness of the monk and of course does quite a bit less in terms of features. Still, doesn't swallow the harmonics at all and also isn't scoopy at all like the "stock" Pendulum is.


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## Alan W (Jan 2, 2023)

jesuscrisp said:


> Tried physically adjusting the LEDs, but that just seems to make it sound thinner. Replacing the main signal IC with an LM348 sort of reduced some pluckiness, but still not a major fix. Replaced the LFO IC with an LM324 too, maybe a tad smoother wobble but may be placebo.
> 
> Left the ICs in, but the major "fixes" to get it as "transparent" as possible are to put a 4n7 cap across the level pot to smooth out the treble and replacing the 1uF output cap with a way smaller value. I chose 68nF, but even 47nF isn't too thin sounding. If you want some slight fattening, I'd go for 100nF.
> 
> Now it's as transparent as harmonic trem can be. Actually prefer it to my harmonious monk in that regard. Doesn't quite have the vocal, round smoothness of the monk and of course does quite a bit less in terms of features. Still, doesn't swallow the harmonics at all and also isn't scoopy at all like the "stock" Pendulum is.


Thanks for these good descriptions. I’m in the process of tuning my Pendulum, and want to try the cap across the level pot. (If it weren’t for the LDRs, I’d just clip in some trials, but getting the circuit board dark enough with kludged parts in it involves more effort…oh, heck, I’m just lazy!)

I went with an A50k pot, so am thinking I’d want to double the cap size? But my real question is what do you mean by “across” in the circuit? From 1 to 3, or from 2 to 3? My low understanding of basic electronics wants this to be 1to 3, but I don’t trust myself.

In my setup, so far having 10n for the high pass, and 27n for the low pass, with C4 lowered to 100n has it sounding very sweet. My main complaint is the upper frequency stridency that is there with a stronger signal coming in. Not sure if this cap across the level pot will help with this or not; if it doesn’t seem to, I plan on increasing the resistors to the LDR LEDs to see if running at 18 v takes care of it.


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