I did a layout for the Hudson Sidecar a couple of years ago, and I retraced my steps recently and found a few things that needed to be updated. The Sidecar is a progression of the 999 Overdrive, which is Hudson's version of a 'green box' overdrive, made for people like me that don't like the green box.
There's also another variation out there called the Motorcycle, which sounds like the same circuit that's been retuned for a bit more low drive, with the addition of an output transformer, not unlike the Broadcast. My guess is the 470n / 1k off the inverted input stage has been adjusted, maybe a tweak to the bass side of the active eq???.
The Fuzztone is an early design of Dan Coggins before Lovetone or Dinosaural appeared.
The first publication in ETI (Electronics Today International magazine) actually had an error on the schematic - it wasn't critical, as it just changed the frequency response a little, and it lost some level along the way in the filter section. Remember that ETI supplied a PCB for the project, so it would have sounded right.
I don't know much about the origins of this one, as PedalPCB don't seem to have listed any information on it (at least that I can find anyway).
The Pendulum is a Harmonic Tremolo, meaning the signal is split in two paths, each with either a high or low pass filter; they're modulated separately and then summed back together for an interesting effect - not your average tremolo.
Lower speed rate mod: Replace the C50K pot with a C100k pot for a lower rate OR increase the value of the 4.7u capacitor. Increasing the cap will reduce the max speed, which is probably not a problem for most people.
Here are the filter cutoffs for each side of the trem - keep in mind as one increases in level, the other decreases. The output will certainly not look like this at any given time.
PEDALPCB HARMONIC TREMOLO - VERO LAYOUT
ON THE BENCH
The screengrab wasn't behaving, so here's a quick and dirty shot from the phone. I used a square wave for this, as a sine wave has no harmonics to demonstrate a harmonic tremolo…. You can see and hear the low-pass and high-pass filters alternating in and out.
My homemade vactrols worked the first go too, which is always nice.
I did end up moving the input cap a row on my build, as the pin spacing was wider than I thought. A standard 1u box cap will fit just fine with the layout above. I picked up a bunch of 63v 1u film caps recently that I wanted to use for this. Apart from being orange and looking colourful, they are narrow compared to regular 100v 1u box caps, which come in handy for many layouts.
The Klon Centaur - no introduction required really. Arguably the most mythical of all overdrives? Likely the most expensive of all overdrives...
This layout took a lot longer than I thought it would. In the end, I also realised that I could have shaved a row off, but hey... maybe I'll come back to it another time.
I used the schematic from Aion FX, minus the pulldown resistor on the input, as this layout does not have the input buffer switch, so it's not really needed (be sure to use a switching scheme with grounded circuit input). There's room on the board if you want to add it, just remember to increase the value of the other 1 meg resistor to 2meg.
The layout works, read past the first comment, and you will see the importance of buying ICs from reputable suppliers.
KLON CENTAUR - VERO LAYOUT
KLON DIODES
CAUTION: nerd alert on the diode videos. Thought it was pointless to post a demo video, so here's a deep dive down the rabbit hole of the mystical Klon Centaur diodes.
The Clown Centurion is a rework of a Klon Centaur by Dylan159 on FSB. Be sure to check the links below, as there's a lot of handy information on this project. I won't attempt to explain it, as you're better off reading what Dylan says.
FSB thread link. Link to Dylan's blog, which is quite cool - a lot of interesting guitar effect circuits that Dylan has developed are discussed; you should check it out. Apart from the Clown, you'll find many other interesting original and derivative projects.
The Gretsch Expandafuzz is a bit of an odd-ball guitar effect from the late sixties / early seventies. Not much out there on these in terms of information and video demos.
First oddity: Apart from having a switch and a knob for almost everything, the one switch it doesn't have is for bypassing the entire effect - it's always on... there's only a choice of the Expanda section (Bass, Mid, Treble) or Fuzz & the Expanda section on together.
Second oddity: There's no master volume. That's right - not only is it always on, but you also have to juggle levels using multiple pots and switches.
Third oddity: There's no choice between straight fuzz or boost. It's either boost or boost with fuzz mixed in, so there's always clean signal present.
Fourth oddity: The schematic shows a 10k resistor from the output of every op-amp in the expanda section going to TP1 - TP4. But there's no other reference to TP1 - TP4 anywhere else on the drawing.
Well, that's cause they don't actually connect to anything. I believe these are just test points, so I've left them off the layout. They do absolutely nothing in LTspice, and I could not find a connection anywhere after staring at photos of the circuit board for way too long. Photos are here by the way
GRETSCH EXPANDAFUZZ - VERO LAYOUT
The input stage switch could be removed and just hardwire the fuzz on all the time and have a normal true-bypass switch - that's what I'll be doing. I'll probably get rid of the blend with the boost and just go for straight-out fuzz... big surprise right. You may also want to add a master volume control.
I didn't bother trying to keep the layout small, as it will need a big box with so many switches and knobs. You could also just leave some switches off if you want to save some space, and hardwire bass, middle and treble on all the time, and just use the pots to control the mix.
There's also a power inverter with filtering included, which is not present on the original as it would have run off 9V batteries. This is a dual rail supply running +/- 9v.
I also left off the small 22pf compensation caps that were required for the vintage opamp. Chances are a modern op amp will sound a little different, but not significantly so.
ORIGINAL SCHEMATIC
LT SPICE ANALYSIS
Note that the switches on the expanda stages are not there. Switches are not actually a component in LTspice, so the schematic looks a bit different in terms of switching (or lack of).
Frequency response of the Fuzz & Boost section
Frequency response of the Expanda and output stage (all pots on 100%)
Traces of the boost and fuzz stage, along with the output of this section - all pots at 100%
Check out the size of the square wave off the output of the fuzz opamp - that's a healthy +/- 9v (or 18v) square wave. This is before it's tamed by hard clipping diodes and resistors in series; otherwise, it would destroy everything that follows it. Although you can bypass or reduce the 220k resistor after the diodes if you want more fuzz.
A classic Boss overdrive - the one that started it all for Boss guitar effects, originally sold from 1977 to 1985. This is one of the later designs that does not use the quad opamp.
Kind of curious that after this, many designs used the Boss version of a discrete opamp that can be seen in several different designs.
BOSS OD-1 OVERDRIVE - VERO LAYOUT
BOSS OD-1 OVERDRIVE SCHEMATIC
BOSS OD-1 OVERDRIVE - VIDEO DEMO
Not strictly speaking a straight demo of the OD-1, but I like Wampler's videos, and this does have a good comparison of the SD-1 and OD-3.
The Gretsch Controfuzz is yet another variation on the Distortion + the key point of difference this time is the clean blend, which makes this a little different than the rest.
This layout does include a mod that increases the 10k distortion control to 100k, as 10k seems to be too small to be workable with this design. I think it must be a typo, as the design really doesn't work with 10k.
GRETSCH CONTROFUZZ - VERO LAYOUT
ORIGINAL BOARD & SCHEMATIC
The original used a slightly odd opamp that required external compensation.
image care of reverb
This is a relatively awful scan of the schematic that was included inside the pedal, which was common practice back in the day to some degree.
I thought I might finish off layouts for the rest of the Dan Armstrong series, as I've already done a few. Anyways, while I was looking at schematics of the Blue Clipper from all the usual sources online, I noticed that the opamp bias looked a bit odd. Then I noticed a few layouts used different values, so I checked out some photos to see if I could make sense of it.
I found a clean photo on a Japanese listing for a Blue Clipper, and these are the values that I could see (trace image below). There was another shot that I found online from a different source that has the same values, so the one below is not an aberration of some kind.
Significant differences are the input bias and the resistor controlling gain. The schematics online that I've seen have a 20k / 240k pair of bias resistors (8.3v bias), whereas the one I'm looking at is a relatively normal 200k / 240k pair (4.9v bias). Did someone miss a zero once and the mistake was copied by others?
The other difference is the online schematics usually have a 2.4k resistor for gain, whereas this one has 150 ohms. That's a pretty big difference on a circuit like this (about 1000 times gain vs 63 times).
So what does it all mean? Well, I do know that I'm certainly not the first person to work this out, as I've since found a few mentions elsewhere of correct values (from decades ago) - and there are of course layouts out there with correct values right now along with the incorrect ones.
The opamp outputs are completely different due to the odd bias and to a lesser extent the lower gain. Blue = traced values. Green = online schematic values
Output level differences aside, the waves are at least similar by the time it's heavily filtered by the 33n cap across the output.
Drop that 33n on the output down to 3.3n and you can start to see some real difference - probably going to sound a bit fuzzy. Blue = online schematic. Green = trace (both using 3.3n on the output). 33n is often reported as being too dark for most people.
3.3n might be too big a drop, so maybe start with something around 10n and see where you land.
Using the 33n cap on both, the frequency response is about the same. The difference is output level is very clear. The peak is at around 250hz / 300hz, which is pretty muddy by most standards.
Here are a few values from the stock 33n to 3.3n. Left to right, 33n, 22, 15n 6.8n 3.3n
DAN ARMSTRONG BLUE CLIPPER - VERO LAYOUT
DAN ARMSTRONG BLUE CLIPPER - VIDEO DEMO
Now I know people hate on JHS for various reasons - but this is a good demo... and face it, the guy is living the dream, right?
A classic - the Dan Armstrong Orange Squeezer. It's a very simple feedback-based compressor using JFETS as variable resistors, driven by a single diode acting as a half-wave rectifier.
This makes it pretty snappy to play, unlike an optical compressor which is traditionally a bit slower and smoother - not that there's anything wrong with optical, just a different feel.
I decided to use a single opamp for this layout. I also started down the rabbit hole of replacing the opamp with a transistor-based amplifier, but more on that in another post.
This puts out a lot of level, and the low cut can put it in treble boost territory on extreme settings without any trouble at all, otherwise generally handy to cut a bit of bass to tighten things up on the lower end.
I haven’t included a trace of the wave, as it basically looks like a big sine wave - a bit of change with the bass cut, but nothing worth looking at.
