DOD: 250

So by this stage, I think we can all assume that I'll be the only one making this.  I have a bunch of tin can LM741 opamps that I forgot about, so I thought why not...  

DOD 250 / DISTORTION + LAYOUT

DOD / MXR: 250, Distortion + component values table

This is probably where it all started in terms of opamp-driven distortion -  in one side of 741 opamp, out the other with some hard clippers.  

DOD 250 / MXR DISTORTION + SCHEMATIC

Direct link to Google Doc

741 SPECS

Numbers vary slightly by manufacturer and grade, but these headline specs are what give the 741 its “personality” in effects land:

• Supply voltage: works on dual or single supplies (it was designed with ± supplies in mind, but can be run single-supply with proper biasing).

• Gain-bandwidth product: around ~1 MHz class.

• Slew rate: about ~0.5 V/µs typical.

• Input bias current: tens of nA typical (bipolar input).

• Not rail-to-rail: inputs/outputs can’t swing anywhere near the rails, especially on a 9V battery. 

What that means in practice: a 741 can sound/feel a bit rounder and more easily pushed in simple dirt circuits, partly because it’s relatively slow and because it doesn’t have huge clean output swing on a 9V single supply.

LM741 PINOUTS

Note the little tab on the side of the opamp is pin 8.

OFFSET NULL

Offset null is a pair of pins on the 741 that lets you trim out its small DC offset so the output sits where you want it (often 0V on a dual-rail supply). 

In pedals it’s usually ignored because stompboxes are typically single-supply with a virtual ground and AC-coupled stages, so capacitors block DC and the tiny offset isn’t audible.

While the pins aren't used, be sure to isolate them anyway.

BIXONIC: Expandora

OK - so this is what happens when you agree to make a pedal, before knowing what someone might ask for.   I'm not sure that this is 100% my kind of thing, but here it is.

Yes it's a huge layout, but it is going in a 1590XX enclosure, so why not.  I started this layout using the Dirtbox Layouts Expandora vero layout (and basically made it wider), as the first version that I did had a few too many rows, for the space available in the enclosure - and I will probably only be making one of these.  So credit where credit is due...  

I may still add the guitar / bass switch - see how it sounds.  There is room on the board for it.  Not hard to work out if you want to add it.  

If you are unfamiliar with the signal flow on the Expandora - it's kind of a Rat with an extra gain stage up front, and an unusual compressor like gain control that's always on, which is combined with a couple of switches to help set the overall gain of that stage.

The fun doesn't start until "forbidden mode" is engaged - which opens the gain right up.  Talking big ugly square waves.  The Expandora moves from a fairly innocuous drive or mild distortion, to a full blown fuzz monster.     

BIXONIC EXPANDORA

This is it on the bench for some testing - just a bit of rough / temporary wiring to confirm all works as expected, before I wire it up properly.    I think the tin can LM308 opamps look cool, and they were all I had.

It's been a while since I worked on small vero, or should I say normal size.   It took some adjustment, and I did have a tiny little copper trace left on a cut that took a decent amount of time to track down.  It took a magnifying glass and a multimeter to track it down - the damn thing was about the size of a bee's dick (which is a unit of measurement in Australia). 

ELECTRO-HARMONIC x JHS: Big Muff 2

It's been a while - and I've probably scared most of you away with obscure amp content, but I have to have a crack at this one.   

Yes, it could have been a smaller layout, but to be honest, I'd still be adding some room around the edges for proper mounting points.  I also left room for a 1meg resistor on the input, if you are that way inclined. 

The schematic can be found here, which is apparently printed on the box.  If you don't have the exact values, use the nearest available (4n7 instead of 5n as an example).

note:  Volume pot is actually B10k. will update the layout later, 100k will still work fine

ELECTRO-HARMONIX x JHS -  BIG MUFF 2 VERO LAYOUT

PETE CORNISH: G-2, 2012, Battery Free Version (Aion FX Trace)

There's been so much speculation about the G2, over many many years.   Aion FX has traced two versions of the Pete Cornish G2, so hopefully this is the end of some very long threads on various forums.  

Long story short, one version is very close to all of the mods that everyone has been doing for years.  Here's the battery free version, which uses a mix of germanium and silicon diodes, and has smaller caps in the required places to fixe the darkness issue.   

I will come back to this at a lter date with more details and a larger layout incorporating the second buffer.  This is it for now...  

PETE CORNISH G2 - AION FX TRACE, 2012, BATTERY FREE VERSION

CASTLEDINE ELECTRONICS: Magical Mystery Box

Since I've been on a slight Beatles related run lately, I thought I should tackle the Castledine Electronics Magical Mystery Box.  

This is Stu Casteldine's version of the Brilliant channel from a Vox Conqueror guitar amp.  Castledine included a gain recovery section at the end and the transistor-based distortion switching has been removed.  I ran both the Castledine version and the original in LTspice, and there was no real difference between the two.  

The thing that really sets these apart from similar Vox amps is the mid-range boost (MRB), which is said to be the precursor to the wah pedal.  The MRB has three different options for the mid-range boost frequency - the sound is what we now refer to as a cocked wah.  i.e. turning your wah pedal on a leaving it at a specific frequency.

As this line of Vox amps were transistor-based, the pedal version will be much closer to the sound of the original than a lot of other amp-to-pedal conversions that just replace valves with JFETs.

CASTLEDINE MAGICAL MYSTERY BOX VERO LAYOUT  

I've not done a layout with a Fasel inductor before, so hopefully I have the sizing about right.   The layout is intentionally wide, as this will be in a large box in landscape orientation (three foot switches and five controls along the top).  

Despite the size, you may need to add some space to mount this using your preferred method.  I strongly suggest testing the layout and sizing before starting construction.  The fasel inductor sits quite high compared to other components.  It would be annoying to get to the end of a more expensive than normal project, only to find that it doesn't fit in the box.

VOX CONQUEROR / DEFIANT / SUPREME PRE-AMP

Several Vox transistor amps shared the same pre-amp including the 30W Conqueror, 50W Defiant, and 100W Supreme.  They were experimenting with modular amp designs at the time - probably to save money and streamline production.

The Brilliant channel is the section on the top-left to centre.  If you compare this to the Magical Mystery Box, you can see they are very similar. 

When the distortion was switched on, it provided a bias current to the base of the transistors, allowing sections of the distortion circuit to connect to ground.

This is a redraw of the original schematic by Chris Devine of Back to the Sixties (link below).

CASTLEDINE MAGICAL MYSTERY BOX

ADDITIONAL VOX RESOURCES

Vox Showroom - https://www.voxshowroom.com/uk/amp/conq.html

Back from the Sixties (scroll down for schematics) - https://www.backfromthesixties.co.uk/vox-supreme

INTERFAX: Harmonic Percolator (modded)

This is a slightly modded Interfax Harmonic Percolator that I made today.  It's an odd little circuit - it can run from clean, a bit overdriven, then into distortion, and finally to overly compressed fuzz madness.  The range of sounds are so broad, it's almost worth setting it up as a dual pedal (which I might do). 

In terms of mods, it's kind of a mix of a couple of schematics, the Land Devices HP-2 and a bit of my own thing.   It's still very much a Harmonic Percolator, that much is sure.  If you want to use the layout for a stock Harmonic Percolator (whatever that may be), there's fairly extensive discussions on the usual forums, including schematics and of course many and varying opinions as to what it should be.

INTERFAX HARMONIC PERCOLATOR - MODDED VERO LAYOUT

When it was on the breadboard I tried a few different transistors.  The differences were noticeable, and I'd recommend testing before soldering, to make sure that you have a combination that you're happy with.  

If you have a breadboard, it's worth getting it on there to play with - there are so many variations on this circuit, and they do make a difference.

The silicon transistor had a hFE of around 240 and the germanium was about 70 with almost no leakage (like many soviet transistors).  The type of germanium and silicon diode is not important.   

ON THE SCOPE

With the input trimmer down, it's a pretty clean signal (called Harmonics on the pedal).  I run a 200mv 440hz sine wave into my scope.

This is with harmonics on full, it's a fairly over the top and very compressed fuzz sound.  Germanium diodes are on.

This is Harmonics on full, diode clipping bypassed - there's a huge jump in level and it's a lot more dynamic.  

VOX: Distortion Booster, Red Box

Still on the Vox thing at the moment - just a little Distortion Booster using a variation on the Colorsound fuzz box layout.  It's the red box version, here's the thread on FSB with the schematic etc.  

Like so many vintage effects, there seems to be a few versions of the circuit.

VOX DISTORTION BOOSTER   |   0.15" VERO LAYOUT

VOX: Distortion Booster V8162

This is a nice simple one, and a slight variation on the Colorsound Fuzz Boxes that I've been building lately.  Basically a silicon fuzz face variant, which is a progression from their original booster that just had an on/off switch.  

VOX DISTORTION BOOSTER  |  0.15" VERO LAYOUT 

And if you're wondering what's going on with the placement of the connection to lug 3 of the distortion pot, I did it that way as I thought it would look cleaner.  Can always move it if you don't like it there.  

ORIGINAL VOX SCHEMATIC

Now this is mainly for my own purposes, as I doubt anyone else will want to build a Rat this way & I only plan on making one.  

Just a standard Rat, built on 0.15" vero and I've prioritised looks of build practicality (or at least what I think looks good anyway).  I have built this, and can confirm that it works   

PROCO RAT - 0.15" VERO LAYOUT

The layout probably makes more sense with a photo as a reference

MYTHOS: Golden Fleece

In Australia we have a lot of unusual sayings - one that comes to mind here is "you've been fleeced".  i.e. you paid too much money for something - specifically a Golden Fleece on the secondhand market when you can still buy perfectly good new one.  

The Mythos Golden Fleece is pretty much a part for part copy of the Alan Yee Fuzzy Nuts, which is a slight variation on the humble Electra Distortion.  Description here from Mythos.

Things to note:  47k on the input drops the input impedance right down.   100pf on the input is an estimate, as far as I'm aware the exact value is unknown.   I think the output pot is actually linear instead of log - you choose.

The Electra is quite a forgiving circuit as far as component values go - as long as you loosely stick to the program you'll probably have something that sounds good.

MYTHOS GOLDEN FLEECE - VERO LAYOUT

ELECTRA: Distortion

I accidentally messed up a small Colorsound Fuzz Box board by drilling mounting holes in the wrong place - but I didn't want to waste the vero board, and I thought an Electra Distortion & Colorsound Fuzz Box might make a nice pair of one-knob pedals.  

Perhaps not the most exciting post to return with after a short break.  I’ve been busy with other projects and haven’t had much time for layouts.  I even took part in a panel discussion about guitars recently, which was a lot of fun.

ELECTRA DISTORTION - 0.15” VERO LAYOUT 

ETI: The Fuzztone, a Dan Coggins Design

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.  

You can find the corrected schematic and a few words from Dan here.

ETI, DAN COGGINS THE FUZZTONE - VERO LAYOUT

FUZZTONE ON LTSPICE

I've not built this yet, but it looks like a distortion/overdrive with a mid-hump and not much top-end on LTspice.

This is sweeping both the sustain and filter pots from 0 to 50% to 100%

JONNY RECKLESS: Reckless Abandon

A recent request.  This is a monster of a pre-amp from Jonny Reckless.  Best to read the details on DIY stomp boxes, as there's a lot to this.

I've not built this, and there's a bit going on with it.  I'd suggest checking it against the schematic before starting.  I've looked over it a few times, but I probably won't be building this one any time soon to confirm it.

Link to thread on DIY Stompboxes

JONNY RECKLESS - RECKLESS ABANDON  VERO LAYOUT

SCHEMATIC BY JONNY RECKLESS

VIDEO DEMO, ALSO BY JONNY

LOVEPEDAL: JTM45

A nice easy one - and I'm not sure if anyone has done more versions of an Electra Distortion than Lovepedal has.  But hey if it's working for them and people like it, who am I to judge?   A JTM45 it is not.

LOVEPEDAL JTM45 - VERO LAYOUT

RIFT AMPLIFICATION: EL34

It's a single transistor boost, not unlike an Electra.  This pedal is somewhat infamous in the DIY community for exaggerated claims about what it sounds like - although no one in their right mind would question the quality of the point-to-point work in the enclosure that Rift did.    

The Boost switch is normally a foot switch.  Note that the gain control does nothing without the boost switch engaged.

RIFT AMPLIFICATION EL34 - VERO LAYOUT

SCHEMATIC & SPICE RESPONSE

It's not much to look at - a bit of boost and dirt at higher settings, low-end is filtered off by the input cap and some highs are taken out with the tone control.  

Schematic redrawn from the Gray Bench trace - check out the youtube channel if you have not already - a lot of good tear-down videos.

VIDEO DEMOS

GRETSCH: Controfuzz

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.   

LTSPICE

GRETSCH CONTROFUZZ - VIDEO DEMO

DAN ARMSTRONG: Blue Clipper

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?