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?

DAN ARMSTRONG: Orange Squeezer

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.

DAN ARMSTRONG ORANGE SQUEEZER - VERO LAYOUT

DAN ARMSTRONG ORANGE SQUEEZER - VIDEO DEMO

After the previous post for the Dan Armstrong Red Ranger, I thought I might do layouts for the rest of the series, starting with the Blue Clipper - I then got sidetracked, and now I'm looking at a Blue Clipper using Joe Davisson's diode-compression opamp.  

I had to change the bias from the original values of the Blue Clipper on the positive input of the opamp to get it to work (update: as it turns out the values on the online schem were wrong).  

The 33n cap at the end of the signal chain is rolling off a lot more high frequencies than I'm normally happy with as well - that will change at some stage.  There's a fair chance this will evolve into something resembling a Distortion + / Pete Cornish SS-2 with mods.  I have the SS-2 version running on LTspice and a layout ready to go.

note:  I did end up turning this into a SS-2, so the Blue Clipper using a diode-compression opamp project will not progress any further, as I'm happy with the SS-2.   

DAN ARMSTRONG BLUE CLIPPER WITH DIODE COMPRESSION OPAMP

DAN ARMSTRONG: Red Ranger

Bass, treble and full range boost - a 1970s classic from Dan Armstrong, although somewhat overlooked compared to its more famous brethren, the Orange Squeezer and Green Ringer.

DAN ARMSTRONG RED RANGER - VERO LAYOUT

RED RANGER VIDEO DEMO

DAN ARMSTRONG: Green Ringer, Point to Point Layout (EQD Tentacle)

The classic Dan Armstrong octave effect - The Green Ringer. 

Great to put in front of a fuzz or distortion pedal.  The Earthquaker Devices Sunn Life pedal is basically a Green Ringer in front of a Proco Rat, with a booster.

DAN ARMSTRONG GREEN RINGER - POINT TO POINT LAYOUT

Earthquaker Devices have a version called the Tentacle, which is almost identical.  For the Tentacle, just do the following:

Change Q1 and Q3 to a 2N5089 

Change 1.5M resistor to 2.2M

Add 100pf capacitor from input to ground

1N4148 Diodes used

I've left some room on the board for power filtering if needed.